NUREG-1669

A Risk Analysis of 

Fixed Nuclear 

Gauges 

U.S. Nuclear Regulatory Commission 

Office of Nuclear Regulatory Research 

Washington, DC 20555-0001
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NUREG-1669

A Risk Analysis of 

Fixed Nuclear 

Gauges

Manuscript Completed: March 2000 

Date Published: April 2000 

Division of Risk Analysis and Applications 

Office of Nuclear Nuclear Regulatory Research 

U.S. Nuclear Regulatory Commission 

Washington, DC 20555-0001
ABSTRACT 

Fixed nuclear gauges containing the radionuclides 137Cs, 6°Co, or 241

Am are used in many industries to 

improve the quality and lower the costs of products for industrial, commercial, and private uses. But gauges 

that are improperly controlled during use and transfer can expose people to radiation and, upon entering the 

stream of recycled steel, can cause steel mills to spend millions of dollars to decontaminate equipment and 

dispose of contaminated materials. The risk to licensees and the recycling industries that nuclear gauges pose is incompletely understood. An analysis of fixed nuclear gauges was performed to study the risk to life and 

property, from facilities where the gauges are used to steel mills where the gauges might be melted. A risk 

analysis should be of interest to all stakeholders- agencies that promulgate regulations, licensees who must 

comply with the regulations, and the recycling industries who use scrap steel as a resource for making products. Although risk could not be estimated because data are lacking, observations and insights were 

made that can be used by all stakeholders to reduce their risk, even if the extent of the reduction is unknown. 

iii NUREG-1669
CONTENTS 

Page 

List of Figures ............................................................................. vii 

L ist of Tables ............................................................................... ix 

List of Text B oxes ........................................................................... xi 

Preface ................................................................................... xiii 

Executive Sum m ary ......................................................................... xv 

Acknow ledgm ents .......................................................................... xix 

Site V isits ................................................................................. xxi 

A bbreviations ............................................................................. xxiii 

List of V ariables ........................................................................... xxv 

1 Introduction 

1.1 D efinitions ........................................................................... 1 

1.2 C oncepts ........................................................................... 1 

2 Subject 

2.1 O verview ........................................................................... 5 

2.2 D efinitions .......................................................................... 5 

2.3 G oal and Objectives .............................................. .................... 5 

2.4 Subject of the Risk Analysis ............................................................ 7 

2.5 Subject as a System To Analyze ......................................................... 8 

2.6 Progression of the Analyses ........ : ................................................... 16 

2.7 Observations and Insights ............................................................. 16 

3 Principles of the Risk Analysis 

3.1 O verview .......................................................................... 19 

3.2 C oncepts .......................................................................... 19 

3.3 Structure of a Risk Calculation ......................................................... 22 

3.4 Products of the Risk Analysis .......................................................... 24 

3.5 Uncertainty in Risk Estim ates .......................................................... 26 

3.6 Illustration of Risk Results ............................................................ 27 

4 Information 

4.1 O verview .......................................................................... 31 

4.2 Concepts .......................................................................... 31 

4.3 Sources of Inform ation ............................................................... 32 

5 Licensees 

5.1 O verview .......................................................................... 39 

5.2 Im portance in Risk .................................................................. 39 

5.3 C oncepts .......................................................................... 40 

5.4 Control M echanism s ................................................................. 41 

5.5 Elem ents of Risk .................................................................... 46 

5.6 Sources of Inform ation ............................................................... 57 

5.7 Observations and Insights ............................................................. 57 

6 Scrap Metal Consolidation 

6.1- O verview .......................................................................... 61 

6.2 Im portance in Risk ................................................................... 61 

6.3 C oncepts .......................................................................... 61 

6.4 Elem ents of Risk .................................................................... 64 

6.5 Sources of Inform ation ............................................................... 68 

6.6 Observations and Insights ............................................................. 68 

v NUREG-1669
Page 

7 Steel Mills 

7.1 O verview .......................................................................... 71 

7.2 Im portance in Risk ................................................................... 71 

7.3 D efinitions ......................................................................... 71 

7.4 Concepts .......................................................................... 72 

7.5 Probability of Detecting a Radioactive Source in Scrap Metal ................................. 78 

7.6 Multiple Passes Through a Radiation Monitor Station ....................................... 84 

7.7 Elem ents of Risk ..................................................................... 93 

7.8 Sources of Inform ation .............................................................. 104 

7.9 Observations and Insights ............................................................ 104 

8 Public Domain 

8.1 O verview ......................................................................... 109 

8.2 Im portance in Risk .................................................................. 109 

8.3 Concepts ......................................................................... 110 

8.4 Elem ents of Risk ................................................................... 111 

8.5 Sources of Inform ation .............................................................. 113 

8.6 Observations and Insights ............................................................ 113 

9 Need for Survey Information to Estimate Risk ................................................ 115 

10 C onclusions ........................................................................... 117 

R eferences ............................................................................... 121 

Appendices

A 

B 

C

ICC D eterm inations .................................................................... 

Survey of Licensees .................................................................... 

Survey of the Steel Industry ..............................................................

Index ................................................................................... 

NUREG-1669 vi

123 

129 

135 

151
LIST OF FIGURES 

Page 

1 Number of outcomes from three binary elements ................................................ 2 

2 Discoveries of radioactive material in the recycling stream ........................................ 9 

3 Nuclear gauges in industries overseen by regulatory agencies ..................................... 10 

4 The recycling stream of scrap steel .......................................................... 11 

5 Product and byproduct pathways from recycled scrap steel ....................................... 11 

6 Nuclear gauges moving from licensees, through the recycling stream, and contaminating 

steel products and byproducts .............................................................. 12 

7 Aspects of the subject deduced from reported discoveries of radioactive material in the recycling stream ... 14 

8 Topics discussed in this report ............................................................. 16 

9 Movement of nuclear gauges through the recycling stream ....................................... 21 

10 Example of a risk calculation .................................................... 23 

11 Resolving the prevalence and consequence of risk estimates ...................................... 26 

12 Differences in perspectives given by a point estimate and the distribution of a random variable .......... 26 

13 A comparison of point estimates can lead to conclusions that differ from a comparison of distributions .... 27 

14 Box-plot (top) and distribution (bottom) of risk estimates ........................................ 28 

15 Visual displays can influence perceptions of risk estimates ....................................... 28 

16 Three stages of nuclear gauges in the recycling stream for illustrating concepts of information........... 32 

17 Analytical history of radioactive material in the recycling stream .................................. 36 

18 Topics taken into account in the analysis of licensees ........................................... 39 

19 Estimating a civil penalty by equating the risk of a civil penalty at licensees to the risk of melting 

a nuclear gauge at steel m ills .............................................................. 44 

20 Analysis of the risk elements in the industrial environments of nuclear gauges at licensees .............. 47 

21 Analysis of the licensees' risk elements (continued) ............................................ 52 

22 Nuclear gauges throughout all industries ..................................................... 53 

23 Logic of the environment/control matrix in Figure 20 ........................................... 54 

24 Venn diagram illustrating the coverage and redundancy of control mechanisms ....................... 55 

25 Topics taken into account in the analysis of scrap metal consolidation ............................... 61 

26 Scrap m etal consolidation ................................................................. 62 

27 Location of potential radiological hazards when a nuclear gauge is shredded ......................... 63 

28 Analysis of risk elements for scrap metal consolidation .......................................... 65 

29 Topics taken into account in the analysis of steel mills .......................................... 71 

30 Radiation monitors at mills throughout the steel industry ........................................ 72 

31 Truck entering a radiation monitor station with a load of scrap metal ............................... 79 

32 Areas of detection in a load of scrap metal .................................................... 80 

33 Hypothetical variability in the detection probability for (A) heterogeneous and (B) homogeneous 

comm odities of scrap m etal ............................................................... 82 

34 Recycling stream illustrated to determine the detection probability of a commodity of scrap metal 

entering a steel m ill ...................................................................... 83 

35 Possible combinations of radioactive material in loads of scrap metal ............................... 85 

36 Relation of monitor response, alarm threshold, and hypothetical distributions of radiation 

levels from background, BC, and sealed sources ............................................... 86 

37 Logic of the one-pass, two-pass, and three-pass strategies for monitoring scrap metal .................. 88 

38 Main pathway and an additional pathway in risk element sequences for scrap metal 

entering a steel m ill ...................................................................... 90

vii NUREG-1669
Page 

39 Configurations of steel mills where a vehicle passes through a monitor station several times; 

(A) with unloading and reloading between passes; (B) without unloading between passes ............... 90 

40 Primary and secondary monitoring .......................................................... 91 

41 Analysis of the risk elements for the configuration of radiation monitors at steel mills ................. 94 

42 Analysis of the risk elements at the entrance of steel mills ....................................... 96 

43 Analysis of the risk elements at the charge bucket of steel mills .................................. 100 

44 Analysis of the risk elements at product and byproduct monitoring at steel mills ..................... 102 

45 Topics taken into account in the analysis of the public domain ................................... 109 

46 Difficulties in determining health impacts at a melt shop ........................................ 112 

47 Reasons for stating that control mechanisms either can or cannot provide immediate and continuous 

control in a given industrial environment ............................................ 124

NUREG-1669 viii
LIST OF TABLES 

Page 

1 Guideposts for developing the risk analysis .................................................... 6 

2 Evaluating changes in risk ................................................................ 25 

3 Sources of information supporting the analysis of risk elements in licensees (Figures 20 and 21) ......... 58 

4 Sources of information supporting the analysis of control mechanisms (Figure 20) .................... 59 

5 Sources of information supporting the analysis of risk elements in scrap metal consolidation (Figure 28) ... 69 

6 Outcomes when a load of scrap metal passes once through a monitor station ......................... 87 

7 Possibilities of finding a nuclear gauge when scrap metal is scanned, unloaded, reloaded, 

and scanned again ....................................................................... 92 

8 Sources of information supporting the analysis of risk elements in monitors at the entrance of steel mills 

(Figures 41 and 42) ..................................................................... 105 

9 Sources of information supporting the analysis of risk elements in yard and charge bucket monitors 

at steel m ills (Figure 43) ................................................................. 106 

10 Sources of information supporting the analysis of risk elements in product and byproduct monitoring 

at steel m ills (Figure 44) ................................................................. 107 

11 Sources of information supporting the analysis of risk elements in the public domain ............... 114 

12 Elements of risk requiring information from surveys of licensees and the steel industry ............... 115

ix NUREG-1669
LIST OF TEXT BOXES 

Page 

Summary of the Reasons for Studying Nuclear Gauges in Recycled Steel ................................ 7 

Sam ple of Convenience ...................................................................... 35 

Reworking a Load of Scrap M etal .............................................................. 74 

Department of Transportation Exemption 10656 ................................................... 75 

An Incident of Radioactive Scrap M etal ......................................................... 77 

Some Factors That Influence the Probability of an Alarm at a Radiation Monitor Station During Multiple Passes 84 

False A larm s .................................. ............................................ 89 

xi NUREG-1669
PREFACE

This report documents a 3 V2 year study on the risk 

of fixed nuclear gauges that began in the autumn 

of 1995. The risk analysis was conducted with the 

assistance of experts in relevant disciplines. Each 

expert listed as a contributor in the 

Acknowledgments was essential to the risk 

analysis. Site visits provided valuable 

perspectives on industrial operations where the 

nuclear gauges are located. Many of the site visits 

(listed on pages xxi and xxii) were made possible 

by two State regulators and an inspector at the 

Nuclear Regulatory Commission (NRC). 

Mentoring from the contributors and discussions 

with employees at industrial facilities allowed the 

principal investigator to make use of decades of 

experience. 

The principal investigator benefited from a series 

of meetings between the NRC and the Agreement 

States . Representatives from industry 

participated in the meetings to give their views on 

what should be done to improve regulatory 

controls. During these meetings, the principal 

investigator learned of the perspectives of 

different industries as people, one after another, 

stated their concerns. The meetings were 

opportunities for the principal investigator to learn

the perspectives in a way that could not have been 

obtained with separate site visits. 

This report requires a basic understanding of 

nuclear gauges, steel making, statistics, systems 

analysis, and risk analysis. However, it is not a 

tutorial in any of these subjects. The study draws 

on these subject areas and explains them enough 

to demonstrate how they were utilized. 

This analysis of one type of device, fixed nuclear 

gauges, consumed considerable resources. The 

concepts and analyses developed for this group of 

radioactive devices are readily applicable to at 

least some other types of devices. Thus, an 

analysis of other devices can benefit from this 

analysis. 

The risk analysis has been documented so that the 

reader can understand how the study was 

conducted without a myriad of details. Some 

detail has been omitted to direct attention toward 

concepts yielding observations and insights. Plain 

English was used instead of jargon to convey a 

common understanding of the subject among 

Federal regulators, State regulators, the public, 

and a wide variety of industries.

t U.S. Nuclear Regulatory Commission, "Final Report of the NRC

Agreement State Working Group to Evaluate Control and 

Accountability of Licensed Devices," NUREG-155 1, October 1996.

NUREG-1669 °.°i
EXECUTIVE SUMMARY

Fixed nuclear gauges containing the radionuclides 

"7Cs, 60

Co, or 2'Am are used in many industries 

to improve the quality and lower the costs of 

products for industrial, commercial, and private 

uses. Gauges that are improperly controlled 

during use and transfer can expose people to 

radiation and, upon entering the stream of 

recycled steel, can cause steel mills to spend 

millions of dollars to decontaminate equipment 

and dispose of contaminated materials. The risk 

to licensees and the recycling industries that 

nuclear gauges pose is incompletely understood. 

This report discusses an analysis of fixed nuclear 

gauges that was performed to study the risk to the 

public, to workers, and to property. All plausible 

scenarios of gauges traveling from facilities where 

the gauges are used to unintended locations where 

adverse consequences might result were 

considered. The focus of the analysis is on the 

recycling stream, where the gauges can be 

breached in scrap yards or melted in steel mills. 

Using established methods, elements of risk are 

examined, the relationships of the elements are 

elucidated, and the data needed to evaluate the 

elements for estimating risk are specified. For 

reasons discussed in this report (principally a lack 

of needed data), a quantitative assessment of risk 

could not be made. 

Industrial facilities that use nuclear gauges are 

required by their licenses to maintain 

accountability. But under some conditions and 

circumstances at these facilities, control 

mechanisms may be compromised, allowing 

gauges to be inappropriately used or transferred. 

For example, gauges have been inadvertently 

locked on instead of off when a process unit is 

serviced, placing workers at risk to radiation 

exposures. Gauges have been improperly 

transferred when a process unit is moved to 

another facility or when equipment is scrapped 

and discarded in landfills or collected for 

recycling. When a gauge enters the recycling 

stream and is processed along with sorted, cut, and 

baled scrap metal, the processing may dislodge 

and disperse the radioactive material in the gauge.

Employees may be exposed to radiation. 

Equipment may be contaminated by radioactive 

material. Sophisticated monitors at scrap yards 

and steel mills can detect minute amounts of 

radiation emanating from loads of scrap metal. 

But an intact gauge may not emit enough radiation 

to be detected, allowing a gauge to be melted with 

scrap metal in the furnace of a steel mill. 

Depending on the type of radioactive material, the 

steel product, the furnace dust, or the slag may be 

contaminated. Finally, there have been instances 

where contaminated steel products have entered 

the marketplace. 

Although many thousands of gauges are used in 

domestic industries, most of them are usually not 

a risk to life and property because they are in use, 

controlling industrial processes. Licensees 

implement control mechanisms to reduce risk. A 

gauge that is at risk (controls have been lost) does 

not necessarily mean that it causes exposures or 

enters the recycling stream; it means that the 

gauge has a potential to do so. An effective 

control is one that operates immediately and 

continuously when gauges are at risk to prevent 

them from being inadvertently removed from their 

intended places. Three effective forms of 

immediate and continuous control (ICC) 

sometimes used at industrial facilities are as 

follows: 

"* Although not typically viewed as a control, a 

gauge in use, controlling production, cannot 

be removed and discarded without drawing 

attention. 

"* When a gauge must be removed from a 

process unit, storage in an area that is 

dedicated only for gauges reduces the chances 

of the gauge being discarded with scrapped 

materials and equipment. 

" An unused gauge that has been returned to a 

vendor is not at risk of being discarded into 

the recycling stream.

XV NUREG-1669
EXECUTIVE SUMMARY

These three controls- in use, interim dedicated 

storage, and return to a vendor-are considered 

hard controls, because they place a gauge in a 

definite location where it is unlikely to be 

removed unnoticed. Whatever reliance that is not 

placed on hard controls is typically placed on so

called soft controls, such as labels, semi-annual 

inventories, education and communications, and 

civil penalties. Soft controls are less effective 

than hard controls in providing ICC because they 

do not always gain enough attention at the right 

times and they can be degraded by conditions and 

circumstances at facilities. A difficulty for 

licensees in maintaining accountability is that they 

lack the collective experience of all industries of 

what does and does not provide ICC. Because 

regulations are necessarily broad and non

prescriptive, licensees have considerable leeway 

to devise their own control programs. Many 

licensees might benefit from learning about 

effective ICC practices. 

Perfect control that eliminates the risk to life and 

property is impractical to require by regulatory 

agencies (i.e., NRC or Agreement States) and 

implement at industrial facilities. Many factors 

placing the gauges at risk are outside the 

jurisdiction of regulatory agencies. For example, 

regulatory agencies cannot direct licensees how to 

perform maintenance shutdowns, a circumstance 

where gauges might be discarded with scrap 

materials. Other factors cannot be completely 

controlled by licensees. For example, former 

employees cannot be told to implement the 

responsibility for gauges at a facility that has 

suddenly closed, a circumstance where gauges 

might be discarded when the facility is dismantled. 

This reality leaves a regulatory agency with the 

task of devising and communicating ICC practices 

that can be efficiently implemented. This reality 

also leaves licensees and the recycling industries 

with the responsibility for making business 

decisions to accept certain risks. For licensed 

facilities, employees may sometimes risk exposure 

to radiation because completely preventing 

exposure is impractical. For the recycling 

industries, scrap metal facilities may sometimes

incur the cost to provide a level of protection that 

is not completely adequate to prevent a nuclear 

gauge from being inadvertently recycled. 

The primary means of ensuring that the gauges are 

kept in their intended locations are controls. 

However, because controls sometimes fail to 

prevent nuclear gauges from entering the 

recycling stream, many scrap yards and steel mills 

have installed radiation monitors. Although the 

radiation monitors are important protection for 

scrap yards and steel mills, too much reliance 

seems to be placed on the technology alone 

instead of understanding the ramifications of using 

the technology: 

"* The chances of detecting radioactive material 

with a radiation monitor are dependent on 

several factors, not always under the control 

of scrap yards or steel mills. 

"* Even when a radiation monitor is present, it is 

sometimes disabled because numerous false 

alarms are annoying and established 

procedures are not always followed. 

"* Some scrap yards and steel mills will prevent 

a truck load of scrap metal from coming onto 

their grounds after a radiation alarm is 

activated and turn the load away without 

assurances that it will be safely investigated. 

A rejected load can be taken elsewhere, such 

as a scrap yard without radiation monitors or 

another steel mill, on the chance that the 

radiation monitors there will not alarm. At 

least some steel mills are unaware of a 

Department of Transportation exemption that 

allows a load that is suspected of containing 

radioactive material to be rejected and then 

readily sent to a facility where it can be safely 

investigated. 

"* Instead of encouraging recycling facilities to 

investigate the cause of a radiation alarm, 

which may just be a benign form of 

radioactive material, contractual arrangements

NUREG-1669 xvi
EXECUTIVE SUMMARY

between steel mills and the scrap yards 

supplying them sometimes encourage 

facilities to reject a load of scrap metal 

suspected of containing radioactive material. 

Furthermore, even when the radiation monitors 

are used as intended, the shielding characteristics 

of large scrap metal loads have not been evaluated

to accurately assess the chances of detecting a 

nuclear gauge in the load. 

A risk analysis should be of interest to all 

stakeholders- agencies that promulgate 

regulations, licensees who must comply with the 

regulations, and the recycling industries who use 

scrap steel as a resource for making products.

xvii NUREG-1669
ACKNOWLEDGMENTS

Name 

Lee 

Abramson 

Steven 

Baggett 

Ann 

Beranek 

Michael 

Calley 

Mark 

Cunningham 

Martha 

Dibblee 

Richard 

Ladun 

John 

Lubinski 

Dan 

Lurie 

Harry 

Martz 

Mary 

Mejac 

Mary 

Meyer 

David 

Nigg 

Samuel 

Pettijohn 

Rayleona 

Sanders 

Maria 

Schwartz 

Harold 

VanderMolen 

James 

Yusko

Affiliation 

Office of Nuclear Regulatory 

Research, NRC 

Office of Nuclear Materials 

Safety and Safeguards, NRC 

Office of Nuclear Regulatory 

Research, NRC 

Lockheed Idaho Technologies 

Co., Idaho Falls, ID 

Office of Nuclear Regulatory 

Research, NRC 

Oregon Health Division, 

Portland, OR 

Region I, NRC 

Office of Nuclear Materials 

Safety and Safeguards, NRC 

Office of the Chief Financial 

Officer, NRC 

Los Alamos National Laboratory, 

Los Alamos, NM 

Office of Information Resources 

Management, NRC 

Los Alamos National Laboratory, 

Los Alamos, NM 

Lockheed Martin Idaho 

Technologies Company 

Office of the Analysis of 

Operational Data, NRC 

Office of Information Resources 

Management, NRC 

Office of the General Counsel, 

NRC 

Office of Nuclear Regulatory 

Research, NRC 

Pennsylvania Department of 

Environmental Protection, 

Pittsburgh, PA

NUREG-1669

Contribution 

Provided conceptual and technical input for statistics and risk analysis. 

Met with the principal investigator weekly to give technical guidance. 

Assisted in developing concepts and writing selected sections. Reviewed 

selected sections. 

Provided an understanding of regulations and communicated regulatory 

needs that the risk analysis is to address. Reviewed the final draft of the 

report. 

Edited notes, letters, memoranda, and selected sections on a short-notice 

basis. Gave valuable opinions on the presentation of concepts. 

Gave support in using a computer program to calculate risk. 

Reviewed and approved the final manuscript to be published. 

Hosted site visits and gave technical support. Provided extensive 

mentoring about licensees in an Agreement State. Reviewed Section 6. 

Hosted site visits during inspections. 

Provided an understanding of regulations and communicated regulatory 

needs that the risk analysis is to address. Reviewed the final draft of the 

report. 

Explained statistical concepts. Met with the principal investigator as needed for technical guidance. Assisted in developing risk analysis 

concepts and writing selected sections. Reviewed selected sections and 

the first draft manuscript. 

Provided consultation early in the study and referral to a professional 

survey designer. 

Edited selected sections of the manuscript early in the study. 

Provided guidance on survey procedures and design. Reviewed licensee 

and steel industry surveys before and during pilot testing. 

Reviewed concept of the detection probability in Section 7.5.2. 

Assisted with an NRC database about incidents of sealed source devices. 

Edited selected sections. 

Provided guidance on laws and statutes. 

Served as a technical and strategic advisor. Assisted in developing the 

concepts in Section 8.4. Provided moral support. 

Hosted site visits and gave technical support. Provided extensive 

mentoring about the subject of the risk analysis. Reviewed Sections 6, 

8.3, and 8.4.

xix
SITE VISITS

3M Co., Cottage Grove Center, Cottage Grove, MN 

Allegheny Ludlumn Corp., Allegheny Ludlum Steel, 

Brackenridge, PA 

Allegheny Power Co., Mitchell Power Station, 

Courtney, PA 

Allied Signal Advanced Materials, Inc., Specialty 

Films, Pottsville, PA 

American Iron and Steel Institute, Washington, DC 

Armco, Inc., Specialty Flat-Rolled Steel, Butler, PA 

Auburn Steel Co., Inc., Auburn, NY 

Bar Technologies, Inc., Johnstown, PA 

Barletta Materials and Construction Co., Inc., Hazelton, 

PA 

Bemis Co., Inc., Film Division, West Hazelton, PA 

BJ Services Co., Fairmount City, PA 

Boise Cascade Corp., White Paper Division, St. Helens, 

OR 

Brandenburg Industrial Service Co., Chicago, IL 

Calbag Metals Co., Portland, OR 

Caparo Steel Co., Farrell, PA 

Cascade Steel Rolling Mills, McMinville, OR 

Columbia American Plating Co., Portland, OR 

East Stroudsburg University, East Stroudsburg, PA 

Erie Forge and Steel, Inc., Erie, PA 

Evergreen Helicopters, Inc., McMinnville, OR 

Faxe Paper Pigments, Johnsonburg PCC Plant, 

Johnsonburg, PA 

First Miss Steel, Inc., Hollsopple, PA 

Gottlieb, Inc., Neville Island, PA 

GS Roofing Products Co., Inc., Portland, OR 

Horsehead Resource Development Co., Inc., 

Palmerton, PA 

Institute of Scrap Recycling Industries, Inc., 

Washington, DC

International Paper, Erie Mill, Erie, PA 

J&L Specialty Steel, Inc., Midland, PA 

Keywell Corp., West Mifflin, PA 

Koppel Steel Corp., Beaver Falls, PA 

Lehigh Asphalt Paving and Construction Co., 

Tamaqua, PA 

Liberty Iron and Metal Co., Inc., Erie, PA 

Lukens Steel Co., Coatesville, PA 

Luria Brothers, Koppel, PA 

Maple Creek Mining, Inc., Preparation Plant, New 

Eagle, PA 

McKeesport Municipal Authority, McKeesport, PA 

Mercer Lime and Stone Co., Slippery Rock, PA 

National Association of Demolition Contractors, 

Doylestown, PA 

Ohmart Corp., Cincinnati, OH 

Oregon Department of Human Resources, Radiation 

Protection Services, Portland, OR 

Oregon Steel Mills, Portland Steelworks, Portland, OR 

Pennsylvania Department of Environmental Protection, 

Field Operations -Radiation Protection, Pittsburgh, 

PA 

Pennzoil Products Co., Rouseville, PA 

Pittsburgh Brewing Co., Pittsburgh, PA 

Schuller International, Inc., Building and Insulation 

Division, Richmond, IN 

Sequa Precoat Metals, McKeesport, PA 

Simpson Timber Co., Oregon Overlay Division, 

Portland, OR 

Smurfit Newsprint Corp., Newberg, OR 

Spang Specialty Metals, Advanced High Technology 

Alloys, Butler, PA 

Steel Dynamics, Inc., Butler, IN 

Steel Manufacturers Association, Washington, DC

xxi NUREG-1669
SITE VISITS

SteelMet, Inc., McKeesport, PA 

The Carbon/Graphite Group, Inc., St. Marys, PA 

Tube City, Inc., Pittsburgh, PA 

U.S. Generating Co., Scrubgrass Generating Plant, 

Kennendell, PA

USX Corp., U.S. Steel Mon Valley Works, 

Dravosburg, PA 

USX Corp., U.S. Steel Gary Works, Gary, IN 

Widmer Brothers Brewing Co., Portland, OR 

Willamette Industries, Inc., Albany Paper Mill, Albany, 

OR

NUREG-1669 xxii
ABBREVIATIONS 

BC benign contamination 

BOF basic oxygen furnace 

DEP Pennsylvania Department of Environmental Protection 

DMR data-mix ratio 

DOT U.S. Department of Transportation 

E&C education and communication 

EAF electric arc furnace 

EPA U.S. Environmental Protection Agency 

GL general license (licensee) 

HLA high-level accountability 

ICC immediate and continuous control 

IDS interim dedicated storage 

IRM iron-rich material 

ISRI Institute of Scrap Recycling Industries 

LU in use 

LANL Los Alamos National Laboratory 

LLW low-level waste 

MW mixed waste 

NMSS Office of Nuclear Materials Safety and Safeguards 

NORM naturally occurring radioactive material 

NRC Nuclear Regulatory Commission 

OMB Office of Management and Budget 

OSHA Occupational Safety and Health Administration 

OU out of use 

P&S plate and structural scrap metal 

QCR query at a change in responsibility 

RSO radiation safety officer 

SL specific license (licensee)

NUREG-1669 °.°i
LIST OF VARIABLES

VI Description

psupply 

P(t) 

Prj 

Pr{FIA} 

Pr{accept} 

Pr{accept}x 

Pr{detect} 

Pr{miss} 

Pr{reject} 

R 

RT 

S 

t 

T 

V 

w 

xj(t)

prevalence of nuclear gauges in the domestic supply of scrap metal 

prevalence of gauges throughout all industries at time t 

probability of a nuclear gauge being in the j1 area of a scrap metal load 

probability of finding a nuclear gauge that has been discarded into the 

recycling stream 

probability of accepting a load of scrap metal containing a nuclear gauge 

probability of accepting a load after only primary monitoring, p, or after 

both primary and secondary monitoring, ps 

prbability of detecting a nuclear gauge in a load of scrap metal 

probability of missing a nuclear gauge in a load of scrap metal 

probability of rejecting a load of scrap metal containing a nuclear gauge 

total aggregate risk 

k' aggregate risk for the j' group of risk element sequences 

aggregate risk for all groups of risk element sequences 

weight of the scrap metal supply 

time 

time period 

volume of a vehicle transporting scrap metal 

width of a vehicle transporting scrap metal 

number of gauges in the j"' location at time t

iriable

.rea n n"' detection area in a load of scrap metal 

C3 consequence of the j1 sequence of risk elements 

Cr.e amount of a civil penalty 

Cmet financial damage of melting radioactive material 

Cp capacity factor of a process unit 

fsupply fraction of the domestic scrap metal supply consumed by a mill 

E:(@) expected value of a random variable, @ 

5i fraction of risk from the jr" group of risk element sequences 

h height of a vehicle transporting scrap metal 

'load incidence of nuclear gauges in a load of scrap metal 

,mill incidence of nuclear gauges reaching a mill 

I length of a vehicle transporting scrap metal 

L tare weight of one load of scrap metal 

M amount of scrap metal consumed by a mill in the period T 

NA number of gauges at risk in a given year 

NF number of gauges found in the recycling stream (both before and after 

melting at a steel mill) in a given year 

N°P number of gauges at a facility in use on operating process units N number of gauges at a facility inut ofuse o but on perating process units 

Nj,k number of gauges in the j' possibility of the kth element 

NF total number of gauges in any location of a facility given the state of the Nr facility (e.g., constant ownership, changing ownership) 

P/ prevalence of gauges along the j' sequence of risk elements 

prevalence of nuclear gauge throughout the U.S. X = GL, SL, or T, for 

Ax the prevalence of generally, specifically, or both generally and 

specifically licensed gauges, respectively

N 

mn 

1 

1

l/time

1 

l1

Nc 

Nc

47

/time 21 

/time 19 

- 81 

- 54 

- 87 

- 93 

- 44 

- 44 

- 87 

C/t 24 

C/t 26 

C/t 26 

tons 21 

ote (b) Note (b) 

)te (b) 22 

ft3 83 

ft 83 

-- 19

(continued next page)

NUREG-1669

1

XXV

Defined 

Units on Page 

-- 81 

ote (a) 24 

onetary 44 

onetary 44 

-- 51 

-- 22 

-- 27 

-- 26 

ft 83 

/time 21 

/time 22 

ft 83 

tons 21 

tons 22 

- 54 

- 54 

- 51 

- 51 

- 51 

- 51 

/time 24
LIST OF VARIABLES

Variable 

P 

(Oj,k 

(P~bnn 

Toup 

(P(t) 

T1blend 

T(A. A•.,) 

T•(A. Nx..) 

o• 

Ti

Description 

change is risk from the ni" alternative expressed as a ratio 

change is risk from the n' alternative expressed as a 

difference 

density of a load of scrap metal 

fraction of gauges at the j' possibility of the k' element 

fraction of gauges on process lines shut down for 

maintenance 

fraction of gauges in use on operating process units 

fraction of gauges out of use on operating process units 

proportion of gauges in the jI location at time t 

expected values (i.e., mean) of a random variable 

probability of detecting a nuclear gauge in a load of scrap metal 

net detection probability for a blend of scrap metal 

commodities 

detection probability in the j' scrap metal commodity 

probability of an alarm on the nth pass through a monitor 

station given an alarm on the (n-I) pass 

probability of an alarm on the nth pass through a monitor 

station given no alarm on the (n-1) pass 

variance of a random variable 

sequence of elements in a risk triplet

weighting factor: relative weight of the j" scrap metal 

Ojo• commodity

I

Nc

Defined 

Jnits on page 

-- 25 

- 25 

ns/ft3 84 

- 51 

- 51 

- 51 

- 51 

- 19 

)te (c) 27 

-- 81 

-- 84 

-- 84

Pronuncia

tion 

gamma 

delta 

rho 

phi 

phi 

phi 

phi 

phi 

mu 

psi 

psi 

phi

- 88 phi 

- 88 phi 

Note (c) 27 sigma 

- 24 tau 

84 omega

NOTES 

(a) Consequences are expressed in units of radioactivity and dollars. Usually expressed as a year throughout this report. 

c Units of the random variable.

NUREG-1669 xxvi
1 INTRODUCTION

1.1 Definitions 

Analyze conveys the notion of separating the 

subject into its parts to identify or study its 

structure, to examine and interpret. An analysis is 

the basis for an assessment. 

Assess means to decide on the amount or fix the 

value. With information, an analysis can be used 

to assess risk. 

Control mechanisms are the means by which 

regulators and licensees keep licensed nuclear 

material in intended locations. Typical 

mechanisms include warning labels and physical 

security. The phrase is mentioned here and 

discussed in detail in Section 5. 

Stakeholders are individuals, organizations, or 

industries that can be affected by changes in 

control mechanisms.

1.2 Concepts 

Radioactive material in the recycling stream is a 

complex subject. A comprehensive analysis 

allows the subject to be systematically examined. 

At first, the subject appears formless. But 

through a risk analysis, the pieces can be sorted, 

disentangled, and unfolded into a clear picture. 

A risk analysis complements and builds on other 

work that has been done: 

1. Identify and document the subject 

Discoveries of radioactive material in the 

recycling stream have been summarized and 

documented in the literature (Ref. 1). 

Reference 1 is regarded by many stakeholders 

as an excellent summary of reported 

discoveries. 

2. Develop solutions. Discussions among 

Federal regulators, State regulators, and

members of industry resulted in 

recommendations to Nuclear Regulatory 

Commission (NRC) staff. 

3. Analyze the subject and evaluate solutions. 

The interaction of the control mechanisms, the 

regulated community (i.e., licensees), and 

other industries (i.e., in the recycling stream) 

forms a complex system that can be analyzed. 

An analysis has value over postulating the net 

effect of the control mechanisms themselves; 

facets of the subject can be delineated, related, 

reviewed, and discussed. 

A risk analysis can also be used to estimate what 

changes in current circumstances may produce 

desired outcomes. Current circumstances are 

reported in Reference 1 and experienced by both 

regulators and industry staff. Desired outcomes 

include making appropriate changes in control 

mechanisms and business practices. 

A risk analysis must consider what is known, 

could be known, and cannot be known: 

"* Known are the implications of the analyses, 

assumptions, and currently available data. 

For example, qualitative observations and 

insights can be deduced from the analyses 

shown in Sections 5.5, 6.4, 7.7, and 8.4. 

Implications of the currently available data are 

discussed in Section 10. 

" Could be known is how risk changes when 

control mechanisms are changed or more 

information became available. The changes 

in the control mechanisms may be postulated 

with expert judgment. The additional 

information may consist of more detail in the 

analyses, more data, or expert judgment. For 

example, the probability of detecting 

radioactive material in the recycling stream is 

poorly characterized (see Section 7.5). The 

analyses can be used to determine how risk 

estimates change as the detection probability 

is changed by postulating plausible values. If 

the risk estimates are significantly affected by

I NUREG-1669
1: INTRODUCTION

the plausible values, then the benefits of 

obtaining more information for more precise 

risk estimates, more accurate estimates, or a 

more solid basis for the risk estimates can be 

related to the expense of obtaining better 

information (see also Section 4.2). 

0 Cannot be known is information for risk 

factors that is impractical or infeasible to 

obtain. The factors are relevant to risk; hence, 

they must be delineated. But information for 

assessing the factors is limited to plausible 

judgments. An example is the effectiveness 

of control mechanisms (see Section 5.5). 

A risk analysis explicitly states the factors that 

have been taken into account to analyze and assess 

risk. Stakeholders (e.g., regulators, scrap dealers, 

demolition contractors, steel mills, gauge vendors, 

radiation monitor vendors) can understand risks 

and how changes in control mechanisms and 

business practices will change the risks. A 

systematic analysis then provides a means to 

discuss and evaluate disagreements. 

A comprehensive risk analysis gives a sound 

foundation by providing assurance that reasoning 

leading to conclusions is cogent. Reference 2 

states that cogent reasoning uses all relevant 

information, valid premises, and correct logic. A 

risk analysis makes these elements explicit: 

N Relevant information. When faced with a 

large number of possibilities, people usually 

limit their view of a problem and focus 

instead on narrow areas. The subject of 

radioactive material in the recycling stream is 

not readily amenable to understanding with 

intuition. The perception of uncertainty 

fundamentally changes the view of a problem. 

When unknowns are acknowledged, clear-cut 

decisions for any stakeholder are shown to be 

overly simplistic (Ref. 3,. page 298, and 

Section 3.5). Hence, neither expert judgment 

nor a simplified analysis are completely 

satisfactory substitutes for an analysis where 

relevant facets of a subject have been 

delineated. Doing so can lead to changes in a

system that have only a secondary effect on 

risk. Any evaluation that fails to look 

systematically at a large fraction of the 

possibilities has a high probability of missing 

important aspects of the problem (Ref. 3, page 

308). 

Figure 1 shows a simple system with three 

elements. Each element has only two possible 

outcomes. The number of possible outcomes 

for the entire system is 2'= 8. When the 

number of elements increases to five, the 

number of outcomes increases exponentially 

to 21 = 32. The subject of the risk analysis, 

viewed as a system, has more than 30 

elements, each element having usually two to 

six outcomes; the number of outcomes to be 

evaluated are far beyond what can be done 

intuitively. But as discussed in Sections 2.4 

and 2.5, some sequences were not taken into 

account; thus some relevant information is 

excluded. In practice, "all" means that which 

is cost-effective to obtain and is necessary for 

making meaningful risk estimates.

Elements of 

the system 

A B C

Success 

success 

Success Failure 

Success 

Failure 

Begin> Failure 

Success 

Success 

Failure 

Failure [ uccess 

Failure e 

Failure

Outcomes

1 

2 

3 

4 

5 

6 

7 

8

Figure I Number of outcomes from three binary 

elements.

NUREG-1669 2
1: INTRODUCTION

* Valid assumptions. The basis for much 

planning and decisions is the assumption that 

circumstances and responses to changes made 

under those circumstances are known. This 

simplifies a complex problem by reducing the 

number of possibilities and ignoring 

uncertainty. However, this assumption, 

although convenient, is usually false (Ref. 3, 

page 272). Circumstances are not fully 

known. With the analyses of the licensees 

(Section 5.5), scrap yards (Section 6.4), steel 

mills (Section 7.7), and the public domain 

(Section 8.4) many possible paths of 

radioactive material through the recycling 

stream are enumerated, expanding the scope 

of the subject beyond what has been reported. 

Proving every aspect of an analysis is 

unnecessary. Assumptions can be made. But 

assumptions should not be made on the points 

of an analysis that are at issue. Within the 

analyses, reasons are given to support the 

claim that assumptions are valid. 

* Correct logic. Sometimes reliance can be 

placed on unsophisticated analyses to identify 

critical issues from a clear perspective; this 

can be more effective than the use of complex 

analyses whose assumptions are partially or 

totally hidden (Ref. 4, page 1). However, a 

highly structured analysis, pulling together 

information about relevant areas of the 

complex subject, is necessary to consistently 

evaluate options, systematically assess 

unknowns, and balance benefits and 

consequences. 

One could argue that Reference I is sufficient 

reason to change regulations. Furthermore, when 

combined with specific information about 

consequences, the empirical data summarized in 

Reference 1 can be used to make a rough estimate 

of risk as defined by the NRC (Ref. 5). But the 

constituents of risk are the sequences of risk 

elements of a radioactive source from licensees 

through the recycling stream, the prevalence of 

nuclear gauges along the sequences, and the 

consequences of thegauges from the sequence of

risk elements. From Reference 1, a few general 

categories of sequences can be defined in terms of 

endpoints, such as finding radioactive material 

before or after it has been melted at a steel mill. 

Consequences can be associated with these 

categories of sequences. Then, using the 

definition of risk in Reference 5, an estimate of 

risk can be computed. However, such an estimate 

is insufficient for predicting the effect of changes 

to control mechanisms because of the following: 

"* A risk analysis must take into account aspects 

of the subject that are relevant to risk. 

"* The situation is complex, reflecting the 

influence of control mechanisms, the radiation 

monitors, the practices of using the monitors, 

the practices of responding to alarms, and the 

practices of record keeping. Likewise, the 

data about the situation are complex and must 

be carefully studied. 

"* The uncertainty in an empirical risk estimate 

cannot be readily determined from the data 

summarized in Reference 1. Uncertainty is 

present; whether or not it is expressed, it is an 

integral part of an estimate. Uncertainty has 

a bearing on how the predicted effects of 

changes are perceived (see Section 3.5). 

"* An estimate of risk from empirical data may 

apply only to the situations from which the 

data are collected. The empirical data 

summarized in Reference I apply only to the 

status quo (more precisely, only the more 

recent part of the data apply because 

circumstances changed as the data were 

collected). Therefore, data are scarce. 

Calculating risk requires information about the 

sequences of events leading to consequences, the 

prevalence of gauges along the sequences, and the 

consequences (e.g., exposure to radiation) of the 

gauges at the end of the sequences. The empirical 

data summarized in Reference 1 supply only some 

of this information. The reference is essential for 

beginning a risk analysis, which in turn can be 

used to evaluate control mechanisms.

3 NUREG-1669
2 SUBJECT

2.1 Overview 

The goal of this study is to analyze and assess the 

risk from using nuclear gauges containing 131Cs, 

6°Co, and 24 1

Am. 

.Reference 1 is an excellent starting point for an 

analysis. The reference clearly documents that 

nuclear devices have been found in the recycling 

stream of scrap steel. The reported discoveries of 

6°Co, 137

Cs, and 24"Am, often used in fixed nuclear 

gauges to control industrial process units, are a 

hazard to life and property. Adverse 

consequences from the gauges have occurred at 

licensees, scrap yards, and steel mills. 

The licensees, scrap yards, and steel mills can be 

viewed as a system to analyze. Although many 

aspects of these area are beyond the jurisdiction of 

regulatory agencies, the aspects can influence both 

the control of gauges in the licensees and recovery 

of gauges from the recycling stream. The data on 

discovered radioactive material reveals aspects of 

this system that need to be taken into account. 

2.2 Definitions 

Benign contamination (BC) refers to innocuous 

forms of radioactive materials, such as NORM 

(defined below) and thorium in alloys. 

A comprehensive risk analysis both accounts for 

all relevant aspects of the subject and gives a 

thorough understanding of the findings. 

A goal is a broadly stated purpose (Ref. 6). 

Label refers to the radiation trefoil. 

Naturally occurringradioactive material (NORM) 

refers to pipe scale, other deposits, dirt, and 

refractory materials. This is the way that NORM 

is characterized in Reference 1. 

An objective is a specific accomplishment 

necessary to achieve a goal (Ref. 6).

Radium refers to discrete sources of 226

Ra used in 

nuclear devices. This is the way that radium is 

characterized in Reference 1. 

A risk element is an event or state placing a sealed 

source at risk. 

A sequence of risk elements is a combination of 

risk elements leading to a consequence. 

2.3 Goal and Objectives 

The goal of this study is to analyze and assess the 

risk from fixed nuclear gauges. The objectives of 

the study are taken from risk analysis in general 

and then from Reference 7. The objectives from 

risk analysis in general are as follows: 

"* Develop a concise and rigorous perspective of 

radioactive material in the recycling stream. 

"* Develop concepts necessary for understanding 

the control of gauges. 

"* Develop a framework for estimating risk. 

"* State observations and insights derived from 

thoroughly studying the subject. 

"* Show what is known, what can be known, and 

what cannot be known. 

"* Estimate risk. 

The objectives from Reference 7 are as follows: 

1. Determine the resources the Nuclear 

Regulatory Commission (NRC) or Agreement 

States should expend in searching for a lost 

device or source that is believed to be in the 

public domain. 

2. Provide a basis for the Office of Nuclear 

Materials Safety and Safeguards (NMSS) staff 

to assess changes to current NRC positions 

regarding nonlicensees who find a lost nuclear 

device.

5 NNUREG-1669
2: SUBJECT

3. Develop a basis for the NMSS staff to propose 

resource allocations for preventing or 

mitigating incidents where radioactive 

material is lost, and determine the impacts of 

proposed changes in control mechanisms. 

4. Develop issues that the risk analysis is to 

address and delineate the necessary technical 

detail to address the issues. 

5. Assess the potential for consequences to 

identify important sequences of risk elements. 

6. Estimate potential doses to occupational 

workers and members of the public.

Table 1 shows supplemental objectives, their 

references, and the means by which they are met. 

The study began as a result of a request from 

NMSS to the Office of Nuclear Regulatory 

Research (Ref. 7). Discussions between the staffs 

of the two offices resulted in specific technical 

requirements (Ref. 8). The Code of Federal 

Regulations (Ref. 9) encompass regulations that 

the NRC establishes. Some concerns were from 

public meetings (Ref. 10) and site visits. 

Objectives 1 through 4 require an assessment of 

risk. The framework for an assessment was 

developed, but an assessment could not be done, 

principally because necessary data could not be 

obtained (see Section 9). Objective 5 was 

accomplished; many issues that were poorly

Table I Guideposts for developing the risk analysis. LEGEND: / indicates facets that are within the scope of the analysis. X indicates that 

an item is outside the scope. 

Guideposts

Item

Risk, probabilities 

Analysis 

Assess changes in control mechanisms 

Technical detail to address relevant issues

Exposures to radiation

Property damage 

State of devices: 

Lost 

Improperly transferred and disposed 

Entering the recycling stream 

Melted in furnaces 

Resources spent to find 

Manufacture and transport 

Activity of radioactive material to regulate

Use empirical data

Code of Federal Regulations (Ref. 9) I Request from regulators (Ref. 7) 

Other request from regulators (Ref. 8) 

I Statements from public meetings (Ref. 10) and site visits IMeans To Accomplish 

i Use the definition of aggregate risk (Section 3.4) 

ZIZIZi Examine the subject (Section 1) 

1 [ Structure of the risk analysis (Section 3.3) 

Delineate risk elements (Section s5.5, 6.4, 7.7, and 8.4) 

V/ / V/ Precluded (Section 8.4) 

/4 i 1 Analyze financial impacts (Section 8.4) 

Concepts of immediate and continuous control, at risk, and 

) probability of improper disposal (Sections 5.3, 5.4, and 

/ 5.5) 

Impacts on scrap metal processors (Sections 6.4 and 7.5) 

Assess changes in risk (Section 3.3) 

X_ Outside the scope of the study 

[ 1 Jj Measures of impacts to health (Section 8.4) 

I Information is specified in Sections 5.6, 6.5, 7.8, and 8.5

NUREG-1669 6
2: SUBJECT

known are discussed throughout this report. 

Objective 6 could not be definitively done; hence, 

an alternative was developed and is discussed in 

Section 8.4. Consequences to life and property 

are discussed in Sections 5.5, 6.4, 7.7, and 8.4. 

The supplemental objectives were met as 

indicated in Table 1. 

2.4 Subject of the Risk Analysis 

The subject of this risk analysis is the 

accountability of fixed nuclear gauges containing 

either '"TCs, 6

°Co, or 24 Am. The gauges are used 

in many industries to measure the density of 

materials in pipes, the amount of materials in 

tanks, the amount of materials on conveyor belts, 

or the thickness of metal films. When 

accountability at the licensees is lost, the gauges 

are usually found in the ferrous metal recycling 

stream. Other places where they may go include 

landfills and other facilities when equipment is 

salvaged. This analysis is focused on the 

accountability at the licensees and on the 

movement through the recycling stream for the 

following reasons: 

E Enough of the subject is analyzed to make 

robust estimates of risk. Many results of the 

risk analysis will apply to other final states of 

the gauges that have not been analyzed. Some

other final states of nuclear gauges do not 

merit an analysis. Gathering information, not 

only to develop an analysis but also to obtain 

data for risk calculations, is expensive. A 

well-designed study will make effective use of 

resources so that the entire subject does not 

have to be analyzed. 

"* Nuclear gauges are often found in ferrous 

scrap metal, possibly because they have a steel 

exterior and are on steel equipment. Scrap 

metal is valuable; most of it is recycled and 

little is discarded. 

"* The risk of melting radioactive material is 

proportional to the consumption of scrap 

metal. Steel mills consume most of the scrap 

metal supply. Therefore, the steel industry is 

subject to most of the risk. 

"* According to the information documented in 

Reference 1, most of the discoveries of 

radioactive material that are dangerous to life 

and property are 'STCs, 6°Co, or 241

Am sources 

in recycled steel. Reference 1 suggests that 

the types of gauges found in the recycling 

stream are those that are attached to pipes or 

tanks, move across conveyor belts, or move 

across metal films. Another source of 

information on the occurrence of nuclear 

gauges in the recycling stream may show

Summary of the Reasons 

for Studying Nuclear Gauges in Recycled Steel

" Most of the subject is analyzed. Many results of 

the risk analysis will apply to other final states of 

the gauges that have not been analyzed. Other final 

states of nuclear gauges do not merit an analysis. 

" The risk of melting radioactive material is 

proportional to the consumption of scrap metal. 

Steel mills consume most of the scrap metal supply. 

Therefore, the steel industry is subject to most of 

the risk. 

