NUREG/CR-6841

ORNL/TM-2003/225

A Risk-Informed Basis for

Establishing Non-Fixed Surface

Contamination Limits for

Spent Fuel Transportation Casks

Oak Ridge National Laboratory

U.S. Nuclear Regulatory Commission

Office of Nuclear Material Safety and Safeguards

Washington, DC 20555-0001 Ad RE(,,
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NUREG/CR-6841

ORNL/TM-2003/225

A Risk-Informed Basis for

Establishing Non-Fixed Surface

Contamination Limits for

Spent Fuel Transportation Casks

Manuscr Completed: November 2003

Date Published. April 2004

Prepared by

R.R. Rawl, K.F. Eckerman, J.S. Bogard

Oak Ridge National Laboratory

Managed by UT-Battelle, LLC

Oak Ridge, TN 37831-6472

J.R. Cook, NRC Project Manager

Prepared for

Spent Fuel Project Office

Office of Nuclear Material Safety and Safeguards

U.S. Nuclear Regulatory Commission

Washington, DC 20555-0001

NRC Job Code B0009

co- "4
ABSTRACT

The current internationally accepted basis for establishing non-fixed surface contamination limits for

spent fuel casks is the same as that for other transportation package types. This study examined the

suitability of the currently used exposure model, taking into account exposure pathways and parameters

representative of typical light-water-reactor spent fuel cask handling, loading, and transportation

activities. Because the currently used model was found to be inappropriate for spent fuel casks, a new

exposure model was developed using pathways and parameters specific to spent fuel casks. Results show

that individual and collective doses to members of the public are very low and that worker doses

dominate the total collective dose from non-fixed surface contamination. Worker doses that vary as a

function of allowable surface contamination limits were calculated and were found to be dominated by

doses due to decontamination and surface contamination monitoring activities performed after the cask is

drained. An approach was developed for evaluating the overall dose implications of higher allowable

non-fixed surface contamination limits. This approach was used to examine the reduction in doses to

workers performing cask decontamination and monitoring activities necessary to offset increased doses

due to other worker and public exposure pathways.

Hi.
CONTENTS

Paae

ABSTRACT .. . . . . . . . . mf

LIST OF FIGURES .................. ix

LIST OF TABLES .................. xi

FOREWORD .................. xiii

ACKNOWLEDGEMENTS .................... xv

INTRODUCTION ..

1.1 FAIRBAIRN MODEL ASSUMPTIONS..............................................................................1

1.2 SHORTCOMINGS OF THE FAIRBAIRN MODEL FOR LWR SNF PACKAGE

A SEIPM ENTS................................................................................................................. 2

1.3 APPLICABILITY OF THE FAIRBAIRN MODEL TO SPENT FUEL CASKS . 2

2 SUMMARY OF CTHER STUDIES..............................................................................................5

3 OPTIMIZATION .. 7

3.1 TOTAL DOSE .7

3.2 WORKER DOSE .7

3.3 PUBLIC DOSE .9

3.4 CALCULATION OF DOSES .10

4 CALCULATION OF WORKER DOSE (Eb)............................................................................. 13

4.1 WORKER EXPOSURE PARAMETERS . . .14

4.2 EFFECTIVE DOSES TO WORKERS DUE TO INTERNALLY DEPOSITED

RADIONUCLIDES (E.6).................................................................................................. 14

4.2.1 Effective Dose to Workers Due to Internally Deposited Radionuclides

from the Cask Surface (EL,) .............................................................................. 14

4.2.1.1 Inhalation (Ej*c 1 )........................................................................14

4.2.1.2 Ingestion (E ,k,, ) ............................................................................ 16

4.2.2 Effective Dose to Workers Due to Internally Deposited Radionuclides

from the Ambient Atmosphere in the Work Area (Em,,,,b) .17

4.3 DOSES TO WORKERS DUE TO EXTERNAL EXPOSURE (E) ... 17

4.3.1 Effective Dose to Workers Due to External Exposure to Removable

Contamination on the Cask Surface and from the Cask Itself (E.,) .. 17

4.3.1.1 External exposure from contamination on the cask surface (Ea..krsf) ... 17

4.3.1.1.1 Direct external exposure from contamination on the cask

surface................................................................................ 17

4.3.1.1.2 External exposures to workers due to transfer

of contamination .19

4.3.1.2 External exposure from the cask contents (E,.,k,) .......................... 22

4.3.2 Effective Dose to Workers Due to External Exposure to Ambient Radiation

in the Work Area (Emu) ............................ 23

4A SUMMARY OF WORKER DOSES ........... ................. 24

4.5 WORKER DOSES AS A FUNCTION OF CONTAMINATION LIMITS .... 25

v
5 CALCULATION OF PUBLIC DOSE ..... 27

5.1 EFFECTIVE DOSES TO THE PUBLIC DUE TO INTERNALLY DEPOSITED

RADIONUCLIDES .... ....................... 27

5.1.1 Exposure Scenaios ...................................................... . 27

5.1.2 Public Inhalation Dose Model ....................................................... 28

5.1.3 Off-Link (Persons Residing in the Vicinity of the Transport Route) ... 28

5.1.3.1 Dose to an individual ........................ .............................. 28

5.1.3.2 Population dose ...................................................... 28

5.1.3.2.1 Multilane divided highway .................................................. 29

5.1.3.2.2 Other highway ...................................................... 29

5.1.4 On-Link (Persons Traveling in the Vicinity of the Shipment During Transport) ... 30

5.1.4.1 Individuals in vehicles following the shipment ....................................... 30

5.1.4.1.1 Multilane dividedhighway ............................................ 30

5.1.4.1.2 Other highway..................................................................... 30

5.1.4.2 Individuals in vehicles passing the shipment in the same direction

as the shipment ........ 31

5.1.4.2.1 Multilane divided highway ...................................... 31

5.1.4.2.2 Other highway ...................................... 31

5.1.4.3 Individuals in vehicles traveling in the opposite direction

to the shipment....................................................................................... 31

5.1.4.3.1 Multilane divided highway ...................................... 31

5.1.4.3.2 Other highway ...................................... 32

5.1.4.4 On-link collective doses due to inhalation ...................................... 32

5.1.5 Doses Due toInhalation at Stops . . .32

5.1.6 Summary of Public Doses Due to lnhalation . . .33

5.2 DOSES TO THE PUBLIC DUE TO EXTERNAL EXPOSURES .... 34

5.2.1 Exposure Scenarios ...................................................... . 34

5.2.2 Public External Dose Model ...................................................... 34

5.2.3 Off-Link Population (Persons Residing in the Vicinity of the Transport Route) ...... 35

5.2.3.1 Dose to an individual ........................ .............................. 35

5.2.3.2 Population dose ...................................................... 35

5.2.3.2.1 Multilane divided highway .................................................. 36

5.2.3.2.2 Other highway..................................................................... 36

5.2.4 On-Link (Persons Traveling in the Vicinity of the Shipment During Transport) ... 36

5.2.4.1 Individuals in vehicles following the shipment ....................................... 37

5.2.4.1.1 Multilane divided highway ............................................ 37

5.2.4.1.2 Other highway..................................................................... 37

5.2.4.2 Individuals in vehicles passing the shipment in the same direction

as the shipment ............................................ 37

5.2.4.2.1 Multilane divided highway.................................................. 37

5.2.4.2.2 Other highway..................................................................... 37

5.2.4.3 Individuals in vehicles traveling in the opposite direction

to the shipment....................................................................................... 37

5.2.4.3.1 Multilane divided highway.................................................. 37

5.2.4.3.2 Other highway..................................................................... 37

5.2.4.4 On-link collective doses due to external exposures ................................. 38

5.2.5 Doses Due to External Exposures at Stops ...... ...................... 38

5.2.6 Summary of Public Doses Due to External Exposure ............................................. 38

5.3 PUBLIC DOSES FROM HIGHER CONTAMINATION LIMITS . . .................................... 40

vi
6 OPTIMIZNG SPENT FUEL CONTAMINATION LIMITS ....................................................... 41

6.1 EFFECT OF ALLOWABLE CONTAMINATION LIMITS ON WORKER DOSES .......... 41

6.2 WORKER DOSES DUE TO SPENT FUEL CASK DECONTAMINATION AND

MONITORING ACTIONS ................................................................ 41

6.2.1 DOE-CHPO-1 ................................................................ 41

6.2.2 CEPN/EDF Report ................................................................ 41

6.2.3 Infrmation froma U.S. Reactor Operator ............................................................ 42

6.3 POTENTIAL WORKER DOSE REDUCTIONS DUE TO HIGHER ALLOWABLE

CONTAMINATION LIMITS ................................................................ 43

6.4 OVERALL DOSE IMPACTS DUE TO HIGHER CONTAMINATION LIMITS ... 46

6.5 CONSERVATISMS AND SENSITIVITIES IN THE MODEL .......................................... 47

7 CONCLUSIONS ................................................................ 49

8 REFERENCES............................................................................................................................ 51

APPENDIX A-SUMMARY OF SELECTED PREVIOUS CONTAMINATION STUDIES .. 53

A.1 SUTMMARYOFNUREGCR-1858 .55

A.2 SUMMARY OF NRPB REPORT .56

A.3 SUMMARY....................................................................................................................... 57

A.4 REFERENCES .57

APPENDIX B-WORKER PARAMETERS FROM DOE-TPOCH-00O. 59

APPENDIX C-MODELING PUBLIC EXPOSURE TO RESUSPENDED SURFACE

CONTAMINATION DURING MOVEMENT . .79

C. 1 SUMMARY OF MODELING APPROACH .81

C.2 ILLUSTRATIVE EXAMPLES .. 84

C.3 REFERENCES .85

APPENDIX D-COLLEC)IVE INTERNAL DOSE TO PASSENGERS IN VEHICLES

DURING TRANSPORT .87

APPENDIX E-INHALATION POPULATION DOSE FROM CONTAMINATION AT STOPS ... 91

E.1 INTRODUCTION .. 93

E.2 PROXIMAL DOSE .. 93

E.2.1 Dose to the Maximum Exposed Individual .95

E.2.2 Population Dose .96

E.3 DISTAL DOSE .. 97

E.4 TOTAL POPULATION DOSE .. 99

E.5 REFERENCE .. 102

APPENDIX F-EXTERNAL EXPOSURES TO MEMBERS OF THE PUBLIC .103

F.I MAXIMUM EXPOSED PERSON .105

F.1.I Dose from Following a Transport at a Fixed Distance .105

F. 1.2 Dose from a Passing Transport............................................................................. 105

F.2 EXTERNAL EXPOSURES-COLLECTIVE DOSE . .106

F.2.1 Average Distance of the Exposed Population from the Transport .......................... 107

vii
LIST OF FIGURES

Figure pag

1 Worker collective dose components ................................................................... 44

2 Collective dose-all groups ................................................................... 47

A. 1 Collective dose vs decontamination time for spent fuel container. ............................................... 56

C.1 Schematic of a divided limited-access highway with the truck (lower lane) proceeding

at speed "v.. ................................................................... 82

C.2 Schematic of a two-lane highway with the truck (lower lane) proceeding

at a speed "v." ................................................................... 84

D.1 Values of XJQ for vehicles following a spent fuel cask transport .................................................... 90

E.1 Values off, for distances of 5 to 100 m from the transport ............................................................. 95

E.2 Atmospheric activity concentration with distance from the source for a 300-mr mixing layer

(A =1 Bq cmd2) ................................................................... 98

E.3 Ground footprint of airborne contamination (10 to 800 m from cask, no inversion) ..................... 100

E.4 Ground footprint of airborne contamination 5 to 10 m from cask (dashed line). ......................... 100

ix
LIST OF TABLES

Table Me

1 Doses that vary due to removable surface contamination on spent fuel casks ................................. 10

2 Reference spent fuel pool water radionuclide composition ........................................................ 10

3 Radionuclide characteristics for reference mixture of contaminants for workers ............................ 11

4 Parameters and doses to workers "doing cask work" due to external radiation from 1 Bq cm72

surface contamination of 6DCo (one cask turnaround cycle) .18

5 Doses due to radiation from the cask contents as a result of cask decontamination

and monitoring tasks to current contamination limits .22

6 Doses due to radiation from the work area as a result of cask decontamination

and monitoring tasks to current contamination limits ........................................................ 23

7 Individual dose to workers by all pathways ........................................................ 24

8 Collective dose to workers by all pathways ........................................................ 25

9 Worker doses that increase due to higher removable contamination levels ..................................... 26

10 On-link collective inhalation doses ........................................................ 32

11 Inhalation doses to the maximum exposed member of the public ................................................... 33

12 Inhalation collective dose to the public ........................................................ 34

13 Collective on-link doses due to external radiation ........................................................ 38

14 External exposure dose to the maximum exposed individual member of the public ....................... 39

15 External exposure collective dose to the public ........................................................ 39

16 Collective and individual doses from higher contamination levels ................................................. 40

17 Increases in public doses due to higher contamination levels ........................................................ 40

B.! Worker parameters from DOE-TPO/CH-01 .61

D.1 Collective dose for on-link exposures .89

F.1 Values of a and b for estimating collective doses from external exposures................................... 108

xi
FOREWORD

Contamination incidents in the late 1990s involving shipments of spent nuclear fuel in Europe highlighted

the need to reexamine the regulatory basis for limiting non-fixed radioactive contamination on the

external surfaces of spent fuel transportation casks. The international transport safety community

responded to this need, and the International Atomic Energy Agency LAEA) initiated a Coordinated

Research Project (CRP) on Radiological Aspects of Package and Conveyance Non-Fixed Contamination.

Several LAEA member states and one international organization participated in the CRP by performing

research related to non-fixed radioactive contamination on all package types (not just spent fuel casks).

The U.S. Nuclear Regulatory Commission represented the United States in the CRP and undertook an

examination of the radiological basis for non-fixed contamination on spent fuel casks. This examination

included identifying the dose pathways for cask contamination and developing calculational approaches

for quantifying resulting doses. This report presents the results of this examination and provides results

for all significant dose pathways, both to workers and members of the public. The results provide

information and approaches that can be used to determine if radiation doses from spent fuel cask

contamination are optimized. Understanding the extent to which these doses are optimized is an important

element in determining if contamination limits are risk informed.

xii
ACKNOWLEDGEMENTS

The authors would lice to acknowledge the contributions by all the participants in the LAEA CRP.

Their work, particularly the work of the Modeling Group, was instrumental in identifying and evaluating

possible dose pathways from non-fixed surface contamination. Several of the approaches used in the

CRP are also used in this report and in other cases were modified for use in this report. By building on

the CRP approaches, this study was able to focus on and expand consideration of the dose pathways

specific to spent fuel cask transportation.

The contributions of B. L. Broadhead and R. L. Coleman, Oak Ridge National Laboratory, in performing

calculations and reviewing the draft report are also gratefully acknowledged

xv
1 INTRODUCTION

The current limits for non-fixed contamination on packages used to transport radioactive materials were

introduced in the 1961 edition of the International Atomic Energy Agency (1AEA) transport regulations

and were based on radiation protection guidance and practices in use at that time. The limits were based

on exposure scenarios leading to intakes of radionuclides by inhalation and external irradiation of the

hands. These considerations are collectively referred to as the Fairbairn model. ' Although formulated

over 40 years ago, the model remains unchanged and is still the basis of current regulatory-derived limits

on package non-fixed surface contamination.

In general, non-fixed contamination on the surface of a package can result in doses through the following

pathways:

* Radiation emitted from the contaminated package surface and incident onto the body (direct

exposure)

* Dispersal of the surface contamination into the air in a handling facility, leading to subsequent

- Inhalation intakes

- Deposition onto the body and subsequent irradiation

* Transfer of contamination to the hands during handling of the packages, leading to

- Irradiation of the hands

- Transfer of contamination from the hands to the face with irradiation of the face

- Ingestion of contamination from the hands

* Direct ingestion (which is considered sufficiently unlikely that it is not considered further)

* Dispersal into the environment

- Inhalation (including material resuspended following deposition)

- Deposition onto the body (including material resuspended following deposition)

- Ground shine (exposure to radiations emitted by contamination on the ground - Ingestion via the food chain

There can also be doses that while not resulting directly from the contamination, are strongly influenced

by and attributable to regulatory requirements for contamination controL For example, actions necessary

to comply with the current derived limits for light-water-reactor (LWR) spent nuclear fuel (SNF) casks

can result in significant external doses to workers. This is due to the relatively high radiation levels

around the loaded casks, where workers must function during the measurement of contamination levels

and while decontaminating the casL In order to optimize the total dose received due to compliance with

cask contamination levels, it is necessary to take into account all the doses that vary as a result of the

regulatory limit.

1.1 FAIRBAIRN MODEL ASSUMPTIONS

The Fairbairn model limits its consideration to inhalation of airborne contamination and transfer of

contamination to the hands under a specified set of exposure scenarios. The permissible levels of

contamination are constrained to not result in (I) an airborne concentration greater than the maximum

permissible concentration in air (NPCa) specified in the 1959 recomnurendations of the International

Commission on Radiological Protection (ICRPii and (2) contamination of the hands beyond what was

considered to be good practice in the 1960s. These constraints were applied to 239Pu (an alpha emitter)

and 9

0

Sr (a beta emitter), which were considered the most hazardous alpha- and beta-emitting

radionuclides at that time. Good practice regarding hand contamination was based on limiting the

irradiation of the basal layer of the skin, because the potential ingestion of contamination from the hands

1
Introduction Section 1

was found to be less restrictive. The model resulted in surface activity limits of 0.4 and 4 Bq cm72for

alpha and beta emitters, respectively.

1.2 SHORTCOMINGS OF THE FAIRBAIRN MODEL FOR LWR SNF

PACKAGE SHIPMENTS

* The exposure scenarios of the model are characterized by conservative parametric values.

This includes the resuspension factor (4 x 10- m1l) and the exposure time (2000 h per year).

Because only a fraction of the workers' time involves package preparation and shipment

activities, this exposure time assumption is extremely conservative for SNF cask operations.

* The radiological parameters used in the model were taken from ICRP Publication 2, issued in

1959, and have been superseded by subsequent ICRP guidance.3 Thus, the model is not

consistent with current practice. For example, current prospective planning constrains a

worker's annual exposure to an effective dose3 of 20 mSv, not the 50-mSv value used in 1959.

Although the effective dose constraint has been lowered, the applicable dose coefficients yield

permissible workplace airborne concentrations for 2'Pu and wSr that are 3 and 30 times higher,

respectively, than the MPCa values used in the model. Thus, the currently accepted ICRP dose

coefficients would result in contamination limits 3 to 30 times higher, assuming the same

resuspension factors are used.

* Given the wide variation in magnitude of the dose coefficients among the radionuclides, a

comprehensive model must be capable of addressing more than two radionuclides. The

Fairbairn model relied on a high degree of conservatism in its selection of model parameters

and in its consideration of only the most restrictive alpha- and beta-emitting radionuclides

(nPu and 9OSr). These radionuclides, while limiting, are inappropriate for LWR SNF

packaging applications. The use of 34Cs, 137Cs, mCo, and 6OCo is more appropriate for SNF

applications, because these are the radionuclides most frequently encountered in significant

quantities on cask surfaces following immersion in spent fuel pools.

* The inhalation intakes are based on a scenario occurring "in a confined space with conditions

arranged to simulate very dusty conditions."' This approach is very conservative, considering

the conditions under which SNF packages are stored, prepared, and transported today.

* The Fairbairn model is based on a transport worker who handles packages and works in the

vicinity of packages continuously for 2000 h per year. The model does not take into account

exposures to the following groups:

- the public, during the course of transport, and

- workers preparing packages for transport.

1.3 APPLICABILITY OF THE FAIRBAIRN MODEL TO SPENT FL

CASKS

In summary, the Fairbairn model is based on exposure scenarios that are not appropriate for spent fuel

casks. The exposure scenarios (e.g., dusty conditions) considered in the model are not representative of

the operational practices and environments associated with handling of spent fuel casks. The model is

based on the outdated "critical organ" approach to radiological protection that poorly, if at all, reflects

actual health risk. The more recent ICRP recommendations are risk based. Furthermore, the model has

no provisions to consider the significant doses to workers resulting from efforts to achieve compliance

2
Section 1 Introduction

with surface contamination limits. Finally, the model does not consider doses to other groups such as

members of the public.

Limits for non-fixed surface contamination on spent fuel casks should be established by using a model

that considers and optimizes the appropriate exposure scenarios both in the workplace and in the public

environment. A risk-informed approach is needed to ensure optimal use of personnel and material

resources for SNF-based packaging operations.

3
2 SUMMARY OF OTHER STUDIES

The studies described in Appendix A-Summary of Selected Previous Contamination Studies

concern previous work aimed at detarmining derived limit values for non-fixed surface contamination

levels.

The NUREG study4 includes both public dose and worker dose contributions to the total dose estimates.

