NUREG-1889 

RASCAL 3.0.5 Workbook 

 

U.S. Nuclear Regulatory Commission 

Office of Nuclear Security and Incident Response 

Washington, DC 20555-0001
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 NUREG-1889 

 

RASCAL 3.0.5 Workbook 

Manuscript Completed: September 2007 

Date Published: September 2007 

Prepared by 

G.F. Athey1 

S.A. McGuire2 

J.V. Ramsdell, Jr.3 

1

Athey Consulting 

P.O. Box 178 

Charles Town WV 25414-0178 

2

Office of Nuclear Security and Incident Response 

U.S. Nuclear Regulatory Commission 

Washington, DC 20555-0001 

3

Pacific Northwest National Laboratory 

P.O. Box 999 

Richland, WA 99352 

Prepared for 

Office of Nuclear Security and Incident Response 

U.S. Nuclear Regulatory Commission 

Washington, DC 20555-0001 

iii

Abstract

The code currently used by NRC’s emergency operations center for making dose projections for

atmospheric releases during radiological emergencies is RASCAL version 3.0.5 (Radiological

Assessment System for Consequence AnaLysis). This code was developed by NRC. RASCAL 3.0.5

evaluates releases from: nuclear power plants, spent fuel storage pools and casks, fuel cycle facilities,

and radioactive material handling facilities.

The workbook contains problems designed to familiarize the user with the RASCALsoftware through

hands-on problem solving. The workbook is primarily for use by students in a RASCAL training course

supervised by a qualified instructor.
iv
v

Table of Contents

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

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

List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1 What Is RASCAL? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2 Getting Started with RASCAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

3 How RASCAL Calculates a Reactor Source Term . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Using RASCAL: Assessing a PWR Core Damage Accident . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

4 Source Term and Release Pathway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

5 Entering Site Meteorological Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

6 Calculate Doses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

7 Transport and Diffusion Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

8 Using the Maximum Dose Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

9 Obtaining Observed Weather Data from the Internet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

10 Obtaining Forecast Weather Data from the Internet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

11 Time for End of Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

12 Displaying Plume Footprints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

13 Comparing Field Measurements with RASCAL Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

14 Normalizing the Model to Match Field Team Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

15 Field Measurement to Dose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

16 Briefing for Non-Technical Decision Maker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

Nuclear Power Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

17 Examining the RASCAL Source Term . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

18 Release Pathway Reduction Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

19 Monitored Mixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

20 Containment Radiation Monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

21 Containment Bypass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

22 Steam Generator Tube Rupture with Coolant Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

23 Coolant Sample . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

24 Ultimate Core Damage State Source Term . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

Spent Fuel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109

25 Assembly Damaged Underwater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

26 Pool Drained . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

27 Dry Cask Rupture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119

Fuel Cycle / UF6/ Criticality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

28 Uranium Process Fire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123

29 Explosion Involving Uranium Oxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126

30 UF6 Cylinder Rupture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

31 UF6 Cascade Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134
vi

32 Criticality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137

Other Radioactive Material Releases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141

33 Radioactive Material in a Fire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142

34 Transportation Accident . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146

Meteorology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150

35 Precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151

36 Calm and Variable Winds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155

37 Elevated Releases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158

38 Adding Weather Stations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163

39 Stability Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166

40 Predefined Meteorological Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169

Decay Calculator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174

Appendix 1: Lessons Learned from Radiological Emergencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
vii

List of Figures

1 Polar receptor grid for the plume model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

2 Cartesian receptor grid for the puff model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

3 PWR containment monitor response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

4 Plume interaction with the mixing layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159

List of Tables

1 Nuclear Power Plant Core Inventory During Operation for Low Enriched Uranium Fuel . . . . . . . . . . 7

2 Radionuclide concentrations in reactor coolant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3 Default distances for close-in polar grid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

4 Distances between Cartesian grid receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

5 Fuel activity release fractions used in spent fuel accidents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110

6 Spent fuel damage estimates based on storage duration and time fuel is uncovered . . . . . . . . . . . . 111

7 Spent Fuel Dry Storage Cask Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119

8 Airborne release fractions and inhalation fractions used in uranium oxide fires . . . . . . . . . . . . . . . 123

9 Airborne release fractions and inhalation fractions for explosions involving U oxide . . . . . . . . . . . 126

10 Health effects due to HF exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130

11 Health effects due to uranium intake by inhalation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

12 Paducah GDP buildings and default inventory and release rates . . . . . . . . . . . . . . . . . . . . . . . . . . 134

13 Portsmouth GDP buildings and default inventory and release rates . . . . . . . . . . . . . . . . . . . . . . . . 134

14 Fission yields used in criticality calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137

15 Fire activity release fractions by element . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142

16 Fire activity release fractions by form of compound . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143

17 Converting rainfall intensity to RASCAL precipitation class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151

18 Selection of Pasquill-Gifford stability class by ΔT/Δz method . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166

19 Selection of Pasquill-Gifford stability class by meteorological conditions . . . . . . . . . . . . . . . . . . 167

20 How RASCAL estimates atmospheric stability class for missing stability classes . . . . . . . . . . . . . 167

21 Limits of atmospheric stability classes based on time of day, wind speed, and precipitation . . . . 168

22 Summary of predefined meteorological data sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
viii

Acknowledgments

The authors would like to acknowledge all the students who have used the workbook over the years.

Your comments and suggestions have been invaluable.
1

Introduction

This workbook is designed to teach you how to use RASCAL through hands-on problem solving. The

problems described within were developed using the December 2006 release of RASCAL v3.0.5. The

workbook may be used with other revisions of the software. However, the results from working the

problems may appear different from those in the workbook.