" According to Reference 1, most of the discoveries 

of radioactive material that are dangerous to life

and property, '"7Cs, "Co, and 241

Am, have been 

found in recycled steel. 

"* The gauges are expected to be mostly in ferrous 

scrap metal because the equipment they are on is 

made of steel. 

"* Scrap metal is valuable and likely to be in recycled. 

"* Two trade associations representing the steel 

industry and a third association representing scrap 

dealers have been most vocal about a need for more 

stringent controls on licensees.

7 NUREG-1669
2: SUBJECT

otherwise. But only the data for Reference 1 

were used in this study. Each database will 

have its own characteristics because each 

database about nuclear gauges is a sample of 

convenience, not a random sample (see 

Section 4.3.2). Limited resources in this study 

precluded comparing and contrasting 

databases, then building a common database. 

Also, the data of Reference 1 are in a form 

that is readily manipulated. Reference 1 is 

recognized as a credible reference. 

0 Two trade associations for the steel industry 

have been pointing out the need for more 

stringent regulations. A third trade 

association, which represents many different 

recycling industries, also recognizes the 

problem as primarily occurring in ferrous 

scrap. 

The number of times different radionuclides have 

been found in the recycling stream are shown in 

Figure 2. The figure shows the reported 

discoveries of radioactive material in the ferrous 

recycling stream, expressed as both a percentage 

of all- reported discoveries and as absolute 

numbers. The radionuclide groups listed in the 

figure are annotated to aid in understanding the 

selection for the subject of the risk analysis. Some 

radioactive material does not present an 

immediate safety concern or is not regulated by 

the NRC. Radioactive materials such as NORM 

(as characterized in Section 2.2) and thorium in 

alloy metals pose little or no radiological danger to 

health or property. Hence, they are of little 

concern in the context of this risk analysis. 

Although 137Cs, 6°Co, and 24Am are not the most 

prevalent radioactive materials in the recycling 

stream, their prevalence cannot be dismissed as 

flukes and their potential to cause damage 

(unnecessary exposures to the public,

contaminated property) warrant concern. '"1Cs, 

'Co, and 24"Am are found in nuclear gauges. 

Most of the nuclear gauges in service contain 

'3"Cs. Based on judgment from regulators, the 

prevalence of gauges containing 137Cs is much 

greater than the prevalence of gauges containing 

6'Co. This is reflected in the number of devices 

discovered in the recycling stream. The 

prevalence of 24

"Am gauges is a little less than the 

prevalence of 137Cs gauges. 

When in use under proper controls, a nuclear 

gauge presents little hazard. But in the recycling 

stream, nuclear gauges potentially threaten life 

and property. If the shutter of a gauge were 

closed, then exposures would be minimal. 

However, without control mechanisms, assurances 

that the gauge is not causing harm are gone; the 

shutter may be open or the sealed source may 

become dislodged from its holder. The recycling 

stream is not designed for radioactive material. 

Unnecessary exposures have occurred in the 

United States; in foreign countries, deaths have 

occurred from other types of devices containing 

sealed sources. 

2.5 Subject as a System To Analyze 

The subject of this risk analysis, fixed nuclear 

gauges in the recycling stream, is illustrated in 

Figures 3 through 6. Figure 3 shows the 

movement of the nuclear gauges by the line 

arrows. Vendors of nuclear gauges are specific 

licensees (SLs) who manufacture and distribute 

nuclear gauges to other SLs or to industrial 

facilities. The gauges are shipped in proper 

packages and installed by qualified people; hence, 

these routes of the gauges are of minimal risk and 

are not analyzed further.

NUREG-1669 8
2: SUBJECT

100%

Percent 

Discoveries 

of Radioacitve 

Material in the 

Ferrous 

Recycling 

Stream 

NOTE: Above 

bars are the 

absolute number 

of discoveries.

Figure 2 Discoveries of radioactive material in the recycling stream. Source: James Yusko, Pennsylvania 

Department of Environmental Protection, Pittsburgh, PA. The data file is dated November 20, 1998. The 

last entry in the file is numbered 3044. Earlier versions of the data are summarized in Reference 1. 

Notes on Figure 2

NORM in this study, is pipe scale, other deposits, dirt, and 

refractory materials. It can .be a health concern when 

radiation levels are high. NORM can cause alarms at portal 

monitors of scrap yards and steel mills. In general, it is not a danger to life or property. 

Unknown, questionable incidents, where the type of 

radioactive material cannot be identified, are of little use in 

making decisions that are costly to many industries. 

Americium, cesium, and cobalt are gamma emitters; hence, 

they can impact health. When these isotopes are melted in a furnace at a steel mill, large financial damages result. Also, "

24

'Am is an alpha emitter, which can be a danger to life if 

such a sealed source is breached and the radioactive material 

is inhaled or ingested. 

Iodine is likely from medical waste. It is not a concern in the 

recycling stream because employees are usually not close to 

scrap metal long enough for harmful exposures. Steel 

products and byproducts will not be contaminated because 

iodine is volatile. 

Krypton is a beta emitter, raising some concerns for 

exposure. Steel products and byproducts will not be 

contaminated because krypton is a gas. 

Radium in this study, refers to a discrete source, not to a constituent of deposits. It is a strong beta and gamma 

emitter. When melted in a furnace at a steel mill, it is thought 

to contaminate mostly slag. Radium is not regulated by the 

NRC.

Thorium is a health concern if ingested or inhaled. Small 

amounts of thorium are sometimes added to metals to 

improve metallurgical characteristics. Thorium is not a concem. 

Tritium is mostly found in self-illuminating exit signs. It is 

usually not a health hazard unless ingested because it is an alpha emitter. 

Uranium has a low activity. Depleted uranium is used for 

counter weights and shielding. Other radioactive materials 

with more significant hazards are found in the recycling 

stream more often. 

Mixtures found in the recycling stream are cesium and cobalt, 

cesium and americium, and uranium and thorium. These 

mixtures were reported without explanation. Also, they are not easily placed in other classes. This group is considered 

to have a low prevalence because it consists of four types of 

mixtures. Thus, this group is of no concern. 

Other radioactive material found in the recycling stream 

includes accelerator products, radium daughter products, 

strontium, germanium, uranium contamination. Some 

materials may be of concern under certain circumstances. 

This group has a low prevalence because it has many types of 

radioactive material. Thus, this group of no concern.

9 NUREG-1669
2: SUBJECT

Regulatory Agencies 

H- Controls on.. 

Desg Use

Figure 3 Nuclear gauges in industries overseen by 

regulatory agencies. LEGEND: GL = general licensee. 

LLW = low-level waste. SL = specific licensee. 

NOTE: Usually "'7

Cs and 6OCo sources can be disposed 

in an LLW site; usually a 241AM source cannot be 

disposed there. 

Regulatory controls are imposed by the NRC and 

Agreement States; this regulatory regime is shown 

at the top of Figure 3. Regulatory controls are 

imposed on the manufacture, transfer, possession, 

use, and disposal of nuclear gauges and are 

intended to prevent nuclear gauges from leaving 

the regulatory regime. The controls on the nuclear 

gauges during use are specified in the terms of the 

license under which the gauge is issued, and may 

include the following: 

" The nuclear gauges are subject to periodic 

inspections and inspections related to events. 

" The licensee must periodically take an 

inventory of the nuclear gauges. 

" Labels must be maintained to identify clearly 

that the gauge contains radioactive material. 

" Usually some training about safe operation is 

provided by the vendor or required by the 

regulatory agency. 

"* Records must be maintained properly.

0 Physical security is necessary. 

A regulatory agency has, or can impose, control 

on only some of the factors that influence nuclear 

gauges. In Figure 3, this is illustrated by the 

controls on use covering only part of the width of 

the box representing industrial facilities. A loss of 

control is notjust a matter of regulations; it is also 

a matter of the many aspects in a facility, most of 

which are not under, or only partially under, the 

jurisdiction of the NRC or the Agreement States. 

(see Sections 2.5, 5.3, and 5.4). In Figure 3, the 

plant controls are inside the box representing 

industrial facilities. 

Depending on the conditions of a license, a 

specific licensee can usually install, remove, and 

service nuclear gauges. A general licensee (GL) 

is usually allowed to use and store a nuclear 

gauge, not to move or service it. An industrial 

facility may be an SL, a GL, or both. 

When the radioactive material in the sealed source 

has decayed and becomes insufficient for use in a 

nuclear gauge, the sealed source is typically 

removed by either the gauge vendor or another 

specific licensee. The sealed source may be 

recycled into another gauge. The disposal method 

for a sealed source that is no longer of use 

depends on the radionuclide and the activity. A 

sealed source that cannot be sent to a low-level 

waste (LLW) site is held in dedicated storage at a 

licensee under a possession-only license or sent to 

a broker who will hold the source indefinitely. 

Otherwise, a sealed source is sent to a LLW site. 

Usually, '

37

Cs and 6

"Co sources meet the criterion 

for disposal in a LLW site (see Ref. 9); usually a 

24'Am source does not meet the criterion. Vendors 

will seldom take back a source manufactured by 

another vendor; if they do, it is taken back as a 

service to their customers or for reuse. 

Figure 4 illustrates the recycling stream. Because 

scrap metal is valuable, most of it enters the 

recycling stream; little is intentionally discarded 

directly into landfills. The value of scrap metal 

and current technology are making landfill mining 

economically feasible, but this industry is still in 

its infancy; because of this, landfill mining is not

NUREG-1669 10
2: SUBJECT

cra Yards& I Stel L... S/eel p4odad

A <+I1s

-Landl

Figure 4 The recycling stream of scrap steel. 

analyzed further. Scrap metal enters the recycling 

stream from many origins in the following groups: 

"* Demolition contractors who renovated or 

dismantled industrial facilities. 

"* Collectors, known as scavengers, peddlers, or 

gypsies, who gathered scrap metal from a 

variety of unspecified places. 

At the smaller scrap yards, metal is collected, cut, 

and sorted. At the larger scrap yards, beyond 

collection and sorting, additional processing is 

done, such as shearing, shredding, cutting, and 

baling. The scrap metal is then sent to steel mills. 

Both integrated mills and minimills consume scrap 

metal. The scrap metal used by steel mills has 

been graded and assayed into lots of known size 

and composition (known to parts per million). At 

a scrap yard or steel mill, a load can be rejected 

because it does not meet specifications (e.g., 

pieces of the wrong size, wrong composition, or 

with undesirable chemical constituents). The 

circular paths on the large arrow represent rejected 

loads of scrap metal. 

Scrap metal that enters the mill is melted to make 

industrial and consumer products. The gray lines 

in Figure 5 indicate the flow of products and 

byproducts to the marketplace. The steel is made 

into products for direct use, such as reinforcing 

rods and plates, or sent to other industries that 

reheat the steel and roll it into other products. One 

byproduct from minimills, furnace dust, is usually 

sent to processors where metals are removed to be

recycled and used in other industries; 

zinc is sent to a zinc plant. Lead and 

copper are sent to smelters. Cadmium 

is sent to a hazardous waste landfill 

because the markets for this metal are 

currently depressed. A liquid 

containing halides (e.g., chloride, 

bromide) is pumped into deep 

injection wells. The destination 

chosen by a mill for the dust is the 

economical pathway. The remaining 

material is rich in iron and is called

iron-rich material. It is used in a 

variety of products, such as aggregate 

material in asphalt and construction or 

as an iron ingredient in cement, and reused in 

manufacturing steel. This furnace dust is 

sometimes glassified and then used in a variety of 

products, such as roofing material and 

sandblasting grit. It can also be sent to a 

hazardous waste site where it is stabilized and then 

buried. Furnace dust from an integrated mill can 

be buried because it is not classified by the 

Environmental Protection Agency (EPA) as a 

hazardous waste. 

Figure 6 is a composite of Figures 3, 4, and 5. On 

the left is the movement within the regulatory 

regime among licensees, gauge vendors, and

Figure 5 Product and byproduct pathways from 

recycled scrap steel. LEGEND: IRM = iron-rich 

material.

11 NUREG-1669
2: SUBJECT

Regulatory Agencies 

H= Controls on... H-ý Deig Us

L..... Radiation ._ _ 

SVisual Detectionr De

..............................------ :X--------------- SLWSt 

Contaminated sklg 

Product & Byproduct < .............. 

Processor

Figure 6 Nuclear gauges moving from licensees, through the recycling stream, and contaminating steel products and 

byproducts. LEGEND: BC = benign contamination. GL = general licensee. LLW = low-level waste. MW = mixed waste. 

SL = specific licensee. ? = unknown. NOTE: Usually "'Cs and '°Co sources can be disposed in an LLW site; usually a 24Am 

source cannot be disposed there.

industrial users. In the middle is the recycling 

stream, consisting of scrap metal collectors, 

demolition and salvage contractors, scrap yards, 

and steel mills. On the right are the destinations 

of products and byproducts, both during normal 

operations and after a nuclear gauge has been 

melted in a steel mill. Steel mills are shown as 

being distinct from industrial facilities having 

nuclear gauges; this is a limitation of the figure. 

Some steel mills use nuclear gauges to measure 

the level of molten steel in the continuous caster 

and the thickness of slabs in the finishing mill. 

Nuclear gauges leaving the regulatory regime may 

enter the recycling stream and landfills or get into 

unknown places, or their use may be

unauthorized. Intuitively, the flow of nuclear 

gauges along the recycling stream is much larger 

than the pathway into landfills because most 

nuclear gauges are attached to metallic 

components and scrap metal is valuable. Some 

flow is, no doubt, outside the ferrous metal 

recycling stream; unauthorized use may involve 

salvage when a process unit is taken apart, moved, 

and reassembled. Unauthorized disposal can also 

occur when the staff at an industrial facility 

improperly transfer a nuclear gauge. Unspecified 

pathways are indicated in Figure 6 by the question 

mark. 

For the most part, little radiation monitoring is 

done at the beginning of the recycling stream. The

NUREG-1669 12
2: SUBJECT

volumetric flow of scrap metal is seldom 

sufficient to justify the expense of large portal 

monitors found further along the recycling stream. 

Radiation detectors are possible along the stream, 

before the large portal monitors at the mill or large 

scrap yards feeding the mills, but the use of such 

equipment, even survey meters, is uncommon. 

Small-scale collectors usually do not have the 

resources required to purchase and operate the 

devices. The primary means of detection is visual 

inspection, which may be impeded in the 

following ways: 

"U The bulk of the scrap metal may hide a 

nuclear gauge. 

"* The orientation of the nuclear gauge may hide 

a label. 

"* Corrosive environments may degrade a label. 

"* Paint and dirt may cover a label. 

"* Ambient conditions, such as snow, rain, and 

fog, may reduce visibility. 

"* Workers may not know what to look for. 

These factors have three implications. First, the 

chances of visually finding a nuclear gauge along 

the recycling stream are remote. Second, if 

gauges are frequently found visually, then many 

nuclear gauges are present in the recycling stream. 

Third, a more durable label, such as embossing, is 

of limited benefit when a gauge is in the recycling 

stream. 

Further along the recycling stream, the volume of 

scrap metal justifies the use of sophisticated 

radiation detectors at the entrances and exits of 

scrap yards and steel mills. Before being sent to 

a steel mill, the scrap metal is sorted, shredded, or 

bundled, compacting the scrap metal. The 

detection of nuclear gauges using radiation 

monitors may be impeded in the following ways: 

a Shielding of the nuclear gauge reduces the 

radiation that can reach the radiation monitor.

"* A large volume and high density of scrap 

metal may shield a nuclear gauge. 

"* The background radiation necessitates a lower 

limit on the alarm point. A point near the 

background level would cause the monitor to 

alarm frequently. 

"* The alarm point may be set high to reduce 

false alarms from background radiation, BC, 

and people who have undergone treatment 

with nuclear medicine. 

When a sealed source is melted along with scrap 

metal, the products and byproducts that are 

contaminated depend on the radioactive material 

that is melted. "

37

Cs vaporizes from the molten 

steel and adheres to the furnace dust. Little if any 

of the cesium remains in the steel. 'Co forms an 

alloy with steel. Because furnace dust and slag 

contain iron, they will also contain 6

"Co (Ref. 11). 

Little is known about the fate of 241

Am, but it is 

believed that it will reside mostly in slag. These 

pathways are denoted by the dotted black line 

arrows to indicate that the sealed source has 

changed from its encapsulated form to a dispersed 

form in the steel, slag, and furnace dust. 

Contaminated steel can go to a low-level waste 

site. Contaminated slag can go to either a 

processor or a low-level waste site. Contaminated 

furnace dust is no longer simply a hazardous waste 

but, instead, a mixed waste (heavy metals and 

radioactivity); it is sent to a processor where it is 

solidified, then buried in a mixed-waste site. 

Figure 7 illustrates some aspects ofthe subject that 

are taken into account in the risk analysis. The 

figure is necessarily qualitative, not quantitative, 

to illustrate concepts. A quantitative illustration 

would leave important areas too small to observe 

and data necessary to report quantitative aspects 

are unavailable. Nevertheless, Reference 1 serves 

as a basis for Figure 7. 

The top illustration in Figure 7 is an overview. 

The rectangle represents all loads of scrap metal 

that are being monitored for radioactive material 

as they enter a steel mill. The area outside the 

larger circle represents the loads that do not cause

13 NUREG-1669
2: SUBJECT

a radiation alarm. The larger 

circle represents loads that alarm 

because they contain only BC A " 

and loads that alarm because ae__04 

they contain a sealed source. A4 4c6• 

Only a portion of the smaller 

circle overlaps with the larger 

circle; these are loads containing 

sealed sources that alarm. 

Illustration (A) in Figure 7 is a 

breakdown of the overlapping 

area loads that alarm and contain Aoa/ ala 

sealed sources. In some of these __& 

loads, the alarm is attributed to 

the sealed sources. In other 

loads, the alarm is attributed to A W4 

BC, not to the sealed sources &akded&M 

that are also in the loads. The a . 

load is superficially 

investigated; if NORM is seen 

or radiation appears to be 

coming from the rib of the Figure 

transporting vehicle, the alarm of radi 

may be attributed to the BC. 

Illustration (B) in Figure 7 

represents sealed sources that 

are missed because either the alarm was attributed 

to BC or heavy shielding around a sealed source 

prevented detection. In either case, the sealed 

source will be melted in a furnace at a steel mill. 

The lighter shaded area represents the incidents 

where a sealed source is melted and then detected. 

The darker shaded area represents the sealed 

sources that are not known to have been melted. 

Although parameters cannot be readily estimated 

from the data summarized in Reference I to obtain 

the relative sizes of the areas in Figure 7, insights 

about the area of undetected meltings in Figure 7 

can be obtained from statistical inferences. 

During the period from 1983 through 1994, 

fourteen incidents of melting 137Cs and one 

incident of melting 'Co at minimills processing 

carbon steel scrap metal were reported. During 

the same period, no such incidents were reported 

at integrated mills. This observation suggests that 

the minimills are more vulnerable to melting 

radioactive material than the integrated mills. The

lled

)

ýB 

461 haae

deftd d&ded4 

7 Aspects of the subject deduced from reported discoveries 

oactive material in the recycling stream. 

reasons given to explain why integrated mills have 

not reported melting radioactive material to date 

are chance and high-quality (e.g., added assurance 

of no radioactive material) supplies of scrap metal 

(Ref. 10). The data summarized in Reference 1 

can be used to estimate the chance. The 

discussion focuses on incidents of 1

37Cs meltings. 

Because of the paucity of data, the discussion of 

'°Co meltings is more tentative. The discussion is 

important for a risk analysis in the following 

ways: 

"* The statistical inference strengthens the 

argument for the existence of the area in 

Figure 7 representing undetected meltings of 

radioactive material. 

"N In the analysis of the steel industry, the 

integrated mills must be taken into account 

when gathering information with a survey for 

the analysis of the steel industry (see Section 

7.7).

NUREG-1669 14

ala~mZ" dtad
2: SUBJECT

Monitoring for '

37Cs 

Minimills currently consume about 70% of the 

scrap metal supply, leaving integrated mills 

consuming about 30%.1 Intuitively, the 

vulnerability of a mill is expected to be 

proportional to the amount of scrap metal 

consumed. Making this assumption of 

proportionality and using the 1996 consumption 

ratio of 70/30, about six meltings would have been 

expected at integrated mills during the 1983 

through 1996 period, yet no meltings have been 

reported. The chance of observing zero meltings 

when about six meltings were expected would 

have been about 1 in 400, which is highly 

unlikely.2 The 1 in 400 chance seems to refute 

one possible reason why integrated mills have not 

melted '1"Cs -good luck. The estimate of 1 in 

400 is a lower bound of the chance. The fourteen 

incidents of "'Cs being melted are those that have 

been reported. Between 1983 and 1996, before 

radiation monitoring became a common practice 

(see Figure 18), radioactive material may have 

been unknowingly melted. More than 14 

incidents at the minimills would mean that more 

than six incidents are expected at the integrated 

mills. 

Another possible reason for the apparent lack of 

meltings at integrated mills is higher quality 

control of scrap metal at the integrated mills than 

at the minimills. This, too, does not seem to be a 

plausible explanation of the observed prevalence 

of melting radioactive material at the minimills. 

High-quality controls also exist at minimills, 

especially at the mills that melted radioactive 

material; yet some of these mills melted 

radioactive material a second time. While 

integrated mills tend to purchase only high-quality 

scrap metal, this should not be confused with a

1 / Source: Telephone conversation on March 6, 1997, with C. 

Bechak, Steel Manufacturers Association, Washington, DC. 

2 / The chance is calculated with the Poisson distribution.

high quality of practices to ensure that scrap metal 

contains no radioactive material. Though 

differences can be found from one mill to another, 

the quality of the monitoring practices at minimills 

and integrated mills seems to be the same. 

Weaknesses in the practices at both types of mills 

are evident (e.g., see Section 7.6). 

Though only speculation is possible at this time, a 

reason for the lack of detection at the integrated 

mills may be the treatment of the furnace dust. 

When melted, 11"Cs vaporizes and adheres to the 

furnace dust. The U.S. EPA classifies dust from 

a minimill as a hazardous waste because of the 

high content of heavy metal. This furnace dust 

cannot be simply buried, but must be sent to a 

processor.3 When hazardous waste is known to be 

radioactive, it must be treated as a mixed waste 

and processed by a more expensive method. The 

expense of mixed waste disposal has created 

incentives for hazardous waste processors to 

monitor furnace dust for radiation before taking 

possession of it; if radiation is detected in the 

furnace dust, the processor will return it to the 

shipper. To avoid the expense of returned loads of 

radioactive furnace dust and other expenses, 

minimills monitor the dust for radiation before 

shipping it to a processor. Therefore, radioactive 

furnace dust is likely to be detected. In contrast, 

the furnace dust from an integrated mill is not 

considered a hazardous waste by the EPA. The 

furnace dust from an integrated mill can be buried 

in a landfill. Although radiation monitors may 

also be at landfills, this does not appear to be the 

case for the landfills receiving the furnace dust 

from the integrated mills. There is no reason to 

monitor this furnace dust. Therefore, radioactive 

furnace dust from integrated mills may not be 

detected.

3 / Furnace dust can be processed by a mill, such as in glassification, 

to make materials that can be used for sandblasting or fillers. Onsite 

processing appears to be uncommon.

15 NUREG-1 669
2: SUBJECT

Monitoring for °Co 

Some steel mills have radiation gauges (nuclear, 

x-ray) to monitor their production lines. These 

same gauges might also detect °Co, which forms 

an alloy with steel; others do not. Some mills 

monitor their product going out of the mill; others 

do not. While test pieces may be monitored for 

radiation (see Section 7.4), both the capabilities of 

the equipment and the practices of using the 

equipment that allows its capabilities to be 

realized vary considerably from mill to mill. This 

raises a concern that products containing 6"Co 

may exit some steel mills without being detected. 

2.6 Progression of the Analyses 

The topics represented by Figure 6 are shown in 

Figure 8 Shade-coded boxes indicate the treatment 

of the topics in the risk analysis. A black box 

indicates a rigorous accounting of a topic. A 

shaded box indicates that a topic is accounted in 

some way, such as in a simplified form or at least 

acknowledged. A white box indicates that the 

topic is not analyzed. The large shaded arrows at 

the top of the figure indicate the progression of

both the nuclear gauges when control is lost and 

the order of the discussions. The thin lines at the 

bottom of the figure indicates that portions of the 

licensees, scrap metal consolidation, and steel 

mills are part of the public domain. 

2.7 Observations and Insights 

1. The data about radioactive material discovered 

in the recycling stream is difficult to analyze. 

2. Much of the reported discoveries of 

radioactive material in the recycling stream 

posed no danger to life and property. NORM, 

iodine, krypton, thorium, and tritium pose no 

danger to the property of the steel industry; 

these radioactive materials constitute 62% of 

the discoveries. 

3. All of the reported meltings of radioactive 

material have been at minimills, and none 

have been reported at integrated mills. 

Differences in the purchasing and processing 

of scrap metal do not seem plausible because 

differences are neither evident in site visits nor 

specified in explanations that have been

Section 5 

o Gauge vendors 

o Gauge design 

* Facilities using gauges 

' Prevalence of gauges 

o Control mechanisms 

* Gauges at risk 

o Proper transfe 

N mpoper transfers 

* Proper disposal 

* improper disposal 

M Demolition & salvage 

Z Unknown use 

S Unauthorized use 

0 Unauthorized disposal 

N Danger to life 

* Danger to property

Section 6 

* Metal collection 

o Landm mining 

* Scrap yards 

* scrap metal processing 

o Visual detection 

1 Radiation detection 

o3 Monitoring practices o3 Rejection practices 

o Proper disposal o3 Improper disposal "* Danger to life "* Danger to property

Section 8 

* Danger to liMf 

* Danger to property o1 Transporting gauges 

El Markets

Figure 8 Topics discussed in this report. LEGEND: Black bullets indicate that a topic is rigorously taken into 

account in the risk analysis. Gray bullets indicate that atopic is qualitatively taken into account. White bullets 

indicate that a topic is beyond the scope of the risk analysis.

NUREG-1669

Section 7 

o Visual detection 

* Radiation detection 

* Detection probability * Scrap metal monitoring practices * Scrap metal rejection practices * Monitoring steel products * Monitoring byproducts * Proper disposal * Improper disposal Danger to life 

* Danger to property

16
2: SUBJECT

offered. If chance is the reason, the integrated 

mills are indeed lucky; the chance is 1 in 400. 

There may be a reason; it is just not evident. 

But the reason should be stated so that other 

mills can benefit. 

4. Visually detecting nuclear gauges in the 

recycling stream is a remote possibility. If

nuclear gauges are visually found in the 

recycling stream, then the prevalence of 

gauges in the stream is high. 

5. If the prevalence of hazardous radioactive 

materials could almost be eliminated, the steel 

industry would still be subject to the costs of 

false alarms from BC.

17 NUREG-1669
3 PRINCIPLES OF THE RISK ANALYSIS

3.1 Overview 3.2 Concepts

The principles of the analyses in Sections 5, 6, 7, 

and 8 need to be understood to understand insights 

and interpret risk estimates. Though the system is 

nebulous at first glance, firm principles clearly 

demarcate what the analyses represent. This study 

is not a straightforward application of systems 

analysis to a device or a facility. The system that 

is analyzed consists of domestic stakeholders 

(licensees, scrap yards, and steel mills). The 

industry wide view is appropriate because the 

problem itself is regional, not localized to a 

particular industry or geographic location. 

For discussing the principles of this risk analysis, 

the licensees are represented simply as the 

prevalence of gauges in all locations throughout 

all industries; the movement of the gauges 

between these locations is irrelevant. The scrap 

yards and the steel industry are represented as a 

stream of scrap steel going from a source to a 

sink; the scrap steel is a carrier medium in which 

the gauges are "floating" past radiation monitors. 

A simple example of a risk calculation shows the 

structure of the analyses that is applied to the 

study of nuclear gauges. Sections 5.5, 6.4, 7.7, 

and 8.4 give the details of particular stakeholders. 

These calculations allows changes in controls on 

the gauges to be evaluated by assessing changes in 

risk. 

Typical products of a risk analysis are insights, 

aggregate risk estimates, and risk triplets. 

Insights, that are of use to all stakeholders, can be 

obtained from a structured analysis without 

calculating risk. Aggregate risk accounts for the 

chances and consequences of all plausible 

pathways. The risk triplet distinguishes between 

high likelihood-low consequence pathways and 

vice versa. Uncertainty is an integral part of risk 

and must be expressed. Clear displays of risk 

estimates facilitate an understanding of 

observations and insights.

The risk analysis reflects a compromise of many 

competing factors. The limiting factor is the 

availability of information for inputs to the 

analyses. Within this limitation, the detail in the 

analyses of licensees, scrap yards, and steel mills 

is more or less the same. 

3.2.1 Licensees 

The prevalence of nuclear gauges at any time 

throughout the United States is the number of 

gauges present at the time. Let x(t)i be the number 

of gauges in thej' location throughout industry at 

a time t. The prevalence is expressed by Equatio.

P(t)= xI(t) 

j=1

[1]

P(t) = prevalence of gauges throughout all 

industries 

x,(t) = number of gauges in thej1 location 

t = time 

m = number of locations 

In the analysis of the licensees, the possible 

locations of the gauges are as follows: 

"* in use, on an operating process unit 

"N out of use, on an operating process unit 

"* on a process unit that is in maintenance 

"N in storage 

"* on a defunct process unit 

"* on a process unit being dismantled 

The proportion of gauges in thej& location at time 

t is given by Equation 2.

•jt= px( p [2]

qj(t) = proportion of gauges in the j

t

1 location 

at time t

19 NUREG-1669
3: PRINCIPLES OF THE RISK ANALYSIS 

Substituting Equation 2 into Equation 1, and 

dividing by P(t) yields Equation 3.

1= {[,(t), + (t)2+ ... P(t).} [3]

Equation 3 is a conservation equation--the 

gauges have to be somewhere. 

With a given set of economic and regulatory 

conditions, an equilibrium is established and T(t)j 

for any location throughout industry is assumed 

constant over time. The equilibrium is a result of 

the market forces for the gauges and the products 

made with the gauges. The equilibrium is also a 

result of the regulatory system in that the system 

imposes costs for using the gauges; high costs 

create incentives for industry to find substitutes, 

either by replacing the gauges themselves with 

another type of measuring device or by changing 

the process so that the gauges are no longer 

needed. The equilibrium has a risk depending on 

the distribution of all gauges among all locations. 

When regulations are changed, stress may be 

placed on the equilibrium, causing it to 

shift-.gauges are redistributed among the 

locations. An example is not allowing unused 

gauges to be stored at a facility. The reestablished 

equilibrium has another value of risk. 

Assumption: The distribution of gauges 

among the locations is approximately 

constant. Basis: The U.S. economy and the 

regulatory systems (environmental, 

occupational, and nuclear) are changing little. 

The gauges in the locations are in an equilibrium. 

Though gauges are being taken in and out of the 

locations, there is no appreciable change in the 

distribution. This is important for three reasons: 

* The transitions during which the gauges move 

among the locations are unnecessary to take 

into account for a risk analysis. A transition is 

not where the risk arises. For example, a 

gauge may not move itself, but instead, the 

process unit changes state, from operating to 

being shut down for maintenance. Or, if the 

gauge is moved, such as to storage, it is being 

taken to a definite place, not being discarded.

In either case, the gauge is not at risk of being 

discarded as a result of the transition from one 

location to another. The risk results from the 

location that the gauge is in at any given 

moment. 

"* The distribution of gauges among the 

locations can be determined from a survey of 

licensees (see Appendix B). The results of the 

survey are relevant so long as economic and 

regulatory circumstances change little. 

"* Time can be dropped from the designation of 

prevalence and location. Thus, P(t) and xY(t) 

can be written simply as P and xj. 

3.2.2 Scrap Yards 

Scrap metal is collected and processed before it is 

sent to the steel mills. The numerous and varied 

routes of scrap metal entering the scrap yards are 

of little consequence for a risk analysis (see 

Section 6.3). The concern, particularly in this 

discussion, is for the supply of scrap metal going 

to the mills along with whatever gauges it may 

contain. Two assumptions are made about the 

scrap metal supply containing nuclear gauges: 

Assumption: The temporal variability in the 

consumption of scrap metal by the mills can be 

ignored. Basis: Economic conditions in the 

United States are relatively stable. 

Assumption: Nuclear gauges are uniformly 

dispersed in the recycling stream. Basis: 

Nuclear gauges are used in many different 

industries throughout the country. The 

recycling stream is dynamic. Scrap metal is 

moved from sources, through scrap dealers that 

process it, to mills that consume it. Sealed 

source devices have been found in the recycling 

stream hundreds of miles from where they were 

licensed to be used. 

Although two mills, Auburn Steel in New York 

and Newport Steel in Ohio, have melted 

radioactive material on two occasions while most 

mills have not had such a melting, this observation 

is statistically consistent with the total number of

NUREG-1669 20
3: PRINCIPLES OF THE RISK ANALYSIS

meltings in the United States (18 

meltings; see Ref. 1) from 1983 

through 1997. If a mill had an 

incidence of four or five 

meltings, then the assumption 

would be doubtful. 

Most of this supply goes to steel 

mills; hence, the risk along the 

pathways to the steel mills is 

assessed. Other destinations of 

scrap metal, occurring in 

smaller proportions, are not 

assessed (see Sections 2.4 and 

2.5).

Scrap Metal 

Supply 

Containing

iN ucli[ U~

(A) 

(B) 

(C)

Radiation 

Monitor 

Station

auges - Steel Mill 

Load of 

scrap metal II 

- "M

Stream of 

$Scrap Metal 11

Figure 9 shows the movement 

of nuclear gauges in the supply (( 

of scrap metal. In Panel (A), (D) 

vehicles are carrying scrap 

metal from a supply into a mill. 

The vehicles can be either 

trucks or railcars. Because the 

supply of scrap metal contains F 

nuclear gauges, some of the 

loads also contain the gauges. 

Along the way from the scrap metal supply to a 

mill, the vehicles pass through a monitor station 

where they are scanned for radiation. The spaces 

between the vehicles are irrelevant. Panel (B) 

illustrates the vehicles without the spaces between 

them. Ignoring the ends of the vehicles, as in 

Panel (C), allows the individual loads to be 

viewed as a stream of scrap metal from the supply 

to a mill. 

Once a load is suspected of containing a 

radioactive source, the radioactive source becomes 

the concern, not the scrap metal. Panel (D) is a 

stylized version of Panel (C), treating the scrap 

metal as a carrier for nuclear gauges moving from 

a supply to a sink. Along the way, the gauges may 

be removed when they are detected with a 

radiation monitor. 

3.2.3 Steel Mills 

Scrap metal arrives at the mills from the supply in 

loads. The supply is replenished with more scrap 

metal (and possibly more gauges). Although

igure 9 Movement of gauges through the recycling stream. 

scrap metal arrives at the mills in loads, the stream 

of these loads, not the individual loads, is relevant 

to a risk analysis. 

Further analysis will explain and justify the stream 

perspective in Figure 9. For clarity, discoveries of 

gauges at the scrap yards have been ignored for 

this discussion. The incidence of nuclear gauges 

in a load of scrap metal going to a mill is given by 

Equation 4.

d =loa = [4] / L

Iad = -- incidence of nuclear gauges in a load of 

scrap metal 

/supply= prevalence of gauges in the supply of 

scrap metal going to a steel mill at any 

time 

L = tare weight of one load of scrap metal 

S = total weight of the scrap metal supply 

The incidence Iload is the mean number of gauges 

in a load of weight L. Because I'oad is a very small

21 NUREG-1669
3: PRINCIPLES OF THE RISK ANALYSIS

number, it can be thought of as the probability of 

a load containing a nuclear gauge. The probability 

of a load containing more than one gauge is so 

small that it can be ignored. 

At the mills, scrap metal arrives in loads L,, L2, 

L. in a time period of length T. The incidence of 

gauges arriving at a mill in the period T is given 

by Equation 5. 

'mill PRuppiy S [5] 

j=l 

Imil = incidence of gauges reaching a mill in a 

period T 

Lj = tare weight ofthejth load of scrap metal 

n = number of loads 

The quantities 1supply and S can be factored out of 

the summation, leaving the summation of the total 

number of loads. This is the consumption of scrap 

metal in the period T. 

ELi [6] Imill = '0 u pl j=1 

'm supply s 

M = IL [7] 

j=l 

Then M is the total amount of scrap metal 

consumed by a mill in the period T. 

The fraction of scrap metal consumed at a mill in 

the period T is given by Equation 8. 

M 

fsppl, = s 191 

Then fs.Iy is the fraction of the domestic supply 

of scrap metal consumed by a mill in the period T. 

Imill = Pispply fsupply E 9] 

Equation 9 shows that the incidence of gauges 

reaching a mill depends on the amount of scrap 

metal consumed relative to the size of the supply

and the prevalence of gauges in the supply of 

scrap metal for the mills. A load is only a means 

of transporting the scrap metal from the yards to 

a mill. Thus, the stream of scrap metal to the 

mills, not the individual loads, is relevant to the 

risk analysis. This is in agreement with Figure 9. 

Considering a load of scrap metal itself for 

analysis, instead of the stream illustrated in Figure 

9, has intuitive appeal because the load is the unit 

of scrap metal that is transported and because the 

size of the load can affect the probability of 

detection (a nuclear gauge is more likely to be 

detected in smaller loads than in larger loads). 

However, difficulties would be encountered when 

collecting information for such an analysis: 

"* At a given mill, and from mill to mill, the 

weight of a load varies. 

"* The data required to determine load variability 

would be too burdensome to request from the 

mills, such as through a survey of the steel 

industry (see Appendix C). 

"* A load is incompletely characterized by just 

its weight. Its volume is also important. Even 

considering vehicles of the same volume, the 

weight of scrap metal can vary, depending on 

the grade of scrap metal. Characterizing the 

loads with a single number, such as an average 

weight, may not represent the loads if the 

variability is high. 

3.3 Structure of a Risk Calculation 

A simple example (Figure 10) illustrates a risk 

calculation if data were available (see Section 9). 

The calculation in Figure 10 begins on the far left 

with the prevalence, P, of nuclear gauges 

throughout all the industries. Three elements 

describe what can happen to the gauges. The 

elements divide the prevalence among the 

plausible sequences of risk elements. A gauge 

subject to a given sequence has a consequence, in 

this example, a cost, Ci.

NUREG-1669 22
3: PRINCIPLES OF THE RISK ANALYSIS

Element II 

Fraction of 

Scrap Metal 

Monitored for 

Radiation

Element III 

Probability of 

Detecting a 

Nuclear 

Gauge in 

Scrap Metal

Sequence 

Frequency 

(U')

Annual 

Excess Costs 

(above base 

licensing fee) 

(C,)

Excess 

Sequence 

Risk 

(f,')(C,)

Aggregate 

Risk 

(fC)(c,) ) 

................................................................................................................................................................................................................................. 

To use 

0,92 55,200.00 X X 

ReturnedReturn 

• 0 3,000.00 0 3,000,000 

% Licensees 

Unknown Search : Excess: 38,643,000 

00 600.00 50,00 30,000,000 Fee: 6,000,000 '- ........ 

Detect Fine/Dispse Total: 44,643,000 

095 12860A2AA -0 nn

0,0

Nick 

59.40 ,0.0 

Melt 1200

594,000,000 

120,000,000

Steel Mills 

Excess: 714,000,000

Figure 10 Example of a risk calculation. LEGEND: A number in a shaded box is an input to the analysis. Other numbers are calculated from the analysis. Solid 

lines ( - ) indicate a sequence of risk elements. ) = beginning of all sequences. 0 = end of a sequence.

NUREG- 1669

Element I 

Fraction of 

of Nuclear 

Gauges in a 

Given 

Disposition

Distributed 

Gauges

Annual Fee 

(S/gauge) 

"*.......T.......... 

Prevalence 

(gauges/yr) 

(f)

I . I I

23

m
3: PRINCIPLES OF THE RISK ANALYSIS

This is the cost in excess of regular licensing fees. 

The product of the prevalence and consequence of 

each sequence is the excess risk of each sequence. 

The sum of the products is aggregate risk. 

In Figure 10, Element I represents the various 

states of the gauges- in use, returned to the 

vendor, unknown, and discarded. Element II 

represents the fraction of scrap metal that is 

scanned for radiation. The scanning can be done 

incorrectly for a variety of reasons (see Item 1 in 

Section 7.4). This element is irrelevant for gauges 

in use and returned; it is undeveloped along these 

branches of Element I. Element III is the 

probability of detecting a nuclear gauge in a load 

of scrap metal. 

The calculations in Figure 10 yield two risk 

estimates, one for the licensees and the other for 

the steel mills. Although the risk to the mills is 

greater than the risk to the licensees in the 

example, this by itself is an insufficient basis for 

evaluating changes in control mechanisms. These 

two estimates only say what Reference 1 already 

clearly documents- a problem exists. The two 

risk estimates are just two constituents of one 

situation; no choice is present. A decision arises 

when there is a choice between two situations. 

This is shown in Table 2. The risk given the 

current situation is considered the base case, RB. 

A proposed change in control mechanisms is then 

represented by changing the inputs to Elements I, 

II, or III and recalculating risk. The result is 

Alternative 1. The comparison quantities in Table 

2 are computed. A decision can then be made 

about the worth of changes. Other changes are 

assessed in a similar manner. 

The example shown in Figure 10 was prepared 

with costs because costs readily lend themselves 

to illustrating a risk calculation for evaluating 

changes in risk. The analysis can also be 

performed in terms of danger to life, expressing 

consequences as the activity of radioactive 

material (see Section 8.4.1). Changes in the 

activity of intact gauges with the shutter closed, 

intact gauges with the shutter open, dislodged 

sources, and breached sources are compared to 

changes in the cost to licensee and regulatory

agencies. Then, as before, changes in controls on 

gauges are evaluated by looking at changes in 

risk. 

3.4 Products of the Risk Analysis 

The typical products of a risk analysis are insights, 

aggregate risk estimates, triplet risk estimates, and 

fractional contribution measures: 

Insights. Qualitative understandings of the subject 

are just as important as the quantitative risk 

estimates. A systematic analysis serves as a 

structure for inductive reasoning. 

Aggregate Risk Estimates. The term risk has 

many definitions. Equation 10 is modified from 

the definition of risk in Reference 5.

R= E PCj 

j=J

[10]

R = aggregate risk 

Pj = prevalence of nuclear gauges on the j1 risk 

element sequence from a licensee to the 

final disposition 

Cj = consequence of the jr" sequence of risk 

elements 

j = sequence of risk elements 

n = number of sequences from the use of 

gauges to the consequences 

Triplet Risk Estimates. The risk triplet is the set 

{Tj, Pj, Cj} in which Tj represents the jr" sequence, 

Pj is the associated prevalence of gauges in an 

environment, and Cj is the resulting consequence 

(Ref. 12). This definition distinguishes sequences 

with low prevalence and high consequence from 

sequences with high prevalence and low 

consequence. Aggregate risk (i.e., Equation 10) is 

appealing because it is a single number, but 

information is lost in going from the risk triplet to 

aggregate risk. The triplets can be displayed as 

shown in Figure 11. The contour lines indicate 

constant risk isorisk curves. The shaded areas 

represent triplets that have been grouped.

NUREG-1669 24
3: PRINCIPLES OF THE RISK ANALYSIS

Table 2 Evaluating changes in risk.

Steel 

Licensee Mill Purpose of the Calculations

Base Case 

RL Rs Evaluate the current situation. 

Alternative 1 

L Rs Evaluate a proposed set of changes in RI RI control mechanisms. 

A= R1 - RA As Decision based on considering 

difference and ratio of risk relative to - the base case. 

Alternative 2 

Evaluate another proposed change in RL Is control mechanisms. 

A 2 =R 2 - RB A' A 

Decision based on difference and ratio 

R2 L S relative to the base case. 

RB 

Alternative n 

RL RL Evaluate the n± set of changes in nE n control mechanisms.

25 NUREG-1669
3: PRINCIPLES OF THE RISK ANALYSIS

-

e4ma/e

> 4. 

Consequences 

Figure 11 Resolving the prevalence and consequence of 

risk estimates. LEGEND: Shaded areas are groups of 

triplets having similar prevalence and consequence. 

1 = quadrant of high prevalence and low consequence risk. 

2 = quadrant of high prevalence and high consequence risk. 

3 = quadrant of low prevalence and high consequence risk. 

4 = quadrant of low prevalence and low consequence risk. 

Fractional Contribution Measure. Sequences can 

be grouped according to the final state of the 

nuclear gauge. The risk from each group is 

computed according to Equation 11.

[11] n• Rj,k I Rk 

j=1 T 

n

5j = fraction of risk from the j1 group of risk 

element sequences 

Ri'k = k' risk estimate of the j"' group of 

sequences 

RT = total aggregate risk for all groups of risk 

element sequences 

n = number of sequences in the jt" group 

3.5 Uncertainty in Risk Estimates 

Figure 10 shows a simplified view of the 

calculations using only one value for each of the 

inputs. A point estimate of risk is computed from 

a single set of inputs. But the practices and

Risk

Figure 12 Differences in perspectives given by a point estimate 

and the distribution of a random variable. 

phenomena represented in a risk analysis are only 

partially understood--there is often much 

uncertainty about the inputs.. For many of the 

inputs, many plausible values may exist; hence, 

many plausible results exist. With uncertainty 

being an integral part of a risk estimate, a point 

estimate is only one of many possible risk 

estimates. A point estimate without an indication 

of the uncertainty can be taken to imply that the 

uncertainties are negligible, which is doubtful. 

A point estimate can be misleading for may 

reasons. Figure 12 shows a hypothetical 

distribution drawn on an arbitrary scale. The 

distribution represents a large amount of 

uncertainty. Given a point estimate and not 

knowing the distribution in advance, where would 

the point value fall in relationship to the 

distribution? 

There is a tendency to try to associate the location 

of the point estimate with the unknown 

distribution by characterizing the input as a "best" 

estimate. This implies that the point estimate 

output of a mathematical function is also a best 

estimate. A problem with the term best estimate 

is that it is vague and seldom defined. One 

possibility is that best means unbiased. An 

unbiased estimate of a parameter is one whose 

mean value is equal to the parameter being 

estimated. Mathematically, the mean of a random

NUREG-1669 26
3: PRINCIPLES OF THE RISK ANALYSIS

variable is called the expected value. The output 

of a mathematical function would be a best 

estimate only for a linear function. Suppose that 

a random variable X has a mean g. Consider the 

function Y = aX. The mean of Y is a[L and is 

written as: 

(Y)-- aR 12l 

E(Y) = expected value of Y 

a = constant 

R = E(X), the expected value of the random 

variable, X 

Thus, if X is a best (unbiased) estimate of R, then 

Y is a best estimate of aR. But the mathematical 

functions in a risk analysis can be nonlinear. If a 

mathematical function is nonlinear, such as 

Z = X2, then a best estimate of [2 should be an 

unbiased estimate of Wt. However, the expected 

value of Z is not R2. Rather, it is:

E(Z)= g±2 + a' [13]

a 2 = variance of X 

If a2 is large (large uncertainty about X), then 

E(Z) would be a highly biased estimate of g2 and 

would not be a best estimate of [12. Thus, the rules 

for propagating point values through the equation 

differ from the rules for propagating both 

distributions and the quantities describing 

distributions (i.e., mean, median, mode). 

Expressing the uncertainties can change the way 

in which risk estimates are perceived. Figure 13 

shows hypothetical point estimates and 

distributions of three quantities, A, B, and C. 

Suppose that the relative importance of A, B, and 

C is to be determined. Using the point estimates, 

C<B<A and C<A. However, using 

distributions is more complicated. Because of the 

large amount of overlap, one concludes that C z B 

and B = A. But one cannot conclude that C = A 

because there is little overlap in these 

distributions. In fact, one could make a case that 

C <A. Thus, transitivity does not hold when 

uncertainty is taken into account. These problems 

do not exist with point estimates, but point

Case 

A 

Case 

B 

CCase

C B A

Risk

9#wcxeaaý Iw~e,- N+

Figure 13 A comparison of point estimates can lead to 

conclusions that differ from a comparison of distributions. 

estimates clearly give a distorted view of the 

relative importance of the quantities. Ranking 

issues and comparing issues is more complicated 

when uncertainties are expressed. 

Figure 13 portrays a situation in which risk 

estimates A, B, and C are independent. 

Dependency must be assessed for it, too, 

influences the way in which the uncertainty in risk 

estimates are perceived. Suppose, for example, 

that A, B, and C were dependent: A = B + k', 

B = C + k" , and k' and k" are positive constants. 

Then each estimate of A, B, and C in their 

distributions is always such that A > B > C; in this 

regard, the overlap of the distributions is 

irrelevant. The spread of the distributions mean 

that A, B, and C cannot be precisely estimated. In 

practice, risk estimates will likely be somewhere 

between independent and dependent. A careful 

analysis of dependencies is warranted. 

3.6 Illustration of Risk Results 

A distribution of risk results is illustrated in Figure 

14. The distribution on the bottom is what is 

calculated. The box-plot on the top is common 

because it is easy to draw and to interpret.

27 NUREG-1669
3: PRINCIPLES OF THE RISK ANALYSIS

much smaller than the intervals on the right. This 

distortion can be removed by dividing the number 

of counts for each block by the interval width. In 

Figure 15, Panel (B) shows what happens when 

this is done. Because the block counts are now 

proportional to the areas, the graph is properly 

called a histogram. The shape of the graph has 

been shifted to the left. But a distortion still 

remains; because of the exponential scale, the 

visual width of the blocks does not correspond to 

the numerical width.

(A)

Risk 

Estimate 

Value

Figure 14 Box-plot (top) and distribution (bottom) 

of risk estimates.