However, only limited dose pathways are considered and the data used in the study are outdated. The

study indicates that for low direct-exposure dose-rate situations (1 wrem h-I in the cask vicinity), it is

possible to calculate an optimum additional decontamination time. This optimal time is dependent on the

efficacy of the decontamination procedure but appears to be about 20 additional minutes for an assumed

decontamination factor of 10 for each 30 min of decontamination effort. On the other hand, the study also

shows that for the envisioned scenarios with direct exposure rates of about 10 nrem h-i (100 IiSv hb-), the

optimal additional decontamination time is zero. This finding indicates that the total dose resulting from

additional decontamination effort increases as additional work near the cask is performed. (A very small

decrease in public exposure due to the reduced contamination levels is greatly outweighed by the increase

in worker exposure.)

The NRPB study5 includes a limited number of pathways but focuses on deriving contamination limits

and does not include public dose contributions. The study does indicate that derived limits of about

500-700 Bq cmn2 are appropriate for typical radionuclides found in spent fuel applications.

The IAEA has undertaken a Coordinated Research Project (CRP) on "Radiological Aspects of Package

and Conveyance Non-Fixed Contamination." Technical contributions to the CRP include development of

a model to calculate doses to the public and workers resulting from surface contamination for four

different package types. The CRP developed a set of dose pathways, exposure parameters, and

calculational techniques for estimating the doses to workers and the public. Where possible, this report

has attempted to use approaches that are consistent with the IAEA CRP. However, since the CRP model

covers four package types (small manually handled, small remotely handled, large remotely handled, and

spent fuel casks), the CRP model is more general in approach than this report (which deals solely with

spent fuel casks). The CRP model does not take into account the doses received due to the contents of the

spent fuel cask, nor does it calculate collective doses to workers and the public (a factor that is necessary

for examining optimization). As described in Sect. 4.3.1.2, doses to workers from the cask contents vary

as a function of the allowable contamination level, because the time required to perform decontamination

and contamination monitoring will vary. Consequently, some variations from the CRP approach have

been made in order to include all significant dose pathways for spent fuel casks.

5
3 OPTIMIZATION

Compliance with radiation protection dose limits does not necessarily lead to realizing the benefit from a

practice that requires radiation exposure to persons while, at the same time, keeping these exposures to

the lowest practicable levels. Radiation protection approaches such as "as low as reasonably achievable"

(ALARA), "as low as practicable" (ALAP), and "optimization" have been incorporated into radiation

protection principles as ways of achieving this objective.

The IAEA Basic Safety Standards' call for the optimization of protection and safety "[i]n relation to

exposures from any particular source within a practice .. ." and state that ". . . protection and safety shall

be optimized in order that the magnitude of individual doses, the number of people exposed and the

likelihood of incurring exposures all be kept as low as reasonable achievable ... within the restriction that

the doses to individuals delivered by the source be subject to dose constraints." In the case of non-fixed

surface contamination on spent fuel casks, exposures to both workers and the public must be considered.

3.1 TOTAL DOSE

Optimization of doses resulting from removable surface contamination on spent fuel casks requires a

consideration of all doses that could result from the contamination itself and doses that vary as a function

of the allowable contamination limit. In this report, when the doses due to surface contamination are

evaluated, these doses resulting from the contents of the cask are ignored except where these doses vary

due to the contamination Umits. That is, where the doses due to the contents are the same regardless of

the contamination limits, they are considered a constant and are not factored into the evaluation.

The total effective dose due to removable surface contamination on the spent fuel casks can be expressed

as

E., = E.+,,+ , (1)

where

Eas = total effective dose,

E., = effective dose to workers, and

Epx = effective dose to the public.

3.2 WORKER DOSE

The effective dose to workers is dependent on all the sources of exposure that vary as a function of the

surface contamination limnits. Since exposures due to decontamination and monitoring functions include

both internal and external pathways, these must be considered in calculating worker exposure.

7
Optimization Section 3

The effective dose to workers (Ew,&) can be expressed as

E. = E., + E. (2)

where

E4, = effective dose to workers from internal exposure, and

E = effective dose to workers from external exposure.

Some internal and all external worker doses will vary as a function of time spent near the cask. Because

the time required to complete tasks necessary to comply with the surface contamination limits will vary

with the contamination limits, these tasks must be considered separately when determining doses to

workers. During these tasks, workers will be exposed to internal and external sources from both the cask

itself and the work area.

The dose designated E.*, consists of all those contributors to internal exposure to workers when they are

performing contamination-related work on the cask and can be expressed as

E.* = Ew*,.A + E,,f,, (3)

where

E.A = effective dose to workers due to internally deposited radionuclides originating from

the cask surface, and

E.*,,b = effective dose to workers due to internally deposited radionuclides from the ambient

atmosphere in the work area.

The dose designated Ew*,,A* consists of two primary pathways by which contamination from the cask

surface can be internally deposited in workers: inhalation of resuspended surface contamination and

ingestion of contamination transferred from the cask surface to workers' hands and subsequently to the

lips and mouth. This can be expressed as

Ems,,, = Eon + E.gc, (4)

where

E 8hn = effective dose to workers due to inhaled radionuclides, and

Ewjg,, = effective dose to workers due to ingested radionuclides.

8
Section 3 Optimization

The dose designated E,, consists of all those contributors to external exposure to workers and can be

expressed as

nu= E, + Ew,() (S)

where

E.,, = effective dose to workers due to exposure to cask-related sources of external

radiation, and

E,,,,& = effective dose to workers due to external exposure to ambient radiation in the work

area.

The dose designated E,,, consists of two cask-related pathways that can lead to worker exposure:

direct external radiation from the contamination on the package surface and external radiation emanating

from the cask itself (due to its radioactive contents). This can be expressed as

Ewxcask = Evxxcasksurf + Ewexcaskon (6)

where

E.,, = effective dose to workers due to direct external radiation from the contamination on

the cask surface, and

E.,, = effective dose to workers due to external radiation from the cask contents.

The equations for worker exposure, both internal and external, can be combined and simplified as

E,,, = Ewncn, + E *.,,n + Ewinamib + E£ ,f + E....n + E.I.

3.3 PUBLIC DOSE

The effective dose to the public can be expressed as

Epb = EAR + E,,, (7)

where

Epi, = effective dose to the public due to internally deposited radionuclides originating from

the cask surface, and

Ep,, = effective dose to the public due to external exposure to removable contamination on

the cask surface.

9
Optimization Section 3

The public dose due to surface contamination on a cask is not a function of the dose rate from the cask

contents or the ambient (e.g., background) dose rate, because these doses do not vary as a function of the

surface contamination. Since these exposures will not be affected by the surface contamination limits,

they are not included in this study. The public dose pathways and dose calculations are presented in

Sect. 5.

3.4 CALCULATION OF DOSES

Table 1 shows the variables that are included in this study of doses due to removable surface

contamination on spent fuel casks.

Table 1 Doses that vary due to removable surface contamination on spent fuel casks

Total dose

(Eta)

Dose to workers

(E*hb)

Dose to the public

(Epub) 4.

Worker

internal dose

(E,*f)

Worker

external dose

(E.)

Public

internal

dose

(Epic

Public

external

dose

(E..)

From cask contamination Ambient From contamination and Ambient

(Ewing (Ewfab) cask contents (E.j,)

Inhalation Ingestion Contamination Cask

(E. . ,)(Em...g.) on surface contents

(Ease,) E..b)

The radionuclide composition of cask surface contamination is dependent on several factors but is most

heavily influenced by the radionuclides present in the pool water in which the cask is immersed. Pool

water radionuclide composition varies widely, so a reference pool water composition has been developed

for this analysis using the values identified in the literature 7 and confirmed qualitatively with another

nuclear plant operator. 8 Four primary contaminants were identified in LWR spent fuel pool water

(

13'Cs, "7Cs, 58 S'Co). Co, and For the purposes of this study, the quantitative results reported in Ref. 7

have been used to derive a reference mix of contaminants on the cask surface that are proportional to their

presence in the pool water, as shown in Table 2.

Table 2 Reference spent fuel pool water radionuclide composition

cAverage activity Fraction of activity RadionIuclide In pool water

(lCi c-3) present

MCo 6 x 104 0.217

6

'co 2 x 10-3 0.722

34Q 7 x 10-' 0.025

37Cs 1 x 104 0.036

10
Section 3 Optimization

Using this mix of contaminants, it is possible to derive reference committed effective dose per unit intake

factors for the mixture, using the fractions and dose per unit intake factors shown in Table 3. The

committed effective doses per unit intake via inhalation for workers [those for e(g)s,, for lung absorption

type MW have been taken from Ref. 6.

Table 3 Radionuclide characteristics for reference mixture of contaminants for workers

Committed effective Committed effective

dose per unit intake dose per unit intake

via inhalation6 via ingestion6 Fraction of activity

Radionuclide (Sv Bq ') (Sv Bq') present

Worker Public Worker

-'Co 1.4 x l1 1.6 x l1 7.4 x 1O-'1 0.217

CoC 7.1 x 10 1.0 x IO- 3.4 x 10' 0.722

13'Cs 9.6 x lw 9.1 x le 1.9 x le 0.025

137Cs 6.7 x le 9.7 x 1e 1.3 x lo0 0.036

Weighted 5.9 x 10' 8.2 x 107 3.6 x le

Factor _ _ _:-.; _ t__ __C__ _ __ _

These weighted committed dose per unit intake factors are used in Sects. 4 and 5 to calculate individual

and collective doses for the exposure scenarios.

11
4 CALCULATION OF WORKER DOSE (EWxR)

Doses to workers resulting from removable contamination on the cask surface can result in both internal

and external exposures. These can result from the following pathways:

* Internal (E,,*)

- Resuspension of the surface contamination into the air, leading to subsequent inhalation

intakes

- Transfer of contamination to the hands during handling of the packages, leading to

* Ingestion of contamination transferred from the hands to the lips and mouth

- Direct ingestion (which is considered sufficiently unlikely that it is not considered further)

* External (Er)

- Radiation emitted from the contamination (external exposure)

- Cloud shine (irradiation by a "cloud" of resuspended contamination)

- Resuspension of the surface contamination into the air, leading to subsequent deposition onto

the body or clothing

- Deposition of resuspended activity onto the floor of the handling facility and subsequent

irradiation from "ground shine"

- Transfer of contamination to the hands during handling of the packages, leading to

* Irradiation of the hands

* Transfer of contamination from the hands to the face, resulting in irradiation of the skin

of the face

The [AEA CRP has examined these pathways and has determined (with sample calculations) that the

following pathways are "minor" and do not contribute significantly to worker dose:

* cloud shine (irradiation by a "cloud" of resuspended contamination),

* deposition of resuspended activity onto the floor of the handling facility,

* deposition of resuspended activity onto the skin, and

* deposition of resuspended activity onto clothing.

Consequently, these pathways are not considered further in this study.

Therefore, the remaining worker exposure pathways from removable surface contamination that are

considered in this study are as follows:

* Internal (E,,,)

- Resuspension of the surface contamination into the air, leading to subsequent inhalation

intakes (see Sect. 4.2.1.1) - Transfer of contamination to the hands during handling of the packages, leading to ingestion

of contamination transferred from the hands (see Sect. 4.2.1.2)

* External (E,,j) (see Sect. 4.3.1.1) - Radiation emitted from the contamination on the cask surface

- Transfer of contamination to the hands during handling of the packages, leading to

* Irradiation of the hands

* Transfer of contamination from the hands to the face, resulting in irradiation of the skin

of the face

13
Calculation of Worker Dose Section 4

Additionally, the following external doses received during decontamination and monitoring activities that

will vary as a function of allowable contamination limits are considered:

* radiation from the cask contents (see Sect. 4.3.1.2), and

* ambient (background) radiation in the work area (see Sect. 4.3.2).

4.1 WORKER EXPOSURE PARAMETERS

In order to calculate the total doses to workers due to the removable surface contamination limits, it is

necessary to determine the following:

1. time and distances spent in the vicinity of the cask and

2. time spent in plant areas that result in doses due to ambient conditions.

In the late 1980s and early 1990s, the U.S. Department of Energy (DOE) sponsored several studies of

doses resulting from spent fuel transportation, including those due to cask-handling operations. These

studies provide detailed breakdowns of cask-handling operations, ambient dose rates in the areas where

work is performed, and resulting doses to workers. One study, DOE-CHMO-001, by Pacific Northwest

Laboratory,' examined a postulated commercial spent fuel transportation system and is particularly useful

in evaluating doses due to spent fuel cask-handling operations.

DOE-CEIPO-001 provides a breakdown of worker tasks by craft function, number of workers present,

time spent in the work area, and time spent near the cask. Using a reference cask and dose rate

projections at various distances from the cask, the report develops dose estimates for each of the

tasks, which can be summed to provide dose projections for an entire cask-handling operation.

Appendix B-Worker Parameters from DOE-TPOICH-001 contains an extract from DOE-CHTrPO001 that provides the details of the cask-handling operations for a pressurized-water reactor (PWR) and a

boiling-water reactor (BWR) truck cask. A spreadsheet was developed from the worker time and motion

information in DOE-CH/TPO-001 so that the information could be aggregated as needed.

4.2 EFFECTIVE DOSES TO WORKERS DUE TO INTERNALLY

DEPOSITED RADIONUCLIDES (EwiN)

In this section worker doses due to inhalation and ingestion of removable surface contamination are

calculated and worker doses due to ambient conditions are addressed.

4.2.1 Effective Dose to Workers Due to Internally Deposited Radionuclides

from the Cask Surface (Ewk)

4.2.1.1 Inhalation (E,,bkt)

Resuspension of the surface contamination into the air, leading to subsequent inhalation intakes, is a timedependent parameter. Using the approach adopted by the CRP, the airborne activity concentration (in

becquerels per cubic meter) in a facility is given by

14
Section 4 Calculation of Worker Dose

RRxAxA, (8)

Vxf,5

where

RR = resuspension rate, 10 Ih-1;

A = surface area of the cask from which resuspension occurs, 130 m2 or 1.3 x 106 cm2*

AC = activity concentration on the package surface, Bq cm72;

V= assumed room volume, 2000 m3 (200-r 2 floor area x 10 m high); and

fa = assumed air exchange rate, 2 hil.

For a unit activity concentration on the cask surface (1 Bq cri 2), Cd is equal to 3.25 x 102 Bq m73.

Assuming that all resuspended activity is respirable (a conservative assumption) and that the airborne

contamination is uniformly suspended in the defined volume near the cask, the committed effective dose

from inhalation of resuspended activity from a cask is given by

E=Cdx TXINHxRPo (9)

where

Cd = airborne activity concentration, 3.25 x 10-2 Bq mn3;

T = exposure time, h;

lNH= breathing rate, taken as 1.2m3 '-i; and

Rio = inhalation dose coefficient for the reference contamination, 5.9 x 1P Sv Bq'

(see Sect. 3.4).

Equation (9) can be used to derive a committed effective dose per unit time:

E = Ct X INH x R,0 . (10)

For the reference mixture of contaminants, this gives an inhalation annual committed effective dose per

unit time of 2.3 x 10-10 Sv h-1 from a unit activity concentration of I Bq cm 2 on the cask surface.

From Appendix B, the individual worker who spends the most time on cask activities can be identified.

Where more than one worker in a craft type is identified as being involved in a task (e g., the entry under

"number doing cask work" is greater than 1), the workers in that craft type are divided into worker

15
Calculation of Worker Dose Section 4

number 1, number 2, etc.). Where only a single worker in a craft is identified for a given task, all the time

is assigned to worker number 1 in that craft type.

If the 200-m2 floor area used in Eq. (8) is assumed to be square and a cask diameter of 2.5 m is taken into

account, all work performed within approximately 6 m (20 ft) of the cask is within the inhalation volume.

Using the spreadsheet representation of Appendix B, it was determined that the worker who spends the

most "activity time in minutes" in the area at a "work distance from cask in feet" of 20 ft or less, is OPI

(a reactor site operator), who has a total time of 14 h in this area. Conservatively assuming that all of the

time of OPN is within the 2000-m3 area of the suspended activity, the maximum individual dose per

cask turnaround due to Inhalation is 3.2 x 10 Sv per unit of surface activity concentration. The total

time that workers are within 20 ft of the cask is approximately 41 person-h per cask turnaround (from

receipt at the plant through dispatch from the plant). This results in total worker exposure per

turnaround due to inhalation of 9A x le' person-Sv.

4.2.1.2 Ingestion (E*,h,.ug,)

Transfer of contamination to the hands during handling of the packages that leads to ingestion of

contamination transferred from the hands is an event-dependent exposure. Even though work processes

in nuclear plants are likely to preclude hand contamination that leads to ingestion of radionuclides, it is

assumed that a worker's hands become contaminated once per cask-handling day. The 1AEA CRP

approach for calculating worker committed effective dose due to ingestion is based on assuming that the

transfer of contamination from the hands to the mouth is due to touching the lips and mouth, from which

the contamination is subsequently ingested. It is assumed that the area of the hands is 400 cm2 and that

1% of the activity on the hands is ingested. This is equivalent to ingesting the contamination on 4 cm2 of

the hands. The equation for calculating ingestion dose is given by

E = A, xareaxf xf , x Rg (11)

where

Ac = activity concentration on the package surface, Bq cm72;

area = area of hands from which contamination is ingested, assumed to be 4 cm2;

f= fraction of activity on the package transferred to the hands, 20%;

frau = fraction ingested of contaminated hand area, 100%; and

R9 = ingestion dose coefficient, 3.6 x l0e Sv Bq-1 (see Sect. 3.4).

The maximum individual dose per cask turnaround due to ingestion is 2.9 x 10' Sv from a unit

activity concentration on the cask surface (1 Bq cm72). Based on the operational analysis in Appendix B,

as many as eight workers could perform cask operations that lead to contact with the cask surface [4 OPs,

I Radiation Monitor (RM), and 3 Maintenance Crafts (M-Cs)]. Consequently, the total worker

exposure per turnaround due to Ingestion is 23 x 10i person-Sv.

16
Section 4 Calculation of Worker Dose

4.2.2 Effective Dose to Workers Due to Internally Deposited Radionuclides

from the Ambient Atmosphere in the Work Area (Eqb)

Information from U.S. utilities indicates that no significant ambient airborne radioactivity occurs that

could lead to measurable inhalation doses inside buildings. Therefore, this parameter is assumed to be

negligible.

4.3 DOSES TO WORKERS DUE TO EXTERNAL EXPOSURE (Em)

43.1 Effective Dose to Workers Due to External Exposure to Removable

Contamination on the Cask Surface and from the Cask Itself (EW, k)

Workers can receive external exposures from the following1. Radiation originating from the contamination on the cask surface

* Direct radiation from the contamination on the cask surface

* Contamination transferred from the cask surface to the hands, with subsequent irradiation of

the skin of the hands

* Contamination transferred from the hands to the face, with subsequent irradiation of the skin

of the face

2. Radiation originating from the cask contents after the cask is loaded with spent fuel

4.3.1.1 External exposure from contamination on the cask surface (Ew.~cgf)

43.1.1.1 Direct external exposure from contamination on the cask surface

Workers will be exposed to direct external radiation from the presence of contamination on the cask

surface. Based on the results of the MAEA CRP, calculations performed with Microshield show that the

dose rate from a unit activity surface contamination is highest for 6DCo. Therefore, the dose rates are

based on this value. Based on an assumed flat vertical surface area of 14.2 rnm the CRP-calculated dose

rate at 1 m normal to the surface is 1.23 x 10s Sv h' for 1 Bq Cm72 of 60Co. In order to calculate the

external exposures to workers from the surface contamination, it is assumed that the dose rate decreases

as a lhr function of distance from the cask surface and that dose rates are calculated for all tasks that take

place at a distance of 50 ft (15 m) or less.

To determine the doses due to contamination, total worker time spent at each distance from the cask was

determined by analysis of the information in Appendix B. Since all workers will be exposed to the

external radiation from the surface contamination and these doses will vary with the contamination limits,

they are included. Some modification of the information in Appendix B was required in order to include

only those steps where workers will receive external radiation exposure that varies with allowable

contamination limits. For example, when the cask is in the spent fuel pool, workers are well shielded

from any radioactive contamination on the cask surface. When the cask comes out of the pool, however,

the contamination on the outer surfaces is dependent on the pool water cleanliness, not on the

transportation contamination limits. Consequently, steps 10 through 13 of Appendix B are not considered

in this pathway.

17
Calculation of Worker Dose Section 4

In some cases the information in Appendix B had to be further analyzed to account for all workers present

for each task. For example, the number of workers in the area is reported but the distance between the

cask and these workers is not reported. Four different cases of reported worker exposures were

considered as follows:

1. Case 1: time spent doing cask work at a specified distance-The "staff number doing cask

work" is multiplied by the "activity time near cask" for each "work distance from cask."

2. Case 2: time spent in the area by staff not doing cask work-The ("staff total number in area"

minus "staff number doing cask work") is multiplied by the "activity time in area." This value is

then added to the "staff number doing cask work" multiplied by ("activity time in area" minus

"activity time near cask'). Since no distance is specified for the distance from the cask, a range

of possible distances were examined.

3. Case 3: time spent at a specified "work distance from cask" when there are no "staff number

doing cask work"-These activity times were calculated for each "work distance from cask."

4. Case 4: time reported in a inconsistent manner-In three instances (steps 1.3, 3.2, and 14.2), the

reported information is not logically complete (e.g., where "time in area" is smaller than "time

near cask"). In these cases, the information was revised to be consistent and exposures calculated

for the revised parameters.

For case 1, corresponding dose rates at the distances reported in Appendix B are shown in Table 4, along

with the calculated total worker time and dose at each distance. These doses are based on "staff number

doing cask work" multiplied by the "activity time near cask."

Table 4 Parameters and doses to workers "doing cask work" due to external radiation

from 1 Bq cmf2 surface contamination of "Co

(one cask turnaround cycle)

Distance Distance Total worker Dose rate Total worker dose

(ft) (m) time (person-h) (Sv h-') (person-Sv)

1 0.3 0.05 4.1 x 104 2.1 x 109

3 0.9 11.8 1.4 x 10 1.7 x 107

5 1.5 6.17 8.2 x 109 5.1 x 10

6 1.8 0.83 6.8 x l0e 5.7 x 10

8 2.4 0.5 5.1 x low 2.6 x 10W

10 3 2.15 4.1 x 1le 8.8 x 1P

20 6 2.42 2.1 x le 5.1 x 1W'

30 9 2.33 1.4 x 10W 3.3 x 104

38 11.5 0 i.1 x l 0

50 15.2 0 8.1 x 10-'° 0

Total 2.5 x 10-7

18
Section 4 Calculation of Worker Dose

For case 2, the effect of an assumed distance from the cask was examined. The time spent in the area at

unspecified distances from the cask that was not reported as "doing cask work" was 1184 person-min

(19.7 h). These activities would result in exposures that range from 1.3 x 10-7 to 1.6 x 104 person-Sv,

corresponding to assumed worker distances from the cask of 1.8 and 15.2 m, respectively.

For case 3, time spent at a specified "work distance from cask" when there are no "staff number doing

cask work" was calculated for each "work distance from cask." These exposures resulted in a total

worker dose of 1.7 x 10- person-Sv.

For case 4. the time and distance values were revised for three steps as follows: step 1.3 - one Site Yard

Driver (YD) for 10 min at 3 mn, step 3.2 - one Security Guard (SG) for 15 min at 1.8 m, and step 14.2 -

two OPs for 45 min at 0.9 m. The resulting total worker dose for these cases is 2.3 x 10 person-Sv.

Combining all four cases shows that total worker dose due to external contamination on the cask surface

varies from 4.2 x le to 3.1 x l0e person-Sv, depending on the assumed distance from the worker to the

cask for case 2. For an assumed distance of 2.5 m during the "tme in area" while not doing "cask work,"

total exposure is approximately 4 x 10-7 person-Sv. This value was chosen to be reasonably

representative of cask operations as reported in Appendix B.

Consequently, the total worker dose per cask turnaround due to external radiation from surface

contamination is 4.0 x l0e Sv from a unit activity concentration on the cask surface (1 Bq cri-).

The information in Appendix B identifies worker OPI as receiving the maximum Individual worker

exposure due to external radiation from surface contamination with a dose of 1.8 x 10-7 Sv per cask

turnaround.

43.1.1.2 External exposures to workers due to transfer of contamination

Transfer of contamination to the hands may lead to irradiation of the skin of the hands and possible

subsequent transfer to the face with irradiation of the skin of the face. This dose pathway is unlikely due

to the contamination control measures and work practices typically employed in nuclear power plants.

However, it is included for completeness in estimating the potential doses to workers. The calculational

approaches used here are derived from the CRP-developed approaches.

Hand contamination. During cask handling, workers typically wear gloves that will provide some

shielding of beta emissions. Because the reference radionuclide mix for spent fuel cask contamination

consists mainly of photon emitters, no shielding due to the presence of gloves is assumed.

Assuming that outstretched hands have an area of 200 cm2 on each side and that contamination occurs

only on the palm side following touching the cask, 400 cm2 of 400-jim-thick skin (palm side) will be

contaiinated.1 0 In the calculation of effective dose, it is assumed that the hands are contaminated for

8 h per day. This assumes that a worker's hands are contaminated at the start of the working day, are

decontaminated (by washing or removal of gloves) during a midday break, and then recontaminated

during the afternoon. The contamination would be ultimately removed prior to exiting the radiologically

controlled area.

DOE-CHITPO-001 indicates that it typically requires approximately 1000 mmn (16.7 b) elapsed time to

turn around a legal-weight truck cask. Based on an 8-h working shift, it is assumed that each worker

receives hand irradiation for 2 days (16 h) per cask turnaround.

19
Calculation of Worker Dose Section 4

The skin equivalent dose resulting from hand contamination is given by

H S,, = A, X f X T X (Hi + ri) (12)

where

Ac = level of contamination, 1 Bq cmn2;

f= fraction transferred, assumed to be 20%;

T = time exposed, assumed to be 16 h per cask turnaround;

Ai = skin equivalent dose rate to the basal layer of skin epidermis for beta irradiation for

400-pm-thick skin, Sv h-1 per Bq cmn2; and

= skin equivalent dose rate to the basal layer of skin epidermis for gamma irradiation,

Sv h' per Bq cni 2.

Using the radionuclide mix described in Sect. 3.4, the beta skin equivalent dose rates from Kocher and

Eckerman," and the gamma skin equivalent dose rates from the CRP report, a weighted total (both beta

and gamma) skin equivalent dose rate of 1.1 x 10-7 Sv h-1 per Bq cn72 was calculated for 400D-m-thick

skin. From Eq. (12), this results in a skin equivalent dose of 3.5 x l0e Sv.

The IAEA CRP approach for calculating worker effective dose due to irradiation of the skin applies a

factor given as the quotient of the area of skin contaminated (for hands, assumed to be 400 cm') and the

total area of ultraviolet radiation-exposed skin (taken as 3000 cm2). This approach is not consistent with

recent recommendations by the National Council on Radiation Protection and Measurements (NCRP) and

the U.S. Nuclear Regulatory Commission (NRC). NCRP Statement No. 9, issued March 30, 2001,

recommends that the dose at a depth of 70 jim be averaged over an area of 10 cm2 (or the exposed area, if

larger) in deriving the skin dose from any external radiation exposure-regardless of the source or

geometry of the irradiation. The NRC endorsed the NCRP recommendations in Commission Statement

SECY-02-0021 titled "Final Rule on Revision of the Skin Dose Limit, 10 CFR Part 20." In this

document the LAEA CRP approach for computing the effective dose to the skin is not used. Instead, an

approach that is consistent with the NCRP and NRC recommendations is applied.

The effective dose from skin contamination due to touching the cask during handling is given by

EsxN= HsnN,, X WSulN (13)

where 12

H- 3- X 10 Sv, and

wsnN = tissue-weighting factor for skin, 0.01.

This results in an effective dose equivalent to an individual worker from contamination transferred

to the hands of 3.5 x 10 Sv from a unit surface activity per cask turnaround. Based on the operational

analysis in Appendix B, as many as eight workers could perform cask operations that lead to contact with

20
Section 4 Calculation of Workcer Dose

the cask surface (4 OPs, 1 RM, and 3 M-Cs). This results in a collective effective dose to workers from

contamination transferred to the hands of 2.8 x 10' Sv.

Transfer of activity to the face. Other areas of skin, for example, the face, could become contaminated

indirectly from the contamination on the hands. In these calculations it is assumed (consistent with the

CRP approach) that 4% (20% of 20%) of the activiti level on the surface of the package is transferred to

the face and that the affected area of face is 100 cm, approximately the area of one cheek. An average

exposure time of 8 h per day has been assumed since Fe face may not be washed during the course of the

day and the contamination would be removed prior to exiting the radiologically controlled area. Based on

an 8-h working shift, it is assumed that each worker receives face irradiation for 2 days (16 h) per cask

turnaround.

The skin equivalent dose resulting from face contamination is given by

H SXRV = X ff. X T X (.8,u + rib (14)

where

X= activity of contamination available for transfer to the face;

Z=AcXf;

and

A,= level of contamination, assumed to be 1 Bq cm42;

f= fraction transferred to the hands, assumed to be 20%;

Aft = fraction transferred from the hands to the face, assumed to be 20%;

T = time exposed, assumed to be 16 h per cask turnaround;

, = skin equivalent dose rate to the basal layer of skin epidermis for beta irradiation for

40jim-thick skin, Sv hi1 per Bq cmn2; and

s,,, = skin equivalent dose rate to the basal layer of skin epidermis for gamma irradiation,

Sv h-' per Bq cmn2 .

Using the radionuclide mix described in Sect. 3.4, the beta skin equivalent dose rates from Kocher and

Eckerman," and the gamma skin equivalent dose rates from the CRP report, a weighted total (both beta

and gamma) skin equivalent dose rate of 1.6 x 10-7 Sv h-1 per Bq cm72 was calculated for 40-pn-thick

skin. From Eq. (14), this results in a skin equivalent dose of 1.0 x le-? Sv.

The effective dose from contamination of the face due to the transfer of contamination from the hands to

the face is given by

ESJN = XsvN,,ez x WSA7N (1S)

where

21
Calculation of Worker Dose Section 4

= tissue-weighting factor for skin, 0.01 (Ref. 12).

This results in an effective dose to an Individual worker from contamination transferred to the face

of 1 x 109 Sv from a unit surface activity per cask turnaround. Based on the operational analysis in

Appendix B, as many as eight workers could perform cask operations that could lead to contact with the

cask surface (4 OPs, 1 RM, and 3 M-Cs) and subsequent transfer of contamination to the face. This

results in a collective effective dose to workers from contamination transferred from the hands to

the face of 8 x le0 Sv.

4.3.1.2 External exposure from the cask contents (E.,crk 1.e)

Workers will also be exposed to external radiation from the loaded cask, particularly when they are

performing work near the cask. Appendix B provides details from DOE-CH/rPO-O0l on the calculated

doses to workers from the cask. These estimated doses are presented in this section to illustrate the

relative magnitude of worker doses received from cask operations. Section 6.2 presents information from

additional sources that are used to derive a more generic estimate of worker doses due to cask contents

during decontamination and monitoring activities.

The worker doses reported in DOE-CH/TPO-001 include several steps that are tied directly to the efforts

required to comply with the current transport surface contamination limits, as shown in Table 5. Since

the doses received from these steps will vary with the allowable contamination limits (less time is needed

to comply with higher contamination limits), they are considered separately from the overall work flow of

cask handling.

Table 5 Doses due to radiation from the cask contents as a result of cask decontamination

and monitoring tasks to current contamination limits

Number Time Dose due to

Step no. Activity and type near cask cask work

of staff* (h) (person-Sv)

14.1 Survey cask surfacet 1 RM 0.25 1.8 x 10l

14.2 Decontaminate cask 2 OP 0.75 3.0 x 10-5

15.2 Decontaminate area between lids 2 OP 0.08 3.3 x l0e

19.1 Radiation survey of cask and vehiclet 1 RM 0.5 5.3 x 105

19.1 Radiation survey of cask and vehiclet I OP 0.4 2.3 x 10-5

19.2 Spot decontamination 1 OP 0.17 5.0 x 1-

21.1 Radiation survey and recordingt 1 RM 0.17 5.8 x le'

21.1 Radiation survey and recording' 1 QC 0.17 5.8 x 106

Total 2.0 x 10'4

* OP = Reactor Site Operator; RM = Radiation Monitor; QC = Inspector.

These doses have been reduced 30% from the doses reported in Appendix B. This reduction is to

account for approximately 30% of the reported dose in these tasks being attributable to radiation level

measurement rather than contamination measurement.

22
Section 4 Calculation of Worker Dose

Consequently, the collective decontamination and monitoring worker dose per cask turnaround due

to external radiation from the cask contents is 2.0 x 104 Sv and the maximum individual dose due to

the cask contents Is On (assumed to be involved In all the OP tasks), with a dose of 1.0 x 10e Sv

per cask turnaround.

4.3.2 Effective Dose to Workers Due to External Exposure to Ambient

Radiation in the Work Area (Ewfxb)

When workers are performing cask-bandling operations, they are also exposed to external ambient

radiation from the work area. These worker doses include several steps that are tied directly to the efforts

required to comply with the transport surface contamination limits, including those shown in Table 6.

Since the doses due to ambient radiation levels in the work areas will vary with the allowable

contamination limits (less time is needed to comply with higher contamination limits), they are

considered separately from the overall work flow of cask handling.

Table 6 Doses due to radiation from the work area as a result of cask decontamination

and monitoring tasks to current contamination limits

Number and Time Dose due to

Step no. Activity type in area radiation

(person-Sv)

14.1 Survey cask surfacet 1 RM 0.33 4.7 x 104

14.2 Decontaminate cask 2 OP 0.83* 1.7 x le

15.2 Decontaminate area between lids 2 OP 0.08 3.3 x le

19.1 Radiation survey of cask and vehiclet 1 RM 0.67 2.3 x l1

19.1 Radiation survey of cask and vehiclet 1 OP 0.4 1.5 x 10l

19.2 Spot decontamination I OP 0.17 8.3 x 10-7

21.1 Radiation survey and recordingt 1 RM 0.5 1.8 x 10l

21.1 Radiation survey and recordingt 1 QC 0.17 5.8 x l0e

Total 3.2 x 1e

* OP = Reactor Site Operator; RM = Radiation Monitor; QC = Inspector.

These doses have been reduced 30% from the doses reported in Appendix B. This reduction is to account

for approximately 30% of the reported dose in these tasks being attributable to radiation level measurement

rather than contamination measuremenL

s The value for "time in area" reported in DOE-CHITPO-001 appears to be in error since it is less than the

time reported for near-cask activities. This value has been revised to be the near-cask time (0.75 h) plus

0.08 h to account for entry and exit from the area. This time correctly corresponds to the reported dose due

to ambient external radiation.

23
Calculation of Worker Dose Section 4

The collective decontamination and monitoring worker dose due to ambient external radiation is

3.2 x 1le Sv, and the maximum individual dose due to ambient external radiation to workers

performing decontamination and monitoring tasks occurs for OPn, who has a dose of 1.3 x iOf Sv

per cask turnaround.

4.4 SUMMARY OF WORKER DOSES

Using the results of Sects. 4.2 and 4.3, the doses to workers resulting from the current contamination

limits of 4 Bq cni 2 for beta and gamma emitters can be calculated. To calculate doses for internal and

external exposures that are consistent with the CRP formulas (calculated for a unit activity concentration

of 1 Bq cnf 2) and the external exposures derived from DOE-CHrTPO-001 (based on experience with

cask operations designed to meet the current 4 Bq cmF2 limits), the values are normalized to 4 Bq cmr2 for

a single PWR cask turnaround. (Where appropriate, the values for dose per unit of surface activity in

Sects. 4.2 and 4.3 are multiplied by 4.) These results are presented in Tables 7 and 8.

Table 7 Individual dose to workers by all pathways

Individual dose to workers (E,,) in Sv - Normalized to 4 Bq crnr 2

Worker Worker

internal dose external dose

(E*) (E.)

From cask Ambient From cask Ambient

(contamination) (E ) (contamination and cask contents) (Ebb)

(E~t.s) (E...*)

NIA 1.3 x 10e

Inhalation: 1.3 x 108 From contamination: (decontamination

Ingestion: 1.2 x 10 Direct - 7.2 x 10i7 and monitoring

Total: 2.5 x 10It Hand - 1.4 x 10-1 only)

Face- 4.0 x 10

Total: 7A x 10 7

From cask itself

(decontamination and monitoring

only) - 1.0 x 104

The results in Table 7 show that the doses to the maximally exposed individual worker can be categorized

by the following:

1. Doses that will increase if contamination limits are raised (inhalation and ingestion, as well as

direct, hand, and face exposures). These doses total 7.7 x 10-7 Sv per cask turnaround, for a

contamination level of 4 Bq cmd'.

2. Doses resulting from decontamination and monitoring tasks that will decrease due to reduced

exposure times if contamination limits are raised (from cask contents and ambient). These doses

total 1.1 x 104 Sv per cask turnaround, for a contamination level of 4 Bq cmi-.

24
Section 4 Calculation of Worker Dose

Table 8 Collective dose to workers by all pathways

Collective dose to workers (E,,*) in person-Sv - Normalized to 4 Bq cm72

Worker Worker

internal dose external dose

(Etj (Em)

From cask Ambient From cask Ambient

(contamination) (E b) (contamination and cask contents) (Em)

(Ed.,

N/A 3.2 x 10 5

Inhalation: 3.8 x 10-8 From contamination: (decontamination

Ingestion: 9.2 x 104 Direct - 1.6 x 106 and monitoring

Total: 1.3 x 10-7 Hand - 1.1 x 10-7 only)

Face- 3.2 x 10i

Total: 1.7 x 106

From cask contents

(decontamination and monitoring

only)- 2 x 10'4

The results in Table 8 show that the collective worker dose can be categorized by the following:

1. Collective dose that will increase if contamination limits are raised (inhalation and ingestion, as

well as direct, hand, and face exposures). These doses total 1.8 x l04 person-Sv per cask

turnaround for a contamination level of 4 Bq cmn1.

2. Collective dose resulting from decontamination and monitoring tasks that will decrease due to

reduced exposure times if contamination limits are raised (from cask contents and ambient).

These doses total 2.3 x 10-4 person-Sv per cask turnaround for a contamination level of

4 Bq cn- 1.

4.5 WORKER DOSES AS A FUNCTION OF CONTAMINATION LIMITS

Based on the results in Sect. 4.4, it is possible to calculate the individual and collective worker doses that

would increase due to higher contamination limits (i.e., dose contributions from all sources of exposure

other than external exposure due to the cask contents during decontamination and monitoring tasks).

These calculations have been performed for limits that are 10 and 100 times higher than the current limit

of 4 Bq cenl for beta and ganm emitters, as shown in Table 9. The dose savings that would result from

reduced decontamination and monitoring times and optimizing overall worker exposures are discussed in

Sect. 6.

25
Calculation of Worker Dose Section 4

Table 9 Worker doses that Increase due to higher removable contamination levels

Type of worker dose Contamination limit Dose

Individual 4 7.7 x 107 Sv

40 7.7 x 106 Sv

400 7.7 x 105 Sv

Collective 4 1.8 x 10' person-Sv

40 1.8 x 10-5 person-Sv

400 1.8 x 104 person-Sv

26
5 CALCULATION OF PUBLIC DOSE

As described in Sect. 3.3, removable surface contamination on a cask surface can result in both internal

and external exposures to members of the public. These doses can be calculated to determine the effect

on both the collective public dose and the dose to the most exposed individual.

5.1 EFFECTIVE DOSES TO THE PUBLIC DUE TO INTERNALLY

DEPOSITED RADIONUCLIDES

Removable surface contamination can be dispersed into the environment, leading to

* inhalation,

* deposition onto the body,

* ground shine (exposure to radiation emitted by contamination on the ground), and

* ingestion via the food chain.

The IAEA CRP performed calculations to determine the magnitude of these exposures and determined

that inhalation of contamination resuspended from the cask surface is the only significant internal dose

pathway. The CRP focused on the maximum individual doses in relatively close proximities to the cask.

5.1.1 Exposure Scenarios

In order to accurately model doses to the public resulting from inhalation of contamination resuspended

from the surface of a spent fuel cask during movement, it is necessary to define the scenarios leading to

the exposures. The parameters in these scenarios vary from country to country and can be set to provide

either country-specific results or to support a more universal contamination dose model. While the doses

from these exposures are extremely small, it is useful to calculate them in order to demonstrate that this

exposure route is not a significant source of exposure to the public.

The exposure scenarios contained in the risk assessment code RADTRAN 5 provide insight into public

exposure groups appropriate for incident-free transportation.13 In RADTRAN 5, the incident-free

exposure scenarios include the following public groups:

1. off-link population (persons residing in the vicinity of the transport route),

2. on-link population (persons traveling in the vicinity of the shipment during transport), and

3. population in the vicinity of the shipment during stops.

These groups would also be the ones exposed to airborne contamination resuspended from the surface of

a cask.

The characteristics of the reference spent fuel cask are consistent with the IAEA CRP and are assumed to

be the following:

1. surface area of cask [130 m2 (1.3 x 106 c2)], and

2. resuspension rate from cask surface [le' ho' (3 x 10i s-')].