Caution is necessary when displaying 

risk estimates. In Figure 15 (A), the 

number of risk estimates in each 

interval is the ordinate. Because the 

abscissa is expressed as an exponential 

scale, only the heights, but not the 

areas, of the blocks are proportional to 

the number of outcomes in the intervals. 

Therefore, Panel (A) is properly 

considered a bar chart, not a histogram. 

The graph can be converted to a 

histogram by converting the abscissa 

from an exponential scale to a linear 

scale, plotting the logarithm of risk. 

Using the logarithm of risk, Panel (A) is 

properly termed a histogram because 

the areas, not the heights, are 

proportional to the number of risk 

estimates in the intervals. The shape of 

the blocks remains the same, but the 

abscissa is now unitless. The difficulty 

with such a transformation is that the 

unitless abscissa has no physical 

meaning; the interpretation of the 

histogram is unclear. 

The exponential scale of Panel (A) 

gives a distorted view of the risk 

estimates from an analysis. The 

intervals on the left of the graph are

The graph can be redrawn to make the visual 

width coincide with the numerical width by 

converting the abscissa from an exponential scale 

to a linear scale, as shown in Panel (C) of Figure

ni

n 

A 

(B) 

n 

A 

(C)

10- 1O-7 10.6 1 0 -s 9 g 

-8 -7 -6 -5 20s &cdý

F

I I 10-8 10"4

1 10..6

1

I 

1O-1

&Pmwek~I aksae 

234zea &'cre

Figure 15 Visual displays can influence perceptions of risk estimates.

NUREG-1669

24

28
15. The shape of the graph is pushed far to the 

left, giving a much different impression of the 

distribution than Panel (A). 

Panels (A) through (C) illustrate how easily 

impressions can be changed simply by changing 

the scale of the abscissa. While bar charts, such 

as in Panel (A), do not in and of themselves 

misrepresent the results of a risk analysis, their 

visual appearance can be misleading. Because the 

appearance of bar charts (e.g., Panels (A) and (B) 

of Figure 15) can change drastically, depending on

3: PRINCIPLES OF THE RISK ANALYSIS 

the scale of the abscissa, the visual interpretation 

of the charts can also change. Inferences made 

from the visual appearance of a bar chart having 

a log scale can be misleading; they are of limited 

use. While Panel (C) accurately represents the 

density function, it too is of limited use because 

the details of the distribution are lost. Other 

pictorial representations on log scales can suffer 

from limitations similar to the bar charts. 

Inferences should be based directly on numerical 

results, not on somewhat uninformative pictorial 

representations.

29 NUREG-1669
4 INFORMATION

4.1 Overview 

Information can be divided into three categories. 

First-degree information are data. Second-degree 

information is informed judgment. Third-degree 

information is plausible judgment. This 

characterization facilitates discussion about the 

information supporting the elements of risk in an 

analysis. 

Reference 1 is an excellent summary of the 

radioactive material discovered in the recycling 

stream. With other information, the data of 

Reference 1 can be reworked to gain insights for 

a risk analysis. But the data are a sample of 

convenience. Because it was not obtained with 

statistical methods, it cannot used to estimate 

probabilities. 

Experiments are needed to characterize the 

probability of detecting a nuclear gauge in the 

recycling stream. To date the capability of some 

radiation monitor equipment have been 

characterized. Ofmore use would be fundamental 

information about the shielding characteristics of 

scrap metal loads that could be used to predict the 

detection probability using other equipment and 

loads of scrap metal commodities. 

4.2 Concepts 

The analysis is to be supported by empirical data 

as much as possible (Ref. 7). A strategy is needed 

to characterize the parameter estimates according 

to the type of information on which they are 

based. Such a strategy consists of three categories 

of information and the resultant parameter 

estimates: 

"* First-degree estimates are completely based on 

data. If the data are sparse or highly variable, 

a first-degree parameter may be highly 

uncertain. 

"* Second-degree estimates are based on 

informed judgments. Informed judgments are

made by experts who are familiar with 

relevant data. Such people may be found in 

industry. The key to informed judgment is 

familiarity with data. Second-degree 

estimates can have varying amounts of 

uncertainty. 

* Third-degree estimates are based on plausible 

judgments. A plausible judgment is based 

only on superficial knowledge and is generally 

highly uncertain. 

Degrees of information are used in Sections 5.6, 

6.5, 7.8, and 8.5 to discuss the information that 

can be obtained for assessing risk. 

Here, for discussion, parameters are sometimes 

referred to by the degree of their associated 

estimates (e.g., a third-degree parameter is one 

that is estimated with third-degree information). 

The quality of risk estimates is a function of both 

the quality of the information used to estimate the 

parameters of an analysis and the significance of 

the parameters in determining risk. Low-quality 

information for estimating some parameters may 

be of little concern if the parameters do not 

significantly contribute to the risk. The 

contribution of parameters estimated with low

quality information may be overshadowed by the 

contribution of parameters estimated with higher 

quality information. On the other hand, 

significant parameters may be unknown. 

The quality of a risk estimate can be determined 

with importance measures (Ref. 5). The measures 

can be applied here to calculate the percent 

contribution of each risk element to an estimate of 

aggregate risk. These percentages can be 

grouped by the degree of information used for 

their respective elements. A ratio can then be 

formed to express the quality of information used 

to estimate risk. This ratio, called the data-mix 

ratio (DMR), conveys the relative amounts of 

information types in the risk estimate. Suppose a 

risk assessment was made and 43% of the risk was 

attributable to elements with first-degree

31 NUREG-1669
4: INFORMATION 

information, 31% to second-degree information, 

and 26% to third-degree information. The DMR 

would be 43:31:26, with the understanding that the 

first number is for first-degree information, the 

second number is for second-degree information, 

and the third number is for third-degree 

information. This particular DMR conveys the 

notion that most of the risk is based on data and 

informed judgment; about a quarter of the estimate 

is based on plausible judgment. 

In addition to examining the elements of risk and 

making risk estimates, the risk analysis serves as 

a structured way to address the issue of what 

resources should be expended to obtain data. A 

simplified analysis is illustrated in Figure 16. The 

figure shows three stages of nuclear gauges--at 

risk, discarded in the recycling stream, and 

detected with radiation monitors at scrap yards 

and steel mills. The shaded area in the box of the 

licensees represents the control mechanisms. The 

controls are imperfect, placing the gauges at risk 

of being improperly disposed of and transferred; 

hence, the regulatory area is shaded, not opaque. 

The extent to which the gauges are at risk is 

measured by the probability of the gauge being at 

risk, Pr{at risk}; this is the extent to which the 

mechanisms operate. The discard probability, 

Pr{discard}, measures the extent to which a 

gauge, which is at risk, will be inadvertently 

discarded into the recycling stream. Toward the 

end of the recycling stream are radiation monitors, 

whose effectiveness is measured by the detection 

probability, Pr{detect}. 

If Pr{at risk} could be made zero, then the 

availability of data for estimating Pr(discard} and 

Pr{detect} would become irrelevant. But some 

gauges are at risk; Pr{at risk) > 0. Hence, the 

availability of data to estimate the discard 

probability and the detection probability is of 

concern. However, if Pr{at risk) is sufficiently 

small, then the quality of information to estimate 

Pr{discard} and Pr{detect} may not need to be 

very high. An analogous argument holds if the 

gauges could always be detected by the radiation 

monitors (i.e., Pr{detect} = 1). But because 

gauges can be missed, Pr{detect) < 1, and the 

availability of data to estimate the probability of

Figure 16 Three stages of nuclear gauges in 

the recycling stream for illustrating concepts 

of information. 

gauges being at risk and being discarded is of 

concern as well. 

A survey cannot be done in stages as parameters 

are known to be important; for convenience, a 

well-designed survey must be done all at once. 

Nonetheless, the above concepts are valid. Valid 

estimates of parameters allow a starting point for 

determining what is and what is not important. 

More attention, possibly supplemented with data 

or expertise from other sources, can then be 

focused on important parameters. 

4.3 Sources of Information 

4.3.1 Surveys 

First-degree and second-degree information for 

most of the elements of risk are readily available 

through surveys (see Appendices B and C). Thus, 

third-degree information is, for the most part, 

unnecessary. Surveys are also needed to collect 

information on the conditions that exist in industry 

in a way that is compatible with the analyses in 

Sections 5.6, 6.5, 7.8, and 8.5. Every licensee is 

unique; there are many practices for caring for and 

maintaining control of nuclear gauges. Every 

steel mill is unique; there is no standard 

configuration of radiation monitor equipment at 

steel mills, nor can there be because what is 

possible at one mill may be impractical at another 

mill. Surveys are the only practical way to obtain 

the technically sound information necessary for 

assessing risk.

NUREG-1669 32
4: INFORMATION

Surveys were developed by consulting experts as 

appropriate. No single review group could have 

developed the surveys because of the diversity of 

expertise needed--survey design, risk analysis, 

industrial operations, regulations, and statistics. 

The development of the survey was guided by a 

professional survey designer at the Los Alamos 

National Laboratory to conform with established 

and tested practices (Ref. 13). But ultimately the 

development of the survey was between the 

principal investigator and people in industry. 

The method for developing the surveys was 

intensive pilot testing (Ref. 13). This method is 

employed when there is a shortage of resources, or 

when the population to be surveyed is small. A 

survey can be tested on a small number of people 

because the testing gathers information that would 

otherwise require a larger sample. During pilot 

testing, the short-term memory of respondents is 

meticulously tapped to determine flawed aspects 

of the survey. While a respondent thinks out loud, 

notes are taken about verbal and nonverbal 

communications (e.g., pauses, hesitations, tone, 

exclamations, emphasis, hand movements, facial 

expressions). The test results were carefully 

studied to understand the flaws in the survey, then 

to decide upon changes to correct the flaws. 

Many times, changes were discussed with the 

survey designer as were intentions to revise the 

survey form and make appropriate adjustments to 

plans for completing the pilot tests. 

Some deviations occurred from the established 

procedures during the test sessions and include the 

following: 

E Respondents reviewed the survey, instead of 

attempting to complete the survey, because 

some information would have to be obtained 

from other people not present at the test 

sessions. The reviews were sufficient for 

exploring the reasonableness of the questions, 

the interpretation of the questions, the 

transitions to parts of the survey, and the 

opinions of the survey. 

* The principal investigator asked questions and 

gave prompts while a respondent was reading 

the survey, instead of waiting until the

respondent had completed the survey. The 

disruption in the flow of thought was traded 

for readily tapping into short-term memory. 

E Some tests were done at facilities previously 

visited, instead of all tests at unfamiliar places. 

The rapport developed during those visits may 

bias the test and make the testing somewhat 

nonrepresentative. Only a few tests were done 

as such, either to ease the principal 

investigator's transition into testing the survey 

at unfamiliar facilities or to readily gain access 

to facilities. 

The deviations were judged to have a minor 

impact on test results. 

The testing addressed difficulties that typically 

arise when conducting a survey. The cover letter 

was the means of motivating respondents. There 

was some concern about proprietary or sensitive 

information but, in general, this concern did not 

dissuade respondents from looking at the 

questions; as respondents read the survey, this 

concern dissipated. The length of the surveys 

was always a concern. Though the number of 

pages of the steel industry survey was a little 

daunting at first, respondents soon found that the 

pages were not completely filled with questions 

and the questions could be readily answered. 

Some questions were about sensitive issues. 

These survey questions were worded, and the 

analysis constructed, to desensitize the questions: 

"* The questions were asked in the future tense, 

"How likely is it that the following would be 

done?" 

"* Nonsensitive possibilities were listed and 

sensitive possibilities were grouped into a 

nondescriptive category called "Other." 

Section 5.6, 6.5, 7.8, and 8.5 show the need for 

each question of the surveys in Appendices B and 

C. The questions themselves focused on issues of 

risk. For example, the survey of the steel industry 

asked about the use of scrap metal. But some 

commodities of scrap metal are unlikely to contain 

nuclear gauges; scrap metal turnings are a

33 NUREG-1669
4: INFORMATION

byproduct of lathes. Also, information about 

scrap metal turnings may be sensitive because 

turnings may contain cutting oil, which is an 

environmental hazard. Therefore, questions 

asking about the use of scrap metal were about the 

commodities that are likely to contain nuclear 

gauges. Focusing on the risky types of scrap 

metal has another advantage; the amount of 

information that is collected through a survey can 

be reduced. 

The testing was done until the changes appeared 

to be getting into the realm of personal 

preferences rather than finding flaws in the 

survey. At this point, respondents said that the 

surveys were very reasonable. The pilot testing 

resulted in surveys that asked for a minimal effort 

from respondents to obtain essential information 

in a proven manner. 

Somepeople might consider a survey to be biased 

because it was reviewed by industry. Bias 

because of self-interest would be a concern if 

industry wanted a particular outcome. But the 

surveys are collecting information about nuclear 

gauges, radiation monitors, and practices. There 

is no obvious reason to bias the response to 

questions. Inaccurate answers may create a view 

of the circumstances in industry that may lead to 

changes in controls on the gauges (see Section 

5.4) that are either more or less stringent than 

necessary. 

4.3.2 Empirical Data 

Reference 1 is an excellent summary of the 

radioactive material discovered in the recycling 

stream. The reference is essential for beginning a 

risk analysis, documenting that control over 

nuclear devices is less than desirable, thereby 

justifying a risk analysis. The data show that the 

loss of control is not an unusual event and is 

recurring. Though the information in Reference 1 

is first degree, it is unsuitable for a risk assessment 

for many reasons. 

Reference 1 is an observational study, not a 

controlled experiment. An observational study is 

useful; many times, this is all that can be done. 

No plant manager of a steel mill is going to allow

sealed sources to be placed in loads of scrap metal 

to determine how many will be found by radiation 

detectors and how many will be found after being 

melted in a furnace. But difficulties in using the 

data stem from the way in which the data were 

necessarily collected and the time over which they 

were collected. 

Collecting Data 

The data summarized in Reference 1 are from 

many sources: 

"* Nuclear Regulatory Commission (NRC) 

reports; 

"* notices from mills of detections in loads of 

scrap metal; 

"* notices from scrap yards of detections in loads 

of scrap metal; 

"* trade associations that collect reports of 

detections from their members; 

"* notices from people in other States who know 

of this database; and 

"* U.S. Department of Transportation Exemption 

10656 reports for returning loads of scrap 

metal suspected of containing radioactive 

material. 

The information in the Reference I database 

focuses on discoveries of radioactive material 

beyond control mechanisms and includes 

materials such as naturally occurring radioactive 

material (NORM) and radium (see Section 2.2) 

that are not regulated by the NRC. Some of the 

data are ambiguous, raising a concern for 

misclassification. Many issues need to be 

thoroughly understood to draw valid conclusions. 

Yet many aspects of the data are unknowable 

considering the following: 

E The criteria forreportingare largely unknown. 

The data summarized in Reference 1 come 

from a variety of sources, some of which have 

no reporting criteria.

NUREG-1669 34
4: INFORMATION

"* The population reporting is unknown. Who 

was aware of the radioactive material in the 

recycling stream and when they were aware 

are unknown. Who was aware of data being 

collected and specifically what was reportable 

(discoveries of any radioactive material, 

NORM, rejected loads) are unknown. 

"* The extent of reporting is unknown. 

Collecting data is not a responsibility of steel 

workers. 

" Many alarms of the radiation monitors are 

unreported. Some mills simply turn away 

loads that cause an alarm (see Section 7.4). 

The extent to which these alarms are recorded 

remains unknown. 

The data summarized in Reference 1 were 

collected as they could be gathered. This means 

that the data are a sample of convenience, not a 

random sample (see box, "Sample of 

Convenience"). Probabilities cannot be estimated 

from a sample of convenience (Ref. 14, page 369). 

With a sample of convenience, uncertainty bounds 

on a point estimate usually do not make sense and 

are likely to be incorrect: formulas for the 

uncertainty bounds have to take into account the 

details of the method used to draw the sample. An 

uncertainty bound is an integral part of an estimate 

that expresses how well an estimate is to be 

trusted (see also Section 3.6). 

Changing Circumstances 

Circumstances have been changing since 1983 

when radioactive material was discovered in the 

recycling stream: 

"* The number of radiation monitors at the scrap 

yards and steel mills is increasing. 

"* The capability of the radiation monitors to 

detect radioactive material is increasing. 

"* The population of nuclear gauges at risk may 

slowly be increasing as increasing demands 

for high-quality products are placed on 

industry.

The problem may be worsening, as might be 

concluded from looking at empirical data. Or the 

awareness of the problem may be increasing, as 

might be concluded considering other factors. 

Although the observed frequency of finding 

radioactive sources has been increasing since the 

first device was discovered in 1983, a closer look 

at matters is warranted. 

Figure 17 illustrates what appears to have 

happened over time. Light gray bars indicate the 

prevalence of NORM as reported in Reference 1. 

Similarly, dark gray bars indicate the prevalence 

of 'S7Cs, 'Co, and 241

Am. Both sets of bars refer 

to the left ordinate. The bars indicate incidents 

where no ambiguity in the type of radioactive 

material was reported. The solid line indicates 

receipts for scrap metal and refers to the right 

ordinate; this information was first compiled by 

the U.S. Bureau of Mines, then later by the U.S. 

Geological Survey (Ref. 15). 

The distribution of nuclear gauges began in the 

late 1950s. Yet the first reported melting of 

radioactive material in a steel mill was not until 

1983 when 'Co, which forms an alloy with steel,

NUREG-1669

Sample of Convenience 

The data summarized in Reference I are recorded 

instances of radioactive material discovered in the 

recycling stream. Because of various difficulties in 

collecting data, the authors of Reference I 

acknowledged that all discoveries were not 

reported. Therefore, the data are a sample, but not 

in the usual statistical sense of the word. 

A model of the situation from which the data were obtained is necessary to make valid inferences 

from the data. The model could then be used to 

design a statistical sampling procedure to estimate 

desired parameters. Such a model is lacking. The 

data were collected without an established 

protocol. In this regard, the data summarized in 

Reference 1 are not a statistical sample. 

For these reasons, the data reported in Reference I can be called a sample of convenience (Ref. 14, 

page 369). The data have some characteristics of a sample but did not result from an established 

protocol. The data are simply what was recorded, 

not a random sample.

35
4: INFORMATION

Bar Chart

Annual 

Discoveries of 

Radioactive 

Material: 

0 NORM 

U '

37

Cs, 1Co, 

&241Am

600o 

400 

200 -

4awwegdu 4 

4adfciý akud 

d~4czeaSQ 

m~wwoa 4 Iva

mal0e ( ýi4 0

1 70 1 72 1 7 1 76 1 78 1 80 82 1 8 I 8'6 1 8'8 I 9 1 92 1 9 91 I Year 

69 71 73 75 77 79 83 85 87 89 91 9 3 9 5 

"'Cs,D'Co,- Mlo An ' 1 0 3 0 3 2 3 2 1 6 1212 7 7 15 ngsof' I I I I I I I I I I I I I I 137Cs, CofZAinI 1 0 2 0 1 0 1 1 0 3 4 2 1 0 3

Figure 17 Analytical history of radioactive material in the recycling stream. Source: Data on the discoveries of 

radioactive material in the recycling stream are courtesy of James Yusko, Pennsylvania Department of Environmental 

Protection, Pittsburgh, PA. The data file is dated November 20, 1998. The last entry in the file is numbered 3044. 

Earlier versions of the data are summarized in Reference I. The information about the consumption of scrap metal is 

from the U.S. Bureau of Mines and the U.S. Geological Survey (Ref. 15); data for the figure came from the Internet at 

htI://minerals.er.usgs.gov. Scrap metal consumption data for the years 1969 to 1990 are in a summary table; 

consumption data for the years 1991 through 1996 are in the co'rresponding annual reports of "Iron and Steel Scrap."

caused a nuclear gauge on a continuous caster to 

give erroneous readings (Ref. 11). The reason for 

the three-decade lag between the first use and the 

discovered melting may be the time that gauges 

were on the process units before the units, and 

their gauges, were later scrapped. Whatever the 

reason, radioactive material was bound to be 

found with the use of nuclear gauges in the steel 

industry. The 1983 incident made people aware 

of radioactive material in the recycling stream. 

For the next few years, radiation monitors, likely 

with sodium iodide detectors, were installed. The 

lack of discoveries between 1983 and 1989 does 

not seem to be based on a lack of radioactive 

material in the recycling stream because NORM 

(see Section 2.2), which has nothing to do with 

regulations, is also apparently lacking. Reference 

I shows that a variety of radioactive material was

found-mostly NORM, but also some "'Cs, 

2'Ra, and uranium. Most of the discoveries were 

made with radiation monitors, but also to a much 

lesser extent with survey meters, and on a few 

occasions, visually. The early versions of today's 

sophisticated radiation monitors were installed at 

scrap yards and steel mills in 1987 and 1988; the 

radiation monitors use large panels of plastic 

detectors to generate signals from radiation that 

are processed with software. From then through 

1989, the increasing rate of discoveries may be 

due to increased awareness that radioactive 

material can be found in the recycling stream and 

to the use of sophisticated monitoring equipment. 

Most of the meltings listed at the bottom of Figure 

17 were of '"Cs. These meltings were discovered 

when steel mills scanned furnace dust before it left

NUREG-1669

Line

j 

Irg

A64 w a2cadi

30,000

20,000 

10,000

||I

36
4: INFORMATION

the facilities for a hazardous waste processor. 

Two meltings were of 'Co, one in 1983 and one 

in 1997. The low prevalence of 'Co has two 

explanations. One, "°Co is used less often than 137

Cs in gauges because of the shorter half-life. 

Two, the detection after melting may reflect a less 

rigorous monitoring of steel after it is melted (see 

Section 7.4). One of the meltings of '

37

Cs in 1997 

also involved 24

"Am. 

Other salient aspects of Figure 17 are as follows: 

" The prevalence of 137Cs, 60Co, and 24

"Am is 

too low to make definitive statements about 

trends. All that can be said is that 1

37Cs, 60

Co, 

and "

4 1

Am have been making their way into 

the recycling stream. 

"* From 1990 and thereafter, the discoveries 

appear to be approaching a steady state. By 

1990, sophisticated radiation monitors had 

been developed and installed. The tapering 

off of the discoveries of NORM also may 

reflect an established reporting system, albeit 

with unknown and uncontrolled reporting 

criteria. It may also reflect the installation of 

radiation monitors at most metal processors. 

" The peak of NORM in 1995 may reflect the 

lack of reporting criteria and controls. Much 

of this peak, 81%, consists of the discoveries 

from two steel mills in Texas where, because 

of a large petroleum industry, much NORM is 

expected.

Reference i not only shows that a problem exist 

but also confirms an intuitive understanding of the 

situation; the discoveries of radioactive sources in 

the recycling stream have been increasing since 

the first discovery. An increase in the rate of 

nuclear gauges entering the recycling stream 

would suggest that control mechanisms have been 

deteriorating. But a more plausible explanation is 

that the use of sophisticated monitoring equipment 

has been increasing. If the frequency of 

discoveries had instead decreased, then further 

investigation would be needed to reconcile the 

observations and intuition. 

Examples of Difficulties in Using a Sample of 

Convenience 

Seemingly obvious "probabilities" computed 

from empirical data can be misleading. Consider 

discoveries of radioactive material either by 

radiation monitors before entering the furnace at 

a steel mill or by monitors of product and 

byproduct material after entering the furnace (after 

melting a sealed source). Suppose there were X 

discoveries with the radiation monitors and Y 

discoveries when a sealed source was melted in a 

furnace and discovered in contaminated product or 

byproduct material. Looking at the reported 

experience of the entire industry, an obvious 

calculation is the probability of detection. 

Radioactive material has been discovered X times 

and missed Y times before entering the furnace. 

In this simple example, all melted radioactive 

material is detected. Then the probability of 

detection is given by Equation 14.

X 

Pr{detectl sealed source} = X+Y [14]

Author's Note 

The discussion of Figure 17 is .a historical 

perspective. For a risk assessment, only a more recent period is of interest a year or so that 

respondents would typically answer from when 

providing information through surveys (see 

Appendices B and C). During a short period, 

economic and regulatory conditions change 

little; the prevalence of gauges used in industry 

is approximately constant. Thus, the assumption 

in Section 3.2.1 of gauges found in industry 

being in a steady state is not contradicted by 

Reference 1.

Equation 14 calculates the probability of detection 

conditional on a sealed source being present in a 

load of scrap metal. Of X + Y sealed sources 

present in the scrap metal being consumed by the 

industry, some of them, Y, are melted. But some 

loads causing radiation alarms are rejected without 

determining the reason for the alarm. Because 

some of the rejected loads may contain sealed 

sources, Equation 14 yields an underestimate of 

the detection probability, where sealed sources 

present in rejected loads are considered to have

37 NUREG-1669
4: INFORMATION

been detected. This underestimated detection 

probability may mislead steel mill managers to 

purchase less radiation monitors than otherwise 

would be purchased. 

An estimate using Equation 14 applies to the steel 

industry as a whole. Of concern to each mill 

manager is not so much what is happening in the 

entire industry but what can happen to their mill. 

Here, too, empirical data are difficult to use. Only 

a few mills have melted radioactive material once. 

Far fewer have melted it twice. No mill is 

reported to have knowingly melted it more than 

twice. An erroneous conclusion is that the 

probability of melting radioactive material at most 

mills is zero or of melting it three times at any mill 

is zero. For many reasons, the detection 

probability at a specific mill may be quite 

different, higher or lower, because of the type of 

monitoring equipment, the placement of 

monitoring detectors, the practices for using them, 

the size of the loads of scrap metal, and the 

commodities of scrap metal purchased. 

4.3.3 Experimental Information 

Three quantities that determine the probability of 

detecting a nuclear gauge in a load of scrap metal 

are the performance characteristics of a detection 

system, the type and activity of radiation emitting 

from a gauge, and the shielding characteristics of 

the scrap metal. Currently, the performance 

characteristics of the detection systems can be 

well established. Characterizing the radiation 

source to be expected in a load of scrap metal is 

much more difficult. But the radiation sources can 

still be analytically characterized, for example, 

from what has been found in the recycling stream 

(Ref. 1) and compared to what is known to be 

distributed from gauge vendors. The shielding 

characteristics of the scrap metal are, for the most 

part, unknown. 

The information available to the NRC staff on the 

shielding characteristics of scrap metal is from 

tests on the detection capabilities of monitor 

systems sponsored by the steel industry.4 This 

4 / Steel Manufacturers Association, Washington, DC.

information, known as the "gauntlet" tests, 

consisted of placing tubes along axes in a 

transporting container on a vehicle, then filling 

scrap metal around the tubes. After a known 

amount of radioactive material was inserted into 

one of the tubes, the vehicle was passed though a 

series of monitor stations. The monitor systems 

that detected and those that missed the source 

were noted. The test was repeated, varying the 

placement of the radioactive source in the tubes. 

These tests determined the capability of 

monitoring equipment to detect sources in loads of 

scrap metal. 

The gauntlet tests are a starting point, but are 

insufficient for thoroughly characterizing the 

shielding of scrap metal loads in a way that is 

suitable for a risk analysis (see Section 7.5). The 

results are difficult to extrapolate to other 

commodities of scrap metal (such as bundles or 

plate and structural scrap) and other monitor 

systems. Experiments need to be designed to 

collect data about shielding from scrap metal 

commodities that can then be used to predict the 

detection probability. An earlier investigation was 

not fully developed. 5 

Modem radiation transport calculations can be 

done to simulate a gauge in loads of various 

commodities.6 From the simulations, experiments 

on loads, typical of those in the recycling industry, 

can be designed to validate the simulations and to 

characterize the variability of random 

arrangements of scrap metal in the loads. The 

shielding from loads of scrap metal could be 

characterized, accounting for the variations in the 

packing of scrap metal in loads (see Section 7.5); 

the detection probability for each commodity 

could then be derived and extrapolated to loads of 

other sizes and detectors with other performance 

characteristics. 

5 / A. Lamastra, "Radioactive Material in Steel Scrap: Its 

Occurrence, Consequence and Detection," Health Physics 

Associates, Inc., Lenhartville, PA, 1986. 

6 / Radiation passes through space according to the inverse square 

law. Transport calculations that predict radiation passing through 

matter account for attenuated, absorbed, and scattered radiation.

NUREG-1669 38
5 LICENSEES

5.1 Overview 

Industrial facilities have complex and changing 

organizations. Most of the time, gauges in these 

facilities are not vulnerable to being inadvertently 

discarded--they are in use controlling industrial 

processes. This circumstance may persist for 

years until an activity, such as renovating or 

dismantling a unit, briefly places a gauge at risk of 

being inadvertently discarded. During this time, 

there is a chance that it will be discarded. 

Analyses of the licensees give an understanding of 

when and how the gauges are vulnerable to'being 

discarded under industrial conditions and the 

consequences thereafter. Two concepts are key to 

understanding how gauges are made vulnerable as 

such: 

N Immediate and continuous control (ICC) 

shows the extent to which mechanisms 

constantly keep attention, in one form or 

another, on a gauge such that if the gauge were 

to be removed, its absence would be soon 

noticed. 

0 At risk shows the circumstances where gauges 

are vulnerable to being discarded. A gauge 

that is at risk is not necessarily discarded; it is 

just vulnerable to being so. 

Successful application of the concepts requires an 

understanding of the industrial environments of 

the gauges. Production, maintenance, renovating, 

and dismantling activities can have a large effect 

on the control mechanisms. 

5.2 Importance in Risk 

Licensees must be taken into account in estimating 

risk because this is where the circumstances that 

place gauges at risk of being discarded into the 

recycling stream are found. Here, a regulatory 

agency can influence some of the factors that 

affect the control of the gauges more so than the 

factors of recovering gauges from the recycling 

stream. Some of the conditions that place a gauge

at risk of being inadvertently discarded violate 

regulations, such as lacking labels or not taking an 

inventory as required. Other conditions that place 

a gauge at risk are in compliance with regulations, 

such as storing a gauge in a cluttered area or on a 

defunct process unit. Most violations are of little 

danger to life or property- people will not be 

exposed to radiation, and equipment will not be 

contaminated. But improper disposal, a violation 

of potentially high consequence, happens quickly, 

often without notice, and is difficult to reverse 

because a gauge in the recycling stream is 

obscured by large volumes of scrap metal. 

The topics taken into accounted in the analysis of 

the licensees are indicated in Figure 18.

Figure 18 Topics taken into account in the analysis of 

licensees. LEGEND: A black bullet indicates that a topic 

is comprehensively taken into account A white bullet 

indicates that a topic is beyond the scope of the risk 

analysis. A gray bullet indicates that a topic is briefly 

taken into account.

NUREG-1669

Section 5 

o Gauge vendors 

o Gauge design 

0 Facilities using gauges 

* Prevalence of gauges 

o Control mechanisms 

* Gauges at risk 

0 Proper transfers 

* Improper transfers 

* Proper disposal 

E Improper disposal 

* Demolition & salvage 

* Unknown use 

E Unauthorized use 

* Unauthorized disposal 

N Danger to life 

* Danger to property

39
5: LICENSEES

5.3 Concepts 

The concept of ICC is essential for understanding 

how control mechanisms function to keep gauges 

out of the recycling stream. Such control is 

immediate when the removal of a gauge other than 

to a desired location is noticed promptly. Such 

control is continuous when it occurs without 

interruption. Two questions must be asked to 

evaluate ICC: 

"* What conditions exist when a gauge is at risk? 

"* What controls are applicable when a gauge is 

at risk? 

To evaluate ICC, control mechanisms must be 

viewed in the context in which they operate--the 

industrial setting. Organizations at industrial 

facilities are complex, changing, and varied. The 

organization must respond to many 

demands - customers, competitors, stockholders, 

corporate oversight, resource suppliers, resources, 

labor, management, contractors, occupational 

regulators, environmental regulators, capital 

maintenance, and capital improvements. 

Controls on a gauge can be compromised to 

different extents by the conditions that exist at a 

facility: 

"* Acute hazards, such as toxic chemicals, heavy 

loads, high pressures, or high temperatures 

may be present. 

"* Employees are concerned about the acute 

demands of business and safety. 

"* Under unusual circumstances, such as a strike, 

administrative jobs may be placed on hold; 

care for the nuclear gauges may be among the 

administrative jobs. 

Many of the controls on nuclear gauges require 

active involvement of employees. Warning signs, 

roped-off areas, and verbal directions are of no 

consequence if people do not take heed. The 

attitudes of employees will have an influence on 

the effectiveness of those controls in a facility. 

Poor attitudes create ambivalence, both for safety

and for a facility. But prescribing every detail of 

every activity becomes unmanageable. In such an 

ambience, the gauges become more at risk to 

being inadvertently discarded because the controls 

that gain the attention of employees are 

compromised. 

Management attention is highly fluid. When an 

incident involving a nuclear gauge occurs, much 

attention is given to the gauges, to the exposures 

that employees may have received, to the 

possibility of regulatory actions (e.g., fines, 

license revocation), and the possibility of 

liabilities. But if another kind of accident occurs, 

such as with a chemical, then attention is given to 

that hazard - at the expense of attention given to 

the gauges. 

Many corporations are image conscious; when this 

occurs, the perspective of employees is that a 

facility cannot do without the support of 

customers, stockholders, and the local population. 

The emphasis on safety begins at the chief 

executive officer level, passes through the line 

organization, and is reflected by labor. 

Communications are kept coherent, such as with 

monthly safety meetings. Although nuclear 

gauges may be discussed only once a year, the 

emphasis on education and communications is 

present. Meetings held to make changes to the 

plant for responding to market forces involve 

people responsible for the gauges. But difficulties 

arise when the employees who purchase 

equipment are unaware that nuclear gauges are 

part of the equipment. 

Attention on these matters is attention that is 

drawn away from the gauges. ICC reflects these 

and other circumstances. 

A regulator is seldom present at a facility to 

ensure the control mechanisms are functioning 

properly, placing much of the responsibility for 

implementing the controls on the licensee. An 

implicit assumption in the regulations is that a 

licensee assumes the responsibilities for 

controlling the gauges. But the incidences 

reported in Reference 1 suggest that the 

assumption is not always met. A licensee may be 

unable to or may not know how to carry out such

NUREG-1669 40
5: LICENSEES

responsibilities in a way to ensure adequate ICC. 

Gauges operate under circumstances where the 

major concerns are for production and 

employment. 

In this context of complex organizations with 

acute demands and acute hazards are the gauges 

themselves. However, gauges do not command 

much attention because they seldom require 

maintenance and are rarely lost. 

5.4 Control Mechanisms 

Control mechanisms may prevent gauges from 

being inadvertently discarded. Typically 16 

mechanisms can be found throughout industry, 

providing ICC on the gauges to different extents. 

These mechanisms can be placed in two 

categories, hard controls and soft controls, 

according to how they provide ICC. An 

understanding of how each of the control 

mechanisms operates is necessary to understand 

why gauges are at risk during the various phases 

of industrial operations.

Interim Dedicated Storage

An area that is used only for temporarily storing a 

gauge, usually during a shutdown for maintenance 

or renovation, is interim dedicated storage (IDS). 

The gauge is returned to the process unit when the 

shutdown is over. Otherwise, it is returned to its 

vendor. The storage area is only for the gauge. It 

is uncluttered, avoiding the possibility of 

inadvertently discarding a gauge with other 

materials. It is interim, avoiding the possibility of 

forgetting about the gauge. It is secure and well 

marked, so that a gauge cannot be readily 

discarded. 

Return to Vendor 

Gauges that are returned to vendors are removed 

by qualified people. Such people can ensure that 

a gauge is removed and transported without 

posing a hazard. A gauge that has been returned 

to its vendor is no longer at risk in the facility 

where it was used. 

5.4.2 Soft Controls

Soft controls operate indirectly to provide ICC by 

getting the attention of employees, often at times 

other than just when needed. These controls are 

5.4.1 Hard Controls more difficult to assess than hard controls.

Hard controls operate directly on a gauge to 

provide ICC by deliberately placing a gauge at a 

definite location at the moment when control is 

needed. Their effectiveness is necessarily high. 

Three hard controls typically found throughout 

industry are using a gauge in production, placing 

a gauge in its own storage area, and returning a 

gauge to its vendor. 

In Use 

A gauge is controlling production when it is in 

use. For some process units, the gauge is critical. 

For other units, the gauge can be removed, such as 

for servicing, but the process unit must be 

controlled manually. In either case, the gauge 

cannot be removed without being noticed.

Inventory 

As the term is used in this risk analysis, inventory 

is done at a facility, initiated by employees, to 

account for the gauges. It differs from the list of 

devices secured during a lockout in that it is an 

accounting of all gauges, not just those on a 

process unit that is taken out of service for 

maintenance. It differs from registration (see page 

45) in that it is initiated at a facility, not by a 

regulatory agency. Typically, inventory is done 

on a semiannual basis. For providing ICC, it must 

be done after activities placing gauges at risk (e.g., 

maintenance, housekeeping); attention is focused 

on the gauges at the moment when they are at risk 

of being unintentionally removed, and it stays 

focused until all of the gauges are taken into

41 NUREG-1669
5: LICENSEES

account and secured. Otherwise, a gauge may 

have been discarded long before an inventory is 

taken. 

Labels 

The primary function of labels is to be a positive 

indication that a component contains nuclear 

material. A label is the radiation trefoil sign on or 

near a gauge warning of the radioactive hazard. A 

label may not be on a gauge itself because the 

gauge is inside a process unit, hidden among 

rollers and supporting beams, or in a harsh 

ambience. People do not always take notice of 

labels, such as when they are distracted or tired. 

Other demands compete for attention; during 

maintenance and dismantling, people are busy 

getting their work done. Environments may be 

dark; although a label may be visible, it may not 

be illuminated. Employees may overlook a label 

or mistakenly perceive that the label refers to the 

contents in a tank or pipe, not the gauge housing.7 

Production materials may obliterate a label in days 

or weeks.

An inspector can usually identify a nuclear gauge 

without the labels by its shape, especially when 

the inspector is familiar with the processes of the 

facility or the facility itself. The same is true for 

process engineers and people who respond to 

emergencies (e.g., fire, hazardous material 

incidents). 

Physical Security 

Physical security is a fence, chain, or lock on or 

around a gauge, or restricted access to a site 

containing a gauge. A lock or cable on nuclear 

gauges can be cut with a torch. Sometimes a lock 

on a storage area can be opened with a 

screwdriver or penknife just as fast as with a key. 

The wire fencing of a storage bin can be easily 

cut. A nuclear gauge is not necessarily secured by 

a fence, chain, or lock. 

7/ See NRC Preliminary Notification of Event or Unusual 

Occurrence, PNO-IV-98-033.

Lockout 

Lockout is a procedure, required by the 

Occupational Safety and Health Administration, to 

secure a process unit for servicing so that the unit 

cannot be inadvertently started, in full or in part, 

while people are repairing or maintaining the 

process unit. Lockout requires that a list of 

components be locked. While checking the list of 

components both before and after the process unit 

is serviced, an inventory of gauges is, in effect, 

taken. But a lockout is not entirely reliable for 

providing an accurate inventory for two reasons: 

"* A lockout may occur during a time when a 

process unit is being disassembled- a gauge 

may be slated to be removed and, therefore, 

may be removed as well from the lockout list 

when the process unit is restarted, losing, in 

this regard, the accountability for keeping it out 

of the recycling stream. 

"* A lockout list may be incorrect. 

The lockout guarantees that a process unit was 

shut down and gives proof that the process unit 

was locked; it does not prevent removal of nuclear 

gauges with a bolt cutter or a cutting torch. 

Incidents have occurred where employees or 

contractors have inadvertently removed and 

discarded nuclear gauges when radiation signs 

were ignored, roped-off areas were entered, or 

components with gauges have been removed. 

Responsibility 

Responsibility is the authority given to a person or 

a group of people in a facility to account for a 

gauge. For specifically licensed gauges, the 

responsibility is clearly defined by the conditions 

of a license; the radiation safety officer (RSO) is 

given the responsibility for a gauge. For generally 

licensed gauges, a responsible person may be 

present although from a regulatory perspective, 

the company, not a person, is responsible. 

Although regulators can assign responsibility on 

a case-by-case basis, there is no one place 

throughout industry where both stability and 

authority can be identified; in some facilities,

NUREG-1669 42
5: LICENSEES

upper management is in flux more than lower 

management and production people, while at other 

facilities the opposite is true. Furthermore, the 

responsibilities for production may be shifting and 

overlapping. 

While regulations convey the responsibility to the 

licensees, they do not provide guidance 

(information and experience) to personnel who 

have to implement and manage that responsibility. 

To provide ICC, a person assigned responsibility 

for the gauges must be close enough to production 

to remain close to the gauges as they are used and 

high enough in the organization to have authority. 

Education and Communication 

Education is a program to inform employees of 

the presence and care of the gauges. 

Communication is the established routes for 

information necessary to control nuclear gauges. 

The responsible person informs maintenance staff 

of the gauges. The maintenance staff inform the 

responsible person of the need to secure a gauge 

for servicing the process unit. Education and 

communication must be supported by facility 

management to be effective. Education and 

communication can be compromised for many 

reasons: 

"* At an industrial facility, people of almost any 

educational level may be found. 

"* Renovations are done continuously to keep a 

facility current. The responsible person may 

not be always around to ensure ICC. 

"* Much outsourcing is done to keep costs down. 

A contractor may be given training on general 

plant safety. Whether or not this training is 

communicated to the contractor workers is 

another matter. 

"* An employee can be assigned to other 

activities, leaving (safety) tasks undone.

High-Level Accountability (HLA)

HLA is holding upper management at a facility 

accountable in some ways for addressing 

regulatory infractions. Management, not the 

person directly responsible for the gauges, 

explains to regulators why an infraction occurred 

and what will be changed to improve matters. The 

effectiveness of HLA might be increased by 

holding the licensee accountable at the location of 

the regulator instead of the regulator coming to the 

licensee; this increases the impact of 

accountability on the management of a facility. 

Inspection 

State and Federal regulators go to a facility to 

evaluate compliance with regulations; they may 

also be done when an incident involving 

radioactive material occurs. Inspections are not 

coordinated with times when gauges are placed at 

risk. Because gauges are subject to ICC for most 

of their service life, inspections can significantly 

reduce risk only when they coincide with at-risk 

periods. 

Civil Penalties 

A civil penalty is a monetary penalty that may be 

imposed for violations of Nuclear Regulatory 

Commission (NRC) rules or orders, or of any 

requirement for which a license may be revoked. 

An assessment of a civil penalty takes into 

account first the severity of the violation and 

second the ability to pay. Violations pertaining to 

greater potential consequences to the public and 

licensee employees receive higher civil penalties 

than those involving lower potential 

consequences. The intention of a civil penalty is 

not to put a licensee out of business; ceasing 

operations is done by suspending or revoking a 

license. The intent of the civil penalty schedule is 

to deter future violations by the licensee where a 

violation occurred, to deter future violations at 

licensees conducting similar activities, to 

encourage prompt identification, to encourage 

prompt and comprehensive corrections, and to

43 NUREG-1669
5: LICENSEES

S craP Steel 

Yards Mill

Cfale ek4i1

Pr{detect} Cfmie 

Pr{miss} Cmelt C.0"&.q"04i 

& dkl eMW~

Figure 19 Estimating a civil penalty by equating the risk of a civil penalty 

at licensees to the risk of melting a nuclear gauge at steel mills.

focus licensees' attention on violations of 

significant concern. The outcome of an 

assessment is either no civil penalty, a base civil 

penalty, or a base civil penalty escalated by 100%. 

The effectiveness of a civil penalty for providing 

ICC is decreased by the circumstances of gauges 

entering the stream: 

" The civil penalty applies to an event that is 

unlikely to occur. Nuclear gauges are a minute 

and reliable portion of operations. Memories 

at facilities fade as the work force changes 

while business demands attention. 

"* The gauges are lost because of the actions of a 

few people, yet a corporation is the entity that 

is fined. 

" A gauge from storage or a dismantled process 

unit may have entered the recycling stream 

long before employees realized it was missing. 

Because scrap metal conceals a gauge from 

both visual and radiation detection, corrective 

actions (e.g., recovering the lost gauge) are 

almost a moot point. 

The proper amount of a civil penalty to provide 

ICC is difficult to determine. A lower limit is

is done twice

obvious for improper 

disposal- it should be greater 

than the cost for proper disposal. 

But how much greater? The 

proper amount will depend on the 

value of resources at a facility. 

The value of resources is 

determined with an economic 

evaluation, which in practice, is 

complex and difficult to do 

correctly (Ref. 3, page 239). A 

way to determine the amount of a 

civil penalty is by determining the 

point at which the risk of a penalty 

to a licensee is equal to the risk of 

a consequence, for example, of 

melting a gauge at a steel mill. A 

simplified circumstance is 

illustrated in Figure 19. On the 

left of the figure, a gauge has been 

improperly disposed. Monitoring 

along the recycling stream. For

simplicity, the detection probability is the same in 

both the scrap yards and the steel mills. If the 

gauge is detected at either the scrap yard or the 

mill, a civil penalty, Cfie, is imposed. If the gauge 

is missed at the scrap yard, it may be detected at 

the steel mill. If it is missed again at the steel mill, 

then the mill incurs financial damages, Cmelt- The 

probability of detecting the gauge is Pr{detect} 

and the probability of missing the gauge is 

Pr{miss}. In Figure 19, each consequence is 

multiplied by the probabilities along the sequence 

of risk elements leading to the consequence; the 

terms for the licensees are equated to the terms for 

the steel mills; solving for Cf,, yields Equation 15.

C [Pr{miss}]2 C.ei, Cn Pr{detect}[I + Pr{miss}] [15]

= [Pr{miss}]2C•,,, 

Analytically, this method seems reasonable. In 

practice, difficulties become evident: 

N The probability of detecting a gauge is 

unknown (see Section 7.4). But whatever it is, 

[Pr{miss}] 2 is small, offsetting the large value

NUREG-1669

flH24epe4

44
5: LICENSEES

of Cm.,t , thus making the civil penalty small. 

For example, with a detection probability of 

99% and costs to steel mills of about $10 

million, the civil penalty is calculated to be 

$1,000. 

"* Financial costs of melting a gauge are highly 

variable. The few incidents limit a good 

characterization of the consequences to 

estimate Cmeit. 

"* These equations imply that the more 

monitoring is done and the more effective the 

monitoring, the lower the civil penalty. A low 

civil penalty may not be a deterrent to a 

licensee. 

"* The purpose of a civil penalty is to deter, in 

this case, improper disposal, not to compensate 

for damages. The civil penalty is collected by 

the treasury of the governing authority, not a 

licensee. Figure 19 illustrates insurance, where 

payments are made by licensees into a fund 

that is used to compensate facilities that incur 

damages. Unless the purpose of a civil penalty 

is altered from a deterrent to compensation and 

a means of transfer payments can be 

established, this method for determining the 

amount of a civil penalty is of little use to 

stakeholders. 

A risk assessment can be a structured way to 

determine the potential for consequences. But a 

determination of the amount of a civil penalty to 

provide ICC with a risk assessment is difficult. 

Revocation 

A license to use a nuclear gauge can be revoked, 

taking away the authority of a facility to possess a 

gauge. Revocation occurs only after a violation 

has occurred. Otherwise, it. is just a possibility 

that may or may not be accurately assessed by 

plant employees. The effectiveness is greatest 

when a violation is being addressed and fades over 

time as other issues at a facility gain attention. 

When a facility is being phased out, revocation 

only hastens the closure. When a facility is 

closed, revocation is irrelevant.

Registration 

Registration is done by an enduring 

organization - a regulatory agency. At a 

regulatory agency, registration is an accounting of 

the nuclear material in the public domain and a 

means for the regulatory agency to keep licensees 

informed of regulatory concerns. Registration 

refreshes memories at facilities where there is 

significant change in the work force. At a 

licensee, registration operates through the 

awareness of employees. But the reason for 

gauges being discarded into the recycling stream 

is much more complicated than a lack of 

awareness of the gauges. Time of registration has 

nothing to do with the activities at a facility that 

place gauges at risk. Annual registration is 

infrequent compared to the time when a gauge can 

be placed at risk and discarded. 

Registration might influence other control 

mechanisms--such as responsibility, education, 

communication, and revocation-that involve 

awareness and maintaining a corporate memory of 

the gauges. Registration only reminds employees 

of gauges in their facility, where the organization 

may be complex, diffusing responsibility and 

impairing communication. 

Followup to registration is necessary if 

registration is used to provide ICC under some 

conditions of industrial facilities. A lack of 

response from a licensee may indicate that a 

facility has been closed or abandoned. A facility 

in either state is subject to pillage, placing the 

gauges at risk of entering the recycling stream. 

The percentage of the gauge population under 

some kind of registration (e.g., accurate 

accounting of all gauges at a facility) is unknown. 

At least some States register gauges. Many 

companies, particularly large ones, conduct 

semiannual inventory of their gauges, which has 

the same effect as registration, although more 

localized and in potentially less enduring 

organizations than government.

45 NUREG-1669
5: LICENSEES

Publicity

The NRC and some States hold companies 

socially accountable for their activities. For 

example, the names of companies out of 

compliance with regulations may be published in 

a newspaper. Such publicity can influence the 

control of nuclear gauges. Many companies are 

image conscious; they seek highly skilled people 

and maintain good relationships with customers 

and stockholders through well-managed 

operations. Adverse publicity tends to counter 

this. But publicity about nuclear gauges is for a 

rare event in the indeterminate future, which tends 

to diminish the influence of publicity on ICC. 

Query at a Change in Responsibility (QCR) 

The current regulations state that informing a 

regulatory agency of a change in the ownership of 

a facility is the responsibility of the licensee. 