27
Calculation of Public Dose Section 5

Using these characteristics for a cask and a reference contamination level of 1 Bq cm-2 results in an

activity release rate of 4 x 10-2 Bq s'-. As shown in Sect. 3.4, contamination on spent fuel casks consists

of a mixture of radionuclides with a weighted committed effective dose per unit intake via inhalation for

the public of 8.2 x 109 Sv B4-1.

5.1.2 Public Inhalation Dose Model

A dispersion model that takes into account dilution of the airborne activity due to mixing in the "wake" of

the moving conveyance was developed to calculate the doses to exposed individuals. The methodologies

used in the model are provided in more detail in Appendix C. Doses can be calculated for individual

members of the public as well as collective dose (if parameters for the route and population along the

route are specified). The model calculates dose (in sieverts) per unit of surface contamination

(1 Bq cm72).

5.13 Off-Link (Persons Residing in the Vicinity of the Transport Route)

5.1.3.1 Dose to an individual

Ordinarily, the population along a route used to transport spent fuel lives some minimum distance away

from the roadway or rail line. In the United States, this minimum distance is typically 30 m for rural

freeways, rural nonfreeways, and suburban freeways and 27 m for suburban nonfreeways.

The exposed population residing along a route will consist of some combination of persons indoors and

outdoors (pedestrians, working, playing, etc.). For simplicity and to be conservative, all persons along the

route are assumed to be outdoors when the shipment passes.

Using Eq. (C-3) of the model in Appendix C, the expected dose from surface contamination to the most

exposed individual at the edge of a road when a cask passes by at 100 km hI-' (30 m from the passing

conveyance) is

E=Q-Ve Q

= (4x10-2 Bq s-')(2.49x l04 S2 m-3)(2.55 x10-4 m3ssl)(8.2x 109 Sv Bq-')

= 2.1 x 10-7 Sv.

5.1.3.2 Population dose

Analysis of a representative spent fuel transport route in the United States (Surry Nuclear Power Station,

Virginia to Yucca Mountain, Nevada) using the ORNL Transportation Geographical Information System

(TRAGIS) routing and population model shows that the route consists of 96% multilane divided highway

and 4% other highway (two or more lanes, noncontrolled access)." The lengths of the route segments are

as follows: 4365 km, multilane divided, and 198 km. other highways. The population within 800 m on

either side of the centerline of the 4563-kmn route is 873,000 people. Assuming that the population is

uniformly distributed within the band of land from 30 to 800 m on either side of the highway (to account

for uninhabited rights-of-way), the land area over which the population is distributed is 7.0 x 109 m2,

giving an average population density of 1.2 x 10' persons per square meter.

28
Section 5 Calculation of Public Dose

Using a two-person crew, it takes the conveyance 47.5 h to make the journey (1.7 x 10 s). The time and

distances spent on the two different road types are as follows:

Type of road Distance Transit time

Multilane divided 4365 1.6 x 10O

Other 198 7.1 x 10

Using Eq. (C-6) of the model in Appendix C, the collective doses for inhalation of resuspended

contamination by the public residing along the route are calculated as shown in Sects. 5.1.3.2.1 and

5.1.3.2.2.

5.1.3.2.1 Multilane divided highway

For multilane divided highways, the dose is as follows:

S p Q X V (Y2 - y,) Ve t Q

= (1.2x104m-2)4xIO-2 Bq s1')(5.61xlO7s m-3 )(2.55xlO-' m3 s-')(770om)(27.8ms-')

(8.2xlO9Sv Bq-')(1.6xlO-s)

= 1.9x 1044 person - Sv.

5.13.2.2 Other highway

For other highways, the dose is as follows:

S = pQ V (Y2 -yd)vet

= (1.2xlO-4m-2)(4x O12 Bqs-')(6.89xlO7sm-)(2.55xlO' m3 s')(770m)(27.8ms-1)

(8.2xlO9Sv B-')(7.1x103s)

= 1.0x 10- 5 person-Sv.

Thus, the total inhalation dose to the public along the route Is 2 x 10-14 person-Sv per cask shipment.

29
Calculation of Public Dose Section 5

5.1.4 On-Link (Persons Traveling in the Vicinity of the Shipment During

Transport)

The exposed groups consist of

* persons in vehicles following the shipment,

* persons in vehicles traveling in the same direction as the shipment and passing it, and

* persons in vehicles traveling in the opposite direction to the shipment.

Parameters were chosen to be representative of highway geometries and, using the model in Appendix C,

the doses in Sects. 5.1.4.1 through 5.1.4.4 were calculated.

5.1.4.1 Individuals in vehicles following the shipment

5.1.4.1.1 Multilane divided highway

It is unlikely that a member of the public would follow a truck traveling at the speed limit on a divided

highway for more than 4 h (1.4 x 104 s) as this is the time at which the drivers would leave the highway to

take a fuel or rest break. Applying Eq. (C-4) of the model in Appendix C (Figure C.1, car #1), the dose to

a member of the public following the cask for 4 h would be

E =Q Z 'V e t

Q

=(4 X102 Bq s-) (1.18x10-4s m-)(2.55x 104m3s-)( 8.2x10'9Sv Bq-) (1.4x104 S)

=1.4x10-1 3 Sv.

5.1.4.1.2 Other highway

Assuming that a person in a car following the shipment on an undivided highway remains behind the

shipment for the entire duration of the "other highway" portion of the journey (7.1 x 103 s), the dose

would be as follows:

E=QQVet Q

=7(4x10-2 Bq s-')(I.18x10 sM-3)(2.55x10-4M3S-')(8.2xl109Sv Bq -)(7.1xlO3 S)

=7.0X 1O-'4 SV.

30
Section 5 Calculation of Public Dose

5.1.4.2 Individuals in vehicles passing the shipment In the same direction as the shipment

5.1.4.2.1 Multilane divided highway

Assuming that the passing vehicle is traveling at 5 km hi' faster than the vehicle transporting the cask and

applying Eq. (C-3) of the model in Appendix C (Figure C. 1, car #2), the following individual dose is

derived:

E=Q Ve Q

= (4x102 Bq s-)(9.79xlO s2 m')(2.55xlO' m's4)(8.2xlO Sv Bq-)

= 8.2x10-7'Sv.

5.1.4.2.2 Other highway

If it is assumed that a vehicle passing the shipment is traveling 5 km If' faster than the shipment when it

is traveling on a nondivided highway and that the lane dimensions are equal, the dose to an individual on

an "other" highway will be the same as that for a multilane divided highway.

S.1.4.3 Individuals in vehicles traveling in the opposite direction to the shipment

Assuming the lane geometry and velocities given in Appendix C, the following individual doses can be

calculated for an individual in these vehicles.

5.1.43.1 Multilane divided highway

Two vehicles are modeled: one in the nearest lane to the shipment (Figure C.1, car #3) and one in the

next lane removed (car #4). The dose to an Individual In car #3, from Eq. (C-3), would be

E =Q - V e Q

= (4x10-2 Bq s-')(1.75xIO-4 S2 m-3)(2.55x 10-4 m's-')(8.2x I V Sv Bq-')

= 1.5x10-'7Sv.

Similarly, the dose to an individual In car #4 would be proportional to the integrated concentration per

unit release rate for car #3:

E 1.54x 10' .5x'lO-)

1.75x'0-4 .

=1.3x10-7 Sv.

31
Calculation of Public Dose Section 5

5.1.4.3.2 Other highway

Also according to Eq. (C-3) of Appendix C, the dose to an individual in a vehicle traveling in the

opposite direction to the shipment In the adjacent lane would be

E =(4x10-2 Bq s-')(3.9x1I0 S

2 m-3)(2.55x1O4 m3s-1)(8.2x104 Sv Bq-1)

= 3.3x10- 7Sv .

5.1.4.4 On-link collective doses due to inhalation

With the exception of cars following the transport vehicle, the collective dose to on-link persons is

influenced by the number of cars approaching or passing the transport vehicle, the assumed occupancy of

the cars, and the individual doses as calculated in previous sections. The modeling algorithms developed

in Appendix C were applied to calculate on-link collective doses and are described in more detail in

Appendix D.

It was assumed that vehicles sharing the highway were following each other with a minimum separation

distance of 55 m and that the traffic stream was continuous in both directions. This very conservative

traffic density over the entire route was offset with an assumption of one person per vehicle. A

spreadsheet analysis was performed as described in Appendix D, and the results are shown in Table 10.

Table 10 On-link collective inhalation doses

Exposed group Lane number Persons affected E

Following shipment-multilane and other

highway 1 100 4.9 x 10 3

Passing in same direction-multilane and

other highway 2 3,968 4.0 x 10-13

Traveling in opposite direction-multilane

near lane 3 162,695 2.9 x 10.12

Traveling in opposite direction-multilane

far lane and other highway 4 165,927 2.8 x 1012

Total 6.6 x 10-u

5.1.5 Doses Due to Inhalation at Stops

The IAEA CRP examined doses to members of the public during stops at distances ranging from 5 to

50 m. The geometric approach used in the CRP was appropriate for relatively short distances but is not

suitable for longer distances unless modifications in the methodology are made to account for additional

atmospheric effects. Based on analysis of the CRP approach, modifications were made that allow

extrapolation out to 800 m. This permitted the development of results that are as consistent as possible

with the CRP results while providing the dose estimates at longer distances required for calculating the

collective internal public dose.

32
Section 5 Calculation of Public Dose

Details of how the CRP approach was extrapolated to longer distances are provided in Appendix EInhalation Population Dose from Contamination at Stops. The approaches described in the appendix

were incorporated into a spreadsheet to calculate the doses.

Assuming a population density as described in Sect. 5.1.3.2 and that there are eleven 0.5-h stops during

the journey (approximately one stop every 4 h) in the band of population from 5 to 800 m, the collective

population dose from inhalation during stops is 3.5 x 1O-" person-Sv. Assuming that an individual

would be present at only one stop during the shipment (resulting in 0.5-h exposure time per shipment) and

the distance at which the exposure occurs is relatively close (5 in), the resulting maximum Individual

dose from Inhalation of 3.3 x 10.4 Sv.

5.1.6 Summary of Public Doses Due to Inhalation

From the previous results, it can be seen that the doses to members of the public from the inhalation of

resuspended contamination from a cask surface are very low. The results are provided in Tables 11 and

12.

Table 11 Inhalation doses to the maximum exposed member of the public

Exposure scenario Individual dose (Sv per cask shipment)

5.1.3.1 Individual at 30 m from route 2.1 x 10-7

5.1.4.1 Following the shipment-multilane 1.4x 10-x

5.1.4.1 Following the shipment-other highway 7.0 x 10-i4

5.1.4.2 Passing shipment in same direction-multilane or

other highway 8.2 x 10-17

5.1.4.3 Traveling in opposite direction-multilane near

lane 1.5 x 10-7

5.1.4.3 Traveling in opposite direction-multilane far lane 1.3 x IU-'7

5.1.4.3 Traveling in opposite direction-other highway 3.3 x 10-17

5.1.5 At stops 3.3 x 10-14

Highest Individual public Inhalation dose (I Bq can 2 ) 1.4 x 10.3

33
Calculation of Public Dose Section 5

Table 12 Inhalation collective dose to the public

Collective dose

Exposure scenario (person-Sv per

cask shipment)

5.1.3.2 Population along the route-multilane and other

highway 2.0 x 10-14

5.1.4.4 Following the shipment-multilane and other

highway 4.9 x 10-'3

5.1.4.4 Passing shipment in same direction-multilane and

other highway 4.0 x 10-13

5.1.4.4 Traveling in opposite direction-multilane near

lane 2.9 x 10-12

5.1.4.4 Traveling in opposite direction-multilane far lane

and other highway 2.8 x 10-12

5.1.5 At stops 3.5 x 10-13

Total collective public inhalation dose (1 Bq cmn2) 7.0 x 10.12

5.2 DOSES TO THE PUBLIC DUE TO EXTERNAL EXPOSURES

5.2.1 Exposure Scenarios

Because there will be direct external exposures to members of the public from the contamination on the

cask surface with exposure scenarios as described previously for inhalation, these doses have been

calculated.

5.2.2 Public External Dose Model

The methodologies used in the model are provided in more detail in Appendix F-External Exposures

to Members of the Public. Using the approach described in the appendix, a spreadsheet was developed

and used to calculate doses for individual members of the public as well as collective doses (using

specified parameters for the route and population). The model calculates dose (in sieverts) per unit of

surface contamination (1 Bq cmi2).

34
Section 5 Calculation of Public Dose

5.2.3 Off-Link Population (Persons Residing in the Vicinity of the Transport

Route)

5.2.3.1 Dose to an individual

Ordinarily, the population along a route used to transport spent fuel lives some minimum distance away

from the roadway or rail line. In the United States this minimum distance is typically 30 m for rural

freeways, rural nonfreeways, and suburban freeways and 27 m for suburban nonfreeways.

The exposed population residing along a route will consist of some combination of persons indoors and

outdoors (pedestrians, working, playing, etc.). For simplicity and to be conservative, all persons along the

route are assumed to be outdoors when the shipment passes.

The maximum expected dose to a person along the transport route resulting from 1 Bq cr62 surface

contamination occurs when a cask passes by at 27 m from a person. The maximum off-link Individual

dose Is 1A x 10.14 Sv.

5.2.3.2 Population dose

Analysis of a representative spent fuel transport route in the United States (Surry Nuclear Power Station,

Virginia to Yucca Mountain, Nevada) using the ORNL TRAGIS routing and population model shows that

the route consists of 96% multilane divided highway and 4% other highway (two or more lanes,

noncontrolled access).14 The lengths of the route segments are as follows: 4365 kn, multilane divided,

and 198 km, other highways. The population within 800 m on either side of the centerline of the 4563 km

route is 873,000 people. Assuming that the population is uniformly distributed within the band of land

from 30 to 800 mi on either side of the highway (to account for uninhabited rights-of-way), the land area

over which the population is distributed is 7.0 x 109 in2, giving an average population density of

1.2 x 10-4 persons per square meter.

Using a two-person crew, it takes the conveyance 47.5 h to make the journey (1.7 x 105 s). The times and

distances spent on the two different road types are as follows:

Tye frodDistance Transit time Type of road) ()

Multilane divided 4365 1.6 x 105

Other 198 7.1 x 103

35
Calculation of Public Dose Section 5

5a3.2.1 Multilane divided highway

The calculation of collective dose to persons along the route due to direct external exposure to the surface

contamination must take into account the greater distance that the population is away from the cask on the

far side of a multilane divided highway. The resulting collective dose is as follows:

Population nearest the shipment: 1.0 x 10- person-Sv

Population opposite the shipment: 7.5 x 10-T0 person-Sv

Total multilane collective dose: 1.8 x 1e person-Sv

5.2.22 Other highway

Exposure distances are slightly shorter for other highways (27 vs 30 m), but the much shorter distances

and lower population counts result in much lower collective doses along these segments:

Population nearest the shipment: 4.8 x 10-1" person-Sv

Population opposite the shipment: 4.5 x 1011 person-Sv

Total multilane collective dose: 9.3 x 10-11 person-Sv

Thus, the collective off-link dose to the public from 1 Bq cni 2 of surface contamination Is

1.9 x 10' person-Sv per cask shipment.

5.2.4 On-Link (Persons Traveling in the Vicinity of the Shipment During

Transport)

The exposed groups consist of

* persons in vehicles following the shipment,

* persons in vehicles traveling in the same direction as the shipment and passing it, and

* persons in vehicles traveling in the opposite direction to the shipment.

Parameters were chosen to be representative of highway geometries. Using the model in Appendix F, the

doses in Sects. 5.2.4 and 5.2.5 were calculated.

36
Section 5 Calculation of Public Dose

S.2.4.1 Individuals in vehicles following the shipment

52.4.1.1 Multilane divided highway

It is unlikely that a member of the public would follow a truck traveling at the speed limit on a divided

highway for more than 4 h (1.4 x 10 s), because this is the time at which the drivers would leave the

highway to take a fuel or rest break. The maximum external dose to an individual foilowing the

shipment on a multilane highway Is 1.6 x 1011 Sv.

5.2.4.1.2 Other highway

Assuming that a person in a car following the shipment on an undivided highway remains behind the

shipment for the entire duration of the "other highway" portion of the journey (7.1 x 103 s), the

maximum dose to an individual following the shipment on an "other" highway Is 1.2 x 10'n Sv.

S.2.4.2 Individuals in vehicles passing the shipment in the same direction as the shipment

5.2.4.21 Multilane divided highway

Assuming that the passing vehicle is traveling at 5 km h-1 faster than the vehicle transporting, the

maximum Individual dose when passing the shipment is 1.9 x 1O-U Sv.

5.2.4.2.2 Other highway

If it is assumed that a vehicle passing the shipment is traveling 5 kmn h-i faster than the shipment when it

is traveling on a nondivided highway and that the lane dimensions are equal, the dose to an individual is

the same (1.9 x 10-12 Sv).

5.2.4.3 Individuals In vehicles traveling in the opposite direction to the shipment

Assuming the lane geometry and velocities given in Appendix C and using the approaches described in

Appendix F, individual doses were calculateL

5.2.4.3.1 Multilane divided highway

Two vehicles are modeled: one in the nearest lane to the shipment and one in the next lane removed. The

dose to an Individual in car #4 traveling In the opposite direction to the shipment Is 7.2 x Urts Sv,

and the dose to an Individual In car #3 is 8.2 x 10-re Sv.

S.M2J Other highway

The maximum dose to an Individual In a vehicle traveling in the opposite direction to the shipment

in the adjacent lane Is 4.8 x 104 Sv.

37
Calculation of Public Dose Section 5

5.2.4.4 On-link collective doses due to external exposures

Using the same assumptions described in Sect. 5.1.4.4, collective doses due to external radiation were

calculated as described in Appendix F and are shown in Table 13.

Table 13 Collective on-link doses due to external radiation

Exposed group Lane number Persons affected E (per son-S v)

Following shiprnent-multilane and other

highway 1 100 1.9x 10 1

-

Passing in same direction-multilane and

other highway 2 4,148 8.1 x 109

Traveling in opposite direction-multilane

nearlane 3 162,695 1.3 x 104

Traveling in opposite direction-multilane

far lane and other highway 4 165,927 1.5 x 1e

Total 1.1 x 11

5.2.5 Doses Due to External Exposures at Stops

In a manner similar to that in described in Sect. 5.1.5, the LAEA CRP approach was extended to allow

calculation of individual and collective doses to the public from external radiation during stops. Details

of how the CRP approach was extrapolated to longer distances and how they were used to calculate

collective doses are provided in Appendix F. The approaches described in the appendix were

incorporated into a spreadsheet that calculated the doses.

Assuming a population density as described in Sect. 5.1.3.2 and eleven 0.5-h stops during the journey

(approximately one stop every 4 h) in the band of population from 5 to 800 mn, the collective population

dose from external exposure during stops is 4.2 x 10' person-Sv. Assuming that an individual would

be present at only one stop during the shipment (resulting in 0.5-h exposure time per shipment) and the

distance at which the exposure occurs is assumed to be relatively close (5 in), the resulting maximum

individual dose from external exposure during stops of 2.5 x 1010 Sv.

5.2.6 Summary of Public Doses Due to External Exposure

From the previous results, it can be seen that the doses to members of the public from direct exposure to

contamination on a cask surface, while higher than those for inhalation, are still very low. These dose

calculations (as described in Appendix F) are summarized in Tables 14 and 15 for the same reference

route used in Sect. 5.1 and a surface activity concentration of 1 Bq cml-2.

38
Section 5 Calculation of Public Dose

Table 14 External exposure dose to the maximum exposed Individual member of the public

Individual dose Exposure scenario Idvpecas se (Sv per cask shipment)

5.2.3.1 Individual at 27 m from route

5.2.4.1 Following the shipment-multilane

5.2.4.1 Following the shipment-other highway

5.2.4.2 Passing shipment in sa m direction-multilane or other

highway

5.2.4.3 Traveling in opposite direction-multilane near lane

5.2.4.3 Traveling in opposite direction-multilane far lane

5.2.4.3 Traveling in opposite direction-other highway

5.2.5 At stops

Highest Individual public external dose (1 Bq an-2)

1.4 x 10-14

1.6 x lo-,

1.2 x 10-1

1.9 x 10-12

8.2 X 1O-5

7.2 x 10-'5

4.8 x 10-1'

2.5 x 10.1-

2.5 x104l

Table 15 External exposure collective dose to the public

Collective dose Exposure scenario Clctsk se (person-Sv per cask shipmnent)

5.2.3.2 Population 30-400 mr from route 1.9 x 10P

5.2.4.4 Following the shipment-multilane and other highway 1.9 x 10i10

5.2.4.4 Passing shipment in same direction-multilane and

other highway 8.1 x 10P

5.2.4.4 Traveling in opposite direction-multilane near lane 1.3 x 1 P

5.2.4.4 Traveling in opposite direction-multilane far lane and

other highway 1.1 x 10'

5.2.5 At stops 4.2 x 10-9

Total collective public external dose (1 Bq cMrf) 1.7 x 10

39
Calculation of Public Dose Section 5

5.3 PUBLIC DOSES FROM HIGHER CONTAMINATION LIMITS

The results of Sects. 5.1 and 5.2 can be extrapolated to predict the maximum individual and collective

public doses that would result from higher contamination levels. The public doses from higher

contamination levels for collective and individual doses are shown in Table 16.

Table 16 Collective and Individual doses from higher contanination levels

Contamination Co . d Maximum exposed

Exposure type value (pective individual dose

(Bq cmn(jero2Sv (Sv)

Internal 1 7.0 x 10-12 1.4 x 10-3

4 2.8 x 1-"1 5.6 x l0-3

40 -2.8 x 10-10 5.6 x lo12

400 2.8 x le 4 5.6 x 10-"

External 1 1.7 X le 2.5 x 10-'0

4 6.8 x le0 1.0 x 10-

40 6.8 x l 7 1.0 x 10-8

400 6.8 x l e 1.0 x 1- 7

For a single cask shipment, the increase in public dose (combined off-link and on-link) due to higher

allowable contamination limits is shown in Table 17.

Table 17 Increases in public doses due to higher contamination levels

Contamination Increase in Increase in

Exposure type value collective dose maximum exposed

(Bq cm 2) (person-Sv) (Sv)

Internal 4 0 0

4.0 2.5 x 10o10 5.0 x l-12

400 2.8 x 1if9 5.5 x 10-

External 4 0 0

40 6.1 x 10o7 9.0 x 109

400 6.7 x le 9.9 x le

The total collective public dose increases (combined internal and external doses) due to higher

contamination levels are dominated by the external collective dose. The increase in collective dose to the

public is almost entirely due to exposure to external radiation originating from contamination on the cask

surface. The resuspension of removable surface contamination and subsequent inhalation by members of

the public is not a significant contributor to the collective public dose.

40
6 OPTIMIZING SPENT FUEL CONTAMINATION LIMITS

6.1 EFFECT OF ALLOWABLE CONTAMINATION LIMITS ON

WORKER DOSES

As discussed in Sect. 4, some worker doses will increase as a result of higher allowable contamination

limits and some will decrease due to shorter working times associated with decontamination and

monitoring activities. It is possible to determine the conditions under which higher allowable

contamination limits will result in offsetting changes to the doses (where increases are equal to savings)

and where overall dose savings are possible.

6.2 WORKER DOSES DUE TO SPENT FUEL CASK

DECONTAMINATION AND MONITORING ACTIONS

This section provides information on doses received by workers during the performance of

decontamination and monitoring activities. These doses are influenced by the times and distances from

the cask that are required to complete the tasks. The reported doses were calculated or measured and

consist primarily of doses due to external radiation from the cask itself (particularly from the cask

contents) and the ambient dose rate in the work area.

6.2.1 DOE-CH/TPO-001

This report' includes the actions, duration, and doses due to decontamination and monitoring activities.

The combined doses reported to workers due to the cask contents and ambient conditions, as analyzed in

Sects. 4.3.1.2 and 4.3.2, are as follows:

Decontamination: 0.13 x 103 person-Sv

Monitoring: 0.1 10 l person-Sv

Total: 0.23 x 10e person-Sv

6.2.2 CEPN/EDF Report

A report published by Centre d'Etude sur l'Evaluation de la Protection dans le Domaine

Nucleaire/Electricitl de France (CEPN/EDF)15 provides detailed information on worker doses that result

from activities related to preparation and shipment of spent fuel casks from EDF power plants. The report

indicates the following findings:

The total dose for all cask dispatch operations is categorized as follows:

Preparation: 5.2 x 10-3 person-Sv

Monitoring: 1.3 x 10-3 person-Sv

Total: 6.5 x 10-3 person-Sv

41
Optimizing Spent Fuel Contamination Limits Section 6

The doses related to decontamination and monitoring are broken down into two values.

* The dose related to prevention and elimination of contamination (Sect. 3.1.4 of the report) is as

follows:

1.51 x 10i3 person-Sv (29% of total preparation dose).

* Monitoring for contamination includes 422 smears taken over 300-cm2 areas by two teams, that

is, double monitoring and radiation-level monitoring. It is stated that 90% of the collective dose

is due to contamination monitoring (Sect. 3.2.3 of the report):

1.17 x 103 person-Sv.

The CEPNIEDF numbers are applicable to well-trained and experienced crews (200 casks per year total,

shipped from several reactor sites on a routine basis).

6.2.3 Information from a U.S. Reactor Operators

This information was collected during ongoing operations that involved experienced crews employed in

regularly making shipments.

Doses due to decontamination (two casks per shipment) are reported as:

Shipment #1: 1.13 x 10-3 person-Sv (0.57 x 10-3 person-Sv per cask)

Shipment #2: 0.85 x 10-3 person-Sv (0.43 x 10-3 person-Sv per cask)

Shipment #3: 0.99 x 10-3 person-Sv (0.5 x 10-3 person-Sv per cask)

Average: 0.99 x 10-3 person-Sv (0.5 x 10-3 person-Sv per cask)

Doses due to health physics (HP) support are also reportd Based on discussions with operations

personnel at the U.S. light-water power reactor, it is estimated that 20-30% of the doses reported under

HP support are due to decontamination monitoring. This value is lower than the CEPN/EDF data since

the reported U.S. operations involve taking most of the contamination smears as the cask is being

decontaminated and are reported as "decontamination" doses. The HP support contamination smears are

more confirmatory in nature. If it is assumed that 25% of the monitoring/HP support dose is due to

contamination monitoring, the doses due to contamination monitoring are as follows:

Shipment #1: 1.8 x 10-4 person-Sv (0.9 x 10'4 person-Sv per cask)

Shipment #2: 1.6 x 10 person-Sv (0.8 x 10 *person-Sv per cask)

Shipment #3: 1.0 x l0e person-Sv (0.5 x 10 person-Sv per cask)

Average: 1.5 x 10'4 person-Sv (0.7 x 10' person-Sv per cask)

42
Section 6 Optimizing Spent Fuel Contamination Limits

A comparison of the collective doses is provided below. These collective doses are in person-sieverts per

cask preparation.

Souce nfomatonDecontaminationMonitoring f 

(person-Sv) (person-Sv)

1. DOE-CH/TPO-001 0.13 x le 0.1 X l0o2. CEPN/EDF report 1.51 x 10-3 1.17 x 10-3

3. US. reactor information 0.5 x 10-3 0.07 x 10-3

Different reactor facilities and cask designs will give rise to variations in decontamination and monitoring

doses. Discussions with other US. utilities indicate that typical decontamination exposures range from

0.4 x 103 to I x 10-3 person-Sv per cask-loading operation.

The decontamination doses given by the CEPN/EDF report and the U.S. reactor operator are 11 and

4 times higher, respectively, than those in DOE-CHRfPO-1, and it appears that the DOE report

underestimates the durations and locations used in performing these tasks. In order to take into account

the most recent operational data available and to reflect international practices, an average of all three

values is used to reflect current decontamination doses (0.71 x 103 person-Sv). The monitoring

doses reported by DOE-CHrPO-001 and the U.S. reactor are within a factor of 2 of each other and are

much lower than the CEPN/EDF values, probably due to the redundant monitoring that is performed in

France. In order to be representative of known spent fuel operations, an average of all three values is

used to reflect current monitoring doses (OA5 x 10- person-Sv). This gives a collective dose for

decontamination and monitoring activities of 1.2 x l0e person-Sv.

6.3 POTENTIAL WORKER DOSE REDUCTIONS DUE TO HIGHER

ALLOWABLE CONTAMINATION LIMITS

Informal communications with reactor operators have shown that no readily available published

information exists on the level of contamination on casks when they are first removed from the spent fuel

pools and air dried. Reported values ranged from 30 to 400 Bq cmr2. This indicates that most

decontamination and monitoring activities could be eliminated if the allowable contamination limits were

on the order of 400 Bq cm4 . Some monitoring activities would still be needed to ensure that no "hot

spots" were present and to provide assurance of regulatory compliance.

For the purpose of examining the effects that higher contamination limits would have on doses, three

cases (i.e., contamination levels) are examined:

4 Bq cnf 2 beta/gamma (current limits)

40 Bq cm 2 beta/gamma (a factor of 10 higher)

400 Bq cm72 betalgamma (a factor of 100 higher)

43
Optimizing Spent Fuel Contamination Limits Section 6

As shown in Sect. 4.5, Table 9, the increases in individual and collective worker doses due to higher

contamination limits can be calculated. These increases would be as follows:

Type of worker Contamination Dose Dose increase

dose limit

Individual 4 7.7 x 10e Sv 0

40 7.7 x 10' Sv 6.9 x 10 Sv

400 7.7 x 10-' Sv 7.6 x 10e Sv

Collective 4 1.8 x 106 person-Sv 0

40 1.8 x l0e person-Sv 1.6 x leF person-Sv

400 1.8 x 10'4 person-Sv 1.8 x 10-4 person-Sv

When considered in combination with the worker dose received during decontamination and monitoring

activities (1.2 x l0e person-Sv, see Sect. 6.2), the worker dose from surface contamination on the cask

(both internal and external pathways, see SecL 4.4) constitutes 0.15, 1.5, and 13% of the worker collective

dose at contamination levels of 4, 40, and 400 Bq cm72, respectively. The collective worker dose due to

decontamination and monitoring activities dominates all dose pathways considered in this study. Figure 1

compares the collective worker doses due to surface contamination with the doses due to decontamination

and monitoring activities.

Worker Collective Dose

1.BOE-03

1.40E-03

9 120E-03

I 1.OOE-03

I 8.00E-04

I 6.OOE-04

4.OOE-04

2.00E04

O.OOE.00

-

IU Dooon and MonfoiNg Does I

|11 Dose from Contamination I

4 40

Contamination level (Bq cm')

400

Figure 1 Worker collective dose components

If the doses to decontamination and monitoring workers decrease by an amount equal to the increase in

doses due to the higher contamination limits, the worker collective dose will remain unchanged If the

doses to decontamination and monitoring workers decrease by a greater amount, there will be a collective

worker dose savings from increasing the allowable contamination limits. The required decrease in

44
Section 6 S 6Optimizing Spent Fuel Contamination Limits

decontamination and monitoring worker dose (dose reduction factor, or DRF) can be calculated as

follows:

or =WCD1

DMWCD

where

WCDI= worker collective dose increase due tohigher levels of removable surface

contamination, and

DMWCD = decontamination and monitoring worker collective dose.

Based on the decontamination and monitoring worker collective dose of 1.2 x 10- person-Sv derived in

Sect. 6.2, the required DRFs to offset the increases due to higher contamination limits are as follows:

Contamination rmit Increase in doses due to higher Required dose reduction

contamination limits factor-DRF

40 1.6 x 10' 0.014 (1.4%)

400 1.8 x 10 0.15 (15%)

Consequently, a 1A% reduction in the dose to decontamination and monitoring workers (due to reduced

time required to perform these tasks) would offset the increase in dose to workers due to raising the

allowable contamination limits to 40 Bq cmF4. Similarly, a 15% reduction in the dose to decontamination

and monitoring workers would offset the increase in dose to workers due to raising the allowable

contamination limits to 400 Bq cnf 2. Greater reductions in doses to the decontamination and monitoring

workers would result in a lower collective worker dose.

The CEPN/EDF reportU provides some insight into dose reductions that could be possible with higher

allowable contamination limits. Section 4 of the report states that ". . . savings could reach more than

11% of the total collective dose if double monitoring was discontinued for every monitoring zone of the

cask." The average reported total collective dose for cask preparation and monitoring was 6.5 x 103

person-Sv. Eliminating the need for double monitoring could therefore save 7.2 x 104 person-Sv per

cask shipment. Based on the reported collective dose for decontamination and monitoring activities of

2.68 x i0-3 person-Sv, this would result in a dose reduction of 0.27 or, 27%, easily exceeding the dose

reduction factor of 15% required to offset the increased worker collective dose resulting from an

allowable contamination limit of 400 Bq cm 2.

45
Optimizing Spent Fuel Contamination Limits Section 6

6.4 OVERALL DOSE IMPACTS DUE TO HIGHER CONTAMINATION

LIMITS

Using the values calculated in Sects. 5.3 and 6.3, the overall increases in collective and individual doses

due to higher allowable contamination limits can be summarized as follows:

Contamination Increase in collective Increase in maximum

Exposed group value dose (Sv) exposed individual dose (Sv)

(Bg cnf 2) (internal + external) (internal + external)

Workers 4 0 0

40 1.6 x 105 6.9 x 106

400 1.8 x 104 7.6 x 10-5

Public 4 0 0

40 6.1x10-7 9.0xl0

400 6.7 x 10' 9.9 x l10

The increase in collective dose due to higher levels of removable contamination is dominated by the

increase in worker doses. The increases in collective worker doses are approximately 20 times higher

than the collective dose increases for the public. Consequently, optimizing the worker doses will result in

optimizing the collective dose due to removable surface contamination on spent fuel casks at levels up to

400 Bq cnf2.

Figure 2 illustrates the relative magnitude of the collective doses calculated for workers and the public

from both internal and external exposures due to non-fixed surface contamination levels of 4, 40, and

400 Bq cmn. These values do not include external doses due to the cask contents (which will decrease as

the allowable contamination limits increase) to workers performing decontamination and monitoring

activities.

Adding the increased collective public dose to that of the workers does not have a noticeable effect on the

DRFs required to realize dose savings. The required DRF for both 40 and 400 Bq cmn2 (rounded to two

significant figures) do not change. Taking into account both the public and worker collective doses, there

will be a reduction in total collective dose if decontamination and monitoring doses can be reduced by

more than 1.4 or 15% for surface contamination levels of 40 and 400 Bq cm 2 , respectively. The relative

insensitivity of the DRF to the public dose is due to the dominance of the worker dose (approximately 20

times higher). Consequently, the optimization of worker dose is the most important aspect of overall dose

optimization.

While consideration of collective dose is necessary to evaluate options for optimizing doses, it is also

necessary to consider doses to the maximum exposed individual. Worker and public individual doses

remain low even at the higher contamination levels.

46
Section 6 Optimizing Spent Fuel Contamination Limits

Collective doses from surface contamination

(not Including doses due to cask contents)

_

8

1.60E-04

1.40E-04

1 20E-04

1.OOE-04

8.00E-05

6.OOE-05

4.OOE-05

2.OOE-05

1.00E-11

a Public Internal

O Public external

U Worker internal

IlWorker external

S _-_

r Worker external

Worker internal

Public external

Public Internal

40 400

Contamination level

(Bq cmr)

4 40 400

O Public internal 2.80E-1 1 2.80E-10 2.80E-09

0 Public external 6.80E-08 6.80E-07 6.80E-06

* Worker internal 1.30E-07 1.30E-06 1.30E-05

13WorkerextemalJ 1.70E-06 1.70E-05 1.70E-04

Figure 2 Collective dose-all groups

6.5 CONSERVATISMS AND SENSITIVITIES IN THE MODEL

Discussions with reactor operators indicate that the worker exposure scenarios in the models for

inhalation, hand and face contamination, and ingestion are very conservative. Radiological control

practices such as protective clothing (sometimes including double layers), work habits (influenced by

extensive training), and monitoring practices (during work and when exiting radiological areas) reduce

incidents of personnel contamination to very few. Consequently, assumptions such as "all workers that

touch the cask have skin and face contamination and ingestion" are conservative and result in high

estimates of the collective doses to these workers. This results in conservative estimates of the increase in

worker collective dose that would occur with higher allowable contamination limits.

Conservative estimates of the increase in worker doses due to higher allowable removable contamination,

combined with realistic estimates of the doses received during monitoring and decontamination activities,

result in very conservative estimates of the DRFs. The actual DRFs that would be needed to produce an

overall dose savings to workers are likely to be much lower than those calculated in this report

Some parameters were chosen to be representative of spent fuel shipment conditions in the United States,

such as a high transport vehicle speed (shipments are required to maximize their use of the interstate

47
Optimizing Spent Fuel Contamination Limits Section 6

highway system), a long-distance route, low overall population density, and long shipment duration.

The outcome of the model used in this study is relatively insensitive to these parameters since the public

dose (collective and individual) during the shipment is low. The highest individual public dose is during

stops, where an individual is assumed to be in relatively close proximity to the cask for a short period of

time Similarly, approximately 25% of the collective public dose is attributable to stops.

48
7 CONCLUSIONS

Doses from removable contamination on spent fuel casks are dominated by the doses received by workers

preparing the cask for transport. The greatest component of the worker dose is due to decontamination

and monitoring work performed in the vicinity of the loaded cask, where the dose rate from the cask

contents is relatively high. Based on the three sources of operational information used in this study, the

collective dose due to decontamination and monitoring activities (1.2 x 103 person-Sv per cask

turnaround at a level of 4 Bq cmn2) is much higher than the dose received by workers from the removable

contamination by way of inhalation; ingestion; and direct, hand, and face irradiation (1.8 x 106 person-Sv

per cask turnaround at a level of 4 Bq cm 2). The relative magnitudes of these doses are reflected in the

low DRFs that would be required to realize lower collective worker doses due to removable

contamination.

Collective and individual doses to members of the public are much lower than those to workers. The

increases in public doses that would result from higher allowable removable surface contamination limits

(up to a factor of 100 higher) are small and do not contribute significantly to the total collective dose.

49
8 REFERENCES

1. Notes on Certain Aspects of the Regulations, Safety Series No. 7, International Atomic Energy

Agency, Vienna, Austria, 1961.

2. Report of Committee 2 on Permissible Dose from Internal Radiation, International Commission on

Radiological Protection, Pergamon Press, Oxford, U.K., 1959.

3. Dose Coefficients for the Intake of Radionuclides by Workers, ICRP Publication 68, International

Commission on Radiological Protection, Pergamon Press, Oxford, U.K., 1994.

4. W. E. Kennedy, Jr., E. C. Watson, D. W. Murphy, B. J. Harrer, R. Harty, and J. M. Aldrich,

A Review of Removable Surface Contamination on Radioactive Materials Transport Containers,

NUREG/CR-1858, PNL-3666, Pacific Northwest Laboratory, 1981.

5. J. IL Mairs, G. A. Smith, and K. B. Shaw, Derived Limits for Surface Contamination of Transport

Packages, NRPB Contract 12485, National Radiological Protection Board, Chilton, U.K., 1987.

6. International Basic Safety Standards for Protection against Ionizing Radiation andfor the Safety of

Radiation Sources, Safety Series No. 115, International Atomic Energy Agency, Vienna, Austria,

1996.

7. M. Mason, et al., Factors Affecting Surface Decontamination of Spent-Fuel Casks, EPRI NP-3906,

Electric Power Research Institute, February 1985.

8. Private communication, operations personnel at a U.S. light water power reactor, to J. Cook

(U.S. Nuclear Regulatory Commission), August 10, 2001.

9. K. J. Schneider, et al., Analysis of Radiation Doses from Operation of Postulated Commercial

Spent Fuel Transportation Systems, DOE-CWrOP-001, U.S. Department of Energy Chicago,

Operations Office, November 1987.

10. MK Harvey, et aL, Principles and Methods for Establishing Concentrations and Quantities

(Exemption Values) Below which Reporting Is Not Required in the European Directive, Radiation

Protection-65, Document XI-028/93, Commission of the European Communities, Luxembourg,

Belgium, 1993.

11. D. C. Kocher and K. F. Eckerman, "Electron Dose-Rate Conversion Factors for External Exposure

of the Skin from Uniformly Deposited Activity on the Body Surface," Health Phys. 53, 135-141

(1987).

12. M. P. Little, et al., Assessment ofSkin Doses, Documents of the NRPB, Vol. 8. No. 3, National

Radiological Protection Board, 1997.

13. K. S. Neuhauser, et al., RADTRAN 5 Technical Manual, SAND2000-1256, Sandia National

Laboratories, May 2000.

14. P. E. Johnson and R. D. Michelhaugh, Transportation Routing Analysis Geographic Information

System (WebTRAGlS) User's Manual, ORNL/TM-2000/86, UT-Battelle, LLC, Oak Ridge National

Laboratory, April 2000.

51
References Section 8

15. J. P. Degrange, C. Benhamou, L. d'Ascenzo, A. Leroy, and E. Vrignaud, "Analysis of the Doses

Associated with the Spent Fuel Shipments from the French NPPS: Are They ALARAM"

8_JDegrange.pdf in Proca of the 3P ISOE European Workshop on Occupational Exposure

Management atNPPS, Portoroz, Slovenia, April 17-19, 2002, available online at

http://isoe.cepn.asso.fr/programPortor.html.