There is no situation analogous to the purchase of 

a house, where the people managing the purchase 

check legal records to ensure that the seller is the 

legal owner. Applying the concept to nuclear 

gauges, a query about the gauges would be 

required before a transfer could be legally 

completed, notifying regulatory agencies and 

asking about records of nuclear material. The 

same concept can be applied to demolition and 

salvage; here, although a contractor does not 

assume ownership, responsibility for the 

demolition and salvage is assumed. The issue is 

who is responsible for the activities at a facility 

where ICC is applicable; hence, the emphasis is on 

the change in responsibility. QCR differs from a 

registration system in that the regulatory agency is 

contacted only when responsibility changes. It 

differs from an inventory in that an entity 

managing the transfer is inquiring with the 

regulatory agency. 

5.5 Elements of Risk 

Figure 20 is an illustration that is central to 

understanding the control of gauges. Here, the 

concept of ICC is applied to 16 control 

mechanisms in 33 industrial environments

throughout industries where nuclear gauges can be 

found. 

Figure 20 shows the applicability of the control 

mechanisms to provide ICC in the environments 

found throughout industry. In some 

environments, many mechanisms operate to 

provide ICC. In other environments, none of the 

mechanisms operate as such. After the 

applicability of the control mechanisms is 

established by Figure 20, both the extent to which 

the gauges are at risk to being inadvertently 

discarded and the fate of the gauges can be 

analyzed. 

The left half of Figure 20 delineates all plausible 

environments of the gauges with three 

elements -the factors that influence risk. Orphan 

sources are treated as a branch of Element 1, but 

listed under Element 3 (location). Because they 

are not part of a facility, they are not properly 

placed under Element 1. Yet they are part of the 

general population of sealed sources. Orphan 

sources can be considered a type of location. 

Given this, the treatment was to consider them a 

portion of the population of gauges by branching 

from Element 1 but classifying them under 

Element 3. 

The right half of Figure 20 shows the applicability 

of control mechanisms (regulations and practices) 

to the gauges in each of 33 environments; a white 

box indicates that the control mechanism cannot 

provide ICC over gauges; a shaded box indicates 

that the control mechanism can provide ICC. The 

reasons for specifying that a control mechanism 

provides ICC in a given environment are provided 

in Appendix A. Some of the control mechanisms 

are regulations while others are practices found in 

industries. Sixteen control mechanisms are 

grouped into hard and soft controls, according to 

the means by which the control mechanism 

functions. A hard control keeps a gauge in a 

definite place either where it is needed or in a 

location where it cannot cause harm or damage. 

Soft controls are warnings (which include barriers 

and chains) or procedures that may allow a gauge 

to be removed unnoticed.

NUREG-1669 46
5: LICENSEES

Elements Forming the 

33 Environments of Nuclear Gauges

1: States of facilities (page 48) 

2: Work force changes (page 49) 

3: Gauge locations I (page 49)

In Use, Operating Unit ->. {1) 

- Out of Use, Operating Unit>- {2) 

Slow Maintenance >- (3) S Storage > (4) 

- Defunct Unit - > (5s 

Operating: Dismantled Unit _ > (61 

Constant 

Ownership In Use, Operating Unit -;- (7) 

- Out of Use, Operating Unit> (8) 

Rapid Maintenance ) (9) Storage > (10) E Defunct Unit - > (11) Dismantled Unit - ).•- (12) 

In Use, Operating Unit -> (13) 

Out of Use, Operating Unit- (14) 

Slow Maintenance - > (15) 

SStorage (16) 

O Defunct Unit - > (17 

Operating: Dismantled Unit > (18) 

- Changed 

Ownership - In Use, Operating Unit -> (19) 

Out of Use, Operating Unit> (20) 

Rapid - Maintenance > (21) 

Storage J (22) 

- Defunct Unit (23) 

Dismantled Unit - > (24) 

In Use, Operating Unit -> (25) 

Out of Use, Operating Unit> (26) 

Phasing Storage > (27) 

Out Defunct Unit > (28) 

Dismantled Unit - > (29}

- Closed

Abandoned > 

Dismantled

.1 

7":' 7

(30) 

{31) 

(32)

OrphanSource >{) 1 I);I 1 1I3 I I I I

Figure 20 Analysis of the risk elements in the industrial environments of nuclear gauges at licensees. LEGEND: A white box (0) indicates that a control cannot provide ICC in a given environment. A shaded box (2) indicates that a control can provide ICC in a given environment. P = prevalence nuclear gauges; x = G for generally licensed gauges; x = S for specifically licensed gauges; x = T for both types of gauges. E&C = education and communication. HLA = high-level accountability. QCR = query at a change in responsibility. The reasons forspecifying given control as applicable or inapplicable in a given environment are in Appendix A. An arrow (>-) indicates that the sequence continues in Figure 21.

NUREG-1669

PxF

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I!_j• 1[• T 

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!1~ ~ ~ F I1f1•1Lo

47
5: LICENSEES

The population or prevalence of nuclear gauges 

throughout all industries in the United States is 

denoted by P. Two populations of gauges, 

generally licensed and specifically licensed, need 

to be kept separate for risk calculations because 

the control mechanisms applicable to the two 

groups differ. For example, at a facility with 

generally licensed devices, responsibility may not 

be assigned as it is required at a specific licensee, 

although some general licensees may have an 

employee fulfilling the activities of an RSO as a 

matter of business. A facility that has both 

generally and specifically licensed devices would 

be treated as the latter. 

Elements 1 through 3 in Figure 20 delineate 33 

environments in which the gauges are found 

throughout industries. The distribution is an 

equilibrium because the number of gauges in 

various environments is approximately constant 

under stable economic and regulatory conditions. 

The equilibrium is also dynamic in that individual 

gauges are moving from one environment to 

another without the distribution of gauges 

changing appreciably. 

Element 1: States of Facilities (Figure 20) 

Operating Under Constant or Changing 

Ownership 

In facilities that are operating under constant or 

changing ownership, production continues without 

interruption. Employees in facilities that are 

operating are concerned about production, safety, 

and their future. To varying degrees across 

industry, there is also an interest in maintaining 

the facility. 

Phasing Out, Closed, or Abandoned Facilities 

Phasing out means that a facility is closed 

gradually, such as over years. No major 

renovations are planned. Gradually production 

may be shifted to other facilities. Employees have 

time to accommodate their circumstance and find 

other work. A closed facility no longer is 

operating, but it still is owned. An abandoned 

facility is closed and without an obvious owner; 

there is no possibility of it being reopened.

Traditionally, industrial facilities closed when 

markets slowly eroded. But now, closing in 

several months is becoming more common. When 

profitability goes below a certain level, the facility 

is shut down. From the employees' perspective, 

a facility can close in days or hours. When this 

happens, (former) employees will be concerned 

about their families, savings, and when they will 

work again, not about otherwise innocuous 

components such as nuclear gauges. What 

happens to the gauges depends on what happens to 

the employees. If the company reassigns its 

people to another operation, then there may be 

more assurances that the current operation will be 

closed in an appropriate manner. If employees are 

left with nowhere to go, their concern is no longer 

with the facility, unless they have other interests, 

such as being employed to dismantle the facility. 

A facility may be closed for years before being 

reopened, either under the same ownership or 

under different ownership. A security guard may 

be on the site. An abandoned facility is left with 

no one accountable for what remains in the 

facility. 

Facilities may be closed or abandoned for years or 

decades before being dismantled. A closed 

facility is subject to pillage for anything of value, 

such as copper, steel, tools, and equipment, and it 

is also subject to unauthorized demolition for 

scrap metal. Thieves do not limit themselves to 

small pieces of scrap; they take large pieces too. 

If pillaging of a facility is indiscriminate, then 

gauges that are in the facility are at risk of 

entering the recycling stream. 

Dismantled Facility 

A dismantled facility is one that has been scrapped 

or salvaged. More generally, dismantling or 

salvage is known as demolition. In general, a 

facility is not dismantled indiscriminately. 

Imploding a building is a minor part of the 

demolition business done by only a few 

companies; afterwards, a pile of rubble must be 

sorted. A large part of the business is industrial 

renovation and salvage. Industrial facilities are 

readily disassembled and reassembled. A facility 

is taken apart, to the extent it can be, as it went

NUREG-1669 48
5: LICENSEES

together. Process units are removed to make room 

for new process units when a company makes a 

new product or when newer technology can be 

used to reduce the cost of making current 

products. Valves are cut away and separated. 

Motors are separated from ferrous scrap metal to 

recover the copper. Reinforced concrete debris 

can be crushed to remove the concrete, leaving the 

rebar. The pulverized concrete can be used as fill 

material. 

Dismantling and salvage are done in four phases, 

each of which has standard operating procedures: 

"* Hazards, such as from chemicals, power lines, 

heavy loads, and radioactive material, are 

identified. 

"* Utility lines are disconnected (some lines may 

remain active for dismantling and salvage). 

"* Hazardous materials are removed. 

"* The facility is dismantled and salvaged. 

Some of the materials from ajob may be prepared 

by separating, shearing, and baling to increase the 

value. The extent to which preparing is done 

depends on the contractor's access to equipment 

and the market price of scrap metal. 

Portions of the demolition industry may be 

difficult to reach in keeping workers informed 

about nuclear gauges. A large, well-established 

company usually specializes in a particular type of 

facility, thus accruing knowledge about the 

intricacies and hazards of such demolition. Such 

companies can be readily informed and kept 

informed. Small operations, some of which may 

not be formal companies and may lack experience, 

are more difficult if not impossible to reach either 

by regulators or trade associations. 

Element 2: Work Force Changes (Figure 20) 

The work force embodies the corporate memory 

of the gauges. Slow turnover allows the corporate 

memory to be refreshed. Rapid turnover 

compromises the corporate memory; here, concern 

may be for continued employment; if so, safety

considerations, such as for nuclear gauges, may 

become secondary considerations. 

Element 3: Gauge Locations (Figure 20) 

In Use and Out of Use on Operating Process Units 

Gauges that are in use on operating process units 

are not at risk of entering the recycling stream 

when the gauges are controlling processes. A 

gauge in use is controlling a process. An out-of

use gauge may be kept on the process unit for 

reasons that include the following: 

"* because no one removed the older gauge when 

a newer gauge was installed, 

"* because of a pending decision to move it to 

another process unit, or 

"* To serve as a backup to an operating gauge. 

Maintenance 

In a large industrial facility, much activity is 

occurring during a maintenance shutdown. Most 

attention is on the shutdown; little attention is on 

the nuclear gauges. A shutdown is thoroughly 

planned; except for minor preventive 

maintenance, it may be scheduled according to the 

demand for the product. The repairs and 

renovations are organized to be done in the 

shortest time. Still, a process unit may be taken 

out of service for days or weeks for major upkeep 

or renovations. Before a unit is shut down, the 

process manager has determined the upgrades to 

be done, the new technology to be installed, and 

the components that need to be repaired. 

Contractors are told about safety procedures. 

Even so, unforeseen difficulties occur. Employees 

may be late to meet each other for performing an 

activity, heightening concerns about completing 

the shutdown. Inventory lists may have errors. 

Delays and unforeseen events pull attention 

further away from the gauges. 

Maintenance activities take place on a shop floor 

that may be cluttered with hoses, electrical wires

49 NUREG-1669
5: LICENSEES

for lights, flexible ventilation pipes, worn parts, 

and replacement parts. A gauge that is removed 

and set on the floor can become lost among the 

clutter. Many activities during maintenance draw 

attention away from the gauges. C: 

"* Cleaning equipment with water hoses and 

pneumatic tools. 

"* Lifting components weighing many tons with 

overhead cranes. 

"* Unlocking a portion of a process unit to rotate 

a component a few inches for gaining access, 

then locking it again according to procedures. 

"* Entering confined spaces must be preceded by 

a check of the oxygen level. 

" Working in tight places that may be poorly lit. 

The work among the contractors is narrowly 

defined. One set of contractors does not 

necessarily know what another contractor is 

doing. A gauge that is set down by one contractor 

may be easily removed by another contractor. 

When many people are involved in a shutdown, 

communications become complex and activities 

become nebulous as compared to operation. 

Consequently, responsibility and fault for 

inadvertently removing a gauge become nebulous 

to attribute to one person. 

Storage 

Gauges not in use may be stored for a variety of 

reasons: 

"* A process unit is down for maintenance. After 

maintenance, the process unit is returned to 

service. 

"* A gauge may need frequent service because it 

operates in a dirty or corrosive environment. 

While one gauge is being serviced, another 

gauge is used to maintain production.

* A gauge is used as a backup when a process 

unit can be damaged. For example, a steel 

mill may use a gauge to monitor the metal 

level in a continuous caster. Should steel spill 

onto the mold where the metal is poured and 

cover the source housing, the mold can be 

replaced with another mold and gauge. 

In general, storage areas throughout industry take 

the following forms: 

"* fenced area or metal room secured with a 

padlock; 

"* brightly painted heavy-gauge box locked shut, 

with a padlock, in production areas; 

"* open crate on the floor of a cluttered 

general-purpose room; 

"* roped-off area of a shop in a facility; or 

"* cluttered corner of a room containing facility 

equipment. 

These practices can persist for decades without 

anything happening to a gauge. 

Some facilities do not store gauges; instead they 

make arrangements with a vendor to have a 

replacement gauge delivered promptly. If the 

source housing is damaged during production, 

most assuredly other portions of the process unit 

that the gauge was controlling will also be 

damaged. The process unit may not be placed into 

service immediately. During this time, another 

gauge can be sent from a vendor. 

Defunct Process Unit 

A defunct process unit is one that is no longer in 

use. Nuclear gauges on such a unit are at risk 

because they are not controlling a process and 

they can be removed without disrupting activities 

in the facility. Employees may have a gauge on a 

defunct unit, anticipating a time when the process 

unit is brought back into service. A manager may 

have no definite plans for restarting the defunct

NUREG-1669 50
5: LICENSEES

unit, and the unit may be in disarray. Although 

other components may have been removed for 

safekeeping, a gauge may remain on the defunct 

unit. 

Orphan Sources 

An orphan source is a discrete radioactive source 

for which no responsible entity (licensee cannot 

be located, licensee is not viable) or no disposal 

option (vendor, another licensee) can be found. 

The phrase orphan source is applied to a variety 

of devices, including nuclear gauges. 

In Figure 20, the prevalence of gauges in the 

environments, not the movement of gauges among 

the environments, is analyzed. Treating the 

prevalence among environments as an equilibrium 

means that the prevalence of gauges in each 

environment is constant. The three elements 

forming the environments change slowly in most 

cases during a reasonable period, such as a year. 

For example, the effects of a change in ownership 

persist both before and after the change; the 

effects stemming from a turnover rate of the work 

force persist. Recognizing that the environments 

change little allows Elements 1 and 2 to be 

defined as Equation 16.

Ni,k 

j L Ni,k [16]

p. k = fraction of gauges at the j' possibility of 

the kr" element 

Nj, k = number of gauges in the jt1 possibility of 

the k' element 

j denotes an element 

k denotes possibility of an element 

Element 3, the location of gauges, presents a 

difficulty. The gauges on operating process units 

move into a risky state, maintenance, and back 

again, within a relatively short period of time 

(e.g., hours to a few days or weeks). The short 

period precludes an accurate inventory of the 

gauges on a process unit under maintenance using 

a survey to collect information. The inventory of 

gauges in a maintenance environment has be

inferred. Let NOJ be the number of gauges in 

use (IU) on operating process units (OP), and 

NOU be the number of gauges out of use (OU) but 

still on operating process units. CP is the capacity 

factor of the process units-the percentage of 

time the units operate. The total number of 

gauges in any location of facilities given the state 

of the facilities (e.g., constant ownership, 

changing ownership) is N F. The two fractions of 

gauges on operating process units (i.e., in use, out 

of use but still on an operating process unit) are 

given by Equations 17 and 18.

OL NIC 

OL NoT CP 

POU -- N 

[17] 

[18]

The fraction for both states of gauges on process 

units that are shut down for maintenance is given 

by Equation 19.

[19] q)I • ln M(NO + NO)(l - C F (P =N M. T

The fractions for the other possibilities of Element 

3 are determined with Equation 17. 

Figure 20 established which control mechanisms 

provide ICC in 33 environments. The extent to 

which the gauges are at risk of being discarded 

given the control mechanisms that are operating, 

and the possible fates of the gauges thereafter, are 

determined by three more risk elements. 

Figure 21 illustrates the remaining three risk 

elements of the licensees. Single black lines are 

sequences of risk elements. An arrow (>-) 

indicates that the sequence continues in Figure 28. 

A dot (0) indicates the end of a risk element 

sequence. An open dot (0) indicates that a 

sequence is unresolved; it continues, but is not 

developed further. Hazard terms are from the U.S. 

Code of Federal Regulations (Ref. 9). A black 

box (U) indicates that a concern is present 

between Elements I through 6 of a particular 

sequence.

51 NUREG-1669
5: LICENSEES

Elements 

4: At-risk potential for a gauge to get beyond 

control mechanisms (page 53) 

5: State of a gauge 

at risk (page 56) 

6: Disposition of a gauge 

at risk (page 56) 

Not at Risk

This figure stems from 

each industrial 

environment of nuclear 

gauges delineated in 

Figure 20 (page 47).

At Risk

Hazards 

in Elements 

4 through 6 

Danger to Life 

Danger to Property

Intact Gauge In place 

With a Closed 

Shutter Relocated 

Scrapped 

Intact Gauge In Place 

With an Open 

Shutter Relocated 

Sealed Source Scrapped > Is Dislodged 

From a Gauge

Figure 21 Analysis of the licensees' risk elements (continued). LEGEND: Single black lines are sequences of risk elements. An arrow 

(>-) indicates that a sequence continues in Figure 28. A dot (0) indicates the end of a sequence. An open dot (0) indicates that a sequence 

is unresolved; it ends here, but not further developed. A black box (0) indicates that a concern is present as of Element 6 of a particular 

sequence. A shaded box ( M) indicates that a concern might be present as of Element 6 of a particular sequence. A white box (0) 

indicates that a concern is not present as of Element 6 of a particular sequence. Hazard terms are from theUS. Code of Federal 

Regulations (Ref. 9).

NUREG-1669 52
5: LICENSEES

A shaded box (IM) indicates that a concern might 

be present. A white box (El) indicates that a 

concern is not present. The hazards to life and 

property are as follows: 

"* A gauge that is not at risk (e.g., in use, 

properly stored) is not a danger to life or 

property. Although a gauge is at risk, it is not 

necessarily a danger. 

" If a gauge is in place or relocated, then the 

sequence terminates. A relocated gauge is 

moved to another location, not discarded. If 

the gauge is scrapped, then the sequence 

continues, but between Elements 4 and 6, it is 

not a danger to life or property. 

"* If the shutter is closed, it is not a danger to 

life. When the shutter of a gauge is open, it 

may be a danger to life. On a process unit 

being serviced, an open shutter may cause 

exposures. When a gauge is relocated or 

scrapped with the shutter open, exposures may 

also occur. 

"* The sequences of in place and relocated 

gauges terminate. The sequences of scrapped 

gauges continue. The sequence for a 

dislodged source at a licensee terminates, but 

is unresolved; for example, it may, in a way 

that is too ambiguous at this time to take into 

account, enter the recycling stream if it is 

lodged in a piece of scrap metal; it may be in 

a sump; it may be an a shop floor. Little can 

be said beyond it is a danger to life and 

possibly property, such as if it is breached 

when hammered or cut with an acetylene 

torch. 

Element 4: At-Risk Potential (Figure 21) 

An important concept for determining the 

effectiveness of control mechanisms is the extent 

to which gauges are at risk of entering the 

recycling stream because this is the jurisdiction of 

the NRC and the Agreement States. Figure 22 

represents the population of devices containing 

radioactive sources. The total population of 

devices is represented by Set {T}. Most nuclear

gauges are in use on production lines. These 

devices are not at risk of being lost because they 

are in place, controlling production. Only a 

portion of the gauge population is at risk of being 

lost. In Figure 22, the population at risk is 

represented by Set {A}. These gauges are at risk 

to being lost because they are no longer under 

hard controls. Instead, they can be removed and 

set aside during renovation, left on a mothballed 

process unit, left in a cluttered storage room, or 

left carelessly in a defunct or abandoned facility. 

The population at risk is necessarily very small 

because almost all of the gauges are used to 

control production. Of the gauges at risk, some 

have been discarded; this is set {D}. Some gauges 

will be found, either before or after being melted 

in a furnace; the gauges that are found in the 

recycling stream are represented by Set {F}. Set 

{A} can be divided into many regions, such as 

gauges that become stranded in the recycling 

stream, buried in a landfill, or disposed of in an 

unknown way. The purpose of Figure 22 is to 

illustrate general states of devices, not to delineate 

all of the possible states of a nuclear gauge. 

From Figure 22, the annual probability of finding 

a nuclear gauge is given by Equation 20.

Figure 22 Nuclear gauges throughout all 

industries. LEGEND: G = set of all gauges. 

A = set of gauges at risk of being discarded 

into the recycling stream. D = set of gauges 

discarded. F = set of gauges found.

53 NUREG-1669
5: LICENSEES

Pr{FIA} - NF 

NA [20 ]

Pr{FIA} = probability of finding a nuclear 

gauge that has been discarded into 

the recycling stream 

NA = number of gauges at risk in a given 

year 

NF = number of gauges found in the 

recycling stream (both before and 

after melting at a steel mill) in a 

given year

The denominator, NA, is the number of gauges at 

risk, not the total number of gauges, NT. 

Replacing NA with NT will result in an 

underestimate of the probability of finding a gauge 

in the recycling stream. In Figure 22, the total 

number of gauges is what can most easily be 

estimated. The number of gauges at risk and the 

number lost are both much more difficult to 

estimate. 

Figure 23 illustrates other 

aspects of Figure 20, 

showing that the at-risk 

potential is a complex 

function determined by the 

control mechanisms that 

operate in a given 

environment to provide 

ICC. Figure 23 is a 

qualitative diagram for 

explaining the matrix, not A 

an illustration for 

computing the at-risk 

probability. The figure 

shows a general form of the 

logical progression for the 

controls on a single gauge 

in any one of the 33 

environments in Figure 20; 

the details of Figure 23 vary 

from one environment to 

the next because the 

controls that provide ICC 

change from one 

environment to the next:

"* A given gauge is either in use or out of use; 

this is depicted in Figure 23 as GATE 1 (an OR 

gate). In use alone is sufficient for ICC; no 

other control mechanisms are needed because 

the gauge is modulating a process. 

"* A gauge that is out of use is either returned to 

its vendor, in IDS, or subject to soft controls; 

this is depicted by Gate 2 (an OR gate). Return 

or IDS is sufficient for ICC; no other control 

mechanisms are needed because the gauge is 

known to be in a secured place. If a gauge has 

not been returned or is not in IDS, then soft 

controls are relied upon. 

"* Soft controls act on a gauge in combination at 

each facility; this is depicted by Gate 3 (an 

AND gate). Each of the 13 soft controls is 

either present or not present at a facility; this is 

depicted by Gate 4 (an OR gate). The number 

of possible combinations of 13 soft controls is 

211 = 8192. In practice, many fewer 

combinations are found throughout industry, 

because many of the controls are required as a 

condition for possessing the gauge.

re 23 Logic of the environment/control matrix in Figure 20.

NUREG-1669

A •u

54
5: LICENSEES

A4hbA aý" a 

fiawfw a

Hard 

controls

Education & 

communication-

(A)

Labels 9.0se#ea1a1 

&aeW)

(U)

Figure 24 Verm diagram illustrating the coverage and redundancy of control mechanisms.

The three hard controls are mutually exclusive. A 

gauge is in a definite place- it cannot be in use, 

in IDS, and returned all at the same time. If a 

gauge is not subject to a hard control, then it is 

subject to a soft control. Soft controls may always 

be present, but ICC is being provided first by a 

hard control, then by a soft control. 

The combination of control mechanisms affecting 

a particular gauge determine the control 

effectiveness. The effectiveness of the control 

mechanisms is not simply the sum of the 

effectiveness of the individual controls. An 

assessment for each environment must take into 

account interactions and redundancy among the 

control mechanisms. For example, consider the 

soft controls of education and communication 

(E&C) and labels. Highly effective E&C may 

compensate for labels that are obliterated by 

process material during normal operation. Thus, 

the effectiveness of a given combination of 

control mechanisms is a function of the 

combination and not of the individual controls.

Figure 24 illustrates another aspect of Figure 

20- describing applicable controls during the 

lifetime of a gauge. Figure 24 presents examples 

of four hypothetical situations. Each part of 

Figure 24 is an example of a Venn diagram. 

Figure 24 is qualitative; the areas are drawn to 

illustrate concepts and are not in proportion. In all 

four panels, the rectangle represents the lifetime of 

a gauge. The shaded areas represent periods when 

controls are present and effective; a gauge is not 

at risk of being inadvertently discarded. The 

white areas represent periods when controls are 

not present or are ineffective; a gauge is at risk. 

N Panel (A): Hard controls cover some of the 

periods during the lifetime of a gauge. Such a 

gauge is in use on operating process units, in 

IDS, or returned to a vendor. This means that 

the gauges are in a definite place; hence, they 

are not at risk. But during other periods (white 

area), controls are not present; the gauge may 

be on a process unit that is being serviced or is 

defunct, or in a general purpose room without 

any soft controls.

55 NUREG-1669
5: LICENSEES

"* Panel (B): A single soft control, E&C, covers 

some of the periods that are not covered by 

hard controls. Periods covered might be all 

those when employees, trained in the proper 

care and use of the gauge, know the 

whereabouts of the gauge, regardless of where 

it is located. Contractors servicing equipment 

or removing scrap from a facility might not 

receive this training, and may inadvertently 

discard the gauge; the white area represents 

these and other times when the gauge is at risk. 

"* Panel (C): Hard controls are present as in 

Panels (A) and (B). Instead of E&C, there are 

labels on the gauge. Again, the coverage of 

the area at risk is incomplete; labels can be 

obliterated with process materials between 

cleanings or go unnoticed in dimly lit rooms. 

"* Panel (D): Hard controls are supplemented by 

both E&C and labels. There is redundancy in 

that employees who are trained will not need 

the labels to know the whereabouts of the 

gauge. For example, a plant engineer would be 

able to locate the gauge on a process unit, even 

when the gauges are covered by grease or dirt. 

But contractors may not have such knowledge 

of the process unit; hence, the labels provide an 

incremental benefit over and above the E&C 

control. 

Figure 24 illustrates an important point--control 

mechanisms can overlap and be redundant. 

Redundancy increases the overall effectiveness 

because it compensates for control mechanisms 

becoming compromised. In the examples of 

Figure 24, E&C can degrade when the work force 

changes rapidly and labels can become obliterated 

or fade. 

Gauges that are at risk can enter the recycling 

stream. This does not necessarily mean that they 

do enter, but that they are at a potential to do so. 

The fate of a gauge that is at risk is represented by 

Elements 5 through 7 in Figure.21. 

Element 5: State of a Gauge at Risk (Figure 21) 

The extent to which the sealed source of a gauge 

is exposed influences the health consequences.

For gauges that are being used in production, the 

radiation exposures are minimal. In use, the 

radiation beam from the source is focused into the 

detector. Also, people seldom linger near the 

gauges on process units; they are at control 

stations or occasionally walking by en route to 

another area in the plant. Most of the production 

areas where the gauges are located are deserted. 

In some environments when a gauge is at risk, 

people are nearby, such as when a unit is being 

serviced; if the shutter of a gauge is open, then 

exposures might occur. In other environments, 

such as a closed or abandoned facility, people, 

such as curious youth, can unknowingly move 

near the gauges. Closed and abandoned facilities, 

and facilities being dismantled, have been 

pillaged. The minimal radiation exposure during 

use is a marketing point of gauge vendors for their 

customers. But the minimal radiation when the 

shutter is closed also makes the gauges difficult to 

detect in the recycling stream. Some people in the 

steel industry would like to have the gauges made 

so that enough radiation emanates to allow a 

gauge to be detected. 

Element 6: Disposition of a Gauge At Risk 

(Figure 21) 

A breakdown in ICC, be it total or partial, does 

not necessarily mean that a gauge will be 

discarded. A breakdown means that there is a 

potential for a gauge to be discarded- a gauge is 

at risk of being discarded. The probability of a 

gauge being discarded is a complex quantity that 

is essentially unknowable; no plant manager will 

allow experiments to be done on a facility to 

collect statistical data. Some values of the 

probability, in a given environment, can be 

intuitively determined to reduce the ambiguity in 

this quantity. If a gauge is in 

use, Pr{discard} = 0 because the gauge is 

controlling a process. If not in use but at a 

facility, then 0 < Pr{discard} < 1. There is at 

least a small chance that it will be removed and 

discarded. If a facility is indiscriminately 

liquidated, then Pr{discard} = 1. Other 

probabilities can be empirically estimated; the 

probabilities in Element 4 can be chosen by trial 

and error so that the predicted prevalence of 

gauges entering the recycling stream is consistent

NUREG-1669 56
5: LICENSEES

with the observed prevalence, such as given by 

Reference 1. Probabilities are not being estimated 

with the data reported in Reference 1; the 

concerns of using a convenience sample (see 

Section 4.3.2) are inapplicable here. The 

probabilities of Element 4 can be chosen to be 

consistent with data. The nebulous quality of 

Pr{discard} is not a hindrance to analyzing risk. 

A use of the analysis is to focus where 

Pr{discard} is well known and on how low 

Pr{at risk} can be made with a realistic amount of 

resources. 

5.6 Sources of Information 

Tables 3 and 4 are summaries of the sources of 

information for developing the inputs of the 

licensee analysis. Along the top are the elements 

corresponding to the elements in Figures 20 and 

21. Along the vertical are classes of information 

(see Section 4.2). A shaded box indicates that 

information is available; numbers refer to survey 

questions in Appendix B; letters refer to notes 

following the table about the information or lack 

thereof. A white box indicates that a particular 

class of information for a particular element is 

unavailable. 

5.7 Observations and Insights 

1. The industrial environments and the control 

mechanisms give rise to a complex system. 

Any assurance that changing controls will 

have the desired effect depends on 

understanding the system. Many aspects of 

this system are outside the jurisdiction of 

regulatory agencies, yet these same aspects 

influence the control of the gauges. 

2. Only a small fraction of the total number of 

nuclear gauges are at risk of entering the 

recycling stream. Most of the gauges are in 

use, controlling process units; such gauges 

cannot be removed without drawing attention. 

The population of gauges at risk is much 

smaller than the total gauge population.

3. The concepts of ICC and at-risk are essential 

for understanding the control of nuclear 

gauges. ICC allows for a determination of 

what keeps a gauge in place when a gauge is 

at risk. The potential for a gauge to be at risk 

determines the extent to which it is vulnerable 

to entering the recycling stream. 

4. Hard control mechanisms operate by placing 

a gauge in a definite location. Soft controls 

operate by gaining attention. Whatever 

reliance is not placed on the hard control 

mechanisms is placed on the soft control 

mechanisms. 

5. The control mechanisms have an implicit 

assumption that a licensee will, can, and 

knows how to assume the responsibility. 

Reference I suggests that the assumption is 

not always valid. 

6. Responsibility for ICC, not for the gauges, is 

difficult to assign in industrial organizations. 

An industrial facility may be complex. The 

responsibilities of employees are overlapping 

and changing to meet market demands and the 

state of a facility. The use of outside 

contractors during system shutdowns for 

extensive maintenance and overhauls 

exacerbates the complexity. 

7. The extent to which high-level accountability, 

civil penalties, and license revocation provide 

ICC is unclear. The chance of these 

mechanisms being called upon (the remote 

possibility of losing a gauge at an unknown 

time in the future) is overshadowed by acute 

concerns and hazards at an industrial facility.

Author's Note 

Observations and Insights resume 

on page 60 after Table 4.

57 NUREG-1669
5: LICENSEES 

Table 3 Sources of information supporting the analysis of risk elements in licensees (Figures 20 and 2 1). LEGEND: A shaded box indicates available 

information; a number in a shaded box indicates a question of the survey in Appendix B and a letter indicates a note following the table. A white 

box indicates unavailable information. Degrees of information are discussed in Section 4.2. 

Elements

Degrees 

of 

Information 

(Section 4.2)

Sources 

of 

Information

1: States of facilities (page 48) 

2: Work force changes (page 49) 

3: Gauge location (page 49) 

4: At-risk potential for a gauge to get beyond control 

mechanisms (page 53) 

5: State of a gauge at risk (page 56) 

6: Disposition of a gauge at risk (page 56)

( Survey 

(page 129) 

1st 

Other 

2nd Survey 

(page 129) 

3rd Plausible judgments

Notes on Table 3

A. See Table 4 for details. 

B. The prevalence of states such as phasing out, closed, and 

abandoned can be inferred from business statistics. Information from 

the demolition industry can be used to infer the prevalence of 

facilities that are being demolished. Judgments from regulators 

about orphaned sources can be used in a similar manner. A rough estimate of the number of gauges in these facilities can be made. 

Such estimates can be used as a basis for bounding risk estimates. 

C. Plausible values can be used to bound risk estimates. To begin, site visits suggest that typically the turnover rate in industrial 

facilities is low.

D. The state of a gauge at risk or after disposition cannot be 

rigorously determined. Some event reports may yield insights into 

the states of the gauge when found. But the event reports are few and 

often sketchy. 

E. The discard probability cannot be determined. Information about 

discoveries of radioactive material in the recycling stream show, in 

some unknown way, the results of the preceding elements and their 

components. With values assigned to Elements 1 through 4, 

probabilities can be selected to make the predicted number of gauges 

leaving facilities agree with the observed number. Otherwise, only 

values to bound risk can be assigned to Element 6.

NUREG-1669 58

E:L 

9
5: LICENSEES 

Table 4 Sources of information supporting the analysis of control mechanisms (Figure 20). LEGEND: A shaded box indicates available information; 

a number in a shaded box indicates a question of the survey in Appendix B and a letter indicates a note following the table. A white box indicates 

unavailable information. E&C = education and communication. HLA = high-level accountability. IDS = interim dedicated storage. QCR = query 

at a change in responsibility. Degrees of information are discussed in Section 4.2.

Degree 

of Source 

Information of 

(Section 4.2) Information 

/Survey __ 

1st (page 129) 

Other 

2nd Survey 

(page 129) 

SPlausible 3rd Judgments

Notes on Table 4

A. Information can be obtained in a consolidated form from gauge 

vendors. 

B. Lockout is a procedure that is required by the Occupational 

Safety and Health Administration. 

C. Discussions with both State and Federal regulators and reviews 

of specific licenses can be used to determine who is usually held 

accountable. 

D. Agreement States can be asked about a civil penalty program. 

E. Federal and State regulatory agencies always have the option of 

revoking a license. 

F. All Agreement States will eventually have a registration program. 

States would still have to be asked aboutthe promptness of following 

up when licensees do not respond to a mailed registration notice.

G. In the NRC's jurisdiction, the names of licensee that are out of 

compliance may be made public. Agreement States can be asked 

if this is done in their jurisdictions. 

H. QCR is not required by the NRC. Agreement States can be asked 

if it is required. 

I. Education and communication would be more difficult in a large 

facility a than in a small facility. 

J. For specific licensees, the license has a name of someone in the 

facility. For general licensees, an indication of HLA may available 

in States that register generally licensed devices. 

K. The effectiveness of control mechanisms to provide ICC is a 

subjective evaluation, done by postulating and discussing plausible 

values among experienced regulators. 

L. Inspections do not provide ICC. See Section 5.4

NUREG-1669

I A 7 

4 2 

L]

- I I I ý -ECý7 D E I F ý G ! H"ý 

E

59
5: LICENSEES

8. A difficulty for licensees in maintaining JCC 

is that they lack the collective experience of 

what works and what does not work for 

providing ICC. The regulations are 

necessarily broad and nonprescriptive to 

cover a diversity of industrial conditions. 

Yet this leaves licensees to devise their own 

control program. Communicating ICC 

practices to licensees might reduce the risk 

of gauges being inadvertently discarded. 

Developing such guidance as a survey (e.g., 

see Section 4.3.1) would make the guidance 

compatible with the demands for more acute 

concerns found in industry. 

9. The decrease in risk from moderately 

increasing the frequency of inspections 

appears to be small. Because gauges are 

subject to ICC for most of their service life, 

inspections can significantly reduce risk only 

when they coincide with at-risk periods. 

10. Registration enhances other controls that 

provide ICC, such as responsibility and

accountability. Registration refreshes 

memory about the gauges, especially 

important when facilities come and go or 

when employees change professions or 

retire. A lack of a response alerts regulators 

to some forms of at-risk conditions, such as 

closed and abandoned facilities. Followup is 

necessary for registration to be effective. 

11. A licensee is required to notify a regulatory 

agency of a change in ownership or when 

going out of business. A mechanism that is 

part of the title transfer or procedures for 

terminating a business, to inform a 

regulatory agency, might reduce the risk of 

gauges being improperly transferred. 

12. Redundancy in control mechanisms 

increases overall effectiveness because it 

compensates for control mechanisms 

becoming compromised. 

-----•lll~~ 3 , wNUREG-1669 60
6 SCRAP METAL CONSOLIDATION

6.1 Overview 

Scrap metal is collected in yards where it is 

prepared for use in steel mills. The scrap metal 

comes from many and varied sources, from 

unskilled individuals to large sophisticated 

companies. Scrap metal can be shredded into fist

size pieces, compacted into bales, sheared, or cut 

with an acetylene torch. During the collection and 

preparation, the shutter of a discarded gauge may 

be opened or the sealed source may become 

dislodged or breached. Many, but not all, scrap 

yards have radiation monitors. 

Difficulties are encountered when analyzing scrap 

metal consolidation: 

"* The routes of scrap metal can be complex and 

changing in response to the supply and 

demand for scrap metal. 

"* The effects of the processes on a nuclear 

gauge are unknown. There are no principles 

or experiments from which to predict what 

will happen to a nuclear gauge when it is 

inadvertently processed with scrap metal. 

"* Reaching the various collectors for 

information is difficult, if not impossible. 

Nevertheless, a meaningful analysis can be done 

by considering the collectors togetherjust looking 

at the processes by assessing the commodities of 

scrap metal received by the steel mills. There are 

far fewer steel mills that can be reached than scrap 

metal collectors that cannot be readily reached. 

6.2 Importance in Risk 

Scrap metal collectors and scrap yards must be 

taken into account in estimating risk because the 

processes of collecting and preparing scrap metal 

can compromise the integrity of a nuclear gauge 

or increase the difficulty in recovering a gauge. 

Health hazards can occur as a result of the 

following:

"* gauge with an open shutter passes along the 

recycling stream; 

"* sealed source is dislodged from its housing 

when the housing is cut, sheared, or shredded; 

or 

"* sealed source is breached from cutting or 

shredding. 

The topics taken into account in the analysis of 

scrap metal consolidation are indicated in Figure 

25. 

6.3 Concepts 

Scrap metal comes from many origins. Though 

some origins are more risky than others, only 

some vague statements can be made about those 

risks:

Figure 25 Topics taken into account in the analysis of 

scrap metal consolidation. LEGEND: A black bullet 

indicates that a topic is comprehensively taken into 

account. A white bullet indicates that a topic is beyond 

the scope of the risk analysis. A gray bullet indicates that 

a topic is briefly taken into account.

NUREG-1669

Section 6 

* Metal collection 

o Landfal mining 

* Scrap yards 

* Scrap metal processing 

o Visual detection 

* Radiation detection 

[1 Monitoring practices 

*] Rejection practices 

o Proper disposal 

o Improper disposal 

* Danger to life 

* Danger to property

61
6: SCRAP METAL CONSOLIDATION

"* Intuitively, scrap metal from industrial 

facilities is more risky than scrap metal for 

other origins; this is where the gauges are used 

and where ICC breaks down. Industrial 

facilities may discard small amounts of scrap 

metal into dumpsters destined for landfills, or 

they may have contractors remove scrapped 

equipment. Some of this scrap metal may be, 

or may have on it, a nuclear gauge. 

"* "Peddlers" (also known as "scavengers" or 

"gypsies") may find nuclear gauges that have 

been improperly disposed of in remote areas 

or that have been found in abandoned 

industrial facilities. 

"* In general, residential scrap metal, such as 

appliances and automobiles, are low risk. 

These items do not use nuclear gauges. But 

the risk of such scrap metal is not zero; 

nuclear gauges have gone through shredders, 

which typically process automobiles. 

Some scrap yards only gather metal. Others 

gather, sort, and process the metal to reduce the 

volume by compacting it. 

Scrap dealers have many concerns that demand 

their time and attention: 

"* Customers and suppliers 

of scrap metal change 

according to market 

pressures. 

"* Large market pressures 

and thin profit margins 

require constant attention. 

"* Rail carriers want the set Scm. 

point of radiation detectors 

at a high value because 

railcars often have slight 

contamination from dirt, 

slag, scale, zirconium 

sand, or refractory brick. 

These forms of benign 

contamination are Figure26 Sc 

discussed further in circles indic• 

larger yards, Section 7.6. shearers.

Sourn

" Steel mills want the set point of radiation 

detectors set low, immediately above 

background levels, to maximize the chance of 

finding radioactive sources. They want a safe 

supply of scrap. 

"* Dealers do not want loads of scrap metal to be 

turned away and do not want questions asked 

about their loads. 

Figure 26 illustrates the routes formed by 

demolition contractors, peddlers, and scrap yards. 

The routes are varied, complex, and change 

according to market pressures. Some scrap yards 

have two radiation monitors, one for trucks and 

the other for railcars. Scrap metal inappropriately 

scanned by one monitor may be appropriately 

scanned by another monitor. Other yards have 

only one monitor; particular pieces of scrap metal 

may be inappropriately scanned both on the way 

in and on the way out of the yard. A given steel 

mill may receive scrap metal from a few to a 

hundred suppliers through a broker; these 

suppliers too may change according to market 

pressures. Specific suppliers to other dealers and 

steel mills change according to the supply and 

demand for scrap metal. Some dealers may have 

radiation monitors; others may not. Along some 

•es of Smetal 

Steel Mills

1%."a .41 a- -4"h~ 

ata04ý0ýM 

Pad-;- dcaq ý 

comd44a a Y40

trap metal consolidation. LEGEND: 0 = scrap yard. Small 

ate peddlers and small yards. Medium and large circles indicate 

possibly with process equipment such as balers, shredders, and

NUREG-1669 62
2i1oded 

deakd oasce

ma1&4w

4ect/ck~f

ma4a1

, Li1 , ,ll ll l 

Shredder Mechanism

Separator

4=47

Figure 27 Location of potential radiological hazards when a nuclear gauge is shredded.

of these routes the scrap metal may be scanned 

multiple times; sometimes the scrap metal will 

have been unloaded; other times it may go through 

several monitors without being unloaded. The 

effect on risk from multiple passes though a 

radiation monitor is discussed in Section 7.6. 

Nevertheless, some generalizations can be made: 

"* Smaller yards may manually compact scrap 

metal before sending it to larger yards. 

" The large-volume process equipment is found 

at the larger yards that are close to, if not 

directly, supplying the steel mills because the 

expense of the equipment can be justified; 

scrap metal is processed by shredding 

(pulverizing), baling (binding into rectangular 

packages), shearing (severing large pieces of 

metal), and burning (cutting pieces too large to 

shear with an acetylene torch). 

"* The sophisticated portal monitors are also near 

the end of the recycling stream. 

The scrap metal industry is, for the most part, 

unconsolidated (Ref. 16), making efforts to reach

most of the scrap dealers very difficult. The scrap 

yards are numerous. Scrap yards themselves are 

also in a state of flux, with piles of scrap metal 

increasing and decreasing during the normal 

course of business. For this reason, collecting 

information through site visits and surveys is 

difficult. An example of such information is the 

number' of radiation monitors along the routes of 

scrap metal going to the steel mills. The difficulty 

of obtaining information is compounded by the 

understandable reluctance of scrap dealers to 

divulge information because of concerns for 

adverse impacts on their businesses. 

Thus, many details of scrap metal consolidation 

cannot be resolved for a detailed risk analysis. 

But useful insights can be obtained from an 

analysis to determine the ramifications from the 

processes. The amounts of the various processes 

are reflected in the amounts of commodities being 

sent to the steel mills. 

Figure 27 shows hazards from processing a 

nuclear gauge. Normally, many kinds of materials 

are in the feed stock of a shredder- magnetic and 

nonmagnetic metals, plastic, dirt. Scrap metal is 

placed (tossed) on the loading conveyor belt with

NUREG-1669

6: SCRAP METAL CONSOLIDATION

63
6: SCRAP METAL CONSOLIDATION

a crane. The loading belt brings the scrap metal 

up to the compactor belt that forces it into a 

shredding mechanism. Here it is reduced to 

fist-size pieces. Light airborne material is 

removed from shredded metal by a ventilation 

system and collected by a cyclone precipitator; 

much of the air is recirculated. Magnetic drums 

remove magnetic metals from the scrap stream; a 

pile of ferrous scrap forms below this belt. The 

nonmagnetic material (e.g., aluminum, copper, 

brass, stainless steel', dirt) are removed with an 

eddy current separator. The remaining dirt is 

disposed in a landfill. 

The shredder mechanism may dislodge or breach 

a sealed source. The shredding mechanism may 

trap the pieces of a breached source in crushed 

metal. The light material separator may disperse 

a breached source. The magnetic and eddy 

current separators may carry an intact gauge or a 

dislodged source with scrap metal. A dislodged 

source may be lodged in a piece of scrap metal. 

Though the hazards at a shredder, or other 

processing (e.g., shearing, cutting with an 

acetylene torch), can be qualitatively described, a 

paucity of information precluded determining risk. 

There have been no studies to determine the 

probability of dislodging or breaching a sealed 

source. There have been no studies to determine 

the probability of a dislodged sealed source 

dropping into the processing equipment, dropping 

to the ground, or being carried along with the 

scrap metal. There have been no studies to 

determine the dispersion of radioactive material 

when a sealed source is breached. Only third 

degree information (see Section 4.2) is possible at 

this time. 

6.4 Elements of Risk 

Figure 28 illustrates the risk elements of scrap 

metal consolidation (e.g., scavengers, scrap 

yards). Single black lines are sequences of risk 

elements. For clarity, common portions of the 

sequences are illustrated in the inset; some of 

8 / The 400 series of stainless steel, some of the 300 series of 

stainless steel, iron, cobalt, and nickel are magnetic.

these sequences are discontinued at -A), then 

continue in the inset at -A); other such sequences 

discontinue at -B), then continue in another inset 

at -B). An arrow (>-) indicates that the sequence 

continues in Figure 41. A dot (0) indicates the 

end of a sequence. An open dot (0) indicates that 

a sequence is unresolved; it can continue, but is 

not developed further. Hazard terms from the 

U.S. Code of Federal Regulations (Ref. 9) apply 

at this point between Elements 7 through 12. A 

black box (M) indicates that a concern is present. 

A shaded box ( Z) indicates that a concern might 

be present. A white box (0l) indicates that a 

concern is not present. 

A paucity of information necessarily means that 

the analysis in Figure 28 is simple. Factors that 

have not been explicitly taken into account include 

the capability of radiation monitors, the practices 

of using the equipment (e.g., see Section 7.6), and 

the characteristics (e.g., volume, density) of scrap 

metal loads. Elements 8, 9, and 12 can be 

assessed only by postulating plausible values to 

determine the effect on risk; a large effect would 

justify the expense of collecting information (see 

Section 4.2). Visual detection has been neglected 

for the reasons discussed in Section 2.5 and 

because of a paucity of information to support an 

assessment. 

Most, but not necessary all, scrap yards supplying 

the mills have radiation monitors. Figure 28 

illustrates this with two sets of sequences. Along 

the sequences branching from (A) are radiation 

monitors. Those sequences branching from (B) 

have no such radiation monitors. 

Radiation Monitors 

" A gauge that goes through the processing 

intact and with a closed shutter is not a danger 

to life and property; if the gauge is detected, 

then the sequence terminates; if the gauge is 

undetected, then the sequence continues. 

" A gauge that goes through the processing 

intact with the shutter open may be a danger to 

life, depending on the orientation and its 

location in the scrap metal. It is not a danger 

to property. Detection only terminates the 

sequence.

NUREG-1669 64
6: SCRAP METAL CONSOLIDATION

Elements

7: Nuclear gauges enter the recycling stream 

when scrapped at a licensee facility (page 66) 

8: Scanning scrap metal for radiation 

scrap metal is consolidated (page 66) 

1A

y: Alarm wnen scrap metal is scanned tor radiation 

before being processed (page 67)

10: Type of scrap metal processing (page 67)

11: Effects of scrap metal processing on a nuclear gauge (page 67) 

12: Alarm when scrap metal 

is scanned for radiation after 

being processed (page 68) 1

Hazards 

in Elements 

7 Through 12

Danger to Life 

I Danger to Property

This figure stems from 

each risk 

element 

sequence in 

Figure 21 

(page 52) 

where nuclear 

gauges have 

been scrapped 

by the 

licensees.

Yes

Scanned _I ~ ~ ~ ~ ~ ........ ~ ~ ................................ ----- . .. 

Intact Gauge, Yes 

Closed Shutter 

Intact Gauge, Yes 

acuOpen Shutter uNro 

Dislodged Source 

Breached Source 

S Intact Gauge, Closed Shutter SI IntactGauge, Open Shutter ' 

W- Dislodged Source0 

I. IBreached Source

No, 

Tossed 

Aside 0

Figure 28 Analysis of risk elements for scrap metal consolidation. LEGEND: Single black lines are sequences of risk elements. For clarity, common elements of the sequences are illustrated in the inset; some of these sequences discontinue at -A), then continue at -A); other such sequences 

discontinue at-B), then continue at-B). An arrow (>-) indicates that a sequence continues in Figure 41. A dot (s) indicates the end of a sequence. 

An open dot (0) indicates that a sequence is unresolved; it ends here, but not further developed. A black box (U) indicates that a concern is present as of Element 12 of a particular sequence. A shaded box (M) indicates that a concern might be present as of Element 12 of a particular sequence. 