52
APPENDIX A

SUMMARY OF SELECTED PREVIOUS

CONTAMINATION STUDIES

53
APPENDIX A-SUMMARY OF SELECTED PREVIOUS

CONTAMINATION STUDIES

A.1 SUMMARY OF NUREG/CR-1858

The U.S. Nuclear Regulatory Commission sponsored a study at Pacific Northwest Laboratory concerning

removable surface contamination on radioactive material transportation containers.Al The study,

NUREI/CR-1858, published in 1981, addresses various categories of radioactive material, including the

consideration of the dose to workers and the public associated with the transport of spent fuels. Estimates

of the additional economic costs incurred by lowering the current limits by factors of 10 and 100 were

presented.

The modeling effort in NUREG/CR-1858 specifies a generic model that is applied across the various

transport containers considered in that study. The potential significant radiation exposure pathways

considered are

* ingestion (intakes of non-fixed contamination transferred to hands);

* inhalation (intakes of airborne contamination resuspended from container surfaces and from

worker's contaminated hands); and

* direct exposure (to container surface contamination, skin contamination, and during

decontamination of container surfaces).

The dosimetric evaluations are based on the pre-ICRP Publication 30 models and thus are more than

20 years out of date. An interesting aspect of the study is the significance attributed to the ingestion

pathway. The exposure scenario involves a transfer of non-fixed contamination from the package

surfaces to the hands, foodstuffs, and other items that enter the mouth. The direct exposure model did not

address exposures to the contents of the containers. The model did consider both workers and members

of the public.

In applying the model to spent fuel casks, it was noted that such containers are in exclusive use and hence

not recycled for other uses, which could potentially lead to contamination entering other pathways leading

to members of the public. Transportation workers were assumed to ingest surface contamination from

5 x l0e m2 for each container. No release of the surface contamination was considered during the actual

transport, and thus the model does not consider inhalation intake by members of the public. The assumed

lack of release from the container also means that members of the public were not directly exposed to

non-fixed contamination (only to direct exposure to the contents of the container). However, despite

stating the assumption of no exposure to the public, an ingestion intake via ten individuals was assumed

as the only source of public exposure to non-fixed surface contamination.

The impact on the collective radiation dose of decontamination activities was evaluated. The analysis

considers the total time spent decontaminating at a fixed rate of decontamination, the exposure rate of the

worker to the contents of the cask and to the non-fixed contamination, and the reduction in the public

dose resulting from the reduced surface contamination. The relative impact of these factors is shown in

Figure A. I (adapted from the study). A surface contamination level of 10'4 jCi cmi2 (4 Bq cm 2) was

assumed, as well as the achievement of a uniform decontamination factor of 10 for each 30 min of effort.

That figure indicates that an optimum decontamination time and total dose occur for a direct exposure rate

of 1 mrem h-l (10 VSv h-1), and as such, dose savings from decontamination are possible only when there

55
Summary of Contamination Studies Appendix A

is a low direct exposure rate. This reflects the finding that it is the worker direct exposure considerations

that are driving this model.

100

o 10-

I.Ya

In 10-2

U

0

C~ 10 -

10-3 L 100

Decontamination time (min)

Figure A.1 Collective dose vs decontamination time for spent fuel container. (Adapted from

Ref. Al.)

A.2 SUMMARY OF NRPB REPORT

The United Kingdom National Radiation Protection Board (NRPB) conducted a studyAl for the U.K.

Department for Transport to establish limits for non-fixed contamination on the surface of transport

packages. This effort included formulation of an assessment model to translate the appropriate dose

limits to derived limits on surface contamination. The study was reported in 1987.

The exposure pathways for workers considered by the NRPB included

* external irradiation of the skin,

* inhalation of resuspended surface contamination, and

* ingestion of surface contamination transferred to the hands.

The model addresses only the exposure to workers, and, while suggesting that the only significant

pathway should be inhalation of dispersed contamination during transport, it is noted that such exposures

are "exceedingly low." Thus, the model includes no provisions for assessing the exposure to members of

56
Appendix A Summary of Contamination Studies

the public. The focus of the NRPB report is on deriving contamination limits and thus does not address

health risk or a balancing of worker and public exposure.

Derived limits were reported for 49 radioisotopes under various parameter assumptions. Of these

nuclides, only two ('ts and '"Cs) were included that would be appropriate for spent nuclear fuel (SNF).

Derived limit results of 600 and 700 Bq cm7 were reported for 137Cs and 134Cs, respectively, assuming

average distance and time parameter values ("choice estimate" terminology used in the report). Values

for fsCo were not reported, but the results for cesium indicate that an increase in the derived limits of

about a factor of 100 is possible for typical SNF applications.

A.3 SUMMARY

The NUREG and NRPB reports are thus somewhat contradictory in their assessment of the relevant

exposure scenarios. The somewhat arbitrary selection of parameter values in the models appears to lead

to conservative assignments as appropriate in the stated application. However, a model suitable for

balancing health risk in the occupational and public exposures as resulting from the level of

decontamination requires use of a more detailed and complete modeling effort. Parameter and model

uncertainties should be addressed in formulating any future models for setting surface contamination

levels.

AA REFERENCES

A. 1. W. E. Kennedy, Jr., E C. Watson, D. W. Murphy, B. J. Harter, R. Harty, and J. M. Aldrich,

A Review of Removable Surface Contamination on Radioactive Materials Transport Containers,

NUREGICR-1858, PNL-3666, Pacific Northwest Laboratory, 1981.

A.2. J. H. Mairs, G. A. Smith, and K. B. Shaw, Derived Limitsfor Surface Contamination of Transport

Packages, NRPB Contract 12485, National Radiological Protection Board, Chilton, U.K., 1987.

57
APPENDIX B

WORKER PARAMETERS FROM DOE-TPO/CH-001

59
Table B.l Worker parameters from DOE-TPO/CH-001

Area Staff Activity Work Dose Dose

dose Total Number Time (min) distance rate for (person-mrem)

Step Description rate Type* number doing In Near from cask cask work Cask Area Total

No. (mrem h-1) in area cask work| ame cask (flt) (mrw h-t) work

_. . _

~'1 ' I;4

;. [.,

:-

1.1

0a

dei tAnSpot vehifle and

tl d"o' se-heradcrier'^

it-,

Vehicle arrives and is spotted

it fixed monitoring location at

outer inspection gate. Check

documentation.

Monitor transport vehicle,

perform security search, perform

visual inspection, and disconnect

carier drive unit from transport

vehicle.

Connect utility drive unit to

transport vehicle.

0

0

0

0

01

00E I0 f,

.:O 0:S

i

TD

SG

RM

QC

SG

2 0

1 0

1 0

1 0

1 0

5 0

5 0

5 0

5 0

5 0

20 5 S

20 5..

0020' 10.

,~ 2D ,0 ff

20

30

30

30

30

I t; 5 -''

, 10 . i

i. ..

0

0 i

0

0

0

f 0.10

0. I

I I , W/,

0.000

0.000

0.000

0.000

0.000

0.000

0.000

0.000

0.000

0.000

0.000

0.000

0.000

0.000

0.000

1.2

1.3

so1

TD .2 0

0.008 .0.000: 0.00

0.008 0.000 0.008

0.000 0.000 0.000

I ' j ~ YD~ C o h o t o .j o - L - " 1 1''o ' . :0.00 0.000 0.000

0.017 0.000 0.017

-I

I1
Table B.l (continued)

Area Staff Activity Work Dose Dose

dose Total Number Time (min) distance rate for (person-mrem)

Step Description rate Type* number doing In Near from cask cask work Cask Area Total

No. . _(mremh_) in area cask work area cask (ft) (mrem If) work

I

!e etranspwi Wucle and cakw

iscda and v~asbdownl:.

2.1 Move from outer guardhouse to

nner guardhouse.

2.2 Pass through inner gate and

travel to inspection and

washdown area.

hehc 777or and 7--

0

0

0

0

0

YD 2 0

SG 1 0

10 0

10 0

10 0

10 0

15 0

20

20

20

20

20

0

0

0

0

0

0.000 0.000

0.000 0.000

YD

OP

SG

2 0

1 0

1 0

0.000

0.000

0.000

0.000

0.000

0.000

0.000

0.000

0.000

0.000

0.000

0.000

0.000

0.000

o

3.1

3.2

3.3

General washdown.

Retract personneL barrier, spot

washdown by wand, tmonitor and

visual inspection.

Air drying.

.: 0 :: jf I OP : 2 -0:2 - - - l ; 1 i j I0 6X- , .j 0I.1 .:f;0 j :0.033 0.000 0.033

0

0

fi 0:: (

OP 0 2 ' 2

OP Z 2 ,.t- d1EI qRM l- .

SG 1 1

'10 10I

10 -o10 

' 10 10

15 0

20

: 3: :

5

5

J: yi:0 .1 :-:

0.2 ~

0.1

0

u 0.067 0.000 -0.067

0,017 T0.000 0.017

. 3 000 00 U33

0.000 0.000 0.000

0.000 0.000

0.150 0.000

0.000

0.150 a
Table B.1 (continued)

Area Staff Activity Work Dose Dose

dose Total Number Time (min) distance rate for (person-mrem)

Step Description rate Type* number doing In Near from cask cask work Cask Area Total

No. _ __ (mrem h-1) in area cask work area cask (ft) (mrem h-') work

x

W

u 2-eMove ean i

r, -a 7UP1a 0-1i-W OE'71. .-

4.1 Move from washdown area to

oading area. L D . ,rp- e casK to l::roI fmoI s.?j.. .... . F . 11>1 W. S. 

F ltranpq *veticl'.emoei

I e - _-1 

0.5

0.5

YD 2 0

M-C 2 0

10 0

5.1 10 0

5.2

5.3

5.4

Obtain and replace power and

hand tools.

Area radiation survey.

Crane retrieves hooks and

grapples for impact limiters.

Impact limiter removal.

Remove impact limiter bolts,

Clamps, etc.

Store impact limiter fasteners.

Ii0.5 IWM, ~-V I It 10i~

20

20

.:~ 3 :0

20

20

::- - :0; :~1

51

10

0

0

0.000 0.167

0.000 0.167

0.000 0.167

0.167

0.167

0.167

0.2 0' 3 0.125 0.158

0.5

0.5

0.5 ~

0.5

0.5

Co

M-C

1 0

1 0

10 0

10 0

10 10&

10:.s 10'

10 0

0

0

0.2

0.1

0

0.000 0.083

0.000 0.083

0.083

0.083

M -C I rr 2 2. 0'

M-C 2 0

" - I: A ....- .- ,,:- . S , 9, -...... ",.I ,

0.067 0.161 0.233

: 0.017 0.083 0.100

0.000 0.167 0.167

-I
Table B.1 (continued)

Area Staff Activity Work Dose Dose

dose Total Number Time (min) distance rate for (person-mrem)

Step Description rate Type* number doing In Near from cask cask work Cask Area Total

No. (mrem h-') in area cask work area cask (ft) (mrem h-') work

5.5

5.6

5.7

Remove impact limiters with

crane, and place in setdown area

(two trips required-time to

complete both trips). Seal bolt

holes.

Tiedown removal. Remove

tiedowns, store tiedowns.

Disconnect cask monitoring

equipment.

Apply lubricant to trunnions.

0.5

0.5 -

Q0.5

0.5 .

0.5

0.5

t 0.5 D.:

CO 1 0

M-C co 00 ~2 0;01:0 2~

M-C- A II

M-C 11

M:C :2 2-

M-C 2 0

15 0

20 10

20 X10

25 :~10

1 0 0

10 5

10 5

20

. I -, t

5 : t .

203

"~. . - 1 

0

0.2

: 0.1 : - .

0 0.1

1 0.2

0

0.2 1

-'-0-2-.

0.000 0.125 0.125

0.067 0333 0A.40

0.017 0.167 00 0.183

0.017 0.167 0.183

0.133 0.500 0.633

0-W0330.250 0.283

0.000 0.167 0.167

0.033 0.167 0.200

;.017 0.083 0.100

;;0.017 .0.042 0.058

OASO 2.875 3.323

IM-C 0 2 - 2 0

O P 1 0 01- 1-*'' 0I2-

0.5 IM-C I I I S 53 I 0 ).2

L i6 as~ro nLhce 

6.1

6.2

Pick up yoke, check operation,

and carry to cask.

Attach yoke.

0.5

0.5

CO 1 0

OP 1 0

CO 1 0

OP I 1

45 0

45 0

5 0

5 .5

30

30

20

, 5 t' I I

0

0

0

. 1e04.1.~

0.000 0.375

0.000 0.375

0.375

0.375

0.000 0.042 0.042

-0.008 0.042 . 0.050

a

w
Tahle 111 (enntniped)

Area Staff Activity Work Dose Dose

dose Total Number Time (min) distance rate for (person-muremn)

Step Description rate Type" number doing In Near from cask cask work Cask Area Total

No. (mremn h-1) in area cask work area cask (ft ) (mrem h-1 work

6.3

6.4

Upend cask and lift off supports.

BWR extra yoke and

adjustment.

0.5

0.5

0.5 0.5

0.5 " v z

;e "I &:

CO 1 0

fop i 0

CO 1 0

OP -1: I 1.

20 0

20 10

30 0

30- 20

15 0

5 10;

20

0

5 5

2010

0

0.1

0

0

I O

0.000 0.167 0.167

0o.017 67 ~0=.183

0.000 0.250 0.250

0.033 0.2 0 .283

0.000 0.125 0.125

0.000 0.125 0.125

6.5 lCarry cask to pad.

U' 6.6 iLower cask to pad and remove

Iyoke.

0 o5 C0 0 0.000 0.042 0.042

i OP ei f t S 5 0 0. ,r*S-c~- 0 .0108 0.1 67i5,- 0.175

6.7 JInstall work platform 2 CO 21 0

2 _aqr; OP "22 15 0

1510

PWR

38

: v-_. 0 

r -

Remoft'ttranspor vehicle fro,

Move vehicle out of loading

area to external parking area.

BWR

0

0

0.000 0.500 0.500

0.033 1.000 1.033

0.067 3.125 3.191

0.100 3.625 3.724

7.1 5 YD 1 0 29 0 N/A 0.000 0.167

0.000 0.167

0.167

0.167

0
Table B.1 (continued)

Area Staf Activity Work Dose Dose

dose Total Number Time (mmn distance rate for (peron-mrem)

Step Description rate Type* number doing In Near from cask cask work Cask Area Total

No.___________ _ (mrem h-1) in area cask work area cask (ft mrem If') work

0

I

ii. Prcpie askfw~ lacmen In

i~aduj pit iunoe outr lid

8.1

8.2

ON

8.3

8.4

8.5

8.6

8.7

8.8

Remnove outer lid bolts and store.

Remove outer lid and stome

Scal bolt and pin holes.

Radiation survey of inner lid.

Mveasure cask cavity pressure.

Sample cask cavity gases.

Vent cask.

Fill cask with water.

2

2

2.

2.

2

2

2

2

CO 10

OP 11

M-C 1 1

10 10

' .10 : 10'

'10 : '10

10r ~ 10

10 10

10 r10

.10: 10

3

3

6

3

0.2

0.2

0.067- 0.667 -0.733

O.9.0 0.333 0.333

0.000~ 0.333 0.333

MOM1 0.333 0.350

~0.033 0.333 0.367

0.033 0 33 0. 7

*rM r I I I s. 5 ,3 If 0.,2 , ,C f 00, 1 70.167 0.183

o f, ~ .1 -,r 1~

1 0 1 3 .2 , 0.0 3 0 33 3 ~ 0 . 6 7

1 0 1 -.0 ) , r .I - 3  ,, II -, 0.2 ' j I ,- .0 3 9. 33 0.367I

2 Op 1 I ~ 5 . 1 .0. 1O67'- 0.183

-Ij 2 o : , I L- .I -rf oI s II I 3 I. f 0.2- . j 0 . 1 7 1 0 0 0 .0I I
TabYA RLI (mntlinivefl

Area Staff Activiqy Work Dose Dose

dose Total Number Time (min) distance rate for (person-nrem)

Step Description rate Type* number doing In Near fromcask cask work Cask Area Total

No. (mnrem If) in area cask work area cask ( ) (mrem h-f) work

8.9 Sample water in cask.

Loosen inner lid bolts.

Remove and store inner

lid bolts.

2 OP 1 0 10 0 20 0

2 :

2

2

2

RM 1 ;:0: 1

.OP - 1 . 1IMC 2 , 2

OP -1 1

20 20

20 20

020: 0E'' 202

10 ::10

10 ': : 10

3'

5 11.=, tQ77

3

:

0.2

0.1

: 0.20

: 1 0.1 .I X

0.000 0.333 0.333

O.133 1.333 1i467

0.067 0.667 0.733

0.033 0.667 0.700

-0.067 0.6670.733

0.017 0.333 -0.350

8.11

S.12kApply lubricant in trunnions. j-2 IMc - 1 5 5 "60. 6 b8 o0%

8.13 iRemove work platform. 1, I

1

_I

9.1

9.2

ren eitmer bolts;: . :

Bring yoke to cask and attach.

li cask, move to loading pit,

ower into water, pause for bolt

and lower to bottom of

zt.

CO 0I:XS: 1 0

OP 2 : 2

CO 1 0

OP I

CO 1 0

WfC I I

RM 1 1

OP :1 I

10 i0

10 10 80 : A 0.1 t:

0.000 0.167 0.167

0.033 0.333 0.367

0.683 9.333 10.017

5 0 j 20 1 0 I0.000 0.167 0.167

5 5 1 3 0. 0.2 2, 1 0..017O.16760.183

4

3

30 0

10 Ri:'S 6

10 10

30 20

20

3 -

3 :

: 3:

0

0: 0.200l

0.2 -

0.2 -

0.000 1.000 1.000

0.033 0.667 0.700

0.033 0.667 0.700

0.067 1.500 1.567

0.150 4.167 4.317

0

I.
Table B1 (continued)

Area Staff Activity Work Dose Dose

dose Total Number Time (min) distance rate for (person-mrem)

Step Description rate Type* number doing In Near from cask cask work Cask Area Total

No. (mremh__ ) in area cask work area cask (ft) (mrem hI1) work

I

10

10.1

Prepare cask for loading,

rnmove inner lid;

inspect and clean inner cavity.

Remove yoke, cask lid, and fue

ipacers: store lid and spacers

on service pad.

10.2 [Flush cask if needed. ON

00

10.3 Inspect cask interior.

2

3 :

t( 3 ::

:: 4

4: :::

4

0 2 0V

2:3.:

, ;0 2 -f:

:: ;0 1:X : 0: 

iOP 1T A 1

op iS ;1 

:C I: :

20f 0'

20' 10

10 10.

10 0

10 0 :10 . 0'

20 20

20 20-

20 10

20

3

20~

20 -

3

3 -

3

0.2T

: Si0.2i00

0 .200

0.000 0.667 0.667

0.033 1.000 1.033

0.033 0.500 0.533

0.000 0.667 0.667

0667: 0.667

0.000 0.667 0.667

0.133, 1.333 1.467

0.067 0.667 0.733

0.033 0.667 0700.

0.300 61.83 7.133

10.4 ICheck lid seals and replace as

11 Move spent fuel assemblies

from storage pool to the loading

,iL Place spent fuel assemblies

n cask.
Table B.1 (continued)

Area Staff Activity Work Dose Dose

dose Total Number Time (min) distance rate for (person-mrem)

Step Description rate Type* number doing In Near from cask cask work Cask Area Total

No. (mrem h"1) in area cask work area cask (ft) (mrem If') work

11.1

0%%o 11.2

12

12.1

12.2

13

Identify spent fuel assemblies

ISFA) to be loaded; perform

accountability.

Move SFA to loading arma and

place in cask.

Install fuel spacera and inner lid

on the shipping cask.

Pick up yoke and lid.

Lower lid into position and

install yoke.

Lift cask from loading pit; install

Foar inner lid bolts; place cask

on service pad.

4

0:: 4 SXt

4

4:.

.: 4 '

4:

OP.: 2 :..: 04::

OP 2

Q C 1 0

OQC~ 1~ 0

OP -20

-OP .

CO - .

IOP I 0

QC 1 0I

300 0

75 0

750 0

5 0 30 0

:75 0

5 5

15. 0

15' 0

i5 0

Not

Applicable

Not,

Applicable

Not

Applicable

Not

Applicable

20.

20,

3

20

20

20

:: 0. .:

:f:f:X0 

04:D :

0.XO. t

. 0z 0

0.000 4.000: 4.000

0.00010.000 10.000D

0002.000 2.000

0.000. 5.000 5.000

0.000 4.000. 4.000

0.00010.000 10.000

0.00010.000 10.000

0.00025.000- 25.000

0.000 0.333 0.333,

0.017 0.333 0.350

0.OOO 1.000 1.000

0.000 1.000 1.000

0.000 1.000 1.000

0.017 3.667. 3.683 0

~19
Table B.1 (continued)

Area Staff Activity _ Work Dose Dose

dose Total Number Time (min) distance rate for (person-mrem)

Step Description rate Type* number doing In Near from cask cask work Cask Area Total

No. (mrem.__) _ in area cask work area cask (ft (mirem if1 ) work

13.1

13.2

13.3

0

Lift cask to water surface.