A white box (0) indicates that a concern is not present as of Element 12 of a particular sequence. Hazard terms are from the U.S. Code of Federal 

Regulations (Ref. 9).

NUREG-1669

when the

Yes

I

65
6: SCRAP METAL CONSOLIDATION

"* A dislodged source is a danger to life, but not 

to property. It will be detected if it is lodged 

in the scrap metal and radiation monitors are 

present. The sequence is unresolved in the 

scrap yard; it may be carried along in the 

recycling stream; it may drop inside 

processing equipment; it may drop on the 

ground. 

"* A breached source is a danger to both life and 

property; nearby populated areas or heavily 

traveled roads may be contaminated. Because 

scrap metal will be contaminated, it will be 

detected; hence, Element 12 is undeveloped. 

The sequence terminates in the scrap yard. 

No Radiation Monitors 

The sequences here present the same dangers as 

the sequences when radiation monitors are present 

but do not activate. The difference is that here, 

there are no chances to terminate sequences 

because there is no detection. 

Other 

"* A nuclear gauge that is detected when entering 

a scrap yard is not a danger to life or property. 

In Figure 28, the three boxes under hazards 

are white. 

" If scrap metal containing nuclear material is 

tossed aside, there is nothing that can be 

definitely said about the danger to life and 

property. The sealed source could be in an 

intact gauge with the shutter closed or open. 

Nothing is known about the orientation of the 

shutter. The source may be dislodged. The 

actions being taken are also unknown. 

Element 7: Gauge Enters the Recycling Stream 

(Figure 28) 

The difficulty in disposing of a nuclear gauge is 

recognized, at least to some extent, in the 

recycling industry:

"* Disposal costs of $5,000 or more may be 

incurred. 

"* Collectors and scrap dealers tend to avoid 

government assistance, even to address an 

alarm of a radiation monitor. 

"* Many people have an alarmist reaction to even 

minute amounts of radiation or radiation 

symbols. 

"* Giving attention to disposing of unwanted 

material is attention taken away from normal 

business. 

There is a reluctance to assume any responsibility 

for a discovered gauge. People collecting scrap 

metal may recognize a gauge and, knowing the 

difficulty in disposal, may simply leave it or cast 

it aside, believing it will be readily detected 

farther along in the recycling stream. 

Element 8: Scanning Scrap Metal for Radiation 

(Figure 28) 

The extent to which scrap metal is scanned for 

radioactive material has implications for risk. 

Scrap metal may not always be scanned for a 

variety of reasons: 

"* Alarms are deactivated because they are 

annoying. 

"* The monitor system may have malfunctioned. 

"* The speed of the vehicle may be excessive, 

allowing insufficient time for a load to be 

scanned. 

" The radiation monitors at low 

volume/throughput yards may not be as 

sensitive as those at the high 

volume/throughput yards. 

Element 8 also applies to scrap yards in which 

scrap metal is scanned with a hand-held survey 

meter, not a fixed radiation monitor. The 

scanning may sometimes be done carelessly.

NUREG-1669 66
6: SCRAP METAL CONSOLIDATION

Sometimes it may not be done because it is 

inconvenient or weather is inclement. The meter 

may be out of calibration. 

The net effect of radiation monitoring, whether 

with fixed radiation monitors or hand-held survey 

meters, is too nebulous to assess. Element 8 can 

be treated by postulating plausible values and 

determining the effect on risk estimates. 

Element 9: Alarm When Scrap Metal Is 

Scanned for Radiation Before Processing 

(Figure 28) 

Scrap metal can be monitored twice, once when it 

enters a yard and again after it has been sorted and 

processed, when leaving the yard. These 

opportunities for monitoring are not equivalent. 

When entering a yard, the dealer has not taken 

possession of scrap metal; when leaving the yard, 

the dealer owns the metal and whatever is in it. 

Processing the scrap metal changes the 

composition and increases the density, which in 

turn, reduces the detection probability. 

Although scrap metal is more densely packed 

when leaving a yard than when entering, the 

processing may have opened the shutter of a 

gauge or breached the housing of a gauge, 

exposing the sealed source; even within densely 

packed scrap metal, an exposed sealed source is 

likely to be detected. A sealed source that has 

been dislodged from its housing and lodged in the 

scrap metal can be easily detected. A breached 

source will contaminate scrap metal, likely 

making the breached source easy to detect. A 

gauge with an open shutter is likely to be detected 

by sensing either the direct radiation or scattered 

radiation. Because of the nebulous state of 

information at this point, Element 9 is simplified 

relative to a more complex treatment discussed in 

Section 7.5, justified here by the paucity of 

information about scrap yards. 

Element 10: Type of Scrap Metal Processing 

(Figure 28) 

While a nuclear gauge is robust, it is not designed 

to withstand the processing of scrap metal. The

processes challenge the integrity of a gauge. But 

the gauges are not equally likely to enter each type 

of process. Specific sources of metal usually go 

through specific processes. Long pieces of pipe or 

beams will be cut with an acetylene torch or 

sheared. Large industrial rollers will be cut with 

a torch. Automobiles will be shredded. 

The possibilities of Element 10 need to be 

weighted in three ways: 

"* weight of the commodities of scrap metal; 

"* tendency of gauges to be in one commodity 

rather than another; and 

"* likelihood of a specific process dislodging and 

breaching a sealed source. 

The first factor can be readily done by 

determining the commodities consumed by the 

steel mills. A paucity of information precludes 

determining the remaining factors; in this regard, 

all commodities should be treated the same unless 

a strong argument can be made to show otherwise. 

For example, turnings come from machine lathes. 

There is no reason to suspect a gauge in turnings. 

Furthermore, getting information about the 

consumption of turnings would be difficult 

because this commodity is sometimes a sensitive 

issue at mills; turnings contain cutting oil, which 

is an environmental hazard. Another source of 

scrap metal that can be excluded is stampings. 

Element 11: Effects of Scrap Metal Processing 

on A Nuclear Gauge (Figure 28) 

A paucity of information leaves much to be 

understood about the effects of processing on a 

nuclear gauge. Nevertheless, statements about the 

effects can be made. 

Shredding. Gauges have been known to pass 

through a shredder intact, although battered. 

Incidents have occurred when the sealed source 

was dislodged or breached. 

Baling. Compacting a gauge in scrap metal will 

not open a shutter or dislodge a sealed source. A

67 NUREG-1669
6: SCRAP METAL CONSOLIDATION

gauge is, for the most part, solid and not readily 

crushed. But baling increases the shielding 

around a gauge, increasing the difficulty of 

detection. The consequences of baling are low but 

the difficulty of recovering a gauge is increased. 

Shearing. The single blade used to cut scrap metal 

that is being held by compressing hydraulic 

equipment is unlikely to damage a gauge. A 

gauge would have to be wedged under the blade 

for it to be cut. 

Burning. The chance of cutting into a gauge with 

a cutting torch cannot be ruled out, although 

intuitively, it is remote. An 0-frame or a C-frame 

gauge with several sources in a housing may be 

dislodged when the frame is cut. The source may 

drop onto the ground, out of the recycling stream, 

where it causes undetected exposures to the few 

workers doing the cutting. Breaching a source 

seems unlikely because the source is small and the 

cutting line is narrow. 

Element 12: Alarm When Scrap Metal Is 

Scanned for Radiation After Processing 

(Figure 28) 

See the discussion in Element 9 on page 67. 

6.5 Sources of Information 

Table 5 is a summary of the sources of 

information for developing the inputs of the scrap 

yard analysis. Along the top are the elements 

corresponding to the elements in Figure 28. 

Along the vertical are classes of information (see 

Section 4.2). A shaded box indicates that 

information is available; numbers refer to a few 

relevant questions in the survey of the steel 

industry (Appendix C); letters are notes following 

the table about the information or lack thereof. A 

white box indicates that a particular class of 

information for a particular element is unavailable. 

Much of the information available for the analysis 

of the scrap yards is third degree (Section 4.2).

Most information about the scrap yard industry is 

inaccessible; this point has been proven by the 

efforts of a trade association to obtain survey 

information of its members. 

6.6 Observations and Insights 

1. A quantity that is difficult to estimate is the 

probability of breaching a sealed source in any 

of these processes; the experiments necessary 

for sufficient data would be costly. The 

fraction of scrap yards with radiation monitors 

supplying the mills is also difficult to estimate 

because the information is difficult to gather 

and would be considered proprietary. 

2. The analysis of the scrap metal consolidation 

necessarily considers this industry as a whole. 

The routes of scrap metal consolidation are 

too complex and varied to resolve. Many of 

the collectors are difficult to reach, for 

example, to request information through a 

survey. 

3. A health hazard from nuclear gauges is at the 

scrap yards. Here, schredding, shearing, and 

burning scrap metal can dislodge and breach 

a sealed source. Installing radiation monitors 

at some point in these processes might be an 

effective way to detect a dislodged or 

breached sealed source. But the use of 

radiation monitors may be impractical for 

these processes. Supports for monitors must 

be placed where monitoring would be 

effective. High vibrations, shock waves from 

explosions (e.g., when a propane tank is 

accidently processed), and stray pieces of 

scrap metal could damage a monitor. 

4. Scrap yards are often located near populated 

areas. Some people can be placed at risk of 

radiation exposure when a breached source is 

dispersed. The extent of the dispersal is 

difficult to predict.

NUREG-1669 68
6: SCRAP METAL CONSOLIDATION

Table 5 Sources of information supporting the analysis of risk in scrap metal consolidation (Figure 28). LEGEND: A shaded box 

indicates available information; a number in a shaded box indicates a question of the survey in Appendix C and a letter indicates a note following the table. A white box indicates unavailable information. Degrees of information are discussed in Section 4.2. 

Elements

7: Nuclear gauges enter the recycling stream 

when scrapped at a licensee facility (page 66) 

8: Scanning scrap metal for radiation when the 

scrap metal is consolidated (page 66)

Sources 

of 

Information

1t Survey ____ Ist < ((page 139) 

2nd Survey 

< (page 139) 

Plausible 3rd judgments

9: Alarm when scrap metal is scanned for radiation 

before being processed (page 67) 

10: Type of scrap metal processing 

(page 67) 

11: Effects of scrap metal process on a 

nuclear gauge (page 67) 

12: Alarm when scrap metal is scanr 

radiation after being processed (page

ned for 

68)

< .. ...... J Bý ......

Notes on Table 5

A. A survey of the scrap yards to determine equipment, practices, 

and experiences could not be done (see Section 6.3). 

B. Same reasons in Section 6.3 apply to the demolition contractors. 

C. The volume of commodities produced by the scrap dealers can be 

estimated as the volume of commodities consumed by the steel 

industry. A survey question in Appendix C asks about the 

commodities consumed at a mill. 

D. The effectiveness of scanning scrap metal commodities is 

determined from shielding calculations as discussed in Section 7.5. 

Here, unlike in Element 9, the shielding properties of scrap metal 

commodities can be better known; they are that of the commodities 

entering the steel mills. 

E. Only anecdotal information is available. Plausible judgments 

may be used to determine the effect of Element 7 on risk. 

F. In a risk analysis, plausible estimates can be made to determine 

the effect on risk. Although information about the radiation

monitors at the scrap yards directly supplying the mills could, in 

principle, be obtained from the survey of the industry, the 

information is largely inaccessible to many steel mills. In general, 

mills have an understanding, in some form, with their supplier(s) 

that scrap metal will be scanned for radioactive material; whether it 

actually is or is not another matter. Some mills have only a few 

suppliers and have insisted on radiation monitors that are operated 

using standard procedures. Other mills obtain scrap metal from as many as a hundred scrap yards through a broker, and the suppliers 

change according to market conditions. Asking for information about 

the monitors at the yards may be a burden for steel mills. 

G. Only plausible judgment about the shielding properties of scrap 

metal entering the scrap yards are reasonable. 

H. Events are known where a nuclear gauge went through a 

shredder. Beyond these incidents, the effects of processing can only 

be speculated. There are insufficient data to determine, for example, 

the probability that the sealed source will remain in the gauge, be 

dislodged, or be breached.

6-NUREG-1669

Degrees 

of 

Information 

(Section 4.2)

69
7 STEEL MILLS

7.3 Definitions

Scrap metal from collectors arrives at steel mills 

where it is melted to make products for industrial, 

commercial, and residential products. The 

chances of radioactive material getting onto a 

mill's grounds or into the furnace vary from mill 

to mill because of differences in the configuration 

of radiation monitors, the equipment, and the 

practices for using the equipment. Radiation 

monitors at the steel mills can detect a nuclear 

gauge in a load of scrap metal, but the detection 

probability is less than 100% and poorly 

characterized. Similarly the ramifications of some 

practices for using radiation monitors are not 

always well understood. The probability and the 

practices have important ramifications for both 

the steel industry and regulatory agencies. 

Radioactive material that has been melted will 

usually be detected, depending on the type of 

radioactive material that is melted and the 

equipment that it passes through. Though test 

pieces taken from the furnace where scrap metal 

is melted are usually scanned for radiation, the 

capability and use of the detection equipment 

varies from one mill to the next. Radiation gauges 

used in the production of steel product also act as 

monitors, and may give erroneous readings when 

steel is contaminated. Usually furnace dust is 

scanned before it is sent offsite to be processed 

because the processors usually scan the furnace 

dust and will not accept it if radiation is detected. 

7.2 Importance in Risk 

Steel mills must be taken into account in 

estimating risk because they are the last point at 

which a nuclear gauge might be recovered before 

high costs are incurred for decontaminating 

equipment and disposing of contaminated steel 

products and byproducts. Also, radiation monitors 

at steel mills offer protection to the public when 

contaminated product and byproduct materials 

(furnace dust and slag) leave a mill. The topics 

taken into account in the analysis of steel mills are 

indicated in Figure 29.

A standard response after monitoring scrap metal 

for radiation occurs when a load without a sealed 

source passes through a monitor station without 

causing an alarm. 

A false alarm occurs when scrap metal is scanned 

for radiation and a monitor alarm activates in the 

absence of a sealed source. A false alarm is not a 

malfunction of the monitor, but rather, a response 

to radiation from benign contamination (BC) or a 

spurious signal strong enough to cause an alarm. 

In either case, the monitor is giving erroneous 

information. See also box entitled "False Alarms" 

on page 89. 

A heat is one batch of steel being melted in a 

furnace. 

A missed detection occurs when scrap metal is 

scanned for radiation and a monitor does not

Figure 29 Topics taken into account in the analysis 

of steel mills. LEGEND: A black bullet indicates 

that a topic is comprehensively taken into account. 

A white bullet indicates that a topic is beyond the 

scope of the risk analysis. A gray bullet indicates 

that a topic is briefly taken into account.A black 

bullet indicates that a topic is comprehensively 

taken into account in the risk analysis. A grey 

bullet indicates that a topic is briefly taken into 

account. A white bullet indicates that a topic is 

beyond the scope of the risk analysis.

NUREG-1669

7.1 Overview

Section 7 

o Visual detection 

0 Radiation detection 

N Detection probability * Scrap metal monitoring practices * Scrap metal rejection practices H Monitoring steel products * Monitoring byproducts * Proper disposal * Improper disposal * Danger to life 

N Danger to property

71
7: STEEL MILLS

alarm but a sealed source is present. The sealed 

source may be highly shielded, preventing a 

sufficient amount of radiation from reaching the 

monitor to cause an alarm. Whatever the reason, 

the monitor is erroneously indicating that a load 

lacks a sealed source. 

A detection occurs when a radiation monitor 

alarms as scrap metal is scanned for radiation, and 

a sealed source is present.

7.4 Concepts

The use of radiation monitors at steel mills to scan 

scrap metal for radioactive material differs from 

mill to mill. Each steel mill has its own 

arrangement of radiation detectors; there is no 

standard design of steel mills or installation of 

radiation monitoring equipment at steel mills. The 

collective locations of monitors throughout 

industry are illustrated in Figure 30; few mills 

have all these means of detecting radioactive 

material. Monitors of one form or another are 

found at the following locations: 

Steel 

Dust 

Sla4 

Scrap Metal [ 

From Suppliers

1. radiation monitors scanning scrap metal 

entering a mill and going to the furnace; 

2. radiation monitors scanning scrap metal 

entering a charge bucket; 

3. radiation monitors scanning a fully loaded 

charge bucket; 

4. survey meter or other detection equipment 

scanning test pieces taken from the furnace; 

5. radiation gauges controlling the flow of steel 

into the caster; 

6. radiation gauges in the finishing mill; 

7. radiation monitors scanning steel product and 

byproduct materials (i.e., slag, furnace dust) 

leaving the mill; and 

8. radiation monitors scanning only furnace dust. 

A given mill will purchase affordable monitoring 

equipment that seems to be the most prudent. If a

Figure 30 Radiation monitors at mills throughout the steel industry. LEGEND: 1 = radiation monitors for scanning scrap 

metal entering a mill and for scrap metal taken from the storage area to the scrap bay. 2 = radiation monitor for scanning the 

charge bucket while it is being filled. 3 = radiation monitor for scanning a fully loaded charge bucket. 4 = survey meter for 

scanning test pieces. 5 = radiation gauge at a caster. 6 = radiation gauges in the finishing mill. 7 = radiation monitor for 

scanning products and byproducts (i.e., slag, furnace dust). 8 = radiation monitor for scanning only furnace dust. C = charge 

bucket. F = furnace. T = transfer ladle.

NUREG-1669 72
7: STEEL MILLS

mill has radiation monitors at all, they will be used 

to scan incoming scrap metal as it enters the mill. 

Keeping radioactive material out of the mill, thus 

avoiding the hazard in its entirety, is of more 

concern than simply relying on monitors at the 

charge bucket, where the mill owns the scrAp 

metal and must bear the cost of disposing of 

unwanted material. Radiation monitors in each 

location listed above are discussed in the 

following sections. 

Item 1 (Figure 30): Monitoring Incoming Scrap 

Metal 

Trucks and trains deliver scrap metal to steel mills 

where it is scanned for radiation. Trucks are 

monitored as they enter a mill. The monitor 

station may be automated; when a radiation alarm 

is not activated, a machine dispenses a pass that 

the driver presents to deliver the scrap metal. The 

monitor station may be manually operated by 

plant personnel at a guard station or at a weigh 

scale; trucks that successfully pass the monitoring 

are allowed to enter the mill. Railcars (e.g., 

gondolas) are left on a spur track by a freight 

carrier. The railcars are brought onto the mill 

property by their own locomotives. Once on the 

property, the railcars are scanned before the scrap 

metal is accepted. Railcars suspected of 

containing radioactive material are set aside. 

A vehicle (truck or railcar) passing through a 

monitor station must remain in front of the 

detectors long enough for a sufficient amount of 

radiation to be received by the detectors. Because 

of the expense of detectors, they are seldom the 

length of the vehicle, which would allow the 

vehicle to be scanned while motionless. Smaller 

detectors are used to keep their cost reasonable; 

therefore vehicles must pass through a monitor 

station slowly to approximate monitoring while 

stationary. Because the sensitivity of a monitor is 

inversely proportional to the speed of a vehicle, 

various methods are used across the industry to 

ensure that the vehicles will move at no more than 

the maximum recommended speed (usually 5 

mph) -radar, monitor station before or after the 

weigh scale, or a speed bump in a road before the 

monitor station. But the recommended speed can 

still be exceeded. Although an overspeed alarm

will activate when a vehicle is passing through a 

monitor station too quickly for effective scanning, 

the alarm is not always heeded. The practice at a 

very busy mill might be to warn truck drivers that 

cause an overspeed alarm to slow down-the 

next time. 

Usually two detectors scan from the sides of the 

vehicle; they can be fixed in a position that is 

close to the vehicles because the vehicle width is 

essentially constant (i.e., as wide as can fit on a 

road or railroad track). Sometimes a third detector 

is also located above the vehicle; this is a little 

more difficult to do because the height of a load 

can vary. Seldom is a fourth detector placed on 

the ground looking up through the vehicle; dirt, 

oil, and precipitation dissuade this location. Also, 

the detector must be protected from the weight of 

the vehicle (e.g., supporting structure for the tires 

and a grating over the detector). 

The practices for responding to a radiation alarm 

when a vehicle passes through a monitor station 

can vary from one mill to the next: 

"* A mill may be encouraged by a scrap dealer to 

accept a load suspected of containing 

radioactive material and then to investigate the 

cause of the alarm. Should radioactive 

material be found, the scrap dealer will pay for 

the disposal. 

" A mill may not fully accept a load of scrap 

metal until it has passed radiation monitoring. 

If a load is suspected of containing radioactive 

material, then the load will be taken apart. 

Should radioactive material be found, the 

scrap metal will be reloaded and sent back to 

the supplier. The investigation may take place 

with a third party present (e.g., a State 

regulator) to witness and certify that 

radioactive material was not added to the load. 

See also box, "Reworking a Load of Scrap 

metal," on page 74. 

" A mill may take a load apart, even if such 

action constitutes accepting the scrap metal. 

Should radioactive material be found, the 

truck is refilled and sent away.

73 NUREG-1669
7: STEEL MILLS

Vehicles that cause an alarm may be rejected 

with no further action. At some mills, local 

authorities, such as police or regulators, may 

be notified. At other mills, they are not. 

Other unknown possibilities are suggested by 

Figure 6. 

The manner in which radiation alarms are 

addressed is influenced by local markets. 

Competing local mills cannot pressure a scrap 

dealer who has alternative customers. For this 

reason, some mills will diversify their suppliers. 

But some mills form a close alliance with a single 

supplier; both have an interest in keeping 

radioactive material out of the furnace. 

In Figure 30, after the vehicle enters the mill, the 

scrap metal is brought to a storage area, where it 

is sorted and temporarily kept. Across the steel 

industry, the area has various names, including 

scrap yard and farm. A mill typically has a 3

week supply of scrap metal in storage, but the 

amount varies from mill to mill. Some mills form 

close -relations with their suppliers, relying on 

just-in-time deliveries, keeping only enough scrap 

metal on their grounds to keep the furnace steadily 

operating during minor fluctuations in supply and 

demand; other mills prefer a diversity of suppliers 

(Ref. 16). From the storage area, metal is brought 

to an area adjacent to the melt shop by truck, 

railcar, or scale car. At some mills, this metal may 

pass again through a monitoring station along the 

way; at most mills, it does not go through a 

monitoring station again. 

The area adjacent to the melt shop is known by 

different names (e.g., scrap yard if it is not 

enclosed, scrap bay if it is enclosed, either scrap 

yard or scrap bay if it is partially enclosed). At 

some mills the scrap bay is small; for example, 

when the scrap metal is loaded onto scale cars, the 

charge bucket on the car is emptied into the 

furnace. Less often, scrap metal is taken directly 

from the transporting vehicle and loaded into the 

charge bucket. This area may receive scrap metal 

from the storage area or directly from outside the

mill. The latter is more prevalent when a mill 

places much reliance on the supplier for 

just-in-time deliveries. 

Additional discussion about monitoring incoming 

scrap metal is in Section 7.6. 

Author's Note 

The term load is used instead of shipment. A 

shipment can refer to an entire train of many 

railcars. Usually only one of the railcars is of 

concern and addressed appropriately. But 

anecdotal information reveals that entire trains 

have been rejected because only one railcar 

caused a radiation alarm.

Items 2 and 3 (Figure 30): Monitoring the 

Charge Bucket 

Some mills are able to monitor the charge bucket 

(Item C, Figure 30). When the charge bucket is 

filled, it is moved on tracks near the furnace (Item 

F, Figure 30), where it is lifted over and unloaded 

into the furnace. In a minimill, the electric arc

NUREG-1669

Reworking a Load of Scrap Metal 

Reasons for not wanting to take a load apart to determine 

the cause of a radiation alarm are easily understood. 

N Vehicles are loaded to be dumped from a truck or 

pulled apart with a magnetic or mechanical grapple 

without people being nearby. Heavy and sharp pieces 

of scrap metal may shift or drop when being moved. 

Heat, cold, rain, and wind may make working 

conditions more hazardous. Thus, pulling a load apart 

with people nearby to search for a particular piece is 

dangerous and costly. 

0 Under some contractual arrangements for purchasing 

scrap metal, taking a load apart is tantamount to 

accepting the load and whatever is in it. 

a There is some lack of awareness among scrap yards 

and steel mills about the Department of Transportation 

(DOT) exemption (see box entitled "Department of 

Transportation Exemption 10656") on page 75.

74
7: STEEL MILLS

furnace (EAF) is charged usually two to three 

times with scrap metal; after the first charge is 

melted, collapsing the voids in the scrap metal, 

another charge is melted to utilize the entire 

volume of the furnace. In an integrated mill, the 

basic oxygen furnace (BOF) is charged first with 

scrap metal, then with pig iron from a blast 

furnace. 

The configuration of the monitors around the 

charge bucket is dictated by the geometry of this 

area and the cost of such monitors in relationship 

to the budget at the mill. Three practices for 

monitoring a charge bucket can be found 

throughout the industry:

Department of Transportation 

Exemption 10656 

The Department ofTransportation (DOT) has requirements for shipping radioactive material (e.g., knowing the type of 

material, knowing the amount of material, labeling the 

container). However, obtaining permission to ship radioactive material can take several weeks. Meanwhile, 

the shipper must pay for use of the transporting vehicle. 

Furthermore, employees who discover radioactive material 

may not want to, and may not be trained to, identify, characterize, or package the material for shipment. The 

exemption allows a load of scrap metal to be turned away 

from a facility without going through the usual DOT 

requirements, yet maintaining accountability, even if the 

load is only suspected of containing radioactive material. 

Attributes of the exemption are as follows: 

"* The radiation from the load must be below a specified level to ensure there is no immediate threat to public 

health. 

"a The exemption is used for loads in trucks and railcars, 

not barges. 

" The exemption is issued by a State Radiation Control 

Agency to the discoverer of the radioactive material. 

Copies are given to the carrier, the sending facility, the 

receiving facility, the receiving State, and the 

discoverer of the radioactive material. 

"* A load of scrap metal suspected of containing radioactive material can be returned to a facility other 

than the originating facility. 

"* The exemption is implemented on a case-by-case 

basis. 

"* Although the exemption was meant for interstate 

shipments, its use within States has been increasing. 

The staffs at some scrap yards and steel mills are unaware 

of the exemption.

NUREG-1669

"* A charge bucket is monitored while it is being 

loaded. The radiation monitor scans 

individual loads from the loading crane as the 

bucket is being incrementally filled. 

"* A fully loaded charge bucket is monitored 

while it is stationary in front of a radiation 

monitor. Before the charge bucket enters the 

melt shop, the charge bucket is stopped in 

front of the detectors for scanning. The 

monitoring time is typically one minute. 

"* A fully loaded charge bucket is monitored 

while it is moving into the melt shop. 

Scanning the scrap metal while filling the charge 

bucket avoids much of the shielding from the 

large bulk of a loaded charge bucket. However, 

protecting fragile detectors from stray scrap metal 

while the bucket is being loaded can be difficult. 

The loading operation must be done quickly to 

allow the remainder of the mill to operate at 

capacity. The scrap bay or yard may lack 

structures that can support and protect detectors 

from stray pieces of scrap metal. Stray pieces can 

miss the bucket, or the load in the grips of a crane 

may collide with a detector. At mills that use 

scale cars to bring scrap metal to the furnace, the 

vibration of the cars during loading damages 

monitor systems; radiation detectors cannot be set 

on scale cars. 

Item 4 (Figure 30): Monitoring Test Pieces 

While the scrap metal is melting in a furnace, test 

pieces (also known as a lollipop sample) are taken 

from the heat to determine the chemical 

composition. A radiation monitor scanning the 

test pieces might detect 'Co, which is known to 

form an alloy with the steel. 

The practices across the industry vary both in the 

equipment that is used and the placement of the 

equipment, both of which affect the detection 

capability. Much of what is done seems to be a 

matter of preference. Across the industry, the 

instruments for scanning range from scintillation 

counters to Geiger counters. Sometimes, the 

detector of a survey meter is an integral part of the

2 --- ---. --- SIEW AR, --'- -- -1- --- 7- 1-7-7- a ------ 7-777-7--'-

75
7: STEEL MILLS

process of analyzing a test piece. The radiation 

monitor may be adjacent to the quench bucket 

used to cool test pieces taken from a heat. Or the 

monitor may be on the spectrophotometer used to 

determine the composition of the test piece. Other 

times, the survey meter is separate from the 

processing of test pieces, such as when the 

monitor is a survey meter on a table near the 

chemical analysis equipment. 

When the sample arrives at the laboratory, it is 

placed under the detector for a short time and then 

removed to determine the chemical composition. 

Usually at least one sample from the furnace is 

scanned. In Figure 30, the monitor is drawn 

across a boundary of the box representing the 

laboratory to indicate that the location of the 

monitor can be found outide the laboratory, such 

as at the quench bucket, or inside the laboratory, 

with the analytical instrumentation. Two implicit 

assumptions are being made when monitoring. 

The first assumption is that the time the sample is 

monitored and the distance of the sample from the 

detector are compatible with the monitor 

equipment. Some arrangements of the monitor 

equipment lack controls on the scanning. A 

survey meter set on a table lacks control on the 

scanning time. A technician places the test piece 

under the detector, waits a moment, then responds 

accordingly. A detector in front of a quench 

bucket lacks controls on the scanning time and the 

distance the test piece is from the detector. 

The second assumption is that the heat is well 

mixed. The box entitled "An Incident of 

Radioactive Scrap Metal," page 79, may cause 

some doubt about this assumption. 

When a heat is complete, it is poured into a 

transfer ladle (Item T, Figure 30). The molten 

steel is brought to one of three places, depending 

on the practices at a mill: 

"* to the caster to begin forming the product; 

"* to the lower power furnace to adjust the 

composition; or

a it is kept in the transfer ladle where minor 

changes in composition are made by passing 

gases through the molten steel. 

Items 5, 6, and 7 (Figure 30): Monitoring 

Product 

The steel product can be monitored for radiation 

at three points: 

"* Radiation gauges are sometimes used to 

measure the height of metal as it is poured into 

a continuous caster (Item 5). 

" Radiation gauges are sometimes used to 

measure the thickness of the steel as it is 

rolled (Item 6). The gauges found in the mills 

usually have 137Cs, 'Co, or 2

" tAm as a sealed 

source for the radiation, but x-ray tubes can 

also be found (see also Section 8.3). 

" Steel product is sometimes scanned with 

radiation monitors as it leaves a mill (Item 7). 

The equipment ranges from sophisticated 

portal monitors to survey meters. 

Sophisticated portal monitors are likely to be 

the same monitors for scanning incoming 

scrap metal; in Figure 30, this monitor is 

indicated separately from the monitors for 

incoming scrap metal for clarity in the 

illustration. 

Items 7 and 8 (Figure 31): Monitoring Furnace 

Dust 

At many steel mills, furnace dust is scanned for 

radiation. When 1

37

Cs is melted, it vaporizes from 

a heat and adheres to the dust. The practices 

found in the steel industry can be placed into three 

categories: 

* Portal monitors (Item 7). The vehicle 

transporting the furnace dust is monitored with 

a sophisticated system that is either dedicated 

for furnace dust or the same system used to 

monitor incoming scrap metal. A dedicated 

monitor may be automated, dispensing a ticket 

that a driver must present to a guard before 

being allowed to leave the mill grounds with 

the dust.

NUREG-1669 76
7: STEEL MILLS

An Incident of Radioactive Scrap Metal

In 1997, a steel mill sent rolls (coils) of steel to a distributor. A manufacturer eventually received the steel 

coils and made 33,000 shovel blades. The shovel blades were tempered in an oven and blasted with shot or grit, then 

quenched in an oil bath. The shot or grit had naturally 

occurring thorium in it. The stampings went through 

another steel company before going to another steel mill 

where a radiation monitor alarmed. The load of scrap 

metal was rejected and sent back to the steel company 

under a Department ofTransportation exemption issued by 

a State. State inspectors expected to find a piece of 

radioactive material, but instead found 17,000 pounds of 

slightly contaminated stampings. 

Samples of the metal were sent to a State laboratory and 

counted overnight. The contamination was found not to be 

thorium, but instead 'Co at a concentration of 7.7 pCi/g 

(-0.2 Bq/g). The Nuclear Regulatory Commission (NRC) 

could not duplicate the radiation levels; nothing was found 

in the other coils and slabs made from the same batch (i.e., 

molten steel in a furnace or heat). A coupon sample was counted overnight and showed levels of 0.4 pCi/g

"* Baghouse monitors (Item 8). The radiation 

monitor, similar to a survey meter, is fixed to 

a portion of the baghouse. A convenient place 

is between the bags, which remove the dust in 

the air steam coming from the mill, and the 

dust silo, where the dust is transferred to a 

vehicle transporting it for disposal. 

"* Survey meters. A person walks around the 

transporting vehicle with a handheld meter 

before the vehicle leaves the mill. The reason 

for this instrument instead of a portal monitor 

can be the high cost of a portal monitor and a 

very limited budget. 

The dust processors also monitor the furnace dust 

and will not accept a load of furnace dust that is 

found to be radioactive. Contaminated furnace 

dust is classified as a mixed waste, which most 

dust facilities are not licensed to accept and 

process. There is some discontinuity in the 

practice of monitoring dust among some steel 

mills and at a hazardous waste processor; a mill 

may be using the portal monitor, but the furnace 

dust processor may be using only a survey meter. 

The waste processor also has potentially high

(-0.OlBq/g) . Two coils of unused steel at the 

manufacturer had radiation levels of 30 R/hr. Additional 

coils received later were also found to be contaminated. 

The contaminated metal was traced to a batch made on 

February 1, 1997. The 48 15-mCi sources in the refractory 

lining of the furnace where the scrap metal was melted were intact. The furnace capacity is 136 to 181 tonnes (150 to 

200 tons); given the 7.7-pCi/g activity, the larger capacity 

figure suggests a 2-mCi source in a 18 1-tonne (200-ton) 

batch. It is not known whether or not the test pieces from 

the molten steel were monitored for radioactivity as the 

steel was being made. The process line has radiation 

gauges, but 0.4 pCi/g would not cause erratic readings. 

Although the shovel blades were declared to be safe, the 

manufacturer sent them back to the steel company. 

Source: NRC Event Report 32021 and discussions with James 

Yusko, Pennsylvania Department of Environmental Protection.

costs for accidentally processing contaminated 

furnace dust. A reason for the portal monitor at 

the mill can, at least in part, be explained by a 

concern for liabilities and public image. Furnace 

dust on its way to a waste processor belongs to the 

mill until the processor accepts the load. If a truck 

carrying contaminated furnace dust were in an 

accident, spilling mixed waste on a highway, the 

potential for liability and the negative public 

perception might be costly to the mill. A mill 

invests in the state-of-the-art technology necessary 

to keep the chance of sending mixed waste out of 

the mill low and to state that whatever is 

reasonably possible is being done in this regard. 

This is especially true when a mill has melted 

radioactive material or has had an investigation 

where this might have occurred. Another reason 

is convenience. Some mills use one monitor 

station to scan everything coming in and going out 

of the mill. 

Item 7 (Figure 30): Monitoring Slag 

Although slag can be scanned in the same manner 

that incoming scrap metal is monitored with a 

portal monitor, some mills may have a reason for

77 NUREG-1669
7: STEEL MILLS

not doing so because refractory materials, also in 

the slag, may be slightly radioactive and cause 

many false alarms (see definition in Section 7.3). 

At other mills, an assumption is made in the policy 

at a mill that radioactive material will be either in 

the steel (e.g., 6

"Co) or the furnace dust (e.g., `"Cs 

or 'Co). The assumption may be questionable 

because little is known about the partitioning of 

materials at high temperatures. 

Slag has several uses, some of which depend on 

its chemical composition. Iron can be recovered 

and reintroduced into the steel-making process. 

Slag can be used as filler material and roadbed 

material. Some slag is highly alkaline and is used 

to control mine drainage. Slag with a high iron 

content may be used directly in future heats. 

Other nonferrous materials in slag may be blended 

with fluxes used in steel making. 

7.5 Probability of Detecting a 

Radioactive Source in Scrap Metal 

7.5.1 Statement of the Problem 

Radiation monitors form the primary defense in 

steel mills (and scrap yards) when a nuclear gauge 

escapes control mechanisms. Yet the 

effectiveness of the equipment, as measured by 

the probability of detecting radioactive material in 

a load of scrap metal, is incompletely known. The 

typical value cited, 99%, is an educated guess, 

based on intuition, what is known about the use of 

monitor equipment, and nontechnical reasons. 

Any number greater than 99% may be questioned 

on the basis of being implausible. A monitor 

vendor cannot state that its equipment is 100% 

effective for the following reasons: 

"* The vendor would be assuming a high degree 

of liability. 

" Some steel mills installed monitors after 

melting radioactive material, yet despite these 

monitors, another nuclear gauge was melted 

(Ref. 1).

Ways are known that can defeat a radiation 

monitor (e.g., a nuclear gauge in the center of 

a bale of scrap metal is unlikely to be 

detected). 

The 99% number is of little use for a risk 

assessment. 

The value of the probability has implications for 

the public, licensees, the steel industry, and 

regulatory agencies. If the detection probability is 

low when monitoring equipment is sophisticated, 

then stringent controls atthe licensee facilities will 

be needed, placing heavy burdens on both the 

gauge users and on the regulatory agencies. If the 

detection probability is high, then the chances of 

recovering a gauge in the recycling stream are 

high; less stringent controls would be needed to 

balance predictable costs against uncertain 

consequences. 

7.5.2 Concepts of the Detection Probability 

Vehicles pass through sophisticated radiation 

monitor stations. A sophisticated monitor station 

is, for this risk analysis, considered to have large 

plastic or multiple sodium iodide detectors, fixed 

in place, the signals of which are processed by a 

system to initiate an alarm. Usually the sides of a 

vehicle will be scanned by a monitor station when 

the vehicle enters a scrap yard or steel mill. A 

monitor station, with side-mounted detector 

panels, is illustrated in Figure 31. The concepts of 

the detection probability developed for this 

situation can be extended to other configurations, 

such as a vehicle between three panels (one on 

each side and one above) and four panels (two on 

each side). An analysis of these other situations is 

beyond the scope of this report. 

Because the scrap metal is randomly loaded, 

irregular gaps are present between the pieces of 

metal. The amount of radiation received by a 

detector depends on the activity of a sealed 

source, the location of the sealed source in a load 

of scrap metal, and the void fraction of the scrap 

metal. The load of scrap metal appears to a 

radiation detector as a pile of leaves appears to a

NUREG-1669 78
7: STEEL MILLS

Radiation 

Monitor 

Station

\ Detector

Figure 31 Truck entering a radiation monitor 

station with a load of scrap metal. 

person. A flashlight in the pile, near the surface, 

will certainly be seen. Deep in the pile, the light 

will not be seen. Between the surface and deep 

within the pile, the light might be seen. A 

compact pile is more opaque than a loosely 

packed pile. The flashlight itself does not have to 

be diredtly seen to be noticeable. Light will pass 

through and be reflected off the surfaces of the 

leaves. 

In an analysis of the detection probability, the 

commodity of scrap metal can be taken as a 

boundary condition. The characteristics of a 

monitor station can be considered another 

boundary condition. The following aspects 

remain to be considered: 

"* activity of the radioactive material; 

"* dimensions of the load; and 

"* position of the nuclear gauge in the load. 

The activity of the sealed source is not an issue as 

this point in the concepts, the radiation level of 5 

mR/hr at one foot can be taken as a starting point. 

Nuclear gauges are designed so that the radiation 

field is low enough to allow their use in an area 

that does not have to be posted as a radiation area; 

this level is 5 mR/hr at a distance of one foot from

the gauge. Once the concepts have been 

established, lower radiation levels can be 

postulated, each time estimating the detection 

probability and the effect on risk estimates. 

A load of scrap metal can be viewed from either 

end of the vehicle. The problem of locating a 

nuclear gauge in the load becomes a 

two-dimensional instead of a three-dimensional 

problem. In doing so, special effects at the ends 

of the load are considered insignificant. Though 

the detection probability is higher when 

radioactive material is near the end of the vehicle 

than when it is in the center of the load, it is 

unlikely that a nuclear gauge is near enough to the 

ends to significantly raise the detection 

probability. 

In Panel (A) of Figure 32, contours represent 

constant amounts of shielding from the scrap 

metal in a load. A nuclear gauge near the sides of 

the load will be shielded little by the scrap metal. 

Deep in the load, a gauge will be highly shielded. 

The contours would be different for different 

commodities of scrap metal. The contours cannot 

readily be determined. Shielding calculations are 

challenging because of the random geometry of a 

load. Also, shielding calculations typically yield 

only the amount of radiation emanating from a 

shielded source, not the probability of detecting 

the source. Experiments to determine the 

probability contours would be challenging as well. 

Many trials would be needed on loads of typical 

sizes and commodities of scrap metal. Loads are 

large; the weight of scrap metal in a truck can be 

as much as 23 tonnes (25 tons) and the weight of 

scrap metal in a railcar can be as much as 91 

tonnes (100 tons). Because of the difficulty in 

performing mathematical studies and experiments 

to determine the detection probability, the 

contours have to be simplified. 

Panel (B) of Figure 32 illustrates how the 

detection probability varies with the location of a 

gauge in a load of scrap metal. The left ordinate 

of the graph is the radiation field, showing the 

field from immediately outside a load as a 

function of the location of a gauge in three

79 NUREG-1669
7: STEEL MILLS

commodities: a low-density commodity gives little 

shielding, while a high-density commodity gives 

a large amount of shielding. The plot for the 

intermediate commodity is used for illustration. 

Effects from the top and bottom of the load have 

been neglected to simplify the illustration. Then, 

the radiation field increases as the detector on the 

other side is approached. When a gauge is near 

either side of the load, the radiation field is high 

and will be detectable. When a gauge is in the 

center, the radiation field is low; depending on the 

commodity of scrap metal, the field may be too 

weak to detect. If a load of scrap metal contains 

a nuclear gauge, the gauge can be anywhere in the 

load with equal probability. 

The right ordinate of Panel (B) in Figure 32 is a 

probability scale corresponding to the chances of

being able to detect a given radiation field. Some 

minimal radiation field is, almost certainly, 

detectable with the radiation monitors found at the 

mills. This level is represented as RFd,,t. For 

radiation levels at RFadec, and higher, the detection 

probability is approximated by one. Similarly, 

there is a level below which a radiation field is 

likely to be undetectable; for this level, RF1,, and 

lower, the- detection probability is approximated 

by zero. For radiation fields between RFdeteet and 

RFmiss, the chance of detection is between zero and 

one because, for many reasons, both the radiation 

and the monitor response may vary. 

In Panel (C) of Figure 32, only the inner and outer 

shielding contours have been drawn, 

corresponding to RFdetect and RFmis,. The detection 

probability is approximately one for a nuclear

Field Strength =f(position) 

Scrap Metal 

Detector

4.&64&-v-i

padkzkoaeh a& r, 

a~ea" h~o p~oa"Ydi4 

Zýa44c edepc&)

- I---- I I

I 

Radiation 

Field 

" RFd~td. 

RE.is

Probability 

,ýA 1

-,.I-I*: /1/II

K idth) 

123 

L

I I

Figure 32 Areas of detection in a load of scrap metal.

NUREG-1669

Probability 

Approxi 

mations 

Pr l

0<Pr< 1

Pr Z0

NN II

_7

J

80
7: STEEL MILLS

gauge in the region outside the outer contour 

(Area 1). The probability that a gauge will be in 

Area 1 is the proportion of Area 1 to the total 

cross-sectional area of the load. This is given by 

Equation 21.

Pr- =Area 1 

Total Area

[21 ]

Pr, = probability of a nuclear gauge 

being in Area 1 of Figure 32.C 

Area 1 = peripheral cross-sectional area of 

a load (see Figure 32.C) 

Total Area = total cross-sectional area of a load 

(see Figure 32.C) 

The detection probability is between zero and one 

in the intermediate region (Area 2). The 

probability of a nuclear gauge being in Area 2 is 

given by Equation 22.

Pr Area 2 

Total Area

[22 ]

Pr2 = probability of a nuclear gauge lying in 

Area 2 of Figure 32.C 

Area 2 = intermediate cross-sectional area of a 

load (see Figure 32.C) 

The detection probability is approximately zero 

inside the inner contour (Area 3). The probability 

of a nuclear gauge being in Area 3 is given by 

Equation 23.

Pr3 = Area 3 

Total Area

[23]

Pr3 = probability of a nuclear gauge lying in 

Area 3 of Figure 32.C 

Area 3 = inner cross-sectional area of a load 

(see Figure 32.C) 

Let T. be the probability of detecting a nuclear 

gauge in the n' area of Figure 32 during one pass 

through a monitor station. The overall probability 

of detection can be expressed as Equation 24.

' = Pr, T1 + Pr2 2 "+ Pr3T,3 [24 ]

TP = overall probability of detection during one 

pass through a monitor station if a gauge is 

present in the load 

Tn is a complicated function that depends on many 

factors. Nonetheless, statements can be made 

about 'n in certain areas of a load. In Area 1, 

where the detection probability is close to one, 

T, = 1. In Area 3, where the detection probability 

is close to zero, T340. In Area 2, T2 is between 

zero and one. Here, T2 is an average value over 

the possible locations of a gauge in Area 2. 

Equation 24 reduces to Equation 25.

P = Pr,+ Prow 2 [25]

Equation 25 is key to understanding the detection 

probability and its ramifications. The equation 

applies when a load of scrap metal passes once 

through a radiation monitor; after the single pass, 

if a radiation alarm occurs, an action is taken; if an 

alarm does not occur, then the load enters the mill. 

For multiple passes (kee Section 7.6), the equation 

is readily modified. 

Although the detection probability in Area 2 

cannot be readily determined, a useful risk 

assessment is still possible by considering two 

bounding cases of T2. Case (A): Compute the risk 

to scrap yards and steel mills postulating that a 

nuclear gauge in Area 2 will be detected. Here,P2 

is set to one and the resulting detection probability 

becomes PA = Pr,+ Pr. Case (B): Compute the 

risk postulating that a gauge in Area 2 will be 

missed. Here, T2 is set to zero and the detection 

probability becomes TB = Pr1 . The actual, but 

unknown, detection probability is bounded by 

Cases A and B, as shown in Equation 26.

PB5 T 'P T 'A [26]

The actual risk is also bounded by Cases A and B. 

If risk estimates made with the bounding cases are 

close together, then a precise determination of T2 

is unnecessary. This would occur when Area 2 in 

Figure 32 is small for one of two reasons. First, 

the void fraction of the scrap metal in the load 

may be large because the scrap metal is loosely

81 NUREG-1669
7: STEEL MILLS

1 

Probability (A) 

Of 

Detection (B) 

0' Front B~ak 

Length of Vehicle 

Figure 33 Hypothetical variability in the detection probability 

for (A) heterogeneous and (B) homogeneous commodities of 

scrap metal. 

packed, giving rise to a large Area 1. Second, the 

void fraction is small because the scrap metal is 

tightly packed, giving rise to a large Area 3. If 

these bounding risk estimates are far apart, then a 

precise determination of T 2 may be necessary. 

This would occur when Area 2 is large. 

The detection probability may vary along the 

length of a vehicle. In heterogeneous 

commodities, such as plate and structural scrap 

(i.e., P&S) or bundles, the variability will be 

relatively large. In homogeneous commodities of 

scrap metal, such as frag, the variability will be 

relatively small. Such variability is illustrated in 

Figure 33. Curve (A) represents the variability in 

a heterogeneous commodity. Curve (B) 

represents a homogeneous commodity. 

A load of scrap metal viewed from the end of the 

vehicle has three concentric cross-sectional areas. 

Also, the scrap metal entering a steel mill can be 

viewed as a continuous stream (see Section 3.2). 

In Figure 34, the concepts of the detection areas 

and the continuous stream are brought together. A 

load will have characteristics (e.g., density, 

homogeneity) that determine the shielding. This 

makes the detection probability dependent on the 

commodity. The detection probability must be 

expressed in a way that is conditional only on the 

relative amounts of each commodity used at a 

mill. The expression must relate Areas 1, 2, and

3 to the terms in which scrap metal is purchased, 

which is weight. Such an expression can be 

readily determined. The following assumptions 

are made: 

Assumption: Nuclear gauges in the recycling 

stream are rare. In the recycling stream, they 

are far apart. A load of scrap metal is unlikely 

to contain more than one nuclear gauge. Basis: 

Reference 1 suggests that sealed sources in the 

recycling stream are rare. An updated version 

of the information is shown in Figure 2. 

Assumption: A nuclear gauge is randomly 

located in a load of scrap metal. Basis: 

Intuitive. The scrap metal is processed and 

loaded into vehicles at random. There may be 

some placement of large pieces to distribute 

weight during transportation, but there is no 

placement of particular pieces. Therefore, 

there is no placement of a nuclear gauge that 

would be on a piece of scrap metal.9 

Assumption: Commodities are not mixed when 

they arrive at a mill. Basis: Steel mills order 

scrap metal from dealers by commodity and 

this is how the orders are filled. 

Figure 34 shows a load of scrap metal viewed 

from above, in a truck or a railcar, passing 

between the detector panels of a monitor station. 

A load is divided into sections that are the width 

of the monitor panels. The dotted lines from the 

detectors to the vehicle represent the view of the 

detector panels. The lighter horizontal lines 

through the cross-sections demarcate Area 1, Area 

2, and Area 3. A nuclear gauge, represented by 

the black dot, is in an area of one cross-section. 

The bottom portion of Figure 34 shows one of the 

cross-sections as viewed from another angle. The 

nondetectable region is represented as a shaded 

elliptical volume. The detectable region is the 

unshaded surrounding volume. 

9 / Deliberate placement to conceal a gauge (i.e., sabotage) is 

beyond the scope of this study.

NUREG-1669 82
7: STEEL MILLS

Considering the stream of scrap metal as 

very long (e.g., scrap metal continuously 

coming into the mill), the widths of the 

cross-section become very small. Also, 

end effects, such as the detector panels 

receiving radiation from adjacent 

cross-sections, become negligible.

Detector Panel

Vehicle

Areas

The amounts of each commodity are 

measured in weight, not volume, because 

this is how scrap metal is purchased. But 

the monitor does not see the weight of a 

load; it looks at the volume of the loads 

passing between the detector panels. The 

vehicles can be represented by a typical 

height and width. There is a tendency to 

use the largest trucks and railcars that 

can fit on the transportation system. 

Roads and tracks can accommodate 

vehicles up to a specific height and 

width. Although differences in the 

heights of scrap metal in railcars and trucks are 

evident, the differences are negligible because of 

other uncertainties. Although differences between 

the cross-sectional areas of old and new railcars 

occur, the differences are of no concern for the 

same reason; other uncertainties are larger. The 

same argument holds for large trucks. 

Assumption: Scrap metal arriving at a mill is 

usually brought in large trucks (tri-axle or 

larger) and railcars. Basis: Although some 

mills will take peddler trade, such sources of 

scrap metal at the mills account for a small 

amount of the scrap metal that is used at the 

mills. Scrap metal is usually taken to the mills 

in the largest vehicles fitting on roads and rails 

to reduce cost. 

Assumption: The cross-sectional area of trucks 

and railcars is about the same and constant. 

Basis: To keep transportation costs low, the 

largest vehicles will be utilized. Limits on the 

transportation system that are soon reached are 

the width and height of vehicles, leaving the 

length that can be readily changed. Even the 

length has limits; vehicles have to be able to 

get around curves.

}Detectable Area 

Non-Detectable 

Area 

Detectable Area

Area 3

Area 2

Area 1

Figure 34 Recycling stream illustrated to determine the detection 

probability of a commodity of scrap metal entering a steel mill. 

The second assumption allows the width and 

height of the vehicle to be represented by a 

constant, k, as in Equation 27.

V= /wh= /k [27 ]

V = volume of the vehicle transporting scrap 

metal 

I = length of the transporting vehicle 

w = width of the transporting vehicle 

h = height, as measured from the bottom to the 

top of the compartment carrying scrap metal 

More generally, the length is proportional to the 

volume.

VO f [28]

The detectors receive radiation through cross

sections of the loads. The cross-sections are along 

the length of the continuous stream of scrap metal 

entering a mill. This length is proportional to the 

volume of scrap metal, which can be related to the 

quantity that is measured--weight. Thus, 

Equation 28 allows the volume of the loads used 

in a period to be used as the factor for combining 

the probability of each commodity used at a mill. 

This is Equation 29.

83 NUREG-1669
7: STEEL MILLS

L 

V-= ()C P [29 ]

p = density of the load 

L = tare weight of the load 

The detection probabilities of each commodity can 

then be weighted for averaging. The average 

probability depends on the relative amount of 

commodities. This is Equation 30.

[301 T'blend - ~ 

j=l

"

T blend = detection probability for a blend of 

commodities used at a mill 

'Pj = detection probability for the jt scrap 

metal commodity used at the mill 

o c = weighting factor: amount of the jth scrap 

metal commodity 

j = index of scrap metal commodities 

n = number of scrap metal commodities 

Equation 30 is applicable to the unconditional 

probability during the first pass through a monitor 

station. Similar expressions can be made for the

conditional probabilities of the second and third 

passes (see Section 7.6). The detection 

probabilities are computed for each mill of a given 

configuration, then aggregated to form a 

distribution. 

7.6 Multiple Passes Through a 

Radiation Monitor Station 

7.6.1 Statement of the Problem 

Three ways of using radiation monitors to detect 

sealed sources in scrap metal appear to be in 

common practice- pass a load through a monitor 

station one, two, or three times. Usually a mill 

will not pass a vehicle through a monitor station 

more than three times because the multiple passes 

are time consuming. The reasons for choosing the 

one-pass, two-pass, or three-pass strategy of using 

a monitor are not always well understood by 

employees who operate the systems. The 

manufacturer of the monitor or a consultant to the 

facility may have recommended passing a load 

through several times without being able to give 

specific reasons. An employee at a mill may pass 

a load through until there is confidence that it does 

not contain radioactive material, without definite 

criteria for deciding whether to accept or reject the 

load. The decision logic for determining when to

Some Factors That Influence the Probability 

of an Alarm at a Radiation Monitor Station 

During Multiple Passes 

LEGEND: 0 = factors that are constant during multiple passes. 0 = factors that can change during multiple passes.

Ambient Conditions 

"O Background radiation levels 

"o Weather conditions 

Radiation Monitor 

"O Type of equipment 

"[ Alarm set point 

"[ Care and upkeep 

"* Diligence in use

Transporting Vehicle 

O Size 

o Construction 

* Speed during monitoring 

O Position of vehicle in a station 

Load of Scrap Metal 

o Type 

o Density 

* Arrangement of scrap metal

Sealed Source 

O State (intact, separated, breached) 

o Source strength 

0 Radionuclide 

* Location in a load of scrap metalt 

Unknowable Factors 

"* Scrap metal shifting between passes 

"* Other

t Movement occurs as a result of shifted scrap metal.

NUREG-1669 84
7: STEEL MILLS

accept a load after one or more passes through a 

monitor station has important implications for the 

capability of keeping radioactive material out of 

its facility. 

7.6.2 Chance of Alarming 

Figure 35 illustrates the possible combinations of 

radioactive materials in loads of recycled metal. 

The figure is suggested by Reference I. BC, 

represented by the larger circle, is occasionally 

found in loads. Sealed sources, represented by 

the smaller circle, are occasionally found in loads 

or, even less frequently, reported as being melted 

at mills. The occurrence of both BC and a sealed 

source in the same load, represented by the 

overlap of the circles in the figure, appears to be 

rare. Background radiation, represented by the 

rectangle, is always present. 

When a vehicle passes through a monitor station, 

an alarm either will or will not activate. An alarm 

depends on many factors that may interact and 

compensate for one another in complicated ways, 

the details of which are beyond the scope of the 

risk analysis. Though a sophisticated monitoring 

system is preferable to an unsophisticated system, 

a sophisticated monitoring system does not 

necessarily guarantee a high assurance of 

detecting a sealed source because other factors 

contribute to the capability of detection (see box 

entitled "Some Factors That Influence the 

Probability of an Alarm at a Radiation Monitor 

Station During Multiple Passes"). 

If all factors remained exactly the same during 

each pass through a monitoring station, the 

outcomes of multiple passes through a monitor 

station would always be the same. But this is not 

the case; all factors do not remain exactly the 

same. Random variations in some of the factors 

occur and, hence, alarming is not predictable from 

one pass to another. Taking the factors together, 

there is an overall probability that the factors 

assume the values necessary to cause a radiation 

alarm. The situation of concern is when the sealed 

source is shielded by its device holder and scrap 

metal, bringing factors near the threshold of 

alarming, where random fluctuations may move 

the factors above or below the threshold.

The distributions of radiation fields a monitor "sees" are illustrated in Figure 36. The figure is 

not drawn to scale, but is drawn to illustrate 

concepts qualitatively. Each curve represents the 

distribution of radiation intensity. The area under 

each curve is equal to one because it accounts for 

all possible radiation levels. For any curve, the 

probability that the radiation intensity would be no 

higher than a stated amount is the area bounded by 

the curve up to the stated amount. Curve (I) 

represents the distribution of only background 

radiation, which varies from one location to 

another and from one time to another, but is 

always present to some degree. Curve (II) 

represents the distribution when BC is present in 

a load. BC is occasionally present; when it is, it 

adds to the background radiation, resulting in 

higher radiation intensities. Curve (III) represents 

the distribution when a sealed source, but no BC, 

is present. Similar to BC, its radiation adds to the 

background radiation, pushing the distribution to 

higher radiation intensities. Many sealed sources 

are stronger than BC, so that the sealed source 

distribution (Curve (III) is generally larger than 

the BC distribution (Curve (II). But some sealed 

sources may be shielded by their holders and their 

position in the load of scrap metal, resulting in the 

tail of the lower intensities. Curve (IV) represents 

the distribution when BC and a sealed source are 

present together in the same load. The radiation 

from both BC and the sealed source adds to the 

background radiation.

Key 

=- B~akgow =d 

F.. BC 

BC & sealed sawe 

Figure 35 Possible combinations of 

radioactive material in loads of scrap metal.

85 NUREG-1669
7: STEEL MILLS

A vehicle undergoing 

radiation monitoring is 

represented by one of the 

distributions. The curve 

that determines the 

probability of alarming 

depends on the specific 

radioactive contents 

(background, BC, sealed 

source) of the load. But the 

radiation monitor cannot 

discriminate between BC 

and a sealed source; it 

detects only the amount of 

radiation.

,.Jpoj. 

"SPOWj,d 

,&.eJp44 

MJedOA"

S (1 OD Background 

04 'A 

S(ID) Background 

& Benign Contamination 

~ A (IMI Background 

& Sealed Source 

z~~. ... -- ~ A1 &(IV) Background 

_ _ _& Benign Contamination 

. ... & Sealed Source 

Threshold: Alarm? 

t No IYes -0

The relationship between 

monitor responses, the Figure 36 Relation of monitor response, alarm threshold, and hypothetical distributions 

alarm threshold, and the of radiation levels from background, BC, and sealed sources. 

hypothetical distributions 

of radiation levels is also 

illustrated in Figure 36. 

The alarm threshold is the vertical dashed line; in increased by the radiation from both BC and the 

sophisticated monitors, the threshold varies to stay sealed source. In this case, BC is beneficial 

at a predetermined amount above the background because it increases the probability of an alarm. 

level at a given moment. Radiation intensities 

below the threshold do not cause an alarm; Figure 36 illustrates difficulties in detecting a 

intensities above the threshold cause an alarm. In sealed source. The shielding from the source 

Curve (I), a load contains only scrap metal, with holder and the scrap metal may make the intensity 

neither BC nor sealed sources. Because the alarm of the radiation from the sealed source similar to 

threshold is above background, the probability of that of BC and background radiation. The BC 

no alarm (and a standard response) is one. In radiation complicates the detection. Were BC 

Curve (II), BC is present and its distribution nonexistent, the matter of detecting sealed sources 

extends above the alarm threshold. This leads to would be simpler. A monitor threshold could be 

the possibility of a false alarm (see definition in set below all of the distribution of radiation from 

Section 7.3) whose probability is the area of the sealed sources. But the distribution of BC 

curve above the alarm threshold; the probability of radiation overlaps the distributions of background 

no alarm is the area of the curve below the alarm and sealed source radiation. This overlap can 

threshold; this is the probability of a standard result in false alarms. False alarms are detrimental 

response. In Curve (Ill), where a load contains a because they consume resources, such as 

sealed source but no BC, the alarm threshold may determining the cause of an alarm or turning loads 

be low enough to detect some, but not necessarily away when they should have been accepted. 

all, sealed sources. The probability of an alarm is 

the area of the curve above the alarm threshold; Table 6 shows all four possible outcomes of a 

this is the probability of detection. The vehicle, with a load of scrap metal, passing once 

probability of no alarm is the area of the curve through a monitor station. The actions taken, 

below the alarm threshold; this is the probability based on the outcomes, are discussed in the next 

of a missed detection. In Curve (IV), where both section. The columns show the two possible 

BC and a sealed source are present in the same responses of the monitor; the monitor will either 

load, the probability of an alarm has been alarm or not alarm. The rows show the two

NUREG-1669 86
7: STEEL MILLS

possible states of the load; the load either does or 

does not contain a sealed source. When a vehicle 

passes through a monitor station, the column 

becomes known. If no alarm occurs, then either 

there is no sealed source (standard response) or a 

sealed source is missed (missed detection). This 

corresponds to Curve (I) or (II) below the alarm 

threshold when no sealed source is present, or 

Curve (III) or (IV) below the alarm threshold 

when a sealed source is present. If an alarm 

occurs, then either there is no sealed source (false 

alarm) or there is a sealed source (detection). This 

corresponds to the area that is above the alarm 

threshold in Curve (II) when no sealed source is 

present, or to the area that is above the alarm 

threshold in Curve (III) or (IV) when a sealed 

source is present. The response of the monitor 

gives the column of Table 6; but it is the row, not 

the column, that is desired. 

7.6.3 Monitoring Strategies 

A common practice at steel mills (and scrap yards) 

is to pass a load through a monitor station more 

than once, given an alarm on the first pass. 

Because of the probabilistic aspects of monitoring, 

the monitor's response may change on subsequent 

passes. After one or more passes through a 

monitor station, a load is either accepted or 

rejected. For any monitoring strategy, let 

Pr{reject} be the probability of rejecting a load 

and Pr{accept} be the probability of accepting a 

load. Then Pr{reject} + Pr{accept} = 1. In the 

discussion that follows, a nuclear gauge 

somewhere in a load of scrap metal is postulated.

One-pass strategy. The most basic decision 

strategy is to pass a load through a monitor station 

once and act according to the outcome of the 

monitoring (see Table 6). The left panel of Figure 

37 illustrates the logic for a one-pass strategy. In 

the figure, the upper branch represents a radiation 

alarm when a vehicle passes through a monitor 

station; the lower branch represents a pass without 

an alarm. If an alarm is activated, then the load is 

rejected; if an alarm is not activated, then the load 

is accepted. In the one-pass strategy, the 

probability of rejecting or accepting a load is 

given by Equations 31 and 32.

Pr{reject} =T 

Pr{accept} = 1- T

[311 

[32]

'P =detection probability as defined by Equation 

25 (page 81). 

Two-pass strategy. The middle panel of Figure 37 

illustrates a typical two-pass strategy. If no alarm 

sounds on the first pass, then the load is accepted 

and delivered to the facility. If the first pass 

results in an alarm, then the vehicle is sent through 

the monitor station again and the load is rejected 

only if the alarm activates on the second pass. 

The vehicle is not unloaded between passes for 

reasons discussed in Section 7.4. Thus, a gauge in 

the load remains fixed in position during each pass 

through a monitor station. To obtain the 

expression for Pr{accept}, the products of the 

acceptance sequences of risk elements are

Table 6 Outcomes when a load of scrap metal passes once through a monitor station. 

Monitor Response 

State No Alarm Alarm 

No sealed source present j Standard Response False Alarm 

Sealed source present Missed Detection Detection

87 NUREG-1669
7: STEEL MILLS

One-Pass 

Strategy 

1" Pass 

Through 

a Monitor 

Station 

Outcome 

T Reject 

Accept

Two-Pass 

Strategy

Outcome 

- Reject 

Accept 

- Accept

Three-Pass 

Strategy

n& Pass 

Through 

a Monitor 

Station 

'1 2 3' Outcome 

-Reject 

Reject 

Accept 

SAccept

Figure 37 Logic of the one-pass, two-pass, and three-pass strategies for monitoring scrap metal. LEGEND: 0 indicates a 

radiation alarm during the n"' pass through a monitor station. Ak = alarm. N. = no radiation alarm. T = probability of an 

alarm on the first pass. 'J(n+l In) = conditional probability of an alarm during the n+1 pass, given the n't pass.

summed. If the passes were independent, then T' 

on the first pass could be used as the detection 

probability on the second pass; then the 

acceptance expressions could be readily 

determined as the sum of the products of the 

probabilities along each sequence of risk 

elements. For example, the rejection probability 

would be Pr{reject} = T'. But the second pass 

is conditional on the first pass, precluding this 

treatment. 

The first pass through the monitor station gives 

information about the location of a gauge. If an 

alarm occurred, then the gauge was in either Area 

1 or Area 2 (see Section 7.5.2 for a discussion of 

the areas); it could not have been in Area 3. If no 

alarm occurred, then the gauge was in either Area 

2 or Area 3; it could not have been in Area 1. An 

alarm or lack of an alarm during the first pass 

precludes one of these areas during the second 

pass. Therefore, the probability of alarming on 

the second pass becomes conditional on the 

outcome of the first pass. Let A1 denote an alarm 

on the first pass and A2 denote an alarm on the 

second pass. The probability of an alarm on the

second pass given an alarm on the first pass 

becomes T'(A2 IA,). 

The first pass also yields information about the 

detection probability of Area 2, TP2. In Equation 

25 (page 81), the probability is an average 

representing the probability gradient shown in 

Figure 32. If an alarm occurred, then the gauge is 

likely to be closer to Area 1 where it can be 

detected. If no alarm occurred, then the gauge is 

likely to be closer to Area 3 where it cannot be 

detected. 

Accounting for dependencies, the probability 

expressions of rejecting or accepting a load are 

given by Equation 33.

Pr{reject} = [T ] [T (A2 IA)] [33]

If a sealed source is present, then the second pass 

will reduce the chance of rejecting the load. The 

two-pass strategy gives a load of scrap metal a 

second chance to enter a facility. But the second 

pass may or may not lead to the correct action.

NUREG-1669 88
7: STEEL MILLS

False Alarms

In Section 7.3, a false alarm was defined as an alarm 

that occurs in the absence of a sealed source when scrap 

metal is scanned for radiation. A false alarm is a 

response of the monitor system to radiation that is not 

from a nuclear gauge. The alarm is "false" in the sense 

that the monitor is indicating that there is something of 

concern in a load of scrap metal, when in fact, there is 

only a benign form of contamination. 

This application of the false alarm concept to radiation 

monitoring may be easier to understand when viewed 

alongside an analogous situation. In the test for 

tuberculosis, the substance used to diagnose 

tuberculosis, called tuberculin, is injected into the skin 

on the arm. If the skin remains unchanged, it is likely 

there is no tuberculosis. If localized inflammation 

occurs, there is a reason for more extensive and costly 

testing. But the inflammation does not necessarily mean 

that the person has tuberculosis because the test is not 

for the presence of the disease state. Instead, the test

Three-pass strategy. A typical three-pass strategy 

is shown in the right panel of Figure 37. As 

before, scrap metal is not unloaded between 

passes. Also, only loads that alarm on the first 

pass are retested. The third pass is used to 

confirm either the first pass or the second pass if 

these passes disagree. The uppermost branch of 

the second pass is not subject to a third pass 

because the second alarm confirms the first alarm. 

To obtain the probability expressions, 

dependencies between the passes must be taken 

into account as in the two-pass strategy. Doing so, 

the probability expressions are obtained by 

multiplying along each sequence of risk elements; 

to obtain the expression for Pr{reject}, the 

products of the rejection sequences are summed.

Pr{reject} = [I] [Tt' (AIA1)]+ [34 ]

[T ] [1 - T (AIA,)] [TP.(A 3jN 2 )] 

The third pass reduces the chances of incorrectly 

accepting a load based on the second pass.

detects antibodies for tuberculosis in the blood that are 

responding to the injection. The antibodies may be 

present because the person has the disease, but 

antibodies may be present for other reasons, too; the 

person may have been exposed to the bacteria without 

developing the disease, may have been exposed to 

similar bacteria, or may have been vaccinated. In these 

latter situations, the person does not have what is of 

concern -tuberculosis. The test result is false in the 

sense that it is taken as suggesting disease. 

Laboratory radiation detectors can discriminate between 

benign contamination and sealed sources. Such a 

system for monitoring scrap metal would be impractical 

in scrap yards and steel mills because the equipment 

would be more expensive than the already costly 

equipment that is used, the time needed for the scanning 

would,be too long to be profitable, and test results may 

be difficult lo interpret. The tradeoff for using a less 

expensive system is a higher possibility for false alarms.

7.6.4 Implications of the One-Pass, Two-Pass, 

and Three-Pass Strategies 

The two-pass strategy makes the facility more 

vulnerable to accepting a sealed source than either 

the one-pass or three-pass strategy. The two-pass 

strategy gives a load that has been flagged as 

containing radioactive material another chance to 

enter the facility; the alarm on the first pass, which 

may be true, can be overridden by the lack of 

alarm on the second pass, which may be false. 

The alarm on the first pass, not the absence of the 

alarm on the second pass, may indicate the true 

state of the load. This situation occurs elsewhere. 

Some people recheck a calculation and, getting an 

answer that differs from the first, instinctively take 

the second answer as correct. The three-pass 

strategy brings the rejection probability up 

somewhat compared with the two-pass strategy 

because the third pass confirms either the first or 

the second pass. However, because the three-pass 

strategy has more pathways for acceptance, it has 

a lower chance of finding a sealed source than the 

one-pass strategy.

89 NUREG-1669
7: STEEL MILLS

t

9

h1asnAn

nt pass through a monitor station 

Ii 2 31

Outcome 

o e '!(A 2 lAl) Reject 

Reject 

Accept 

Figure 38 Main pathway and an additional 

pathway in risk element sequences for scrap 

metal entering a steel mill. 

If the primary concern is detecting sealed sources, 

then the best of the three strategies considered 

here is the one-pass strategy. The decision to 

reject or accept a load would be made on the first 

pass through a monitor station. The two-pass and 

three-pass strategies reduce the probability of a 

false alarm at the risk of missing a sealed source. 

However, if the primary concern is false alarms, 

then the best of these strategies is the two-pass 

strategy. In practice, both detection and false 

alarms are of concern; the three-pass strategy is a 

compromise between the one-pass and two-pass 

strategies. 

The effect of the multiple passes, given an alarm 

on the first pass, is to bring more scrap metal into 

the facility. Loads that have alarmed on the first 

pass are given another chance to enter the facility. 

The price for giving loads another chance to enter 

a facility is the higher chance of missing a sealed 

source. Figure 38 illustrates this with the 

three-pass strategy.

7.6.5 Secondary Monitoring 

In the strategies illustrated by Figure 37, a high 

probability of alarming when a sealed source is 

present is critical for protecting the facility

because there is no redundancy in monitoring after 

the first pass on the acceptance pathway. Each 

strategy accepts a load if there is no alarm on the 

first pass. But some mills conduct monitoring at 

the charge bucket or in the yard. At either 

location, secondary monitoring refers only to 

when scrap metal is scanned, unloaded from the 

transporting vehicle, reloaded, and scanned again. 

Monitoring at the charge bucket is discussed in 

Section 7.4 (Items 2 and 3). Charge bucket 

monitoring is the more common form of 

secondary monitoring than monitoring in the yard. 

Monitoring in the yard takes two forms: one form 

occurs when scrap metal is unloaded in the yard, 

then reloaded prior to monitoring; the other form 

occurs when scrap metal passes through the 

second monitor without unloading and reloading. 

The yards may have developed as the mill 

operations were expanded. Several layouts are 

illustrated in Figure 39; the versions are a 

consequence of the layout of the mill, not a result 

of arriving at a means of improving monitoring 

effectiveness. After passing through the second 

monitor, the vehicle is unloaded in the storage 

area. Panel (A): At some mills, scrap metal is 

scanned once, then unloaded, sorted, and reloaded 

into vehicles, going from the storage area to the 

scrap bay/yard where it is scanned again. Trucks 

(A) •Inner Storage 

LMelt Shop 

.. wM 1111,

(B)

?ad

St(rag

Figure 39 Configurations of steel mills where a 

vehicle passes through a monitor station several 

times; (A) with unloading and reloading between 

passes; (B) without unloading between passes.

NUREG-1669 90
7: STEEL MILLS

(n ass Thoug aýý Monitor Station 

I1 2 31

MossdM~41 a. 

cha~, e 9

ia ae

Reject Outcome 

Accept r d- 4- Rework 

A Pr{accept}1 s)--e SAccept)•l L......., Accept

Figure 40 Primary and secondary monitoring.

pass through a radiation monitor and are weighed, 

then unloaded in a scrap yard near the entrance. 

As the scrap metal is needed, railcars on a spur 

track are loaded and switched onto a track leading 

into the mill, where they again pass through the 

same monitor station. Panel (B): At other mills, a 

vehicle passes through another monitor while 

remaining in the same vehicle. Railcars are 

brought into the mill and temporarily stored on 

spur tracks. When operations permit, the railcars 

are moved off the spur tracks; to clear the rail 

switch, all of the railcars must be brought through 

the monitor station, then pushed through the 

monitor station again onto tracks going into the 

mill. Railcars may also be brought directly into 

the mill and unloaded in the storage area. 

These two layouts give rise to very different 

chances of detecting a nuclear gauge. In Panel 

(A), unloading and reloading a vehicle randomizes 

the placement of the scrap metal in the vehicle. It 

also randomizes whatever else was in the load. If 

a nuclear gauge was in the nondetectable region 

while going through the first monitor station, it 

might be in the detectable region while going 

through the second monitor station. If the gauge 

was in the detectable region while going through

the first station, it would have been detected. If it 

was in the intermediate region and missed while 

going through the first station, it may be in the 

detectable region or again in the intermediate 

region while going through the second station. In 

Panel (B), a pass through a second radiation 

monitor without unloading and reloading leaves 

the gauge in place in the vehicle. Ifthe gauge was 

embedded deep within a load, then it might not be 

detected, no matter how many monitor stations it 

passes through. If it was near the surface of a load 

where it is easily detected, then it would have 

been found when passing through the first monitor 

station. If it is in the intermediate area, another 

chance of detection arises. Because nothing more 

definitive can be said about intermediate area, 

which is Area 2, statements can be made only 

about Areas 1 and 3. If any one of these regions 

is large, then it "squeezes" out the other regions. 

If a region is small, then the relative size of the 

other two regions is unknown. 

Table 7 states four cases. White boxes show what 

can be stated. Grey areas indicate what cannot be 

definitively stated. The following preferences can 

be stated when information about the processing 

of scrap metal is taken into account.

91 NUREG-1669
7: STEEL MILLS 

Table 7 Possibilities of finding a nuclear gauge when scrap metal is scanned, unloaded, reloaded, and scanned again. 

LEGEND: Pr{detect} = net detection probability.

After 

Reloading

Area 

3

Large

Large

Chance 

of Finding 

a Nuclear 

Gauge 

Large 

Large 

Large 

Small

Notes

Pr(detect) is large because the detection region (Area 1) is large 

in both the original load and the reload. 

Pr(detect) is large because the detection region (Area 1) is large 

in the original load. Scanning the reload becomes irrelevant. 

Pr(detect} is large because the detection region (Area 1) in the 

reload is large. 

Pr(detect) is small because detection region (Area 1) is small in 

both the original load and the reload.

Case I > Case II > Case III > Case IV 

Case I is most desirable because the region where 

the detection probability is one (Area 1) is large in 

both the original load and the reload. Case II is 

preferable to Case III: from the standpoint of 

readily disposing of a gauge at no expense, it is 

best to find it in the original load; here, the scrap 

metal can still be rejected. Case IV is undesirable; 

here, the detection regions in both the original 

load and the reload are small. 

In general, the detection probability during 

primary monitoring is not equal to the detection 

probability during secondary monitoring because 

the circumstances of monitoring change. 

Examples include the following ways: 

"* The density of a scrap metal load may change 

during sorting and blending. The probability 

of alarming may or may not change in either 

direction. 

" The structure of the vehicle passing through 

the secondary monitoring may be different 

from that of the vehicle passing through the 

primary monitoring. The walls of a charge 

bucket are several inches thick, while the 

walls of a railcar are typically about 21/2 cm 

(1 inch) thick; both are made of steel. The

walls of a truck are thinner, less than about 

1 cm (1⁄2 inch) thick, and are made of steel, 

aluminum, or an alloy. The probability of 

alarming is lower with the thicker walled 

container because of the higher shielding. 

U When a charge bucket is monitored while it is 

being loaded, the metal is in the small amounts 

that can be lifted by the crane loading the 

charge bucket, not in the one large amount of 

a vehicle load, which is about 91 tonnes (100 

tons) in a railcar and about 23 tonnes (25 tons) 

in a truck. The probability of alarming is 

increased by monitoring smaller amounts of 

scrap metal. 

Usually monitoring the reload occurs at the charge 

bucket where the load is smaller. Also, scrap 

metal is often scanned as it is placed into the 

charge bucket. 

A view of secondary monitoring is shown in 

Figure 40. The primary monitoring is the three

pass strategy; here, scrap metal can be rejected 

when the radiation alarms suggest that a load of 

scrap metal contains radioactive material. The 

secondary monitoring is a one-pass strategy, 

which is applicable to monitoring a charge bucket 

while it is being loaded. Figure 40 shows that

NUREG-1669

Original 

Load

Area 

Case 1 

I Large 

II Large 

IV

Area 

1 

Large 

Large

Area 

3

Large 

Large

92
7: STEEL MILLS

secondary monitoring gives another level of 

protection against a missed detection on the 

acceptance sequence. Because the scrap metal is 

unloaded after primary monitoring, then reloaded 

for secondary monitoring, the primary and 

secondary monitoring are independent, allowing 

their probabilities to be multiplied. Thus, the 

probability of accepting a nuclear gauge is given 

by Equation 35, where p denotes primary 

monitoring and s denotes secondary monitoring..

Pr{accept}p, = Pr{accept}p T. [351

7.7 Elements of Risk 

Element 13: Configuration of Radiation 

Monitors at Steel Mills (Figure 41) 

Each location of radiation monitors illustrated in 

Figure 30 has benefits and drawbacks, giving rise 

to a level of protection against melting radioactive 

material and detecting when radioactive material 

has been melted. A particular combination of 

monitors influences risk differently than another 

combination. For example, one configuration is 

only a portal monitor for incoming scrap metal. 

Another configuration is a portal monitor and a 

charge bucket monitor. To analyze and assess 

risk, steel mills throughout the industry must be 

aggregated according to their combination of 

monitors. 

Some of the different configurations of radiation 

monitors found throughout the steel industry are 

represented in Figure 41. The eight possible 

locations of monitors shown in Figure 30 give rise 

to 21 = 256 possible configurations throughout the 

steel industry. In practice, there are far fewer 

configurations because some combinations of 

monitors make little sense. For example, furnace

dust would not be monitored without monitoring 

incoming scrap metal. Neither would the charge 

bucket be monitored without monitoring incoming 

scrap metal. Almost all mills have portal 

monitors. Far fewer mills have both portal and 

charge bucket monitors. 

The branches of Figure 41 must be emphasized in 

some way to show that combinations are not 

equally prevalent. The branches of Element 13 

could be weighted by the number of mills with the 

given configuration of monitoring equipment. But 

such a weighting would ignore the differences in 

the sizes of mills. A more appropriate weighting 

that accounts for the different sizes of the mills is 

the total amount of scrap metal passing through all 

mills of a given configuration. But the 

commodities of scrap metal are not equally likely 

to contain a nuclear gauge. Commodities, such as 

machine turnings, that are unlikely to contain a 

nuclear gauge are irrelevant to risk. Only the 

commodities of scrap metal that are relevant to 

risk need to be taken into account by Element 13. 

The lowest branch of Element 13 can be used to 

ascertain what might not be taken into account by 

the risk analysis. The production of steel is 

reported by the U.S. Geological Survey; the 

amount of steel that is reported through a survey 

can be determined-the difference is what has 

not been analyzed. 

An assumption is are made about the supply of 

scrap metal to represent the consumption of scrap 

metal in the analysis of monitor configurations. 

Assumption: The probability of a mill being at 

risk for radioactive material in the recycling 

stream is proportional to the amount of scrap 

metal that is consumed by the mill. Basis: See 

Section 3.2.3.

93 NUREG-1669
7: STEEL MILLS

Element 

13: Configuration of radiation monitors 

(e.g., portal, charge bucket, radiation 

gauges) at steel mills (page 93)

This figure continues 

the risk element 

sequences in scrap 

metal consolidation 

illustrated by Figure 28 

(page 65). I

No Radiation Monitors 

Only Portal Monitors 

Another Configuration of Radiation Monitors

Notes 

Determine consequences and estimate risk. 

Analysis of portal monitors in Figure 42 

(page 96). 

Analysis of steel mills with the same 

configuration of radiation monitors (no 

specific figure given).

Unaccounted Steel Mills Speculate risk based on the risk at accounted 

steel mills and the amount of scrap going to 

the unaccounted mills. 

Speculate risk based on the risk at accounted 

steel mills and the amount of scrap going to 

the foundries and forges.

Foundries & Forges

Other Speculation.

Figure 41 Analysis of the risk elements for the configuration of radiation monitors at steel mills. LEGEND: Single black lines are 

sequences. An arrow (>-) indicates that a sequence continues in a subsequent figure (e.g., Figure 42). A dot (0) indicates that a sequence 

is unresolved; it continues, but is not further developed.

NUREG-1669 94
7: STEEL MILLS

Figure 42 illustrates the risk elements at the 

entrance to a steel mill. Single black lines are 

sequences of risk elements. For clarity, common 

elements of the sequences are illustrated in the 

inset; some of these sequences discontinue at -A), 

then continue in the inset at -A); other such 

sequences discontinue at -B), then continue in 

another inset at -B). An arrow (>-) indicates that 

a sequence continues in Figure 43. A dot (0) 

indicates the end of a sequence. An open dot (0) 

indicates that a sequence is unresolved; it 

continues, but is not developed further. Hazard 

terms are from the US. Code of Federal 

Regulations (Ref. 9). A gray box (E) indicates 

that a concern is present in Elements 14 through 

23 of a particular sequence. A white box (0) 

indicates that a concern is not present. The danger 

to life and property are as follows: 

"* When regulators are notified of a rejected 

load, sufficient controls are in place to remove 

danger to life and property. In these cases, 

sequences usually terminate. When only the 

supplier is notified, a potential remains for the 

load to be inappropriately addressed, 

improperly disposed, or sent to another steel 

mill where it might not be detected. The 

shutter of a gauge may be open or the sealed 

source may be dislodged, presenting a danger 

to life. If no one is notified, the load can go 

anywhere; nothing more can be said and the 

sequence remains unresolved. 

"* A reworked load gives rise to opportunities to 

find and secure a gauge. But if BC is also in 

a load, a radiation alarm may be attributed to 

it instead of a gauge; the gauge may be 

missed, thus, the sequence continues. A 

danger to life remains. 

"* If scrap metal is not scanned for radiation, 

there may be a danger to life. The shutter of a 

gauge may be open. The source may be 

dislodged.

E Between Elements 14 and 23, there is no 

danger to property. Nothing is happening to 

breach a sealed source because scrap metal is 

being transported into a mill, not processed. 

Element 14: Scanning Scrap Metal for 

Radiation (Figure 42) 

Scrap metal may not be properly scanned for 

radiation, even though a mill has a radiation 

monitor, for many reasons: 

"* The monitor is malfunctioning. 

"* The settings on the monitor have been altered 

to reduce the frequency of false alarms. 

"* The monitor has been deactivated because the 

alarms are annoying. 

In Element 14, the phrase proper scanning also 

includes a proper response to a radiation alarm; 

the alarm is not ignored because it is annoying or 

arbitrarily attributed to BC. 

Determining the availability of a monitor system 

at a given location is fraught with difficulties. 

Records of the out-of-service time are unlikely to 

be kept by the mills. Monitor vendors may have 

some records of unavailability through 

telecommunication links with their monitoring 

equipment, but not all monitors are linked to their 

vendors. Even if such information were available, 

associating it with a given site is unreasonable 

because vendors may be reluctant to disclose the 

identity of their customers and the survey for 

collecting information from steel mills is 

anonymous. Another difficulty in obtaining 

information about the availability of monitors is 

that deactivating monitors and ignoring alarms are 

sensitive matters; reliable responses from a survey 

would be doubtful.

NUREG-1669

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7: STEEL MILLS

Elements

14: Scanning scrap metal for radiation at the entrance of steel mills (page 95) 

15: Strategy to monitor loads of scrap metal for radioactive material (page 97) 

16: Alarm on the first pass through a monitor station, T' (page 97) 

17: Alarm on the second pass through a monitor station, Tl2nd lIst) (page 97) 

18: Alarm on the third pass through a monitor station, 'F(3rd 1 2nd) (page 97) 

19: Response when a vehicle causes 

a radiation alarm (page 97) 

20: Controls on a load rejected because of 

a radiation alarm, not reworking (page 98)

21: Probability of BC given a 

source is also in the load (page 98) 

22: Confirm the cause of a 

radiation alarm (page 98) 

23: Controls on a load rejected 

because of reworking 

"(pT¶ 98)

Hazards 

in Elements 

14 Through 23 

Danger to Life 

Danger to Property

U ............................. ...................................... 

IB)-

Figure 42 Analysis of the risk elements at the entrance of steel mills. LEGEND: Single black lines are sequences of risk elements. For clarity, common elements of the sequences are illustrated in the inset; some of these sequences discontinue at-A)then continue at-A); other such sequences 

discontinue at-B), then continue at-B). An arrow (>) indicates that a sequence continues in Figure 43. A dot (4) indicates the end of a sequence. 

An open dot (0) indicates that a sequence is unresolved; it ends here, but not further developed. A black box (I indicates that a concern is present 

in Elements 14 through 23 of a particular sequence. A shaded box (M) indicates that a concern might be present. A white box (E) indicates that a concern is not present. Hazard terms are taken from the US. Code of Federal Regulations (Ref. 9).

NUREG-1669

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7: STEEL MILLS

More difficult to take into account than the 

unavailability itself is the use of the monitors at a 

given mill: 

"a A mill may draw on its inventory, not 

accepting additional scrap metal, while its 

monitor station is inoperative. 

"* Another mill may have several monitors; 

when one is out of service, vehicles are sent 

through the other monitor. 

" Still another mill may have several monitors, 

but they are dedicated, one to trucks, the other 

for railcars. Rerouting scrap metal from a 

malfunctioning monitor may be impractical. 

"* Some mills that are closely tied to their 

supplier may take the risk of using unscanned 

scrap metal, relying on the radiation 

monitoring done by their supplier. 

For a risk analysis, the issue is not the availability 

of the monitor nor the factors giving rise to scrap 

metal entering the mill without being properly 

scanned. The issue is the amount of scrap metal 

that is correctly scanned for radiation. The survey 

asks for an educated guess about the fraction of 

scrap metal that is correctly scanned for radiation. 

Elements 15 through 18: Monitoring Strategies 

and Confirming a Radiation Alarm (Figure 42) 

Three practices of sending a vehicle through a 

radiation monitor station are typically found in the 

steel industry (see Section 7.6): 

"* One-pass strategy. If there is a radiation 

alarm, then it is addressed according to the 

practices at a given mill. The one-pass 

strategy is represented in Figure 42 by 

Element 16. 

"* Two-pass strategy. If the first pass results in 

an alarm, then the vehicle is sent through the 

monitor station again. The two-pass strategy 

is represented in Figure 42 by Elements 16 

and 17.

N Three-pass strategy. If the first pass results in 

an alarm and the second pass occurs without 

an alarm, then a third pass is used to confirm 

either the first or the second pass. If it 

confirms the first pass, then the alarm is 

addressed. If it confirms the second pass, then 

the load enters the mill. The three-pass 

strategy is represented in Figure 42 by 

Elements 16, 17, and 18. The uppermost 

branch of Element 17 is undeveloped because 

the second alarm confirms the first alarm, 

making a third pass unnecessary. Element 17 

is developed in the case where an alarm 

occurs on the first pass and does not occur on 

the second pass. 

One could argue that the monitoring strategy is of 

no concern; the only concern is the final outcome 

(i.e., accept, reject, or rework a load). While this 

treatment simplifies the risk analysis, it also limits 

the usefulness of the results. This study is an 

analysis of risk, not just an assessment. While the 

risk could be determined without considering the 

number of passes through a monitor station, the 

understanding of the risk estimates would be 

hampered. The empirical rejection probability 

will depend on the monitor strategy, the monitor 

characteristics, and the composition (metal, BC, 

sealed sources) of the load. An analysis is desired 

that separately accounts for these aspects. 

Element 19: Response When a Vehicle is 

Rejected Because of a Radiation Alarm (Figure 

42) 

If the monitoring does not detect radiation, then 

the load is considered to be free of radioactive 

material and is accepted. If a radiation alarm 

suggests that radioactive material is present, then 

the load is either rejected or reworked. Several 

practices of reworking a load are found as 

discussed in Section 7.4. The various ways that a 

load can be rejected are not delineated; the only 

issue at this point is that a load is rejected.

97 NUREG-1669
7: STEEL MILLS

Element 20: Controls on a Load Rejected 

Because of a Radiation Alarm (Figure 42) 

Notifying local authorities ensures to various 

degrees that disposal is properly done. Sometimes 

regulators are called. Other times, police may be 

called if a truck driver refuses to remain at the mill 

until the reason for a radiation alarm is 

determined. Still other times, no one is called. 

Lacking controls means that a truck can go 

anywhere, as sometimes has been known to occur; 

an analogous situation does not exist on railroads 

because arrangements must be made with a carrier 

to have the rail car removed and sent to a specific 

destination. Some possibilities of how a nuclear 

gauge might be improperly disposed are discussed 

in Section 7.4. These possibilities could not be 

determined directly through a survey (see Section 

4.3) The responses can be aggregated into 

distributions to assign to Element 20. 

Element 21: Probability of Benign 

Contamination Given a Radioactive Source 

(Figure 42) 

Many types of radioactive material can be 

detected with a radiation monitor. The plastic 

detectors of the monitors are unable to 

discriminate between a radioactive source and BC. 

Essentially, the only way to confirm the cause of 

an alarm is to rework the scrap metal in some way. 

The coincidence of BC with a nuclear gauge 

cannot be definitively analyzed. Instead, it is 

treated in a way to bound its effect on risk. Such 

an analysis need be done only at the portal 

monitors, not at later points of the risk model, 

such as at the charge bucket. A charge bucket 

itself will not have BC when it is monitored 

because radiation alarms would always be 

occurring. A mill owns the charge bucket and will 

have it cleaned. The same can be said when 

monitoring vehicles bringing scrap metal from the 

storage area to the furnace. 

Element 22: Confirm the Cause of a Radiation 

Alarm (Figure 42) 

A radiation alarm may occur for many reasons, 

including the presence of a nuclear gauge or many 

forms of BC. Monitors with plastic detectors are

unable to discriminate sources of radiation. 

Various practices can be found in the steel 

industry to confirm the cause of an alarm: 

"n A load of scrap metal will not be accepted at 

a mill unless it can pass through a monitor 

station at the mill without causing an alarm. 

When a rejected load is returned to the 

supplier, it will pass through a portal monitor 

of the scrap yard. The alarm at the scrap yard 

may not occur for unknown reasons. But the 

lack of an alarm at the scrap yard may be 

irrelevant in light of the attitudes at the 

mill- monitor at the mill is the basis for the 

decision. 

"* A survey meter may be used to scan a vehicle. 

If the alarm of the portal monitor can be 

attributed to a structural member in the cargo 

hold of the transporting vehicle or to pipe 

scale on the scrap metal, then the load may be 

accepted. 

"* The load is reworked. Because of the 

difficulty in taking a load apart, sometimes a 

load will be partially reworked. 

The only way of ensuring that a nuclear gauge is 

not in a load is to rework the load. Without 

knowing for sure, an implicit assumption is 

made-there is only one source of radiation in 

the load. Most of the time, this assumption is 

correct. But an assumption should not be made on 

the points of a matter that are at issue, in this case, 

the radioactive material in a load. Also, the 

financial consequences for being wrong are large. 

The other ways of "confirming" the cause of a 

radiation alarm do not confirm in and of 

themselves, but only because the implicit 

assumption happens to be correct for the 

suspected load of scrap metal. 

Element 23: Controls on a Load Rejected 

Because it Was Reworked (Figure 42) 

Reworking a load has different ramifications at 

different mills. Sometimes, reworking a load is 

tantamount to accepting the load and whatever 

radioactive material it may contain. Other times, 

a load is not fully accepted until a radiation alarm

NUREG-1669 98
7: STEEL MILLS

has been fully investigated. Because ramifications 

for reworking a load differ, the probabilities of 

what controls would happen differ. 

Figure 43 illustrates the risk elements at the 

charge bucket of a steel mill. Single black lines 

are sequences of risk elements. For clarity, 

common elements of the sequences are illustrated 

in the inset; some of these sequences discontinue 

at -A), then continue in the inset at -A); other 

such sequences discontinue at -B), then continue 

in another inset at -B). An arrow ())"indicates 

that a sequence continues in Figure 44. A dot (0) 

indicates the end of a sequence. An open dot (0) 

indicates that a sequence is unresolved; it 

continues, but is not developed further. Hazard 

terms are taken from the US. Code of Federal 

Regulations (Ref. 9). A gray box (M) indicates 

that a concern is present in Elements 24 through 

27 of a particular sequence. A white box (0) 

indicates that a concern is not present. The danger 

to life and property are similar to those discussed 

in Figure 41, the difference here being that a mill 

now owns the scrap metal and cannot simply 

reject a load. The following can be said about the 

sequences: 

" If a nuclear gauge is detected and regulators 

are notified, the danger to life is removed; it 

will either be properly disposed or properly set 

aside (temporarily). If only the supplier is 

notified, there is a chance for danger to life 

and the sequence remains unresolved. 

"* The sequences other than disposal or set aside 

are unresolved; here, information is limited by 

what can be reliably collected with a survey of 

the steel industry. If a regulator is notified, a 

gauge will be properly secured. If only a 

supplier is notified, there is a chance that it 

will not be properly secured, giving rise to a 

danger to life. 

"* If scrap metal is not scanned at the charge 

bucket, there may be a potential for nearby

employees to be exposed. The exposure may 

be brief if the nuclear gauge goes into the 

charge bucket. The exposure may be longer if 

it should happen to miss the charge bucket, 

falling to the ground, when scrap metal is 

loaded; if a radiation monitor is present, then 

the exposures may be brief because an alarm 

would activate. 

E There is no danger to property between 

Elements 24 and 27 because scrap metal is 

only being moved. 

Elements 24 Through 27: Charge Bucket/Box 

(Figure 43) 

The analysis of charge bucket monitoring is 

similar in many respects to the analysis of the 

portal monitors and scanning a vehicle after 

reloading. The analysis of the charge bucket 

monitoring is illustrated in Figure 43. For many 

reasons, not all scrap metal is scanned (Element 

24). Whether being scanned while being loaded 

or upon completion of the loading, the shielding 

from the scrap metal gives rise to a probability of 

an alarm of the radiation monitor (Element 25). 

At the charge bucket, the scrap metal is owned; it 

cannot be returned to the scrap dealer if 

radioactive material is found. Radioactive 

material can be disposed, set aside, or addressed in 

other unspecified ways (Element 26). The 

controls placed on the radioactive material give 

varying levels of assurance of proper disposal 

(Element 27). 

Author's Note 

The risk elements in rescanning scrap metal in 

the yard of a steel mill are analogous to those in 

the analysis of the charge bucket (Figure 43). 

For brevity, the risk elements for the yard are 

not discussed. Instead, the discussion resumes 

at the charge bucket.

99 NUREG-1669
7: STEEL MILLS

Elements

24: Scanning scrap metal for radiation at the charge bucket (page 99) 

25: Probability of an alarm, T2,,d (page 99)

26: Response when a charge bucket 

monitor alarms (page 99) 

27: Controls on radioactive 

material found at the charge 

bucket (page 99)

Hazards 

in Elements 

24 Through 27 

Danger to Life 

Danger to Property

Yes A) 

This figure 

continues from Scanned 

Figure 42 (page 96) No 

at any risk element B) 

sequence where a 

gauge is (or can be) 

missed. SNot Scanned B)

n B- . . ....

Figure 43 Analysis of the risk elements at the charge bucket of steel mills. LEGEND: Single black lines are sequences of risk elements. For clarity, 

common elements of the sequences are illustrated in the inset; some of these sequences discontinue at -A) then continue in the inset at-A); other 

such sequences discontinue at -B1 then continue in the inset at-B). An arrow (>) indicates that a sequence continues in Figure 44. A dot (0) 

indicates the end of a sequence. An open dot (c) indicates that a sequence is unresolved; it continues, but is not further developed. A black box 

(U) indicates that a concern is present in Elements 24 through 27 of a particular sequence. A shaded box ( U ) indicates that a concern might be 

present. A white box (0) indicates that a concern is not present. Hazard terms are taken from the U.S. Code of Federal Regulations (Ref. 9).

NUREG-1669 100
7: STEEL MILLS

A difficulty in the analysis is determining the 

composition of the scrap metal for evaluating the 

detection probability. The blend of scrap metal 

commodities of the scrap metal going from the 

storage area to the scrap bay or yard may change 

as scrap metal is sorted before being loaded into 

the charge bucket. But in the long run, limits on 

the changes occur because scrap metal does not 

accumulate at the storage area- it is all used. 

These changes are beyond the resolution of the 

risk calculations and the capability to collect 

information through a survey. Hence, the 

composition of the scrap metal entering a 

monitored charge bucket is studied in the risk 

analysis by exploring the effects on risk of 

plausible compositions. The difficulty can be 

addressed either by trying bounding values or by 

making an assumption. 

Assumption: Forthe most part, the commodities 

of the scrap metal going into the charge bucket 

or box are similar to the commodities coming 

into the mill. Although sorting and blending are 

done at.the yard, single commodities are used in 

bulk. Basis: The principal investigator observed 

charge buckets being filled. Also, scrap metal 

does not accumulate in the storage area because 

there are costs associated with storing and 

handling deferred scrap metal. 

Figure 44 illustrates the risk elements of products 

and byproducts at steel mills. Single black lines 

are sequences of risk elements. A dot (0) 

indicates the end of a sequence. An open dot (0) 

indicates that a sequence is unresolved; it 

continues, but is not developed further. Hazard 

terms are taken from the U.S. Code of Federal 

Regulations (Ref. 9). A black box (N) indicates 

that a concern is present in Elements 28 through 

35 of a particular sequence. A shaded box (Z) 

indicates that a concern might be present. The 

danger to life and property are as follows:

"* Melted '"Cs poses a small danger to life; 

employees at the mills may be exposed to 

small amounts of contaminated furnace dust 

that escapes the ventilation system of the melt 

shop. Property damage, in the form of lost 

production because equipment has to be 

decontaminated, occurs if radiation is 

detected. But radiation may not always be 

detected; the possibility for this is discussed in 

Section 2.3. 