Install four lid bolts.

Lift cask out of water and allow

to drip dry (wash cask during

ift).

Move cask to service pad.

Place cask on service pad.

Disengage yoke and install work

platformn

4.:

4.

4

:2.::W:

2

:2 

2

2

-2

co. 0

ROM 1 O 1 .

M-C I

R0 ? 1 - 1 -

OP 1 1

O M 1 1 ..

~Co i L

CO. 1 .

eop i.~~2 i

CO 1 1

O P .. 2 00 -2 

10 10

10 5-1

10 2 ;

5. 5

.15 101

15~ 10

.15 10

10 10

5 5

5 5

10 10

10 10

::20 :

: 10

,5.

20v

: i:5A 

).D200 .1 0(A .

.0

02

:i 10'

2

u 0;: : :

0

0 - : 0 ;X.CA

0

0.000 0.667 0.667

0.167 0.667 0.833

0.000 0.667 0.667

0.833 0.333 .1.167

0.167 0.333. 0.500

:0.0 0 1.000 .000W

0.000 1.000 1.000

0.000 1.000 1.000

.0.000 0.333 0.333

0.000 0.333 0.333

0.000 0.167 .. 0.167

O.00 0. 167 0.167

0.000 0.333 .0.333

0.000 0.667 0.667

1.167 7.667 8.833

0

I

e.

13.4

13.5

13.6
Table B.l (continued)

Area Staff Activity Work Dose Dose

dose Total Number Time (min) distance rate for (person-rnrem)

Step Description rate Type* number doing In Near fromcask cask work Cask Area Total

No. (mrem hW-) in area cask work area cask (flt) (nrem h1) work

I

_ I 

-14.1

LecPOn inacaskpefterr. "i

Survey cask surface.

Decontaminate cask.

2 piT.Y..7.7-77 2 7r- 1 -[- )2 0.667 0.911

14.2 2w-s 2 2' 1 25 Z 45f i 3 j. 7-7 3.000 1.667 4.667

3.250 2.333 5.583

1.5.000 1.500 :16.500

' 0.500 0.500 1.000

, 0.500 0.500 1.000

-J

b15.1 Install inner lid bolts. 2

2

f :2

M-C :3 ;E. .- 3

OP 1: 1

QC 1 a I ^

15 15

15 10

15 10

3 -

3Vf(

.3:

fXSz20 t

13

3 0

15.2 Decontaminate area between

lids.

2 . OP 2 f S 2 13 120 .333 0.333 3.667

15.3 IRntall instrumentation. 2 O1 P ,2 : 1I 1 30Ij6 1o ~ 1 -- 3 I 1 I i . 0 2.000 ~2.500

15.4 Flush and drain cask ..t i2 ^ I ^';'

15.5 Dry cask cavity. 2'- :

OP 2... 1

'@ ''-''2 - '' ' i" -"'

0 0

0 0

30 3 3

10 3

60 0 NA 0

10.000 0.667 10.667

0.000 0.000 0.000

1 - 200 j .. 10.000 .< 12.

I
Table B.1 (continued)

Area Staff Activity Work Dose Dose

dose Total Number Time (min) distance rate for (person-nrem)

Step Descnption rate Type* number doing In Near from cask cask work Cask Area Total

No. (mrem h-') in area cask work area cask t (mremh ') work

aI,-

15.6 Leak test cask inner lid seal. 2

2

OP 2 - 1

QC_ 1 1 :,

10, 3

10 10'

3

5;: ::.

:200

I10

10.000 0.667 10.667

f 1.667 0.333 2.000

15.7 Fill cask with inert gas. : 2::: I OP : 1j: - :1E:I.: 1o 5 00 [0 30 [ I 10 : j 0.0830-.333 OA17

15.8 Plug and lockwire cavity

opening8s

I 1 2

22. .- 

. M-C .2 2

OP .I1" , 1,x = =

5 _ 5

5 : I ::5

3 ::

::. . .s: 

200

30V' :'

33.333 0.333- 33.667

500W 0.167 q :2.I667

15.9 Ispect outer lid, gaskets, etc. I -,,;,,,Z,,, '',_ J __' ' :';', A'. '' '" - " 0' - , : ''I I ,30 .' -, I- "'' Q. 1'" ;1 -

-,  I '"A  , ' -' , '-" 1-1 ' " '' I" I 'A W.z ' '' -QW  - 30'

-43

15l101Install outer lid. -1 2 -- _

-: 2; 1

2

,CO " I 1 " % 1 '

M-C 2 : 2

QP , . ,I

. 10. 10 °

20- 10

20 15

m : :^ -20 3A X V

AE- 3 ''I:

2 t

30: -

J 10;., I

0.333 0.333: 0.667

10.000 1.333 11.333

I.:2.50 0.667. 3.167

1.67, q0.333 2.000

102.91714.000116.917

15.Iljlnstallwater-absorbentmnaterial j, 2 j~I:OP 2~R - 2 j 5 , 5 1 3 1 J I

around cask lid.

IE o stoebclWodm

16.1 Move yoke to cask. :: , I I co J1 j0:io tof'1 W20 :.2 2 0.3330.333 0.667 : 

16.2 PRemove work platform.

; 2,

CO 1 . I I ' I

^ -OP 2,x.. :2 ::

-10 : 10

10 0 10

: .20 : 2

]'~10

0.333 0.333: 0.667

: 3.333 0.667 4.000 i

tj

e-x

W
Table B.1 (continued)

Area Staff Activity Work Dose Dose

dose Total Number Time (min) distance rate for (person-nmem)

Step Description rate Type* number doing In Near from cask cask work Cask Area Total

No. . (mrem I-1) in area cask work area cask ( I If') Crem work

16.3

16.4

Attach yoke to cask.

Lift cask and travel to loading

ar

T move ^ tve h' ; 77

17.1 Move vehicle into loading area.

Op"IMM-0-M-m

-jW

2

2

2

0.5

0.5,

0.5

0.5

0.5M

OP t

CO I I

YD 1 0

CO.ff1 I:

OP 1 ;.

°Pop: 1, 1

10 . a. 2-

1515 f15 5;.

20 0

15 15

.10 0'50

30 30

30 30

5 5

10

30

: 10 : .

50

... "I',, v .... (V A20::

3

20-

10

3

X2a 8 

1A0i0 :

8:i

200

Wt2 t

8 ;

10 -vw /

0.000

0.000

0.167

0.167

0.167

0.167

0.333 0.333 0.66

II 0.267 0.333: 0.600

0. -0.7O

0.667 0.500 01.167

5.517 3.000 8.517

F 18 # ac c

18.1 Lower cask into position on

vehicle.

18.2 BWR extra yoke adjustment.

Of* 00 .125 0.675

1.667 0.0830 0 1.750

1.000 0.~250 f.s 0

4.000 0.250 4.250

0.833 0.042 0.875 18.3 Remove absorbent material from

cask top.

'1

I
Table B.1 (continued)

Area Staff Activity Work Dose Dose

dose Total Number Time (min) distance rate for (person-mnrem)

Step Description rate Type* number doing In Near from cask cask work Cask Area Total

No. (mrem h-1) in area cask work area cask (ft) (mrem h'l) work

a

18.4 Disconnect, remove yoke, and

store

19.1 Radiation survey of cask and

vehicic

19.2 pot decontanination.

7( hpicnt-ins1 casktied , ., ac wpersme 1n and 

I. Q b - ,> K,}-s .S . f

-46

0.5 -

0.5 ;

0.5

0I .5: 

.0.5,

0.5

0.5- 0-5 , I

0.5

; 05: r ;

0.5

9 0.5 i:

CO :1 1

RM I 1

OP if: .1 )- .:a 1,i-.

o 1- I0

.OP. P.: 4f: .,T

M-C 2 2

CO 1 ='

:OP :: :1; ;::1 ;

10 5

.10 2

PWR

BWR

0 40 300

25 25 ,

10 10

20

I 95

:: ::,;10 T; - , I10

:. -T I3 

2

,$_20 . _ ,

15 ,1 

30

:X : .:.... . .

0.167 0.083 0.250

0.667 0.083 0.750

3.833 0.417 4.250

8.833 0.917 9.750

7.500 0.333 07.833

3.333 0.208 t 3.542

5.000 0..083 5.083

15.833 0.625 16.458

0.000 0.250 0.250

.6,7, 0.25.0 0.917

20.000 05 20.500

31.667. 0.250 1.917

13.333 0.500 13.833

0.667 0.167 0.833

2.50 0.250 2.750

20.1 Pick up and store yokes and

hooks.

30 ' 20

30, ; 20 S

20

2 0 r ,. .

20.2 Rlstall cask dedowns. : 30 20:

-30 I 20.

30 20:

- 20:$: 20

.30. 30

;3032 S . _

It'll .' 5 . _--I:

': : 2 i ;

.,: 2 . I

;f 30 i:

I ,,- 1.,,

' 20'

2: : -

- 5

20.3 Install impact limiters.

I
Table 13.1 (eontinued)

Area Staff Activity Work Dose Dose

dose Total Number Time (min) distance rate for (person-mrem)

Step Description rate Type* number doing In Near from cask cask work Cask Area Total

No. (mrem, h__) in area cask work area cask (ft) (em I') work

20.4

20.5

Install monitoring equipment.

Install personnel barrier and

ecurity seals.

0.5

0.5

M-C 2 ... 2

OP 1 1

-g t:lf^; t2 'a2

-p 1 : 1;D :

30 5

i30 5: 5 

, 10 : 10

53

:S r ' ,5 : 0.417 0.250 0.667

I I "_~~ 0.5,,

3

- 5

I s- 20 '' S 

- -- - - - -,

21.1

21.2

mtnsp<; we&n. ..d ; r, .,; ,,

Radiation survey and recording.

General inspecion of cask and

vehicle.

0.5

0.5

0.5

0.5

0.5

: nX ;:

RM 1

OP 1 1

M-C 1

-QC, 1: 1

30 10

:10 t

30 30

30 -30

20 20

10

10

:

; 5

10

I 15 D~ rs --

? 10 -

10

5

6.667:0.167 6.833

0.833 0.083 0.917

48A17 3.167 51583

0.833 0.250 1.083

0.833 0.083 0.917

-5.000 0.250 5.250

5.000 020 5.250

1.667 0.167 1.833

13.333 1.000 14.333

.;

,

V . ..A

22.1 Move vehicle to parking area

mear guardhouse.

10 e 10 ; '20-: 2 r - - 0.33 Q0.083 0.417

0.333 0.083 0.417

C,

S.,

I

S... C,
Table B.1 (continued)

Area Staf j_- Act Ij Work Dose Dose

dose Total Number Time (mi) distance rate for (persoo-mrem)

Step Description rate Type* numbe doing In Near from cask cask work Cask Area Total

No. (_rmIfI) in auea cask work area caslk (f) (Mj m I') work

I

tw-rq_, t+w

:,.,,j .,

23.1

Udfiostl re Waste

Connect trasporm webickc to

=aTia-'s drive unit.

:0 , ' , :

%. : .

Yr, I. I

TD 2 4

: 5 '

.0 ' -5 . I

:'i'to .::: . 5 ,:

10' ' '

I I 10 : :

21, 11

1 - 2" 11- 

,167 G0 -, 0.167

: 23.2 0.167 0.000 0t.167 -cOA

23.3

23A

23.5

:0430, l.1 isj soj A

CompIfe certfication m~d

ir& Ws Cask to carncr.

0 4 I

0

0 , a 1 S ::

S 1 0

D 15 IS 5 0

15 i '15.

145 150 I '

30 0

- - 30 0

Z.: 30, :

.-,.X30 ..

0

:: -X I f.: :S

,0 -? - .

I I ..

0

I I am.OOO: 0.250

:0. 250f1 0. 0.250

,:250 O.00 ,,) 0250

Notify approprnae organuzatons

of the shipment departure

0.000 0.000

1.3 0.000

0.000

1 333

I
Table B.1 (continued)

Area Staff Activity Work Dose Dose

dose Total Number Time (mi distance rate for (person-nrern)

Step Description rate Type* number doing In Near fromcask cask work Cask Area Total

No. (mrem h-1) in area cask work area cask (ft) (nirem h-l) work

PWR cask Total Dose = 197.767 72.792 270.557

BWR cask Total Dose = 202.800 88.792 291.590

Worker Dose

Group (person-rem.) ___

TD 0

SG 0

RM 7.4

QC 30.4

YD 1.184

co 37.22

S 1.333

OP 274

M-C 21.26

Total 372.8

* CO = Crane Operator; OP = Reactor Site Operator, RM = Radiation Monitor; QC = Inspector; TD = Offsite Truck Driver/Rail Crew;

YD = Site Yard Driver; SG = Security Guard; M-C = Maintenance Craft; S = Supervisor

0
APPENDIX C

MODELING PUBLIC EXPOSURE TO RESUSPENDED SURFACE

CONTAMINATION DURING MOVEMENT

79
APPENDIX C-MODELING PUBLIC EXPOSURE TO

RESUSPENDED SURFACE CONTAMINATION

DURING MOVEMENT

C.1 SUMMARY OF MODELING APPROACH

During movement, removable contamination resuspended from the package surface will disperse

into the environment. The airborne activity concentration resulting from this resuspension

depends primarily on the rate of release, Q, and the speed of the transport vehicle, v. The activity

concentration can be estimated using the Gaussian plume model. The activity concentration

distribution per unit release rate at location (x, y) from a ground-level point source is given by

Ory

2cQ(xy)=2 y ) (C-1)

Jr vayaz

where ay and az denote the variance of the Gaussian distribution in the y (crosswind) and z

(vertical) direction, respectively.c' The values of ay and a. are functions of the downwind

distance x and depend on the "stability" of the atmosphere. The calculations performed here

assume a stability class C and utilize the so-called Pasquill-Gifford curves for the variances as a

function of downwind distance 2

Consider a divided limited-access roadway as shown in Figure C. 1.

Activity released from the truck will initially be diluted by the turbulence in the wake of the

truck. The point source formulation of Eq. (C-1) can be corrected by considering a virtual source

displaced by a distance xo that corresponds to the dilution due to mixing in the truck's wake.CI

The activity concentration in the wake per unit release is given by the reciprocal of the product of

the cross-sectional area of the truck and its speed. The practice of constraining the wake dilution,

in this case to one-third the theoretical value, is followed here.C3

81
Modeling Public Exposure Appendix C

Figure C.1 Schematic of a divided limited-access highway with the truck (lower

lane) proceeding at speed "v." The screen shows the calculation of the concentration or

time-integrated concentration per unit release for various individuals and an assumed

uniform population adjacent to the roadway. See the text for further details.

Consider an individual located at a distance d from the edge of the road with lanes of width dW.

The closest individual is at a distance d + 0.5 dl from the centerline of the truck. The integrated

airborne concentration per unit release rate v / Q at the location of the individual is

TIQ= JZIQ(xo +vt, d +0.5 dl) dt (C-2)

where

v the speed of the truck.

The effective dose E to that individual resulting from inhalation of the dispersing activity is

E=Q - Ve (C-3) Q

where

Q = the activity release rate (Bq s1'),

v / Q = the integrated airborne concentration per unit release rate (s2 m3),

V = the individual's air intake rate (m3 s-'), and

82
Appendix C Modeling Public Exposure

e = the effective dose coefficient (Sv Bq4-).

The airborne activity concentration in the car following the truck is given by Eq. (C-1), with x

being the sum of the displacement of the virtual source xO and the separation distance of the

vehicles (55 m in Figure C.1). The effective dose E to an individual in the car resulting from

inhalation is

E=Q tVet (C-4)

where

Z XQ = the airborne concentration per unit release rate (s mn3), and

t = the time the car follows the truck (s).

All other terms are defined above. Similar equations can be written for individuals in cars

approaching or passing the truck.

Consider a population of uniform density located between y, and Y2 from the edge of the roadway.

The airborne concentration averaged over the population is given by

Y2 Y2

XIQ =0.5 Idt Jdy ZIQ(xo+vt, 0.5 dl+y) + Jdt Jdy ZIQ(xo+vt, 3.5 dd2+y) (C-5)

Yl Y1

where the first term corresponds to the population adjacent to the lane containing the truck, the

second term represents that on the opposite side of the highway, and d2 is the width of the center

strip (see Figure C.1).

The collective dose S (in person-sieverts) due to inhalation is

S = p Q X V (Y2 - Y1 ) vet (C-6) Q

where

P = the population density (# mn2),

y2 and y, = the upper and lower bound distances (m) of the population from the roadway,

v = the speed of the truck (mn s~), and

t = the total travel time (s) in the populated region.

83
Modeling Public Exposure Appendix C

The dispersion data for a two-lane roadway (state highway) are shown in Figure C.2.

Figure C.2 Schematic of a two-lane highway with the truck (lower lane) proceeding

at a speed lv." The screen shows the calculation of the concentration or time-Integrated

concentration per unit release for various Individuals and an assumed uniform population

adjacent to the roadway.

C.2 ILLUSTRATIVE EXAMPLES

A few illustrative sample calculations are presented based on Figure C. 1 and the dispersion

parameters in the figure Assunm that the release rate of 137Cs from the truck is 1 Bq s-1. The

committed effective dose coefficient for inhalation of 1

37

Cs by an adult is 4.6 x 10 Sv Bq1l

(Ref. C.4), and the air intake rate is 22 m3 da-' or 2.55 x 10 m3 s-' (Ref C.5). The dispersion

parameters are shown in Figure C.1.

Car #1. Assuming that the car follows the truck for a period of 3 h (1.08 x 104 s), then the

effective dose [per Eq. (C-4)] is

E =Q - V e t

Q

= (1.0 Bq s-)(I.18x 10's m-3)(2.55x 10'm's-')(4.6x1OSv Bq-)(1.08ox104 s)

=1.5xlO-It Sv .

84
Appendix C Modeling Public Exposure

Car #2. The dose to an individual in car #2 [per Eq. (C-3)] is

E=Q - Ve

Q

=(.O Bq s')(9.79x10-4 S2 m-) (2.55A0x 4 m3s-)(4.6x10- Sv Bq-')

=1.2 10-' 5Sv.

Collective dose: Assuming that a strip of land (30 to 800 m wide) adjacent to a highway has a

population density of 80 kmnf2 (8.0 x 10-5 nm2) and that the extent of this strip is such that it takes

the truck 4 days (3.46 x 105 s) to traverse, then the collective dose [per Eq. (C-6)] is

S = p Q X 1V (y 2 - y,) v e t Q

= (8.0 10 m-2 ) (1 Bq s-') (5.6110-7 s m- 3) (2.55 104 m3 s( ) (770 m)

(27.8 m s-1) (4.6 10Sv Bq-1) (3.46 10 5s)

= 3.9 1 0- person - Sv.

C.3 REFERENCES

C. 1. D. B. Turner, Workbook of Atmospheric Dispersion Effimates, Publication 999-AP-26,

Public Health Service, Cincinnati, Ohio, 1967.

C.2. F. A. Gifford, Jr., "Use of Routine Meteorological Observations for Estimating

Atmospheric Dispersion," Nucl Saf 2(4), 44-57 (1961).

C.3. W. G. Snell and R. W. Juback, Technical Basis for Regulatory Guide 1.145, NUREG/CR2260, U.S. Nuclear Regulatory Commission, Washington, D.C., 1981.

CA. International Commission on Radiological Protection, Age-Dependent Doses to Members

of the Public from Intakes of Radionuclides, Part 4, ICRP Publication 71, Pergamon Press,

Oxford, U.K., 1995.

C.5. International Commission on Radiological Protection, Human Respiratory Tract Modelfor

Radiological Protection, ICRP Publication 66, Pergamon Press, Oxford, U.K., 1994.

85
APPENDIX D

COLLECTIVE INTERNAL DOSE TO PASSENGERS IN VEHICLES

DURING TRANSPORT

87
APPENDIX D

COLLECTIVE INTERNAL DOSE TO PASSENGERS IN VEHICLES

DURING TRANSPORT

The calculation of the collective internal dose to the public in vehicles due to inhalation of resuspended

surface radioactivity from fuel casks transported by highway uses the algorithm discussed in Appendix C,

which calculates the time-integrated value of X/Q for vehicles following, passing, and meeting the

shipment on a multilane highway (Figure C.l) or other highway (Figure C.2).

The collective internal dose for vehicles following (traffic lane #1) the shipment is estimated by using the

summation of X]Q (s me) for the first 100 vehicles behind the transport, corresponding to a distance of

5.5 km for a following distance of 55 m between each vehicle. The value of XIQ falls rapidly with trailing

distance, as shown in Figure D. 1, so that the exclusion of vehicles beyond 5.5 km does not affect the

estimate appreciably. The resulting summation gives the following value:

100

E ( I = 3.31 x 10 4 sm 3 .