" Melted 6

"Co poses a small danger to life for 

two reasons. First strong sources in nuclear 

gauges (a few curies) will be diluted in many 

tons of steel. Second, contaminated steel 

shields itself. The danger to life is not zero. 

Unnecessary exposures to low-level radiation 

will occur both at the mills and, for a longer 

time, to the public. Because steel is 

contaminated by 6'Co, property damage 

occurs. As in the case of '"Cs, this type of 

property damage does not "occur" unless 

radiation is detected. 

"* Little is known about the phenomena when 

241Am is melted; nothing definite can be said, 

though there is the belief that it will reside in 

slag. There may be a danger to life. Property 

damage, taking the form of contaminated 

equipment, occurs. As with '3"Cs and 60

Co, 

property damage does not "occur" unless 

radiation is detected. 

Element 28: Radionuclide Melted in Furnaces 

(Figure 44) 

Three types of radioactive material commonly 

found in nuclear gauges are '17Cs, 6°Co, and 241

Am. 

Cesium vaporizes and adheres to furnace dust. 

Although cobalt forms an alloy with steel, furnace 

dust and slag are also contaminated (Ref. 11) 

because these byproducts contain steel. 

Americium is treated as if it concentrates in slag. 

Element 28 of Figure 44 is the relative prevalence 

of gauges containing '37Cs, 6°Co, and 241Am.

101 NUREG- 1669
7: STEEL MILLS

Elements

28: Radionuclides ('37Cs, 6"Co, and 241Am) melted in a 

furnace (page 101) 

29: Monitoring equipment for test pieces is capable of 

detecting dilute "°Co in heats (page 103) 

30: Level or thickness monitoring with 

a radiation gauge during production (page 103)

31: Scanning steel product for radiation 

(page 103) 

32: Scanning furnace dust for radiation 

(page 104) 

33: Scanning slag for radiation 

(page 104) 

34: Contamination steel 

beyond mills (page 104)

Hazards 

in Elements 

28 Through 34

getting Danger to Life 

Danger to Property

I 

I

Not 

Scanned

Figure 44 Analysis ofthe risk elements at product and byproduct monitoring at steel mills. LEGEND: Single black lines are sequences of risk 

elements. A dot (0) indicates the end of a sequence. An open dot (0) indicates that a sequence is unresolved; it continues, but is not further 

developed. A black box (U) indicates that a concern is present in Elements 28 through 34. A shaded box (M) indicates that a concern might 

be present. A white box (0) indicates that a concern is not present. Hazard terms are taken from the US. Code of Federal Regulations (Ref. 

9).

NUREG-1669

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7: STEEL MILLS

The "'Cs, 60

Co, 241

Am prevalence ratio assigned to 

Element 28 would be most easily determined as 

the prevalence of the gauges that are distributed 

by the gauge vendors. Radionuclides may not be 

moving in this ratio through the recycling stream, 

for example, because some radionuclides are 

easier to detect in the recycling stream than others; 

hence, some gauges may be more selectively 

removed from the recycling stream than others. 

The selection can be taken into account in two 

ways: relative to Element 1, postulate changes in 

the prevalence ratio for Element 28; before 

Element 1, the prevalence of gauges containing 

11'Cs, 'Co, and "4Am can be determined 

separately and risk can be estimated for each 

group of gauges. 

Element 29: Scanning Heats for Radiation 

(Figure 44) 

Element 29 branches from the middle branch of 

Element 28, which represents 6

`Co because cobalt 

forms an alloy with steel. Cesium does not form 

an alloy with steel, hence, Element 29 does not 

branch from the upper branch of Element 28. The 

extent to which 241

Am will reside in steel is poorly 

understood, hence, as illustrated in Figure 44, 

Element 29 does not branch from the lower branch 

of Element 28. Figure 44 is to explain concepts; 

modifications can be made as more information 

about americium becomes available. 

Element 29 represents the capability of the units 

for monitoring test pieces to detect contaminated 

steel. The element is used to bound risk estimates, 

postulating two cases to bound the effect on 

risk- always detected (probability of detection is 

one) and never detected (probability of detection 

is zero). The survey gives only a clue as to what 

the probability may be, but because it is a facet of 

risk, it must at least be acknowledged. 

Elements 30: Level or Thickness Gauges 

(Figure 44) 

Radiation gauges that are in the process line are 

represented by Element 30, which is developed 

when contamination is missed when monitoring 

the test pieces (Element 31). Element 31 is 

undeveloped when contaminated steel is detected

by scanning test pieces because further processing 

has ceased. 

A prohibitive amount of information about the 

characteristics of the radiation gauges and the 

arrangement of radiation gauges would be needed 

to evaluate Element 30. Nevertheless, because the 

element is a method for detecting melted 

radioactive material in steel, it is a facet of risk 

that needs to be taken into account. Element 30 is 

treated to bound its effects on risk. 

Elements 31: Scanning Steel Product 

(Figure 44) 

Element 31 represents steel product being scanned 

for radiation as it is transported in trucks or by rail 

out of the mills. The probability of detection is 

represented in a simple way, unlike the monitoring 

of scrap metal, where the heterogeneity of a load 

and the transporting vehicle shield radioactive 

material that itself may be in a highly shielded 

holder. In a steel product, 60

Co in the steel would 

be dispersed, bringing the radioactive material 

within view of a detector. Because of the 

dispersion, the concepts of detection areas 

developed in Section 7.5 do not apply here. The 

notion of the monitoring strategy (see Section 7.6) 

is a moot point; given that there is enough 

radioactive material to detect, the radiation will, 

for most concerns, always be or never be detected. 

The same is not true of the gauges in the scrap 

metal. The fixed nuclear gauges of concern have 

enough radioactive material to be detected; the 

problem is the shielding from the housing, the 

vehicle, and the scrap metal. 

Assumption: If steel product is contaminated, 

then the probability of detecting the 

contamination with a radiation monitor is one. 

Basis: Steel product is homogeneous. The 

composition of steel does not change as steel is 

tapped from a furnace. 

The assumption reduces the analysis product 

monitoring to the fraction of product that is 

scanned and unscanned; if steel product is 

scanned, then radioactive contamination will be 

detected.

103 NUREG-1669
7: STEEL MILLS

Element 32: Scanning Furnace Dust for 

Radiation (Figure 44) 

The element represents the fraction of the dust that 

is scanned, given that monitoring is done. The 

element is relevant for both 1

37

Cs and 6Co. The 

low volatility of 137Cs driving it from molten steel 

where it condenses on furnace dust has been 

discussed. Though 'Co forms an alloy with steel, 

furnace dust contains iron; this explains the 

contaminated furnace dust reported in Reference 

11. The contamination will be dispersed; hence, 

the same assumption and simplification given for 

Elements 30 and 31 with regard to product 

monitoring are made in the analysis of furnace 

dust monitoring. 

Element 33: Scanning Slag for Radiation 

(Figure 44) 

As in the analysis of product monitoring 

(Elements 30 and 31) and furnace dust (Element 

32), here too, in the case of slag monitoring, the 

detection probability is treated as being one if the 

radioactive material is at all detectable. Element 

33 is developed for both 2" 1Am and 'Co. Also, 

because the contamination will be dispersed, the 

same assumption and simplification made with 

regard to product monitoring are made here. 

Element 34: Contaminated Steel Getting 

Beyond Mills (Figure 44) 

Contaminated steel has gotten beyond mills and 

into the public domain. Reference 1 discusses the 

first time this was known to occur. Reference 11 

and the box in Section 7.4 entitled "An Incident of 

Radioactive Scrap Metal" suggests a potential for 

contaminated material to get into the markets.

7.8 Sources of Information 

Tables 8, 9, and 10 summarize the sources of 

information for developing the inputs of the steel 

mill analysis. Along the top are the elements 

corresponding to the elements in Figures 41, 42, 

43, and 44. Along the vertical are classes of 

information (see Section 4.2). A shaded box 

indicates that information is available; numbers 

refer to survey questions (see Appendix C); letters 

refer to notes following the table. A white box 

indicates that a particular class of information for 

a particular element is unavailable. 

7.9 Observations and Insights 

1. Research is needed to characterize the 

.commodities of scrap metal and to determine 

the detection probability for each commodity, 

not just to determine the detection capabilities 

of specific systems as has been done. With a 

characterization of the commodities, the 

capabilities of equipment could then be 

predicted without having to conduct a field 

trial each time the technology changes. Field 

trials may still be necessary to validate 

predictions, but as yet, there is sparse 

quantitative basis for making predictions.

Author's Note 

Observations and Insights resume on page 108 

after Table 10.

NUREG-1669 104
7: STEEL MILLS 

Table 8 Sources of information supporting the analysis of risk elements in monitors atthe entrance of steel mills (Figures 41 and 42). LEGEND: 

A shaded box indicates that information is available; a number in a shaded box indicates a question of the survey in Appendix C and a letter indicates a note following the table. A white box indicates unavailable information. Degrees of information are discussed in Section 4.2. 

Elements 

13: Configuration of radiation monitors (e.g., portal, charge bucket, radiation gauges) at steel 

mills (page 95)

Degrees 

of Source 

Information of 

(Section 4.2) Information 

1st Survey 

1 (page 135 

2nd Survey 

(page 135) 

3rd Plausible ( judgments

14: Scanning scrap metal for radiation at the entrance of a steel mill (page 97) 

15: Strategy to monitor loads of scrap metal for radioactive material (page 97) 

16: Alarm on the first pass through a monitor station, YI (page 97) 

17: Alarm on the second pass through a monitor station, IF (2nd[ 1st) (page 97) 

18: Alarm on the third pass through a monitor station, IP (3rdl2nd) (page 97) 

19: Response when a vehicle causes a radiation alarm (page 97)

20: Controls on a load rejected because a radiation alarm, 

not reworking (page 98) 

21: Probability of BC given a source is also in the los 

(page 98) 

22: Confirm the cause of a radiation alarm (page 

23: Controls on a load rejected because of re 

(page 98)

id 

98) 

working

Notes on Table 8

A. The analysis of the steel industry requires that the steel mills be 

grouped according to the location of radiation monitors. Each group 

is homogeneous, having mills with radiation monitors in the same location(s). Questions 2, 6, 7, 10, 12, 20, 21, 25, 26, 29, 34, 39, 40, 

43,44,47, and 48 determine the location of radiation monitors. The 

replies to Questions 3 and 4 are used to emphasize configurations 

according to the amount of risk scrap metal that they consume; 

Reference 1 indicates that mills producing carbon steel are more at 

risk than mills producing stainless steel. 

B. The number of times that a vehicle passes through the monitor 

station influences the risk of nuclear gauge entering the mill (see 

Section 7.6). 

C. The placement of detector panels is one of many factors that 

determines the probability of detecting radioactive material in a load 

of scrap metal (see Section 7.5). 

D. A mill is at higher risk of receiving radioactive material in 

proportion to the amount of scrap metal that is not scanned for 

radiation. Anecdotal information suggests that radiation monitors 

are sometimes turned off because the alarms are annoying or activate 

for superfluous reasons.

E. Question 16 determines the basis for rejecting a load of scrap metal. At some mills, a radiation alarm is sufficient for rejecting; at 

other mills, an alarm serves as a basis for further investigation. Questions 17 and 18 determine the controls that are placed on a load 

that is going to be rejected; in Question 17, the rejection is based 

only on an alarm (the load is only suspected of containing a nuclear 

gauge because the alarm may be due to BC); in Question 18, the 

rejection is based on reworking the load (a nuclear gauge was found). 

Question 14 refers scrap metal that hasnot been unloaded; Question 

19 refers to scrap metal that has been unloaded. 

F. Speculation may be done, based on Reference 1, and used in 

calculations to bound risk estimates.

OTHER NOTES: Questions 1, 38, and 39 are used to support the 

inferences discussed in Section 2.5. Question 53 is used to verify the 

burden estimates made during pilot tests.

105 NUREG-1669
7: STEEL MILLS 

Table 9 Sources of information supporting the analysis of risk elements in yard and charge bucket monitors at steel mills (Figure 43). LEGEND: 

A shaded box indicates that information is available; a number in a box indicates a question of the survey in Appendix C, and a letter indicates a 

note following the table. A white box indicates unavailable information. Degrees of information are discussed in Section 4.2. 

Elements 

Monitoring in the Yard

Scrap metal going directly to the melt shop area (page 99, "Author's Note") 

Scrap metal rescanned without unloading (page 99, "Author's Note") 

Scrap metal rescanned after reloading (page 99, "Author's Note") 

Monitor strategy (page 99, "Author's Note") 

Alarm on passing through a monitor station, qP2d (page 99, "Author's Note") 

Actions following an alarm (page 99, "Author's Note")

Charge Bucket Monitoring 

Configuration of detectors around the charge bucket (page 93) 

Mode of scanning the charge bucket (page 93) 

24: Scanning scrap metal for radiation at the charge 

bucket (page 99) 

25: Probability of an alarm, P,2d (page 99) 

26: Response when a charge bucket monitor 

alarms (page 99) 

27: Controls on radioactive material 

found at the charge bucket (page 99)

1st Survey (page 135) 

Survey 

2nd (page 13 5 ) 

3rd Plausible 3r judgments -

wwwB --7iF wThJh

Notes on Table 9

A. Question 12 determines whether or not the secondary monitoring 

is done. Question 21 determines whether or not secondary 

monitoring is done after scrap metal is reloaded from the storage 

area. 

B. The number of times that a vehicle passes through the monitor 

station influences the risk of a nuclear gauge entering the mill (see 

Section 7.6). Here, Question 23 refers to the strategy after 

reloading. 

C. The question establishes the size of the transporting vehicle in 

sufficient detail for shielding calculations. In the context of a risk 

analysis, the difference between cross-sectional areas of tri-axle (or 

larger) trucks and railcars is insignificant. 

D. The location of the detector panels will, in part, determine the 

detection areas in a load of scrap metal (see Section 7.5). 

E. The mode of scanning a charge bucket influences the detection 

probability. Monitoring a charge bucket as it is filled allows small 

amounts of scrap metal to be scanned; a stationary bucket allows for 

more radiation to reach a detector than when the bucket is moving. 

F. The detection areas for the detection probability are determined 

from Questions 25, 26, 27, and 28.

G. Question 15 distinguishes between the two routes shown in 

Figure 42: one route is to the storage and processing area, the other 

route is to the scrap bay/yard next to the melt shop. 

H. The difference between monitoring again after reloading and 

monitoring without reloading is discussed in Section 7.6. 

I. By this time in the recycling stream, the scrap metal, and 

whatever may be in the scrap metal, is owned by the mill. 

Radioactive material cannot simply be returned to the scrap dealer. 

The second part of the question asks what controls are placed on the 

material. 

J. Charge bucket monitors are not always operational. The loading 

process is violent and the detector panels are fragile. The protection 

over the panels must be minimal and the detectors must be as close 

as possible to the charge bucket to take advantage of detection 

capabilities. Detection panels are sometimes damaged while the 

charge bucket is being loaded. A monitor can be offto the side of its 

mountings for no apparent reason. Scrap metal that is not scanned is 

more risky than scrap metal that is scanned.

NUREG-1669

Degrees 

of 

Information 

(Section 4.2)

Source 

of 

Information

106
7: STEEL MILLS 

Table 10 Sources of information supporting the analysis of risk elements in product and byproduct monitoring at steel mills (Figure 44). LEGEND: 

A shaded box indicates that information is available; a number in a shaded box indicates a question of the survey in Appendix C and a letter indicates a note following the table. A white box indicates unavailable information. Degrees of information are discussed in Section 4.2. 

Elements

28: Radionuclides ('"Cs, 'Co, and "AAm) melted in a 

furnace (page 101)

Source 

of 

Information

29: Monitoring equipment for test pieces is capable of 

detecting 'Co levels expected in a heat (page 103) 

30: Level or thickness monitoring with a radiation gauge during production (page 103) 

31: Scanning steel product for radiation 

when leaving a mill (page 103) 

1 121 ýrA - 1 .- .JLo. oUlk U! alUtell%.4 UU3L UL at 13 i .slsannU 

for radiation (page 104) 

33: Scanning slag for radiation 

(page 104) 

34: Contaminated steel gettii 

beyond mills (page 104) 1

/Survey 1st (page 135) 

2nd Survey 

K (page 135) 

3rd Plausible 

( judgments

Notes on Table 10

A. Question 35 gives an indication of general practices and 

equipment. There is also an implication, although vague, as to the assurance that the monitoring is done. For example, when 

monitoring is done with a desktop unit, the sample of a heat may 

have been inadvertently skipped because the laboratory technician was fatigued or distracted. Question 36 is used to suggest the extent 

to which radioactive material that forms an alloy with steel can be 

detected. 

B. Radiation gauges in the process line may act as a form of 

monitoring of the steel product, thus possibly giving assurance that 

contaminated steel will not leave the mill site. 

C. Question 49 indicates the potential for contaminated steel to be 

detected as it leaves a mill. 

D. If furnace dust is not scanned, then a melted '37Cs source will go undetected. Question 40 is used for a subjective evaluation of the 

monitoring effectiveness. When weather is inclement, monitoring 

with a survey meter may not be done or an alarm from a portal 

monitor may not be investigated. Question 41 is used to suggest the 

potential for contaminated furnace dust to leave a mill site. Some

mills have strict policies about monitoring everything entering and 

leaving the site. Other mills may not be so strict. 

E. Slag may be used for road material or processed to recover iron. 

Question 44 suggests the rigor of the monitoring; Question 45 

indicates the potential for contaminated slag to leave a mill. 

F. Reference 1, records, and opinions from regulators may be used 

to determine plausible values of the relative prevalence of '"Cs, 60Co, and 241

Am. 

G. The concentration of radionuclides in a furnace suggests the 

extent to which radiation gauges will detect melted radioactive 

material. Furnaces of different sizes may be used to different extents. 

For example, in a small furnace at a facility that is seldom used, the 

concentration of radioactivity in the melted steel would be high, but 

the chance of it being contaminated would be low. 

H. Little is known about the extent to which contaminated steel has 

gone beyond mills into the markets. Only plausiblejudgments, based 

on a few reported incidents, are possible.

NUREG-1669

Degree 

of 

Information 

(Section 4.2) ng

107

ýA

71C -ILY Vq 40. 4-4, 

49 41 45
7: STEEL MILLS

2. Figure 32 has important implications for the 

scrap yards and steel mills. If Area 2 is small, 

then the practice of passing a load through a 

monitor station multiple times is of no 

consequence. A nuclear gauge in Area 1 will 

always be detected. A nuclear gauge in Area 

3 will never be detected, no matter how many 

times a load is passed through the monitor 

station. If Area 2 is large, then there is a 

chance that a nuclear gauge will be detected, 

and hence, multiple passes through a monitor 

station are useful. 

3. Highly sophisticated monitors alone cannot be 

entirely relied on to detect radioactive 

material in scrap metal loads. 

4. Proper use of monitors is important in 

ensuring a high probability of rejecting a load 

when radioactive material is present. 

5. If the primary concern when monitoring scrap 

metal is detecting sealed sources, then the 

best of the strategies considered is the 

one-pass strategy. The decision to reject or 

accept a load would be based on the first pass 

through a monitor station. If the primary 

concern is false alarms, then the best of these 

strategies is the two-pass strategy. The three

pass strategy is a compromise between the 

one-pass and two-pass strategies. 

6. When 11'Cs is melted, it adheres to the furnace 

dust. Most, but not all, of the dust is collected 

by the ventilation system of the melt shop. 

Some of the dust escapes into the melt shop. 

The amount varies from mill to mill. The 

amount of contaminated dust escaping into

the melt shop is difficult to determine, 

depending on when the sealed source melts in 

relation to when the furnace is open and the 

capacity of the ventilation system to collect 

dust. 

7. When a 6°Co source is melted, the cobalt 

forms an alloy with the steel. The radioactive 

material is at least somewhat diluted in the 

heat. The steel gives self-shielding. The 

furnace gives additional shielding until it is 

tapped. Some 'Co gets into furnace dust, 

some of which escapes the ventilation system. 

8. Little is known about what will happen when "

42

'Am is melted. The current understanding 

is that it will reside mostly in slag. 

9. When a radiation alarm is to be confirmed to 

determine whether or not to allow the load of 

scrap metal into a mill, only reworking the 

load (i.e., by dumping the load and sorting 

through the scrap metal) gives adequate 

assurance about the cause of the alarm. 

Scanning a load with a survey meter and 

attributing an alarm to the rib of a vehicle or 

pipe scale assumes a nuclear gauge is not 

present in the load. Most, but not all, of the 

time, this assumption is correct. However, 

until further study is done, making the 

assumption is inappropriate considering the 

possible consequences (melting radioactive 

material) of being wrong. 

10. Some methods for monitoring test pieces have 

much uncertainty in detecting when 

radioactive material has been melted in a 

furnace.

NUREG-1669 108
8 PUBLIC DOMAIN

8.1 Overview 

Though nuclear gauges are physically a minuscule 

part of a process unit, often the gauges are critical, 

convenient, and irreplaceable for producing high

quality products at competitive prices. But the use 

of gauges also has consequences. People have 

been overexposed to radiation and equipment 

along the recycling stream has been contaminated. 

The public domain is where the risk element 

sequences of the nuclear gauges end. Some 

sequences are short. Other sequences are long. 

All of the sequences end in consequences of some 

kind, from benign to hazardous: 

"N The consequences to health are usually 

expressed in terms of injury, disease, or dose. 

But in the study of nuclear gauges, a surrogate 

measure may be more practical because of the 

complex circumstances in which the 

consequences arise. Also, a gauge that is 

intact is still of concern, even though disease, 

injury, and dose are not occurring, because it 

has a potential to do so. 

"* The consequence to property is often 

expressed in terms of costs. Available cost 

estimates to the steel industry are poorly 

characterized. Little is known about what the 

cost estimates represent; it is unclear whether 

or not the estimates were adjusted to present 

dollars. The predicted damages from melting 

a gauge at an integrated mill lack a firm basis. 

Accurate information, in a form that is suitable for 

a risk analysis, was unavailable for this study. 

8.2 Importance in Risk 

In this study, the public domain is that segment of 

the population in which the net effects to society 

from nuclear gauges are apparent. Most segments 

of the licensees (Section 5), scrap yards (Section 

6), and steel mills (Section 7) are in the public

domain because a worker is a person licensed to 

work with nuclear material (Ref. 9). Although a 

licensee can be a corporation, the definition of a 

worker in Reference 9 refers to only those people 

designated to handle nuclear material. Other 

people in a workplace in which nuclear material is 

used, who are not designated to handle nuclear 

material, are considered the public. These "non

workers" are most of the population in industrial 

facilities. 

Changes in control mechanisms can affect various 

groups within the public domain in various ways. 

A positive consequence is a benefit; conversely, a 

negative consequence is a cost. 

The relation of the public domain to other 

constituents of the risk analysis is shown in Figure 

45.

Figure 45 Topics taken into account in the 

analysis of the public domain. LEGEND: A 

black bullet indicates that a topic is 

comprehensively taken into account. A white 

bullet indicates that a topic is beyond the scope 

of the risk analysis. A gray bullet indicates that 

a topic is briefly taken into account. LEGEND: 

Black bullets indicate that a topic is rigorously 

taken into account in the risk analysis. Gray 

bullets indicate that a topic is briefly taken into 

account. White bullets indicate that a topic is 

beyond the scope of the risk analysis.

109 NUREG-1669
8: PUBLIC DOMAIN

Some portions of the public domain are not taken 

into account: 

"* Transporting a nuclear gauge has negligible 

risk. When a nuclear gauge is transported, the 

gauge is deliberately sent to a specific 

destination, to a person expecting it, in a 

package that can withstand likely accident 

conditions. The delivery systems are reliable 

and usually have means of keeping account of 

packages to ensure that gauges arrive at their 

intended destinations. 

"* Markets (movement of materials and products 

among industries and consumers) are beyond 

the scope of this risk analysis. Their 

complexity precludes a meaningful analysis 

within the resources allocated to this study. 

8.3 Concepts 

Nuclear gauges allow industries to conveniently 

and precisely control processes that otherwise 

would be difficult to control. Although they are 

physically a minuscule part of production, for 

many industries gauges are critical for making 

high-quality products. Other devices measure 

attenuated radiation to control industrial processes 

without using a sealed source. A reasonable 

question to ask is why nuclear gauges are used at 

all. Indeed, radar and x-ray tubes use radiation at 

a lower spectrum energy than sealed source 

gauges containing 1

37

Cs, 6Co, and 241

Am. The 

most popular replacement for a nuclear gauge is a 

radar gauge. However, even a radar gauge has 

limitations. A radar gauge is defeated by foaming 

and buildups in industrial processes and is more 

limited than a nuclear gauge in applications in 

high temperatures and pressures; also, the radar 

waves will pass through materials that have a low 

conductivity without being attenuated for 

Author's Note 

The term public domain is defined in Figure 

45 for use in this risk analysis. It is not a 

statutory term.

measurements. Gauges that use x-rays are less 

precise compared to sealed source gauges because 

the broader (bremsstrahlung) spectrum of x-ray 

radiation is more difficult to measure than the 

relatively narrow spectrum from a sealed source. 

In principle, an x-ray type of device that emits 

gamma rays too would have a broad spectrum that 

hampers measurement; such a device has a 

nonradiological hazard from the high voltage 

needed to produce the gamma rays. The sealed 

source used in a nuclear gauge produces a 

comparatively narrow high-energy spectrum for 

precise measurements. At industrial facilities, 

there have been instances when nuclear gauges 

have been replaced with another type of 

measuring device that in turn, was replaced again 

with a nuclear gauge after a hazardous material 

overflowed a tank. These facilities have found 

that the radiological hazards and regulatory 

burden are often much more acceptable than the 

hazard of an awry industrial process requiring 

accurate and reliable control. At least in the short 

run, nuclear gauges are not only an integral part of 

some process units, but also an irreplaceable part. 

Gauges reliably, accurately, and precisely measure 

thickness, level, density, or consistency of 

materials under a variety of conditions-hot, 

corrosive, dusty, dirty, or humid. Nuclear gauges 

are used in many ways to control industrial 

processes. Some examples of the measurements 

made by the gauges include the following:: 

"* level of steel as it is poured into a caster; 

"* thickness of steel that is rolled into sheets for 

cars, cans, and electronic components; 

"* height of liquid in industrial autoclaves for 

making graphite electrodes used in steel 

minimills; 

"* thickness of coatings on steel used to make 

food cans; 

" thickness of tar in the production of roof 

shingles; 

"* level of molten glass in a furnace for 

producing fiberglass insulation;

NUREG-1669 110
8: PUBLIC DOMAIN

"* density of slurries in the air pollution control 

equipment of a fossil fuel power plant; 

"* density of fluids in pipes of a coal processing 

plant and paper mill; 

" height of liquids in tanks of a chemical plant 

making industrial and commercial products; 

" height of coal entering a coal crusher of a 

fossil fuel plant; 

"* height of lime rock entering a cooler after 

being made anhydrous for industrial uses; 

"* height of wood chips in tanks beginning the 

manufacture of pulp in a paper mill; and 

"* amount of recycled cardboard on a conveyor 

belt at a paper mill. 

But gauges also can result in costs: 

"* Exposures to workers have occurred when 

tanks have been serviced while the shutter of 

a gauge was inadvertently left open. 

"* Exposures to workers have occurred when 

gauges have been removed while the shutter 

was inadvertently left open. 

"* Exposures to workers have occurred when 

improperly disposed gauges in the recycling 

stream have been processed at scrap yards. 

"* Millions of dollars have been spent to 

decontaminate steel mills that have 

inadvertently melted gauges. 

"* Radiation alarms at scrap yards and steel mills 

require the attention of employees who have 

other responsibilities for production. Most of 

the alarms seem to be caused by naturally 

occurring radioactive material (see Figure 2). 

"* Regulators are often called to assist in placing 

controls on a load of scrap metal that is 

suspected of containing radioactive material 

so that the load can be moved to a place where

it can be safely taken apart to determine the 

cause of the radiation alarm. 

0 Resources have been expended to investigate 

and contain amounts of radioactive material 

that have no impacts on health. 

8.4 Elements of Risk 

In the public domain, the elements of risk are the 

consequences of the sequences in Sections 5.5, 

6.4, and 7.7. Two types of consequences are 

impacts to health and the cost of restoring a 

facility after breaching a sealed source. 

8.4.1 Danger to Life 

Risk, in terms of danger to life, is usually 

expressed as injury, disease, or dose. In this 

study, the risk to life is expressed in terms of the 

activity of the sources because of the 

circumstances in which nuclear gauges can inflict 

consequences on life. The states of gauges (intact 

with the shutter closed, intact with the shutter 

open, dislodged source, breached source) and 

scrap metal consolidation create complex 

circumstances that are difficult to characterize for 

dose calculations. The necessary simplifications 

and assumptions would severely limit the 

usefulness of such risk estimates, complicating the 

way in which such risk estimates are interpreted. 

A surrogate measure of consequences to health is 

the activity of sealed sources. This surrogate 

measure circumvents the problems of determining 

the dose under the complex and variable 

environment of a scrap yard and the populations in 

the surrounding area. The surrogate measure also 

covers intact gauges in the recycling stream, 

which though not causing exposures, are still a 

concern because they are beyond controls. 

At present, a quantitative evaluation of the impacts 

to health from melting a nuclear gauge at a steel 

mill is difficult to perform. Three parameters are 

unknown: the furnace size, the partitioning of 

radionuclides between product and byproduct 

materials, and the collection effectiveness of the 

ventilation system in the melt shop. Qualitative

III NUREG-1669
8: PUBLIC DOMAIN

statements can be made from the reported 

incidents of radioactive material melted at mills 

and are illustrated in Figure 46: 

(1) Furnace size. A wide range of furnace 

capacities can be found across the steel industry; 

the principal investigator visited mills with 

furnace capacities ranging from 59 tonnes to 145 

tonnes (65 tons to 160 tons). A large amount of 

steel, although contaminated, will give more 

shielding than a small amount of steel. Also, a 

large amount of steel means that the concentration 

of radioactive material (e.g., 'Co) will be low in 

any product that is made. 

(2) Partitioning. `

37

Cs: the partitioning is well 

known. Cesium vaporizes from molten steel and 

slag and resides in the furnace dust. 

Contamination is not found in steel when cesium 

has been melted. 6"Co: some information is 

known, but this partitioning has not been 

characterized. Cobalt forms an alloy with steel. 

Because some steel is in the slag and furnace dust, 

these byproducts will also be contaminated (Ref. 

11). "

4Am: little is known about the partitioning, 

but it is suspected to reside in slag. 

(3) Collection efficiency. A ventilation hood in a 

melt shop collects dust from the furnace. At some 

mills, the furnace is ventilated while it is 

operating. When a furnace is opened, a plume of 

dust rises up to the hood, but not all of the plume 

enters the hood. Inhalation exposures are more 

than just a function of the collection efficiency. 

Predicted exposures are complicated by the rate at 

which radionuclides are purged from molten steel. 

Little is known about the purge rate. 

In addition to the above points, predicting 

exposures from inhaling and ingesting radioactive 

material, as well as external exposures, is difficult 

owing to differences in facilities.

8.4.2 Danger to Property

Baghaouse • 

Meltshop 

SConsumer 1 

& Industrial Uses

Figure 46 Difficulties in determining health impacts at a melt 

shop. 

Licensees 

Unless a facility has many nuclear devices, there 

is seldom one person whose only responsibility is 

the care of nuclear gauges. An employee who is 

responsible for nuclear gauges usually has other 

responsibilities. That person may be an 

environmental engineer, the chief electrical 

engineer, a production manager, or a safety 

engineer, having critical responsibilities in an 

expensive process. The time spent on 

administering regulations is time that is taken 

away from other safety concerns (e.g., chemicals, 

high-voltage lines, heavy loads, falls) and 

production. The expense to the facility is not just 

a licensing fee or the time of the person at an 

hourly wage; it is the cost of taking that person 

away from production matters that can affect the 

safety of employees and the populations 

surrounding a facility. While all of the aspects of 

costs may not be explicitly represented in an 

analysis, a comprehensive analysis will at least 

acknowledge their existence.

Scrap Yards and Steel Mills

The burden to industry from more stringent 

controls and the damage to property when a 

nuclear gauge is compromised can be 

conveniently expressed in a common 

term-costs.

When radioactive material has been accidentally 

melted, the costs to decontaminate a mill and 

dispose of contaminated products and byproducts 

has been reported to be from $2 million to $23 

million (Ref. 10). Reference 3 (pages 263 through

NUREG-1669 112
8: PUBLIC DOMAIN

270) states that costs are often difficult to use. 

Problems exist with the cited figures of financial 

damage: 

"* The costs by themselves are poorly 

characterized. Only a range of costs is given, 

sometimes with a vaguely defined average. 

"* Money has a value that changes over time. 

The costs of incidents need to be stated with 

respect to an applicable time frame. 

"* Costs are often misstated from the view of a 

systematic analysis because of accounting 

practices. Accounting practices usually do 

well in keeping track of receipts and expenses 

by placing costs into conventional categories, 

avoiding subjective appraisals of value. But 

the categories may be inappropriate for a risk 

analysis. For example, a nuclear gauge may 

have been melted shortly before a scheduled 

shutdown; attributing the entire cost of a 

shutdown to melting a nuclear gauge would 

overstate the consequences. The constituents 

of the cost figures must be known. 

Accurate cost information, in a form that is 

compatible with a risk analysis, is essential for 

assessing financial risk. The costs expected in an 

integrated mill have not been rigorously 

determined, although figures have been stated 

(Ref. 10). Minimills that have not melted nuclear 

devices have expected costs too, but the estimates 

are poorly founded."

8.5 Sources of Information 

Table 11 is a summary of the sources of 

information for developing the inputs of the steel 

mill analysis. Shaded cells indicate that 

information is available. Numbers in cells refer to 

survey questions in Appendix C. Letters in cells 

are notes following the table about the information 

or lack thereof. White cells of the table indicate 

that a particular class of information for a 

particular element is unavailable at a reasonable 

cost. 

8.6 Observations and Insights 

1. Nuclear gauges allow industries to 

conveniently and precisely control processes 

that otherwise would be difficult to control. 

Although they are physically a minuscule part 

of production, for many industries gauges are 

critical for making high-quality products with 

less risk from the processes themselves. 

2. Use of nuclear gauges also have 

consequences. People have been overexposed 

to radiation when gauges have been 

improperly used or disposed of in the 

recycling stream. Property has been 

contaminated and financial losses have 

occurred when sealed sources have been 

breached within the recycling stream. Most of 

the people who are vulnerable to the 

consequences are members of the public; 

workers trained in the use of nuclear material 

are not considered the public. 

3. An assessment of risk in terms of impacts to 

public health is hampered by a paucity of 

information on relevant parameters.

10/ This statement is based on pilot tests of the steel industry survey 

in Appendix C.

113 NUREG-1 669
8: PUBLIC DOMAIN 

Table I 1 Sources of information supporting the analysis of risk elements in the public domain. LEGEND: A shaded box indicates available 

information; a number in a shaded box indicates a survey question in Appendix C and a letter indicates a note following the table. A white box 

indicates unavailable information. Degrees of information are discussed in Section 4.2.

Degrees 

of Source 

Information of 

(Section 4.2) Information

Consequence Measures 

Health 

Economic

1st Survey 

(page 118) 

2nd Survey 

(page 118) 

Plausible 3rd judgments

Notes on Table 11

A. Question 5: The type of processing of scrap metal that is done at a mill can influence health risk. Sorting, shearing, and cutting may 

dislodge a sealed source from its holder. Cutting may also breach the source. Currently, the information is used for qualitative purposes 

because such an element of risk would be difficult to quantify. 

Question 32: The size of the furnaces is used to compute the 

concentration of radionuclides in a heat when a nuclear gauge is 

melted. This will give an indication of activities to expect. From the 

activities, the hazard posed to workers in a melt shop can be 

postulated. Also, these concentrations may suggest the extent to 

which radiation gauges will detect melted radioactive material. 

Furnaces of different sizes may be used to different extents. For 

example, a small furnace at a facility may seldom be used; although 

the concentration of radioactivity in the melted steel would be high, 

the chance of it being contaminated would be low.

B. Question 51 directs respondents away from these cost questions 

at mills where there have been no meltings of radioactive material. 

While staff could be asked to predict costs, pilot tests of the survey 

revealed that predictions amount to guesses that have little 

quantitative merit and may even be incongruent with one another. 

The costs should not be strongly dependent on the strength of the 

sealed source in nuclear gauges; for most activities found in most 

nuclear gauges, the same decontamination procedures will occur regardless of the source strength. Question 52: Three costs are relevant: downtime, decontamination, and disposal. The year of the 

incurred costs is asked to adjust the costs to present value. The 

question is relevant to mills where radioactive material has been 

melted. Questions 11, 24,30,37,42,46, and 50 suggest the impacts 

to mills from having to monitor scrap metal; an impact to a mill is 

the rate of alarms, which a mill expends resources to investigate.

NUREG-1669 114
9 NEED FOR SURVEY INFORMATION TO ESTIMATE RISK

The need for survey (Appendices B and C) 

information to estimate risk is shown in Table 12. 

Gray boxes indicate the risk elements where at 

least some information from surveys is needed.

White boxes indicate the risk elements where the 

surveys in Appendices B and C do not cover. 

Sources of information for all of the risk elements 

are discussed in Sections 5.6, 6.5, 7.8, and 8.5.

Table 12 Elements of risk requiring information from surveys of licensees and the steel industry. LEGEND: Gray 

box = at least some information from the surveys in Appendices B and C. White box= surveys in Appendices B 

and C do not cover. 

Analysis Elements

Licensees 

Scrap Metal Consolidation

Steel Mills

. 1. 2 3~ 4v 4E 15 16

Element1 dniicto for Tab 19 

28 130 1319.

Public Domain

Element Identification for Table 12

Licensees 

/A: prevalence of nuclear gauges (page 48) 

1: States of facilities (page 48) 

2: Work force changes (page 49) 

3: Gauge locations (page 49) 

4: At-risk potential for a gauge to get beyond controls (page 53) 

5: State of a gauge at risk (page 56) 

6: Disposition of a gauge at risk (page 56) 

Scrap Metal Consolidation 

7: Nuclear gauges enter the recycling stream (page 66) 

8: Scanning scrap metal for radiation (page 66) 

9: Radiation alarm before scrap metal is processed (page 67) 

10: Type of scrap metal processing (page 67) 

11: Effects of scrap metal processing on a nuclear gauge (page 67) 

12: Radiation alarm when scrap metal after is processed (page 68) 

Steel Mills 

Entrance 

13: Configuration of radiation monitors at steel mills (page 93) 

14: Scanning scrap metal at the entrance of steel mills (page 95) 

15: Strategy to monitor loads of scrap metal (page 97) 

16: Alarm on the first pass through a monitor station (page 97)

Steel Mills; entrance (continued) 

17: Alarm on the second pass through a monitor station (page 97) 

18: Alarm on the third pass through a monitor station (page 97) 

19: Response when a vehicle causes a radiation alarm (page 97) 

20: Controls on a load rejected because of an alarm (page 98) 

21: Probability of BC given a source is also in the load (page 98) 

22: Confinr the cause of a radiation alarm (page 98) 

23: Controls on a load rejected because of reworking (page 98) 

Charge Bucket 

24: Scanning scrap metal at the charge bucket (page 99) 

25: Probability of an alarm (page 99) 

26: Response when a charge bucket monitor alarms (page 99) 

27: Controls on radioactive material found (page 99) 

Products and Byproducts 28: Radionuclides melted in a furnace (page 101) 

29: Capability of monitoring equipment for test pieces (page 103) 

30: Level or thickness monitoring; radiation gauge (page 103) 

31: Scanning steel product for radiation (page 103) 

32: Scanning furnace dust for radiation (page 104) 

33: Scanning slag for radiation (page 104) 

34: Contamination steel getting beyond mills (page 104) 

Public Domain 

CH: Health consequences (page 115) 

CF: Financial consequences (page 116)

115 NUREG-1669

17 1 8 9 1 1 1 1,2
10 CONCLUSIONS

Licensees

The licensees, scrap yards, and steel mills take 

actions every day without explicitly analyzing 

their risk. The judgment of risk is clearly an 

intuitive one that is based on experience and 

working knowledge. The complexity of the 

system formed by the industrial environments and 

the control mechanisms, which is illustrated in 

Figure 6, suggests that an accurate assessment of 

the risk from nuclear gauges in the recycling 

stream needs a more careful analysis than can be 

done intuitively. In this study, risk analysis 

methods were applied to examine the subject of 

nuclear gauges in the recycling stream: 

" An accurate assessment of risk was precluded 

by a paucity of data for the elements of risk. 

Nonetheless, the analysis yielded observations 

and insights of interest. To quantify risk, 

information from surveys about licensees (see 

Appendix B) and the steel industry (see 

Appendix C) is needed. 

"* Any assurance that changing controls will 

have the desired effect must be based on 

detailed knowledge of the system illustrated in 

Figure 6. 

"* Evaluating the effect of modifying a control 

mechanism or introducing a new one using 

empirical data will take years because of the 

time necessary to collect and analyze data. 

Furthermore, it will be difficult to evaluate the 

efficacy of the changed or new control 

mechanisms because the observed changes 

may depend on many changing and poorly 

understood factors that may not be readily 

taken into account. But with data from 

surveys and other sources, a risk analysis can 

be used to evaluate changes in risks to 

stakeholders from a modified or new control 

mechanism.

Licensees are confronted with making business 

decisions to devise practices that provide 

immediate and continuous control (ICC). Such 

decisions must balance the predictable cost of 

maintaining control over nuclear gauges against a 

chance of inadvertently discarding gauges. ICC 

practices take three forms: 

"* Although not typically viewed as a control, a 

gauge in use, controlling production, cannot 

be removed and discarded without drawing 

attention. 

"* When a gauge must be removed from a 

process unit, storage in an area that is 

dedicated only for gauges reduces the chances 

of the gauge being discarded with scrapped 

materials and equipment. 

"* An unused gauge that has been returned to a 

vendor is not at risk of being discarded into 

the recycling stream. 

The above practices place a gauge in a definite 

location from which it is unlikely to be removed 

unnoticed-risk, as far as the licensees are 

concerned, is kept to a minimum. These practices 

are collectively referred to as hard controls. 

Whatever reliance that is not placed on hard 

controls is typically placed on so-called soft 

controls, such as labels, semi-annual inventories, 

education and communication, and civil penalties. 

Soft controls are less effective than hard controls 

in providing ICC because they do not always gain 

enough attention at the right times and they can be 

degraded by conditions and circumstances at 

facilities. Redundancy in control mechanisms 

increases overall effectiveness because it 

compensates for control mechanisms becoming 

compromised.

NUREG-1669

General

117
10: CONCLUSIONS

The way to evaluate any control is to evaluate its 

capability to operate immediately and 

continuously when gauges are at risk to prevent 

them from being inadvertently removed from their 

intended places. From the concept of ICC, 

statements can be made about common forms of 

control: 

"* The extent to which high-level accountability, 

civil penalties, and license revocation provide 

ICC is unclear. The chance of these 

mechanisms being called upon (the remote 

possibility of losing a gauge at an unknown 

time in the future) is overshadowed by acute 

concerns and hazards at an industrial facility. 

"* The decrease in risk from moderate increases 

in the frequency of inspections appears to be 

small. Most of the time, gauges are not at risk 

to improper disposal-other control 

mechanisms (e.g., in use on an operating 

process line) are functioning. Because 

occasional inspections are unlikely to be done 

when gauges are at risk of improper disposal, 

moderately increasing them will have little 

effect on risk. 

"* Registering gauges enhances other controls 

that provide ICC, such as responsibility and 

accountability. Registration refreshes memory 

about the gauges; this is especially important 

when facilities are closed or when employees 

change professions or retire. A lack of a 

response alerts regulators to some forms of at

risk conditions, such as closed and abandoned 

facilities. Followup is necessary for 

registration to be effective. 

"* Responsibility for ICC, not for the gauges, is 

often difficult to assign in complex industrial 

organizations. The responsibilities of 

employees may be overlapping and changing 

to meet market demands and the state of a 

facility. The use of outside contractors during 

system shutdowns for extensive maintenance 

and overhauls exacerbates the difficulties in 

assigning responsibility for ICC.

Another important element of risk is the extent to 

which gauges are at risk of entering the recycling 

stream. The at-risk potential is a complex 

function determined by the gauge environment, 

the applicability of control mechanisms to each 

environment, the prevalence of the control 

mechanisms, and the effectiveness of the control 

mechanisms. Most nuclear gauges are not at risk 

because they are in use controlling industrial 

processes. Even when a gauge is at risk, it may 

not enter the recycling stream. The potential for 

a gauge to enter the recycling stream is 

represented in this analysis by the probability of a 

gauge being discarded. 

Regulatory agencies do not continuously verify 

that licensees implement control mechanisms. 

Accordingly, an implicit assumption is being 

made that licensees will, can, and know how to 

assume their responsibilities. Reference 1 

suggests that the assumption is not always valid. 

A difficulty for licensees in maintaining 

accountability is that they lack the collective 

experience of what does and does not provide 

ICC. Because current regulations are broad and 

non-prescriptive, licensees have considerable 

leeway to devise their own control programs. 

Many licensees might benefit from learning about 

effective ICC practices. 

Perfect control that eliminates the risk to life and 

property is impractical to require by regulatory 

agencies (i.e., the Nuclear Regulatory 

Commission or Agreement States) and implement 

at industrial facilities. Many factors placing the 

gauges at risk are outside the jurisdiction of 

regulatory agencies or cannot be completely 

controlled by licensees. Many of the control 

mechanisms are compromised in the complex, 

changing, and hazardous environments of 

industrial facilities. This leaves a regulatory 

agency with the task of devising and 

communicating ICC practices that can be 

efficiently implemented.

NUREG-1669 118
10: CONCLUSIONS

Recycling Industries 

Scrap yards and the steel industry are confronted 

with making business decisions to invest in a level 

of protection against the danger of nuclear gauges 

in the recycling stream, balancing the predictable 

cost of protection against a chance of incurring 

consequences. The following practices are 

decisions to accept an unknown level of risk: 

"* Using radiation monitors throughout a scrap 

yard or a steel mill provides a level of 

protection against the consequences of 

processing a nuclear gauge. The level of 

protection depends on both the number and 

location of the monitors. 

"* Turning off radiation monitors because the 

alarms are annoying increases risk. 

"* Bringing scrap metal into a mill in large 

amounts and in highly packed forms to reduce 

costs compromises the protection given by 

radiation monitors. 

"* Rejecting a load of scrap metal suspected of 

containing nuclear material without notifying 

authorities may increase the risk of another 

scrap yard or steel mill. The load may be 

taken to another facility where it might be 

accepted because there the radiation alarms 

might not activate. 

"* Typically vehicles entering scrap yards or 

steel mills with scrap metal are passed through 

a radiation monitor station one, two, or three 

times. If the primary concern is to detect 

sealed sources, then the decision to reject or 

accept a load would be based on one pass 

through a monitor station. If the primary 

concern is false alarms, then decision would 

be based on the second pass, given an alarm 

on the first pass. The three-pass strategy is a 

compromise between the one-pass and two

pass strategies. 

"* Reworking a load of scrap metal suspected of 

containing radioactive material reduces risk. 

By dumping the load and sorting through the 

scrap metal, all possible causes of a radiation 

alarm can be assessed. Scanning a load with

a survey meter and attributing an alarm to 

benign contamination (e.g., dirt in the rib of a 

vehicle or pipe scale) assumes a nuclear gauge 

is not present in the load. Most, but not all, of 

the time, this assumption is correct. However, 

until further study is done, making the 

assumption is inappropriate considering the 

possible consequences (dislodging, breaching, 

or melting a sealed source) of being wrong. 

Research is needed to characterize the 

commodities of scrap metal and to determine the 

detection probability for each commodity, notjust 

to determine the detection capabilities of specific 

systems as has been done. With a characterization 

of the commodities, the capabilities of equipment 

could then be predicted without having to conduct 

a field trial each time the technology changes. 

Field trials may still be necessary to validate 

predictions, but as yet, there is sparse quantitative 

basis for making predictions. 

The probability of detecting a nuclear gauge in a 

load of scrap metal is poorly characterized, yet it 

has implications for the public, licensees, the steel 

industry, and regulatory agencies. Ifthe detection 

probability is low when using state-of-the-art 

monitoring equipment, then stringent controls at 

the licensee facilities would be needed to control 

the risk, placing heavy burdens on both the gauge 

users and on the regulatory agencies. If the 

detection probability is high, then less stringent 

controls would be needed. Therefore, the 

detection probability should be determined and 

thoroughly understood. 

The recycling industries sometimes place too 

much reliance on sophisticated radiation monitors 

alone instead of understanding the ramifications of 

using this technology. The basis for choosing to 

pass a vehicle through a radiation monitor one, 

two, or three times for deciding to accept or reject 

a load of scrap metal is seldom known. Some 

methods for monitoring samples from a furnace 

for contamination leave much uncertainty in 

detecting contaminated steel in a furnace. 

Scrap Yards 

* Scrap yards are often located near populated 

areas. Portions of these populations can be

119 NUREG-1669
10: CONCLUSIONS

placed at risk of radiation exposure when a 

breached source is dispersed. The extent of 

the dispersal is difficult to predict. 

"* A health hazard from nuclear gauges may 

occur at the scrap yards. Here, shredding, 

shearing, and cutting (burning) scrap metal 

can dislodge and breach a sealed source. 

Installing radiation monitors near some of 

these processes might be an effective way to 

detect a dislodged or breached sealed source. 