Using this value with the other factors given in Sect. 5.1.4.1 gives a collective dose of 4.9 x 10'3 personSv. The total affected population is 100, assuming there is one passenger per vehicle.

Collective internal doses to passengers in vehicles passing (traffic lane #2) or meeting (traffic lane #3 and

lane #4) shipments of spent fuel casks are estimated as the product of the number of affected passengers

and the integrated values for XIQ provided in Appendix C. The number of affected passengers is related

to the number of vehicles going past the transport, given as the product of the total time en route and the

speed of vehicles in the other lanes relative to that of the shipment, divided by the following distance of

the vehicles going past the transport. The total time en route is the ratio of total distance to transport

speed on a multilane roadway for lanes #2 and #3. The total time for lane #4 takes into account both

distance on multilane roadways and on other roads (state highways). Estimates of the collective doses

using the same factors as in Sect. 5.14A.2 (lane #2) and Sect. 5.1.4.3 (lane #3 and lane #4, multilane

highway, and lane #4, other highway) are shown in Table D. 1.

Table Dl Collective dose for on-link exposures

Lane Persons E affected (person-Sv)

2 3,968 3.96x 10-13

3 162,695 2.90 x 10-12

4 165,927 2.78 x 10-12

89
Collective Internal Dose to Passengers Appendix D

1.4e-4

1.2e-4

1.Oc-4

&O-S

6 GOe-5

4.0e-5 -

2.Oe-5

0 1000 2000 3000 4000 3000

Distance Behind Transport (m)

Figure D.A Values of XIQ for vehicles following a spent fuel cask transport

90
APPENDIX E

INHALATION POPULATION DOSE FROM

CONTAMINATION AT STOPS

91
APPENDIX E

INHALATION POPULATION DOSE FROM

CONTAMINATION AT STOPS

E.1 INTRODUCTION

The committed effective dose equivalent (CEDE) from inhalation is givenF' by

E = Cd f TBwb Rlo

where

Cd = the airborne activity concentration (Bq m3 ),

f = the respirable fraction,

T = the exposure time (b),

Bi& = the respiration rate (in3 b-f), and

Rio = the inhalation dose coefficient (Sv Bq' ).

The CEDE due to resuspended activity from a contaminated shipping cask during a stop (such as for food

and fuel) is estimated by assuming that the exposed population is uniformly distributed in concentric rings

around the transport in the direction of the wind. There are two such rings in our analysis-one adjacent

to the shipment and an adjoining one at greater distances. Therefore, the total CEDE is the sum of the

proximal dose Ep (from intakes up to 100 m from the cask) and the distal dose Ed (for intakes >100 m

from the package):

E=EP+Ed (E-1)

(Gaussian plume diffusion models may be used, if desired, in estimating airborne concentrations and

doses at distances >100 m from the source.) All factors used in calculating CEDE for a population are the

same in the two rings, except for the airborne activity concentration, which diminishes as the

contamination diffuses into a larger volume downwind from the source. The number of exposed

individuals also changes with distance from the source (because of lateral and vertical dispersion of the

contamination) when calculating population dose.

E.2 PROXIMAL DOSE

The proximal dose to the population is calculated using an average airborne activity concentration for the

exposed population from a minimum distance a to 100 mi from the source. (Minimum distances from 5 to

75 m are defined by Ref. E.1 for populations exposed during different stop scenarios.) The average

airborne concentration is defined as

93
Inhalation Population Dose -Appendix E

100

f C, dr

Cd = oo (E-2)

Jdr

_-a

When the transport is outside, the airborne activity concentration Cd (Bq nfl) is a function of the distance

r downwind from the source and is given by

RAA C (E-3) Cd = Q

where

R = the resuspension rate (10-4 h-),

A = the surface area of the cask (130 mn),

A, = the non-fixed areal contamination density (Bq m72

),

C = the containment factor (C = 0.01 for covered casks and C =1 for uncovered), and

v = the average wind speed (2 m sin).

Parameter values, where given, are from Ref. E.1.

The variable Q represents the effective cross-sectional area of the plume as a function of distance from

the cask:

Q= lOf, A, (E-4)

wheref, takes on the values belowEl for specific values of r.

r(m) 5 10 30 50

f, 1.5 2 6 10

To determine values off, for 5 to 100 m from the cask for the proximal dose,f, can be modeled using the

information above by noting that

f,=(0.I ra+ 1), for5m r< lOim,

and

£=0.2r, for 10m r 50 nm.

Extrapolating f, from 50 to 100 m,

94
Appendix E Inhalation Population Dose

f,=O.2r, for50m<r5 100m.

The resulting relation Offr to r over the whole range 5 m S r < 100 m is shown graphically in Figure E. 1.

20

IS

fr

10

S

0

f=0.2 r, for r from So to 00 m (extrapolated)

0.2rforr from 10 to 5Orn

(regression of values frcx ref El)

J =(0.1 r+1),forrfromSto 10m

(regression of values from ref. E. 1) 0

0 20 40 60 80 100

Distance from Transport r (m)

Figure E.1 Values Offr for distances of 5 to 100 m from the transport

E.2.1 Dose to the Maximum Exposed Individual

The maximum exposed individual is located in the proximal region for all scenarios proposed by the

International Atomic Energy Agency (IAEA) Coordinated Research Project (CRP) modeling group for

stops during highway or rail transport.sL The activity concentration Cd at a specific distance r, and not

the average concentration, is used in determining dose to the maximally exposed individual. The dose to

the maximum exposed individual is given by

Ea. = Cdf TBRo RIO =R f TB RAC R1O. vQ fB~R 1

=0 1 ffTB (Es)

95
Inhalation Population Dose Appendix E

E.2.2 Population Dose

The estimates of doses from contamination at stops assume that the downwind direction is toward

populations on the same side of the road as that on which the stops occur. An average airborne

concentration for evaluating doses to a population from a distance a, 5 to 100 m from the transport, is

calculated using

100 100 dr 10

JCddr RAAcCCLA JL

Cd - lOOAv 100 10v 'm

f dr fdr Idr

MA r-a MA

To account for the case where the closest exposed individual is less than 10 m from the transport

(i.e., for 5 m S a < 10 m (since a 2 5), the expression for average airborne concentration becomes

10dr' 100

R AcC+ .r RACC 10 n(l+ 1]r) I + 5 Inr I _____ _____ _I + _ _____ ____ __ R A C M M r=10

C'00 V 0° lOv 100

Jdr Jdr (E

i-a -a-7

(2 2

RAcC In 10 + 0.la)+ 113

lov 100- a

If, on the other hand, the closest exposed individual is 10 m or more from the transport (i.e., 10 m S a

S 100 mn, then

1 [ 100] io

-RaC £|.2r l RaC 5nr| RaC 5In 100

'lOv 100 [ 10 lOv 100-a

'T'vJ uv L r [a

The average CEDE in the proximal exposure region, then, is given by one of two expressions, either

R. &C 010 1n(7 2l) + 11-5

E= RACC v - f TBR RI |.s ioin(1 , fora< 10, (E-9)

or

96
-Appendix E Inhalation Population Dose

RAc fTBOR , for 10• a• 100. (E-10)

E.3 DISTAL DOSE

To estimate an average airborne concentration at distances exceeding 100 mn, for determining the distal

dose, it is assumed thatf, = 0.2 r. Howeverj is constrained to take on a constant value (f, = 0.2 rb)

beyond the downwind distance rb, where the height of the cross-sectional area thatf, defines becomes

equal to the height hb of the mixing layer (planetary boundary layer). This constraint addresses the

situation in a thermal inversion, when warm air aloft prevents vertical diffusion and curtails dilution of

airborne contaminants.

The cross-sectional area defined by the quantity Q is assumed to be a square with its bottom edge at

ground level, so that rb is determined from

Q= l0Af7, = l0A(0.2 rb)=h , (E-11)

giving

kb: (E-12)

rb 2A

Note that rb > 800 m (andf, is, therefore, unconstrained by the mixing layer in our analysis) unless the

height of the mixing layer is less than about 456 m. The average airborne concentration in the region

from 100 to 800 m from the transport is then given, when rb< 800 m(hbz 456 m), by

RAcC Af -Ovr L[wa2r+,L0.rb]

Cd.IOO-WOlo SWgl0oo ,o ~.~&

F-100r-100

lOv (800- 100) 5lnr L + rb rep, 7000v [ 1n 100) + b J

=I + A5200A) 8 0 0 - )J

and, when rk 800 In (hb 456 m), by

97
Inhalation Population Dose Appendix E

-C rCjfr R4C [ d I

Cd,100400 = 0 i - goo -I 0lOv IOvr 1 r-100 r

*AOD r-1(0

=70400v 20A)

(E-14)

A graphical representation of the activity concentration with distance from the cask for a non-fixed

surface contamination level of 1 Bq cm72, mixing layer at 300 m, and representative values of the other

parameters from Ref. E. 1 is shown in Figure E.2.

le-5

g: le-6

le-7

0 200 400 600 800

Distance from Cask (m)

Figure E.2 Atmospheric activity concentration with distance from the source for a 300-m

mixing layer (A, = 1 Bq cn"2)

98
Appendix E Inhalation Population Dose

One of two equations is then used to determine the average CEDE in the distal exposure region, either

Ed =700 f TBh Rio 5 In i + '2 (800- -) for e 456m, (E-15)

or

Ed = 7RA C f TB [IO 5In( M K1 fora > 456 m. (46 7000v [\20 A)J

EA TOTAL POPULATION DOSE

Population dose is the product of the number of exposed individuals and the average dose, summed over

each region of exposure,

(E-17)

Epw, n, E

The number of exposed individuals in the ith region is the product of population density (m72) and area

(mi) subtended by the plume of airborne contamination. The contamination is assumed to disperse into a

cross-sectional area defined as the product (10 AJf), and with the simplifying assumption that this area is

a square with one edge, having length 4(10 Afi), at ground leve. The dispersion footprint of the plume of

contamination is shown in Figures E.3 and E.4. Figure E.3 shows the dispersion footprint at distances

between 10 and 800 m downwind from the source of contamination, corresponding to the region where

fi = 0.2 r. Figure E.4 shows the dispersion footprint between 5 and 10 m downwind, wheref, = (I +

0.1 r).

99
Ilthalation Population Dose Appendix E

200

I

0I I.

100

0

-100

-200

0 200 400 600 Bo0

r(m)

Figure E3 Ground footprint of airborne contamination (10 to 800 m from cask, no inversion)

401

30 p

.11.

.1

I

I

0

20 F

10!.

0

Cask

1--

_ 5 _

l7::7

Downwid Catdaline

-10 F

-20 .

--- .. -- .1

-30 .

-40

-10 -s 0 (

r (m)

10 15

Figure E.4 Ground footprint of airborne contamination S to 10 m from cask (dashed line).

Area subtended by the plume of contamination is bounded by the solid lines. The footprint for

distances exceeding 10 m from the cask is shown (dotted line) for comparison.

100
Appendix E Inhalation Population Dose

The area subtended by the plume of contamination at distance r from the cask is the integral of the length

of cross-sectional area at ground level,

(E-18)

Q. = V+i-O-Adr.

,

This integral solves to give

a, 3 i~ r2 a"1) , for a>2 10 m, (-9

and

a, = 43 'f _ a32) + flOA (ram - a) , for a < 10 m .(E-20)

Dispersion in the proximal area, then (since r,. = 100 m) leaves a footprint of

a = > (100oo2 - 1032)+ 2 (103-2 - a 32)+ (10- a) J4TA (E-21) 3 3

for a < 10 m, and

a 3 (2oo3/2 -a) (E-22)

for a 10 mn.

Both lateral and vertical dispersion are assumed to cease when a thermal inversion exists at the point

where the dispersion height equals the height of the mixing layer [i.e., when rb < 800 m (hb s 456 m)].

The area subtended by the plume of airborne contamination constrained in this way in the distal region is

rectangular, with width hb and length (r.x - rb). The total area subtended by the plume of contamination

in the distal region is given, therefore, by

a,. d 3 (rb -a )+ hb(r -r b)

= 2 i~7 |( ) _ 003]+ hb (800O- )

3 (A A

when an inversion exists [i~e. irb < 800 m (h,, < 456 in)], and by

101
Inhalation Population Dose Appendix E

a d (r -a ) a'. d 3 ':133Za

2ft2X (800 32 _ 1003/2)

(E-24)

when rb 2 800 m (hb 2 456 m).

E.5 REFERENCE

E.1. Personal communication, Xavier Bernard-Bruls, nternational Atomic Energy Agency (IAEA),

Vienna, Austria. to R. R. Rawl, ORNL, August 13, 2003, transmitting The Radiological Aspects of

Package and Conveyance Non-Fixed Contamination (Version August 2003, Final draft report of an

IAEA Coordinated Research Project).

102
APPENDIX F

EXTERNAL EXPOSURES TO MEMBERS OF THE PUBLIC

103
APPENDIX F

EXTERNAL EXPOSURES TO MEMBERS OF THE PUBLIC

F.1 MAXIMUM EXPOSED PERSON

The maximum exposed person from the on-link population must be determined from persons in another

vehicle passing or meeting the shipment in an adjacent lane or immediately following the shipment in the

same lane. The maximum exposed person from the off-link population is a stationary individual located

beside the roadway immediately adjacent to the lane of a passing shipment.

F.A.A Dose from Following a Transport at a Fixed Distance

The external dose E to a person following a transport at fixed distance d is simply the product of dose rate

D at that distance and the following time t. At the distances applicable to exposure to members of the

public, the dose rate is related to the reference dose rate D0 by the inverse square of distance, so that

E = Dt=D=f-i) 0 {d-) 

where do is the distance at which D0 is determined

F.1.2 Dose from a Passing Transport

In this scenario, the exposed person is standing unshielded at a fixed distance from the roadway. A cask

with a surface contamination reference dose rate at 1 m ( D0 ) passes the person at a fixed rate. The timedependent distance from cask to person is given by

d 2 =a2 + (rt)2 (F-2)

where d is the distance from cask to person, a is the distance of the person from the roadway, r is the rate

of travel of the cask. and t is time. The instantaneous dose rate to the person, assuming lId1 dependence

(appropriate for the distances in these scenarios), is

d d a'a+(r0)'

105
External Exposures to Members of the Public Appendix F

and the total dose delivered by the passing cask is

E = fD(t) dt =2 f(t)d2f = 2D dt ' dt=

L= O I, I a 2 + (a) 2 *r2 (\a2 t~ t=O '= 1 J + t 2

(F4)

where t = 0 is the time when the cask-to-person distance is the minimum distance, a. The integral is of

the form

J dx

b2 +x2

1 4X

b b

(P-5)

which yields a solution for the total dose,

E =2 0 tan

ra AC1I)TAIDO

t=0 ra (F-6)

The minimum distance a for a person standing by the roadside depends on the type of highway.

For interstate highways, a = 30 m; for other highways, a = 27 m.

This same expression can be used to determine the dose to on-link individuals in vehicles passing or

meeting the transport. The value of r in this case is the relative velocity between the cask and the

passenger vehicle. The minimum distance a is taken as the distance between centerlines of the lane of

travel of the cask and that of the passenger vehicle (a = 4 m for passing vehicles and for vehicles meeting

the transport on other highways; a = 23 m for vehicles meeting the transport on multilane divided

highways).

F.2 EXTERNAL EXPOSURES-COLLECTIVE DOSE

Collective doses from external exposures to on-link populations (passengers in vehicles) in lanes #2, #3,

and #4 are estimated using the same expression as for dose from a passing shipment and the number of

persons affected. Doses to passengers in lane #1 are estimated using the distance-corrected dose rate to

the first 100 vehicles behind the shipment. An "effective distance" (corresponding to the average dose

rate) can be used for aU 100 vehicles, as described below, to simplify this calculation. The time of

exposure is the duration of the shipment.

Collective doses from external exposures to off-link populations can be estimated using the same

expression as for dose from a passing shipment if the entire population in contiguous exposed areas is

assumed to be concentrated at a distance from the roadway receiving a dose rate equal to the average dose

rate for the dispersed population. The population thus concentrated is in an annulus around the cask

during stops and is in a line along the roadway when the cask is in motion.

106
Appendix F External Exposures to Members of the Public

F.2.1 Average Distance of the Exposed Population from the Transport

The population living near a highway where spent fuel casks are transported is assumed in this analysis to

be uniformly distributed within a strip with its nearest boundary a distance a from the roadway and its

furthest boundary a distance b from the roadway. A cask on the roadway delivers a dose rate to an

individual in this strip given by

D(r) = Dot-L2J 'F7

where I) a is the reference dose rate from the surface contamination at distance d, and r is the

individual's distance from the cask (a S r 5 b). The average population dose rate is given by

jb(r)dr D.O (-2) dr D5d 2(r2

Ls- b b b

Jdr Jdr Jdr

-a r-a r-a

D d2(- 1) b | 21 1

=a _ _ a .

- - b-a

The average population dose rate corresponds to the dose rate delivered by a cask with the reference dose

rate but delivered at a distance given by

rd=

This effective distance is used in estimating population doses from a shipment on the highway. If the

reference distance is 1 rn. then the expression for total unit collective dose delivered by the cask in motion

along the entire length of its route is found by substituting reIr for r in the equation. The unit collective

dose for a stopped transport is the product of dose rate at rtff and the time interval that the transport is

stopped. Values for a and b depend on the location of the population segment with respect to the

transport and on the type of roadway, as shown in Table F. 1.

107
External Exposures to Members of the Public Appendix F

Table F.1 Values of a and b for estimating collective doses

from external exposures

a b

Highway Population segment (m) (m)

State Nearest to transport 29 798

State Opposite from transport 33 802

Interstate Nearest to transport 32 786.5

Interstate Opposite from transport 59 813.5

A spreadsheet was developed to apply the above approaches to calculate the individual and collective

doses reported in Sect. 5 of this report.

108
Y

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BIBLIOGRAPHIC DATA SHEET

(See Iusions on he revise)

2. TITLE AND SUBTITLE

A Risk-informed Basis for Establishing Non-Fixed

Surface Contamination Umits for Spent Fuel

Transportation Casks

1. REPORT NUMBER

(Asuigned by NRC. Add Vol., Supp,

Rev., and Addendum Numbers,

K any.)

NUREG/CR- 6841

ORNLUtM-2003/225

3 DATE REPORT PUBLISHED

April 2004

4. FIN OR GRANT NUMBER

B0009

6. AUTHOR(S) L TYPE OF REPORT

R. R. Rawi, K. F. Eckerman, and J. S. Bogard Technical

7. PERIOD COVERED icldusve Cat)

1. PERFORMING ORGANIZATION-NAME AND ADDRESS p1INR4, prvie Dlvidon Offte orRegior4 U.S. Nuciw Regulatory COmmssn, and manling Mddys;

' lconlrector, provide name and mailing addrs)

Oak Ridge National Laboratory, Managed by UT-Battelle, LLC

PO Box 2008, Bldg. NTRC, MS-6472

Oak Ridge, Th 37831-6472 USA

C. SPONSORING ORGANIZATION - NAME AND ADDRESS (if NRC tpe 'Same as ebovwlrcontruwtor, provide NRCvislion, Office reon, U5 Regubtaty

CommissIon, and mailng addres.)

Spent Fuel Project Office

Office of Nuclear Material Safety and Safeguards

U.S. Nuclear Regulatory Commission

Washington, DO 20555-0001

10. SUPPLEMENTARY NOTES

J. R. Cook, NRC Project Manager

11. ABSTRACT 200 words ores)

The current internationally accepted basis for establishing non-fixed surface contamination limits for spent fuel casks is

the same as that for other transportation package types. This study examined the suitability of the currently used

exposure model, taking Into account exposure pathways and parameters representative of typical light-water-reactor

spent fuel cask handing, loading, and transportation. Because the currently used model was determined to be

Inappropriate for spent fuel casks, a new exposure model was developed using pathways and parameters specific to

spent fuel casks. Results show that Individual and collective doses to members of the public are very low and that

worker doses dominate the total collective dose from non-fixed surface contamination. Worker doses that vary as a

function of allowable surface contamination limits were calculated and are dominated by doses due to decontamination

and surface contamination monitoring activities performed after the cask Is drained. An approach was developed for

evaluating the dose implications of higher allowable non-fixed surface contamination limits.

12. KEY WORDSfDESCRIPTORS (Lst words erphrases Vt will assist researchers i oting th repat) 13. AVAILABIY STATEMENT

unlimited

spent fuel, cask, surface contamination, transportation, radiation doses

14. SECURITY CLASSIFICATION

(fTh Pae) unclassified

(i Report) unclassified

1. NUMBER OF PAGES

1. PRICE

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