But the use of radiation monitors may also be 

impractical for these processes. Supports for 

monitors must be placed where monitoring 

would be effective. High vibrations, shock 

waves from explosions (e.g., when a propane 

tank is accidently processed), and stray pieces 

of scrap metal (e.g., from loading shredders 

and balers) could damage a monitor. 

Individuals who cut scrap metal move around 

the yard. 

"* Information about the scrap yards is difficult 

to obtain. For example, which scrap yards 

supplying the mills use radiation monitors 

would be considered propriety information by 

the scrap metal industry. Other information 

might require costly experiments, for example, 

the probability of breaching a sealed source. 

Steel Mills 

E When '

37

Cs is melted, it adheres to the furnace 

dust. Most, but not all, of the dust is collected

by the ventilation system of the melt shop. 

Some of the dust escapes into the melt shop. 

The amount of contaminated dust escaping 

into the melt shop is difficult to determine, 

depending on when the sealed source melts in 

relation to when the furnace is open and the 

capacity of the ventilation system to collect 

dust. 

"* When a 'Co source is melted, the cobalt 

forms an alloy with the steel. The radioactive 

material is at least somewhat diluted in the 

heat. The steel provides self-shielding. The 

furnace provides additional shielding until it is 

tapped. Some 6

'Co gets into furnace dust, 

some of which escapes the ventilation system. 

"* Little is known about what will happen when 

241

Am is melted. The current understanding is 

that it will reside mostly in slag. 

"* Accurate cost information, in a form that is 

compatible with a risk analysis, is essential for 

assessing financial risk. Trade associations 

report costs from melting nuclear material that 

range from $2 million to $23 million (Ref. 

10). But these costs are poorly characterized. 

Only a range of costs is given, sometimes with 

a vaguely defined average. The damage 

expected in an integrated mill has not been 

rigorously determined, although figures have 

been stated (Ref. 10). 

- 0340900 , ..

NUREG-1669 120
REFERENCES

1. Lubenau, J. and J. Yusko. "Radioactive 

Sources in Recycled Metals." Health 

Physics. Vol. 68, No. 4: April 1995. 

Lubenau, J. and J. Yusko. "Radioactive 

Material in Recycled Metals--An Update." 

Health Physics. Vol. 74, No. 3: March 1998. 

2. Kahane, H. Logic and Contemporary 

Rhetoric, sixth edition. Belmont, CA: 

Wadsworth Publishing Company. 1992. 

3. de Neufville, R. Applied Systems Analysis. 

New York, New York: McGraw-Hill 

Publishing Company. 1990. 

4. de Neufville, R. and J. Stafford. Systems 

Analysis for Engineers and Managers. New 

York, New York: McGraw Hill Publishing 

Company. 1971. 

5. Nuclear Regulatory Commission (U.S.) 

(NRC). NUREG-1489, "A Review ofNRC 

Staff Uses of Probabilistic Risk 

Assessment." NRC: Washington, D.C. 

March 1994. 

6. Gore, M. and J. Stubbe. Elements of Systems 

Analysis for Business and Data Processing, 

second edition. Dubuque, Iowa: Wm. C. 

Brown Company. 1979. 

7. Memorandum from R.M. Bernero, Director, 

Office of Nuclear Material Safety and 

Safeguards, to E.S. Beckjord, Director, 

Office of Nuclear Regulatory Research. 

"Request for Risk Analysis of Generally 

Licensed Devices Having Sealed Sources." 

NRC: Washington, D.C. 22 November 

1994. Memorandum from Carl J. Paperiello, 

Director, Office of Nuclear Material Safety 

and Safeguards, to David L. Morrison, 

Director, Office of Nuclear Regulatory 

Research. "Request To Amend the Risk 

Assessment of Generally Licensed Devices." 

NRC: Washington, D.C. 16 May 1995. 

8. Memorandum from R. Baer, Chief, Source 

Containment and Devices Branch, Division 

of Industrial and Medical Nuclear Safety,

Office of Nuclear Material Safety and 

Safeguards, to M.A. Cunningham, Chief, 

Probabilistic Risk Analysis Branch, Division 

of Systems Technology, Office of Nuclear 

Regulatory Research. "Risk Analysis of OL 

Devices." NRC: Washington, D.C. 28 

March 1995. 

9. US. Code of Federal Regulations, Title 10, 

Energy. 

10. Transcript of a Nuclear Regulatory 

Commission Briefing. "Material Control of 

Generally Licensed Devices." NRC: 

Rockville, MD. 21 January 1998. 

11. Nuclear Regulatory Commission (U.S.) 

(NRC). NUREG-1 188, "The Auburn Steel 

Company Radioactive Contamination 

Incident." NRC: Washington, D.C. January 

1986. 

12. Kaplan, S. and B.J. Garrick. "On the 

Quantitative Definition of Risk." Risk 

Analysis. Vol. 1, No. 1: 1981. 

13. Meyer, M.A., and J.M. Booker. Eliciting 

andAnalyzing Expert Judgment." A Practical 

Guide, Vol. 5. London, England: Academic 

Press. 1991. 

14. Freedman, D., et al. Statistics, second 

edition. New York, New York: W.W. 

Norton and Company. 1991. 

15. Department of the Interior (U.S.)(DOI), 

Bureau of Mines Annual Reports, "Mineral 

Industrial Surveys. "DOI: Washington, D.C. 

1969-1990. Department of the Interior 

(U.S.) (DOI), U.S. Geological Survey 

Annual Reports, "Mineral Industrial 

Surveys." DOI: Washington, D.C. 

1990-1996. 

16. Broughton, A.C. "Consumers and 

Processors: Strategic Alliances." Recycling 

Today. November 1996. Broughton, A.C. 

"Optimizing Ferrous Scrap." Recycling 

Today. March 1997.

121
APPENDIX A

ICC DETERMINATIONS

The analyses of the licensees are discussed in 

Section 5. There, the key concept of immediate 

and continuous control (ICC) was developed and 

applied to control mechanisms of nuclear gauges. 

In Appendix A, the reasons are given for 

determining whether or not a control mechanism 

can provide ICC in a given environment. 

Figure 20 is reproduced and annotated as Figure 

47. As before, the elements of risk are at the top 

left of Figure 47. Beneath the element titles the 

possibilities of each element are delineated. The 

left half of Figure 47 delineates the 33 industrial 

environments of the gauges. The right half of 

Figure 47 indicates the capability of the control

mechanisms to provide ICC; a white cell indicates 

that the control mechanism cannot provide ICC 

over gauges; a shaded cell indicates that the 

control mechanism can provide ICC. Numbers in 

each of these cells refer to notes following Figure 

47. These notes give reasons for stating that a 

control mechanism can or cannot provide ICC in 

a given environment. 

Figure 47 shows the applicability of the control 

mechanisms to a gauge in a given environment. It 

does not show the logical relationships of the 

control mechanisms, which are shown in Figure 

23.

123 NUREG-1669
APPENDIX A: ICC DETERMINATIONS

Elements Forming the 

33 Environments of Nuclear Gauges 

1: State of facilities (page 48) 

2: Work force changes (page 49) 

3: Gauge location (page 49)

Slow•

In Use, Operating Unit 

Out of Use, Operating Unit 

Maintenance 

Storage 

Defunct Unit 

Dismantled Unit

In Use, Operating Unit 

Out of Use, Operating Unit 

Rapid -Maintenance Storage E Defunct Unit 

Dismantled Unit 

In Use, Operating Unit 

Out of Use, Operating Unit 

Slow Maintenance 

Storage 

Defunct Unit 

Dismantled Unit 

In Use, Operating Unit 

Out of Use, Operating Unit 

Rapid -Maintenance Storage 

- Defunct Unit 

-Dismantled Unit

- In Use, Operating Unit 

- Out of Use, Operating Unit 

_ Phasing Storage 

Out Defunct Unit 

Dismantled Unit

(1) 

(2) 

(3) 

(4) 

(5) 

(6) 

(7) 

(s) 

(9) 

(10) 

(11) 

(12) 

(13] 

(14) 

(15) 

(16) 

(17) 

(15) 

(19) 

(20) 

(21) 

(22} 

(23) 

(24) 

(25) 

{26} 

(27) 

(28) 

(29)

Si

6 2 _ ý55,6 5 1 

ý 16 H1166 &21 2 23191 9 - 20 10

(30) 1341351361361371371 7136136136138139139140M151

- Abandoned 

- Dismantled 

Orphan sourcce

(31) 1341351361361371371 7 136136136138139134041 

(32) 134W-M 4 46f4 i

(33) I l I I I I j

Figure 47 Reasons for stating that control mechanisms either can or cannot provide immediate and continuous control in a given industrial environment. 

LEGEND: A white box (0) indicates that a control cannot provide ICC in a given environment. A shaded box (M) indicates that a control can provide ICC in a given environment. P = prevalence nuclear gauges; x = G for generally licensed gauges; x = S for specifically licensed gauges; 

x = T for both types of gauges. E&C = education and communication. HLA = high-level accountability. QCR = query at a change in responsibility.

NUREG-1669

Operating: - Constant 

Ownership 

Operating: 

-Changed 

Ownership

M& &o 

OAade 

iome4e 

?lth

- Closed

124
APPENDIX A: ICC DETERMINATIONS

Notes on Figure 47

1. Unlike the other environments, Environments 

1, 7, 13, 19, and 25 are a control mechanism- in 

use. Nuclear gauges are controlling production. 

The gauges are not at risk of being discarded 

because they are in use. Some process units can 

operate without the gauges providing control 

signals, but when the process unit must be 

controlled manually there is still an awareness of 

the gauges or the lack thereof. When a gauge is 

in these environments, it is automatically under a 

hard control mechanism. Therefore, the soft 

controls are not an issue. The same cannot be said 

about the other environments. Interim dedicated 

storage (IDS) and return to vendor are applicable 

only when a gauge is not being used. 

2. IDS is applicable for gauges that are normally 

in use, but must be removed while a process unit 

is serviced. A gauge cannot be in use and out of 

use. 

3. A gauge that is not being used to control a 

process can be returned to its vendor. 

4. The process unit is operating; employees are 

unlikely to remove a component from an operating 

unit. Inventory would have to be done after any 

servicing to provide ICC. Here, servicing is 

minor. An inventory is impractical for minor 

servicing because such servicing may be frequent 

and the servicing is localized. 

5. Although a label is just a reminder, it is one of 

the few ways to identify a nuclear gauge. Shape 

and color are other ways, albeit much less 

conspicuous than a radiation trefoil. Labels can 

be effective in many environments. For example, 

during maintenance workers are focused on their 

tasks, not on gauges. While some storage areas 

are dedicated to nuclear gauges, storage areas are 

seldom dedicated and may be cluttered with other 

materials. When a process unit has been unused 

for a long time, labels remind people who have

forgotten about the gauges and provide awareness 

as the work force changes. 

6. Physical security, such as a chain, cage, or 

padlock, gives a warning that something should 

not be removed. 

7. Lockout is applicable to a process unit that is 

being taken out of service for maintenance. 

8. Someone close to the process units is 

knowledgeable of the gauges and can be held 

accountable for the day-to-day activities of the 

gauges. The person knows of the gauges 

wherever they are - in use, in storage, on defunct 

units, or on units that are about to be dismantled. 

A person has to be educated in ICC. 

Communications is necessary because a 

responsible person cannot know from one moment 

to the next which gauges are being placed at risk. 

9. Holding upper management of a facility 

accountable prompts management to support the 

people who are close to the process units and 

responsible for the gauges. The process units may 

be operating, in service, defunct, or in the process 

of being dismantled. Management are still at a 

facility that is being phased out over a period that 

may be years. 

10. Inspections are infrequent and brief. An 

inspection may coincide with persisting 

environments where gauges are at risk, but many 

of these environments may not be matters of 

compliance. Although these conditions may 

persist for extended periods, the moment when the 

gauges are being discarded may be brief. 

Maintenance and renovation activities are unlikely 

to coincide with inspections. 

11. A civil penalty can be levied against a facility 

that is operating.

125 NUREG-1669
APPENDIX A: ICC DETERMINATIONS

Notes on Figure 47

12. The gauges are often vital to the processing. 

If the gauges cannot be used responsibly, revoking 

a license is tantamount to closing down a 

profitable facility for a legitimate reason-to 

protect public health. Even when a facility is 

changing ownership, it is viable. The possibility 

of having the license revoked is a clear message to 

the management of the facility, who are 

accountable to their customers and stockholders. 

13. Registration provides awareness, at least to 

some people, of gauges in a facility, regardless of 

where they are located. The awareness has the 

capability of providing at least some ICC. 

Through education and communication (E&C), 

registration provides awareness to contractors 

during maintenance or to hourly employees who 

might be removing scrap materials or cleaning out 

storage areas. 

14. An image-conscious company draws 

stockholders to invest, skilled people for 

employment, and customers who can rely on a 

facility to supply products on demand. 

15. Query at a change in responsibility is 

applicable when ownership is changing, not when 

ownership is constant. A closed facility may still 

be owned by a corporation. When a facility is 

abandoned, ownership is not being transferred. 

16. Gauges that are in use on a process unit 

cannot be on a process unit that is undergoing 

maintenance or storage, on a defunct unit, or on a 

unit that is being dismantled. 

17. In IDS, a gauge is in a known, definite, and 

well-marked location while it is not in use. The 

gauge is not subject to being forgotten, lost among 

clutter on a shop floor while maintenance is done, 

lost among clutter in general storage, or simply

left on the side of a process unit or shop floor; in 

these situations, a gauge is at risk of being 

mistakenly discarded with other materials. 

18. Process units are shut down for brief 

periods--too brief to have a gauge returned to its 

vendor. 

19. An inventory done after maintenance or 

before materials leave a facility is ICC. 

20. Chains, bolts, and welds are easily severed 

with a cutting torch. People servicing a process 

unit are busy, possibly overlooking physical 

security as a warning of something that should not 

be removed. 

21. Lockout is a form of inventory that is done 

both before and, more importantly for ICC, after 

maintenance. 

22. IDS is storage on an interim basis only, while 

a process unit is out of service for maintenance. 

23. Returning a gauge that is in storage (other 

than IDS), on defunct units, or on units being 

dismantled removes the gauge from being at risk. 

24. Annual registration operates through E&C to 

provide ICC. But dismantling is often done by a 

contractor, leaving a high potential for E&C to 

fail. A contractor representative may be informed 

of a gauge, but the employees dismantling a unit 

may not be informed or may not appreciate the 

information. 

25. Storage in a room or on a defunct unit is 

continuous. Discarding a gauge occurs rapidly. 

Inventory is periodic and brief. Between 

inventories, a gauge may be discarded. Unless the 

inventory is frequent, ICC will not be provided.

NUREG-1669 126
APPENDIX A: ICC DETERMINATIONS

Notes on Figure 47

26. During a rapid turnover of the work force, 

three control mechanisms are compromised in 

four environments in which employees are needed 

for control: K0 A responsible person may not 

always be at the facility. 0> E&C are compromised 

because few people stay long enough to maintain 

the memory of the gauges. 0> Publicity is not a 

concern for employees who have little interest in 

the facility; publicity works when someone is at a 

facility to be held accountable to customers and 

stockholders. 

27. When a facility changes ownership, 

regulatory agencies are contacted by the new 

owner before the title transfer is complete. 

Awareness is heightened so that gauges are not 

discarded when process units are renovated or 

dismantled. 

28. A facility that is being phasea out is still 

operating. The same points as in Note 1 are 

relevant here. 

29. A civil penalty is essentially of no use at a 

facility that is being phased out. A large civil 

penalty pushes a facility closer to its inevitable 

ending. When a company is liquidated, a 

regulatory agency is treated as an unsecured 

creditor; secured creditors will be paid before the 

regulatory agency. 

30. Revoking a license on a facility that is being 

phased out is meaningless. Revocation will only 

do what is inevitable. Yet gauges in storage, on 

defunct units, or on units being dismantled are at 

risk. 

31. A facility that is being phased out is 

functioning. Registration provides awareness of 

the gauges. 

32. Publicity is relevant to a facility being phased 

out if the facility is owned by an image-conscious 

corporation.

33. In a facility that is being phased out, attention 

will be on future employment and financial 

security, not on a facility that has no future. Little 

concern will be given for E&C.

34. The facility is no longer operating. 

gauges are no longer in use for ICC.

The

35. IDS might serve as a warning because it is 

distinct. A gauge may have been in IDS at the 

time the facility closed. But closed and 

abandoned facilities are subject to being pillaged, 

which is not always done with discretion. 

36. No one is in a closed facility. Controls (e.g., 

return, inventory, responsibility, E&C, and high

level accountability) requiring employees to 

perform ICC are irrelevant. 

37. Labeling and physical security are relevant 

only when employees are in a facility. People in 

a closed or abandoned facility are likely to be 

thieve, looking for tools and scrap metal. Signs 

and physical security are not necessarily within 

their attention or concern. Labels are likely to be 

overlooked. Physical security is of little use 

against cutting torches. 

38. Inspections are infrequent. A facility may be 

closed or abandoned for years before regulators 

are aware of it and can ensure that the gauges 

have been properly disposed. In the meantime, 

such facilities can be pillaged. 

39. A civil penalty and revocation are irrelevant 

to facilities that are closed or abandoned. 

40. In a closed or abandoned facility, no one is 

present to provide ICC bythe increased awareness 

from registration. A regulator may eventually be 

alerted to something wrong when registration is 

not completed. But registration is too infrequent 

for ICC.

127 NUREG-1669
APPENDIX A: ICC DETERMINATIONS

Notes on Figure 47

41. Publicity is relevant whenever a facility is 

owned by a corporation trying to stay in business. 

An abandoned facility has no owner. A closed 

facility is still owned and can be reopened. A 

dismantled facility may be owned, such as by a 

corporation. 

42. IDS may be conspicuous enough to draw 

attention to a hazard when a facility is being 

dismantled. At least some demolition contractors 

evaluate environmental hazards before 

dismantling a facility. 

43. A responsible demolition company may 

return a gauge. Any cost to the company would 

be a disincentive. But the control is still 

applicable. 

44. The responsible person may not be present at 

a facility that is being dismantled to take an 

inventory. The demolition contractor is not 

responsible because title to the facility is not 

transferred or assumed. 

45. Labels and physical security may serve as a 

warning when a facility is being dismantled by a 

responsible company. 

46. Lockout is an activity done during 

maintenance. 

47. E&C are relevant to demolition and salvage 

companies. The difficulty is in reaching all of the

demolition companies and employees within those 

companies who dismantle the facilities. 

48. Management at the corporate level may be 

held accountable for ensuring that a facility has 

been properly closed before being dismantled. 

49. Inspections are too infrequent to occur with 

assurance when a facility is dismantled. 

50. A civil penalty may be relevant when a 

facility is owned by a corporation. 

51. Revoking a license is irrelevant because the 

facility is not operating. 

52. Dismantling is done by a contractor, not an 

owner. The organization receiving the registration 

is not the organization causing a gauge to be 

discarded. 

53. Regulations have an assumption that the 

gauges will be properly disposed. But no 

mechanisms exist to ensure that the gauges are 

properly disposed. An inquiry with a regulatory 

agency, asking what gauges are known to be in a 

facility, would alert demolition employees to look 

for the gauges. 

54. Orphaned gauges are beyond regulatory 

control mechanisms and cannot be traced to their 

owner.

NUREG-1669 128
APPENDIX B

SURVEY OF LICENSEES 

Letter to Industrial Facilities with Nuclear Gauges: 

Nuclear gauges (typically devices for measuring thickness, density, level, or consistency of materials along 

process units) have been inadvertently discarded from facilities of many industries into the scrap metal 

recycling stream. Facilities can incur high costs to retrieve gauges known to have been lost or compensate other facilities that have been damaged when a lost gauge was processed with scrap metal. For regulatory controls to be effective, they have to address conditions as they are in industry, acknowledging the demands 

on employees, organizations, and facilities, which can be complex and changing. 

The NRC is doing a comprehensive risk analysis of the use and storage of nuclear gauges. The gauges of 

interest are found on such places as pipes, tanks, vessels, channels, and along conveyor belts, and they use 

cesium, cobalt, or americium for radioactive material. 

NRC records indicate that your facility has nuclear gauges. Please answer the attached questions about the 

nuclear gauges themselves and a few questions asking for very general information about your facility. The 

answers to your questions will be compiled with other replies for use in the analysis to estimate risk. 

Your answers are important so that the analysis can account for the characteristics of a facility such as the 

one in which you work. The responses to the questions are voluntary and anonymous. 

I recommend that the person who should complete the survey should be a radiation safety officer or someone 

else who has responsibility for the gauges, such as a plant engineer or plant manager. 

These questions can be completed without looking through records. Please answer the questions 

based on your knowledge. 

Please mail your answers in the enclosed prepaid envelope. 

Your time and effort are very much appreciated. 

Thank you.

129 NUREG-1669
APPENDIX B: SURVEY OF LICENSEES

Important Points 

VW For this survey, a facility is a building or group of related buildings, under one plant 

manager. Please use a survey form for each facility.

!1 Complete this survey for nuclear gauges that ... 

Sare fixed onto pipes, tanks, vessels, channels, or on 

conveyor belts. 

V contain cesium, cobalt, or americium 

V measure the density, level, or consistency of 

materials or the thickness of metal foils and slabs. 

In general, a fixed nuclear gauge looks like this ... 

On a tank, the detector may also look like an 

unattached pipe.

Detector •• • -Housing 

for radioacitve 

material

OIW Do not complete this survey... 

X for nuclear equipment in a laboratory 

X portable nuclear gauges 

X gauges measuring the thickness of paper or non-metallic films 

OW If your facility never had or no longer has fixed nuclear gauges or has for some reason 

returned the housing containing the radioactive material, then discard this survey.

NUREG-1669 130
APPENDIX B: SURVEY OF LICENSEES

(1) Typically, how many gauges are at the following locations? 

gauges in use on operating process units 

gauges not in use, but still on operating process units 

gauges on unused process units 

gauges in a storage area (room) that is used only for the gauges 

gauges in a storage area (room) that is also used to store other materials and equipment 

NOTE: This is permitted by regulations. 

(2) If no attention was given to a nuclear gauge, about how much time would you expect the radiation 

caution label on the gauge to remain visible? 

0 About days, weeks, months, indefinitely. 

NOTE: You may specify a range. Circle one 

0 Don't know 

(3) Who checks for the presence of the gauges, either as required by regulations or by your own 

practices? How often is the check done?

By process unit operators 

Check 0 if not applicable. 

By plant engineers or the person(s) 

responsible for the gauges ... Check 0 ifnot applicable. 

By staff from headquarters ... 

Check 0 if not applicable.

typically, about every months, years. 

Circle one. 

typically, about every months, years. 

Circle one.

typically, about every __ months, years.

Circle one.

(4) When else is the presence of the gauges checked? 

"C After a machine shutdown for maintenance 

"C After a machine shutdown for changing the product 

Ol Before a process unit is relocated 

13 Before a process unit is dismantled for scrap or salvage o1 Other

Specify

1 Check all that apply.

131 NUREG-1669
APPENDIX B: SURVEY OF LICENSEES

(5) When are the following groups of people made aware of the gauges? 

NOTE: Check all that apply.

El El 

El 

El

Never 

Soon after coming on site 

Once a year 

Other 

Please specify.

El Not sure

El El 

El 

El

Never 

Soon after coming on site 

Once a year 

Other 

Please specify.

El Not sure

Outside contractors working 

in buildings (shops) where 

gauges are located

I¢

El El 

El

Never 

Before coming into the facility 

Other 

Please specify.

El Not sure

(6) What is done to maintain control of gauges in storage? 

FO Gauges are not kept in a storage area for a short time

Open area off to side X 

Fenced off area 

Storage box 

Room 

Cabinet 

Check all that apply.

E verbal warnings 

El signs 

El ropes or tape 

El locks

I 

I

to remind people

Check all that apply.

El Gauges are not kept in a storage area for a long time

Open area off to side 

Fenced off area 

Storage box 

Room 

Cabinet 

Check all that apply.

with 1

"D verbal warnings "El signs 

E1 ropes or tape 

El locks 

Check all that apply.

to remind people

(7) Are there cages, chains, or locks on gauges themselves (not the shutter on the gauge) that are in 

use on process units? 

"El All of the gauges 

"El Some of the gauges 

"El None of the gauges

NUREG-1669

People working on or 

around process units

Plant 

Management

El El 

El 

El 

El

Short 

term 

Long 

term

El El 

El 

El 

El

132
APPENDIX B: SURVEY OF LICENSEES

(8) Is the radiation safety officer or plant engineer responsible for the gauges kept informed of 

maintenance, renovation, and dismantling activities on process units ... 

wrNo with nuclear gauges? 0 Yes

any process unit? 7 YNo ] EYes

(9) Has the facility changed ownership in the last year? 

D Never changed ownership. 

0 Yes 

As far as you know or can remember, how many times has your facility changed ownership. 

times in the past _ years. 

(10) Typically, for how much time is a process unit shut down for maintenance, calibration, or product 

change?

"fhours\ 

Odays in atypical 

Oweeks 

O Emonths/

"j day 

"El week 

[ month 

0 year

(11) In regards to the work force at the facility with nuclear gauges (not a site with many facilities) ... 

o Approximately, how many people work in the facility?

Where in the organization at the facility is the 

radiation safety officer? 

0. Where in the company are other people with any 

responsibility for the care and control of the gauges?

to 

C

Not applicable 

First line supervisor 

Middle management 

Plant manager 

Other 

Specify. 

Operators 

First line supervisor 

Middle management 

Plant manager 

Headquarters staff 

Other 

Specify.

Check all that apply.

NUREG-1669

About

133
APPENDIX B: SURVEY OF LICENSEES

(12) Typically, 

o how long has a process unit been dormant (mothballed, no plans to restart)? 

0 No process units have been dormant (mothballed) 

O Weeks 

"O Months 

"O Years 

o how much time is taken to dismantle a process unit for scrap or salvage? 

O Less than a day 

0 Days 

0 Weeks 

O Months 

El Years 

O Done as people are available 

5/ anh you.

NUREG-1669 134
APPENDIX C

SURVEY OF THE STEEL INDUSTRY 

Letter to Steel Mills: 

Radioactive material is being found in and melted with scrap metal used by steel mills. Even the best 

radiation monitors can miss radioactive material deep within a load of scrap metal. Since 1983, steel mills 

have melted radioactive material 26 times; the cost of decontaminating the mill, disposing of contaminated 

products and byproducts, and lost revenue has ranged from $2 million to $23 million. A risk analysis is a 

technique to systematically understand and characterize all of the reasonable and possible routes from the 

industries that use the gauges to the steel mills. NRC is collecting necessary information for inputs to an 

analysis with the attached questions so that the steel industry can be accurately taken into account. 

To answer the questions, please talk to the people at the mill who know about the radiation monitors and 

purchasing of scrap metal. These questions can be completed without looking through records. Please 

answer the questions based on your knowledge. 

The responses from all mills are anonymous. I will compile the answers and make them available to the trade 

association. 

Please mail your answers in the enclosed prepaid envelope. 

Your time and effort are very much appreciated. 

Thank you.

135 NUREG-1669
APPENDIX C: SURVEY OF THE STEEL INDUSTRY

DIRECTIONS 

"* Do not look through records or measure anything, but answer the questions 

carefully. 

"* Talk to the people who know about the radiation monitors and purchasing of 

scrap metal. 

"* If you need additional space, then write in the margins or on the back of a page. 

"* Please write legibly.

0

Part 

A 

B 

C 

D 

E 

F 

G 

H 

I 

J 

K 

L 

M

Subject 

Description of the Steel M ill ................................ 

Purchased Scrap M etal ..................................... 

Outside onto the Site ...................................... 

Actions Taken Before Taking Possession of Purchased Scrap Metal 

Between the Storage/Process Areas and Melt Shop .............. 

Charge Bucket or Charge Box for Any Type of Furnace .......... 

Furnace ................................................. 

Actions Taken Once Scrap Metal is Unloaded .................. 

Samples (Test.Pieces) Taken From Heats ...................... 

Furnace Dust ............................................ 

Slag ................................................... 

Steel (Bars, Slabs, Coils, plates) Product ....................... 

C osts ...................................................

Page 

141 

142 

143 

145 

146 

147 

148 

149 

150 

151 

152 

152 

153

NUREG-1669 136
APPENDIX C: SURVEY OF THE STEEL INDUSTRY

A. DESCRIPTION OF THE STEEL MILL 

(1) Which best describes your site as it is currently operated? (Check one.) 

0 Integrated mill 

0 Mini-mill 

0 Other 

(specify)

(2) At your site, are radiation gauges (x-ray, radioactive material) used to directly measure the level or 

thickness of steel after it is taken from the furnace?

O Yes - Approximately, what is the total annual licensing fee? 

13 No

$

(3) Typically, what percentage of your production is stainless, carbon, and alloy steel? 

Type Percentage 

of Steel of Production 

Stainless % 

Carbon % 

Alloy %

137 NUREG-1669
APPENDIX C: SURVEY OF THE STEEL INDUSTRY

B. PURCHASED SCRAP METAL 

(4) Estimate the amount of each commodity (grade) of purchased scrap metal used by your site in a typical 

amount of time.

Commodities (grade) 

of Purchased 

Scrap Metal

Bundles 

Sheared scrap 

Plate and structural (P&S) 

Shredded scrap (frag) 

Heavy Melt

Typical 

Amount Time Period (Check one.)

0 month 

Tons per El quarter Op year o1 Other

(5) What kinds of processing are done to purchased scrap metal at your site? (Check all that apply.) 

"El Sorting 

"C Cutting 

"C Shearing 

"C Other 

Specify

NUREG-1669

Typical Amount

138
APPENDIX C: SURVEY OF THE STEEL INDUSTRY

Purchase £cr etal

C. OUTSIDE ONTO THE SITE

(6) At your site, is purchased scrap metal coming from the outside 

onto the site scanned for radiation? 

El No - Go To Page 146, Part E. 

El Yes 

(7) How many monitor stations are there for scanning this scrap meta 

coming from the outside onto your site? __

(8) How are the detectors mounted in 

relation to the trucks or railcars at 

each station? 

(9) What percentage of all the 

purchased scrap metal entering 

the site passes through each of 

these stations? 

(10) Are the vehicles (trucks or 

railcars) moving or stationary 

when being scanned? 

(11) About how often do radiation 

alarms occur at each station 

when purchased scrap metal 

material is being scanned?

Station 

No. 1 

"El One side 

"El Both sides 

El Top 

"El Bottom 

"El Moving 

"El Stationary

- per time

Detector 

Trucks or 

rail cars 

Detector 

Example of I monitor station 

with 2 detector panels.

Station 

No. 2 

"El One side 

"El Both sides 

El Top 

El Bottom 

El Moving 

El Stationary

- per time

Station 

No. 3 

"El One side 

"El Both sides 

"El Top 

El Bottom

"El Moving 

"El Stationary

- per time

S139 NUREG-1669
APPENDIX C: SURVEY OF THE STEEL INDUSTRY

C. Outside onto the Site (continued) 

(12) Along the way into your site, do trucks or railcars pass through more than one radiation monitor 

or the same radiation monitor without unloading? 

See figure for examples. =m (A) Trucks 

0 No - Go To Question 13. 

[Yes, explain below. , ~~~~~~~Rail Rl nnnnnm -- JH: t , 

CarsI•n-' Ul 1 __ __________________________________ onit~or omTor ,Sor ag 

(B) Raln-I•inmpm.uu 

Monitor 1 I 

&Sal .cl gej IProce~ig 

Examples of railcars scanned several times 

without unloading: (A) Passing one monitor for 

railcars and another for both for railcars and 

trucks. (B) Passing through one station to be 

stored on spur tracks, then weighed, then 

brought into the site. 

(13) After a vehicle passes through a monitor station and causes a radiation alarm, is the vehicle passed 

through the station again to confirm the alarm? 

0 No 

EO Yes, explain below. 

(14) About what percentage of the time do you accept scrap metal, even though a radiation alarm continues 

to occur, because you attribute the alarm to benign sources of radiation in or around the scape metal, 

such as pipe scale, thorium in a weld, dirt or sand in a rib of the vehicle? 

%: accept 

(15) What percentage of the purchased scrap metal goes directly to the storage/processing area and the melt 

shop after passing through the radiation monitors? 

__ % Storage/processing area 

__ % Melt shop 

100 % TOTAL

NUREG-1669 140 •
APPENDIX C: SURVEY OF THE STEEL INDUSTRY

D. ACTIONS TAKEN BEFORE TAKING POSSESSION OF PURCHASED 

SCRAP METAL 

(16) When a truck or railcar from the outside onto the site causes a radiation alarm and issuspected of 

containing radioactive material, how likely would the following events occur? 

_ % Turn away the truck or railcar based only on the radiation alarm(s) 

% Poke into the scrap metal to determine the cause of the alarm with a survey meter 

% Unload the scrap metal to investigate determine the cause of the alarm 

100 % TOTAL 

NOTE: Answer Question 17 if vehicles are TURNED AWAY without poking into or unloading 

scrap metal. 

(17) How likely is it that the following events would happen after a radiation alarm occurs when a scrap 

metal is rejected? 

% Only authorities (regulators, police) are notified 

% Only the scrap metal supplier is notified 

% Both authorities (regulators, police) and supplier are notified 

% No one is notified 

100 % TOTAL 

NOTE: Answer Questions 18 and 19 only if vehicles are POKED INTO or UNLOADED to 

investigate the cause of a radiation alarm. 

(18) How likely is it that the following events would happen after poking into or reworking (dumping) a 

load taken from the outside to the storage area is suspected of containing radioactive material? 

% Only authorities (regulators, police) are notified 

% Only the scrap metal supplier is notified 

% Both authorities (regulators, police) and supplier are notified 

% No one is notified 

100 % TOTAL 

(19) How likely is it that you would accept scrap metal when a radiation alarm continues to occur 

because you have found what you believe is causing the alarm, such as dirt or pipe scale?

141 NUREG-1669
APPENDIX C: SURVEY OF THE STEEL INDUSTRY

E. BETWEEN THE STORAGE /PROCESS AREAS AND MELT SHOP 

(20) How is scrap metal brought to the area near the melt shop? 

0 Scale (transfer) cars - Go To Page 147, Part F. 

0 Trucks or railcars 

(21) Along the way from the storage/process areas and to the melt shop, is purchased scrap metal scanned 

for radiation? 

0 No - Go To Page 147, Part F. 

!J Yes - Explain below. 

(22) What percentage of purchased scrap metal from the storage/process areas to the area next to the 

furnace would you guess is scanned for radiation? % 

(23) After a vehicle passes through a monitor station and causes a radiation alarm, is the vehicle passed 

through the station again to confirm the alarm? 

O No - Go to Question 24. 

C Yes - Explain below. 

(24) How often do radiation alarms occur when purchased scrap metal is scanned when going from the 

storage/process area to the melt shop? 

per 

(time period)

NUREG-1669 142
APPENDIX C: SURVEY OF THE STEEL INDUSTRY

F. CHARGE BUCKET OR CHARGE BOX FOR ANY TYPE OF FURNACE 

(25) Is the charge bucket or charge box scanned for radiation?

El Never - Go To Page 148, Part G. 

El Sometimes 

El Always

(26) On these sketches of 

charge buckets/ boxes, 

mark the location of the 

detectors around each 

charge bucket/box on 

the figures. Also, 

indicate the distance in 

feet from the bucket or 

box by marking the 

same diagram.

Top 

View 

Side 

View

(27) Is a bucket or a box used to fill 

your furnace(s)? 

(28) Approximately, what are the 

linear dimensions of the charge 

bucket or box?

(29) How is each charge bucket/box 

monitored? 

(Check all that apply.) 

(30) How often do radiation alarms 

occur? 

(31) About what percentage of scrap 

metal passing through each 

charge bucket/box is scanned for 

radiation? Please account for 

times when a monitor is 

inoperative.

1't Charge 

Bucket/Box 

L-. )

i' -

"E Charge bucket 

"El Charge box 

feet 

Linear dimensions 

"El While the 

bucket/ box is 

being filled? 

"El After loaded, 

while the 

bucket/box is 

stationary? 

"El After loaded, 

while the 

bucket/box is 

moving?

2 nd Charge 

Bucket/Box 

It S 

I - - -

El Charge bucket 

El Charge box 

feet 

Linear dimensions 

El While the 

bucket/box is 

being filled? 

El After loaded, 

while the 

bucket/box is 

stationary? 

El After loaded, 

while the 

bucket/box is 

moving?

3 rd Charge 

Bucket/Box 

I, S 

IS -

El Charge bucket 

El Charge box 

feet 

Linear dimensions 

El While the 

bucket/box is 

being filled? 

El After loaded, 

while the 

bucket/box is 

stationary? 

El After loaded, 

while the

bucket/box is 

moving?

% 

Sum to 100% 0I 

000 - 0

NUREG-1669

C 0%

143
APPENDIX C: SURVEY OF THE STEEL INDUSTRY

G. FURNACE 

(32) How large are the furnaces for melting scrap metal, how many of each size are at the site, how large 

are the charges of scrap metal, and what percentage of the production is made in each?

Type of furnace

Rated capacity 

of each furnace 

(Tons) 

/St 

Size of charges Crd 

(Tons) 

5 1h

Percent of total production ( 

made in each furnace

Furnace 

#1 

DEAF 

O BOF

Furnace 

#2 

D EAF 

O BOF

Furnace 

#3 

" EAF 

" BOF

____ 4. J ____________

04

Furnace 

#4 

" EAF 

"F BOF

Sum to 100% 

: % %1/

NUREG-1669

Furnace 

#5 

0 EAF 

0 BOF

%J

144
APPENDIX C: SURVEY OF THE STEEL INDUSTRY

H. ACTIONS TAKEN ONCE SCRAP METAL IS UNLOADED 

(33) When a radioactive source is found in unloaded scrap metal, how likely is it that the following events 

would occur in the long term to the radioactive source and to notify someone?.

Radioactive 

Source {

____% Disposed of by the mill employees, consultant, or regulator 

% Kept in an unused area to deal with at an unknown time in the future 

% Other 

100 % TOTAL

Notify f 

Someone

% Only authorities (regulators, police) are notified 

___.% Only the scrap metal supplier is notified 

____% Both authorities (regulators, police) and supplier are notified 

___% No one is notified 

100 % TOTAL

145 NUREG-1669
APPENDIX C: SURVEY OF THE STEEL INDUSTRY 

Entrance 

Stoas Shop FWurnce Dust 

& Procss I4~collectionI 

or 

I. SAMPLES (TEST PIECES) TAKEN FROM HEATS 

(34) Are the samples taken from the heats to determine the composition also scanned for radiation? 

"El Never - Go below to Page 151, Part J. 

"El Sometimes 

0l Always 

(35) Where is the radiation detector? (Check all that apply.) 

"El At the quench bucket 

"El In the chem lab, as part of the chemical analysis unit 

"El In the chem lab, separate from the chemical analysis unit. 

"El Other 

(SP e c f) 

(36) About what percentage of heats would you guess are scanned for radiation? % 

(37) How often have the radiation alarms occurred when samples (test pieces) are scanned? 

- per 

(time period)

NUREG-1669 146
APPENDIX C: SURVEY OF THE STEEL INDUSTRY

J. FURNACE DUST 

(38) Currently, what is done with furnace dust? (Check all that apply.) 

EAF BOP 

"El Bury at a disposal site El Bury at a disposal site 

"El Send to a hazardous waste recycler off site El Send to a hazardous waste recycler 

"El Process on site El Sintering "El Other __ Other 

Specify Specify 

(39) Is the furnace dust scanned for radiation before leaving the site? 

"El Never, Go To Page 152, Part K. 

"El Sometimes 

"El Always 

(40) What best describes the radiation monitor used to scan the furnace dust for radiation? (Check all that 

apply.) 

"El Same monitor system used for scanning scrap metal coming into the site. 

"El Separate monitor dedicated for scanning the product 

El Hand-held survey meter 

"El Along the dust collection ductwork going to the baghouse or pollution control system 

"El Inside of the baghouse or pollution control system 

"El While exiting the baghouse or pollution control system 

"El Other 

Specify 

(41) What percentage of furnace dust would you guess is scanned for radiation? % 

(42) How often do radiation monitors alarm when furnace dust is scanned? __ per (time period)

147 NUREG-1669
APPENDIX C: SURVEY OF THE STEEL INDUSTRY 

K. SLAG 

(43) Is slag scanned for radiation before leaving the site? 

"El Never - Go below to Part L. 

"El Sometimes 

"El Always 

(44) What best describes the radiation monitor used to scan the slag for radiation? 

"El Same monitor system used for scanning scrap metal coming into the site. 

"El Separate monitor dedicated for scanning the product 

"El Hand-held survey meter 

"El Other 

(Specify) 

(45) What percentage of slag would you guess is scanned for radiation? % 

(46) How often do radiation alarms occur when slag is scanned? __ per (time period) 

L. STEEL (BARS, SLABS, COILS, PLATES, FINISHED) PRODUCT 

(47) Is the steel produced at this site scanned for radiation before leaving the site? 

"El Never - Go to Page 153, Part M. 

"El Sometimes 

El Always 

(48) What best describes the radiation monitor used to scan the steel product for radiation? 

"El Same monitor system used for scanning scrap metal coming into the site.. 

"El Separate monitor dedicated for scanning the product. 

"El Hand-held survey meter. 

"El Other 

(Specify) 

(49) What percentage of steel product would you guess is scanned for radiation? % 

(50) How often do radiation alarms occur when steel produced at the site is scanned? 

- per (time period)

NUREG-1669 148
APPENDIX C: SURVEY OF THE STEEL INDUSTRY

M. COSTS 

(51) Was a radioactive source melted at your site? 

1J No - Go To Question 53. 

5 Yes 

(52) At your site, what year was a radiative source melted and what were the down-time, decontamination, 

and disposal costs?

Year that the radioactive 

material was melted 

Down time costs 

Decontamination costs 

Disposal of contaminated 

products and byproducts.

1" Occurrence 

19 

$ 

$ 

$

2 nd Occurrence 

19 

$ 

$

(53) Optional. About how much staff-time did people at your site spend gathering information and 

completing the survey? 

hours, minutes

149 NUREG-1669
INDEX

analyze, 1 

assess, l 

assumption 

basis of decisions, 3 

charge bucket, 101 

gauges in the recycling stream, 11 

hidden, 3 

implication of, I 

in complex analysis, 3, 111 

in health consequences, 11l 

inappropriate, 3, 98 

mixing of commodities, 82 

monitoring steel product, 103 

proportional risk to a steel mill, 15, 93 

randomly located, 82 

rare event, 82 

responsibility for gauges, 40, 57 

size of vehicles, 83 

temporal variations, scrap metal, 20 

validity, 3 

at risk 

population, 53 

trends, 35 

BC see benign contamination 

benign contamination 

as a risk element, 98 

assumption when monitoring scrap 

metal, 14 

benefits, monitoring scrap metal, 86 

defined, 5 

distribution of radiation levels, 86 

best estimate, 26 

business decisions 

invest in protection 

circumstances 

to account for when regulating, 40 

civil penalty 

defined, 43 

equation, 44 

communication 

see education and communication 

control 

compromised, 40 

evidence of a problem, 24 

mechanisms, 41 

control mechanisms, I 

hard, defined, 41 

list of, 41 

soft, defined, 41 

cost 

difficulties in determining, 113 

of melting a gauge, 15 

justifying a portal monitor, 13 

to licensees, 112 

to scrap yards, 112 

to steel mills, 112 

data 

see empirical data 

decisions 

basis for, 3 

made with risk estimates, 24 

influenced by uncertainty, 27 

influenced by illustrations, 27 - 29 

deficient control 

see control 

degrees of information 

see information 

demolition 

controlling gauges, 46

phases of, 49 

detection 

defined, 72 

missed, defined, 71 

detection probability 

conditional, 88 

equation, 81, 84 

experimental information, 38 

from empirical data, caution, 37 

implications, 78 

incompletely known, 78 

DOT Exemption as a source of information, 34 

description, 75 

lack of awareness, 74 

education and communication, 43 

empirical data 

analytical history, 35 

changing circumstances, 36 

deficiencies, 34, 35 

expected value, 27 

biased estimate, 27 

unbiased estimate, 27 

expert judgment 

limited views, 2 

substitute for an analysis, 2 

developing solutions, I 

false alarm as primary concern, 90 

defined, 71, 89 

furnace dust 

classification, 15, 77 

monitoring for radiation, 76, 104 

gauges see nuclear gauges 

goal of the risk analysis, 5 

heat 

molten steel, 71 

ICC 

see immediate and continuous control 

immediate and continuous control, 40 

information 

degrees of, 31 

inspection 

defined, 43 

inventory 

contrast to registration, 41 

defined, 41 

jurisdiction, 10, 57 

just-in-time deliveries, 74 

label, 5, 42 

implications of, 13 

limited benefit, 13 

load, 74 

lollipop sample 

see test piece 

lost device, 53 

monitoring 

see radiation monitoring 

NORM 

characterized, 5 

discoveries of, 9 

nuclear gauges 

benefits, 110 

prevalence of, 48, 53 

substitutes, 110 

objectives of the risk analysis, 5 

observational study, 34 

penalty see civil penally

point estimate 

perceptions, 26 

QCR 

see query at a change in responsibility 

query at a change in responsibility, 46 

radiation monitoring 

basis of strategies, 84 

charge bucket, 74, 99 

furnace dust, 76 

implications, 89 

in-coming scrap metal, 73, 95 

multiple passes without unloading, 87 primary concern, 90 

slag, 77, 104 

steel product, 76, 103 

test piece, 75, 103 

radioactive material 

discoveries of, 9 

radium 

characterized, 5 

discoveries of, 9 

registration 

as a control mechanism, 45 

contrast to inventory, 41 

contrast to QCR, 46 

expectations, improving control, 45 

interaction with other controls, 45 

risk 

danger to life, 11l 

danger to property, 112 

element, 5 

equation, 24 

estimating with empirical data, 3 

risk analysis 

account for relevant information, 2 

assessing changes, 24 

comprehensive, 2 

correct logic, 3 

need for, 1 

risk estimates 

aggregate, 24 

distribution of, 26, 27 

example calculation, 23 

fractional contribution, 26 

point, 26, 27 

triplet, 24 

sample of convenience, 35 

shipment, 74 

stakeholders, 1 

standard response 

defined, 71 

when monitoring for radiation, 87 

survey 

applying to improve control, 60 

bias, 34 

length, 33 

determining gauge location, 51 

method to develop, 33 

need for, 32 

sensitive questions, 33 

testing, 33 

test piece 

as a risk element, 103 

defined, 75 

uncertainty 

decisions, 3, 27 

dependence, 27 

perceptions, 3, 28 

visual detection, 13 

worker, 109

151
NRC FORM 335 U.S. NUCLEAR REGULATORY COMMISSION 1. REPORT NUMBER 

(2-89) (Assigned by NRC, Add Vol., Supp., Rev., NRCM 112 BIBLIOGRAPHIC DATA SHEET and Addendum Numbers, If any.) 

3201, 3202 BBIGAHCDT HE 

(See instructions on the reverse) 

2. TITLE AND SUBTITLE NUREG-1 669 

A Risk Analysis of Fixed Nuclear Gauges 3. DATE REPORT PUBLISHED 

MONTH YEAR 

April 2000 

4. FIN OR GRANT NUMBER 

5. AUTHOR(S) 6. TYPE OF REPORT 

Technical 

7. PERIOD COVERED (Inc/usive Dates) 

1995-1998 

8. PERFORMING ORGANIZATION - NAME AND ADDRESS (If NRC, provide Division, Office or Region, U.S. Nuclear Regulatory Commission, and mailing address; if contractor, 

provide name and mailing address.) 

Division of Risk Analysis and Applications 

Office of Nuclear Regulatory Research 

U.S. Nuclear Regulatory Commission 

Washington, DC 20555-0001

9. SPONSORING ORGANIZATION - NAME AND ADDRESS (If NRC, type 'Same as above', if contractor, provide NRC Division, Office or Region, U.S. Nuclear Regulatory Commission, 

and mailing address.)

Same as above.

10. SUPPLEMENTARY NOTES

11. ABSTRACT (200 words or less) 

Fixed nuclear gauges containing the radionuclides "

t7Cs, 'Co, or 24

.. Am are used in many industries to 

improve the quality and lower the costs of products for industrial, commercial, and private uses. But gauges 

that are improperly controlled during use and transfer can expose people to radiation and, upon entering the 

stream of recycled steel, can cause steel mills to spend millions of dollars to decontaminate equipment and 

dispose of contaminated materials. The risk to licensees and the recycling industries that nuclear gauges pose 

is incompletely understood. An analysis of fixed nuclear gauges was performed to study the risk to life and 

property, from facilities where the gauges are used to steel mills where the gauges might be melted. A risk 

analysis should be of interest to all stakeholders- agencies that promulgate regulations, licensees who must 

comply with the regulations, and the recycling industries who use scrap steel as a resource for making 

products. Although risk could not be estimated because data are lacking, observations and insights were 

made that can be used by all stakeholders to reduce their risk, even if the extent of the reduction is unknown.

12. KEY WORDS/DESCRIPTORS (List words or phrases that will assist researchers in locating me report.) 13. AVAILABIUTY STATEMENT 

immediate and continuous control unlimited 

nuclear gauge 14. SECURITY CLASSIFICATION 

risk analysis (This Page) 

scrap yard unclassified 

steel mill (This Report) 

unclassified 

15. NUMBER OF PAGES 

16. PRICE

NRC FORM 335 (2-89)
Federal Recycling Program
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POSTAGE AND FEES PAID 

USNRC 

PERMIT NO. G-67

UNITED STATES 

NUCLEAR REGULATORY COMMISSION 

WASHINGTON, DC 20555-0001 

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PENALTY FOR PRIVATE USE, $300