Attempt to do each problem using the computer and answer all the associated questions. Blank tables are

provided for you to record your results. A description of how the problem may be solved and a discussion

of the results are included with each problem.

You must understand the risks and uncertainties inherent in dose projection models before using this tool.

Contact Information

Please direct any questions, suggestions, corrections or comments concerning this workbook to the

following:

Stephen A. McGuire

Office of Nuclear Security and Incident Response

U.S. Nuclear Regulatory Commission

Washington, DC 20555-0001

sam2@nrc.gov

George F. Athey

Athey Consulting

PO Box 178

Charles Town, WV 25414-0178

atheyconsulting@frontiernet.net

Lou Brandon

Office of Nuclear Security and Incident Response

U.S. Nuclear Regulatory Commission

Washington, DC 20555-0001

lkb1@nrc.gov

Registration

To become a registered RASCAL user and receive program updates automatically, e-mail your contact

information to George Athey.

Distribution

RASCAL was developed by the NRC using entirely government funds. As such, it has no copyrights or

commercial restrictions. RASCAL can be freely copied, installed, and distributed. It contains no licensed

components and requires no registration, activation, or royalties.

For information on how to obtain the RASCAL computer code or a PDF version of this workbook,

contact George Athey.
2

1 What Is RASCAL?

RASCAL, which stands for Radiological Assessment System for Consequence AnaLysis, is the software

developed and used by the U. S. Nuclear Regulatory Commission (NRC) Emergency Operations Center

to estimate projected doses from radiological emergencies.

RASCAL consists of two main tools: the Source Term to Dose model and the Field Measurement to

Dose model.

Source Term to Dose

Use the Source Term to Dose model when you want to enter information about plant conditions or

accident conditions in order to estimate projected radiation doses from a plume to people downwind.

The Source Term to Dose model will first generate a time-dependent “source term”. This is the release

rate for each radionuclide from the facility as a function of time. This time-dependent release rate (the

“source term”) then provides the input to an atmospheric dispersion and transport model.

The atmospheric dispersion and transport model estimates radionuclide concentrations downwind, both

in the air and on the ground due to deposition. The calculated concentrations are then use to estimate

projected doses. The dose pathways are: cloudshine from the plume, inhalation from the plume, and

groundshine from deposited radionuclides (assuming 4 days of exposure to groundshine).

Field Measurement to Dose

Use the Field Measurement to Dose model when the plume-phase of the accident is over and you are in

the intermediate-phase. The Field Measurement to Dose model estimates doses based on measurements

of the radionuclide activity in the environment. The model will use the ground concentration of

radionuclides to calculate intermediate-phase doses.

Two additional RASCAL Tools

Use the Decay Calculator to evaluate the radioactive decay of a radionuclide mixture over a user

specified decay time.

Use the Nuclide Data Viewer to examine the contents of the RASCAL radionuclide database. This

database contains information on individual radionuclides such as half-life, dose conversion factors, and

inventories.
3

2 Getting Started with RASCAL

RASCAL is started by selecting in Windows:

Start | All Programs | RASCAL v3.0.5

This will display the opening screen with version number and date of release.

Click the OK button to continue to the main RASCAL access screen (shown below).

The four big buttons start the respective tools. Since the first section of the workbook deals primarily

with the Source Term to Dose model, click that button.
4

Basic Features of the User Interface

This is the main screen of the Source Term to Dose model as seen when first starting up the program.

1. The menu bar at the top provides the standard Windows functions such as file management and help

as well as access to two data viewers.

The Nuclide Data Viewer can be used to examine the contents of the RASCAL radionuclide

database. The database contains nuclide specific information such as inventories, dose conversion

factors, and half-lives.

The Site / Facility Data Viewer can be used to display data on each of the facilities in the RASCAL

database. This includes geographic coordinates and a brief location description plus details about the

facility. For reactors it includes parameters used by the model such as volumes, pressures, and leak

rates.

2. The main input to the program is controlled via the buttons on the left side; starting from the top and

working downward. The buttons are blue with a question mark when they are available but the topic

area has not yet been defined. The buttons display a checkmark when the step has been completed.

3. The right portion of the screen contains a set of three tabs. These tabbed areas provide easy viewing

of the inputs and some of the generated results. Initially, only the case summary tab is active and

updates as the problem is defined. After a set of calculations has been completed, the Source Term

Summary and Maximum Dose Values tabs become active to show results. More results are accessed

via the Detailed Results button.
5

4. The Save Case button is used to create a single file containing all the inputs and results from a

single modeling run. (The save file is really just a zipped archive containing all the input and output

files generated during the building and running of the case. You could use an unzip utility to extract

and examine files in the saved case.)

All the user inputs are remembered after the calculations. Thus, it is very easy to go back and change a

single input and recalculate without having to completely redo the case inputs.
6

3 How RASCAL Calculates a

Reactor Source Term

The RASCAL source term calculations for nuclear power plant accidents are based largely on the

methods described in NUREG-1228 (McKenna and Giitter 1988).

The basic method first determines activity present by radionuclide. Then, the method multiplies the

activity present by the fraction of the material present that is available for release. This product may be

multiplied by a reduction factor, if appropriate. Examples of reduction mechanisms are filters, plateout,

and removal by containment sprays. This product is then multiplied by a leak rate.

For example, this calculation could describe the release of radionuclides from a reactor core to a

containment building or it could describe the release of radionuclides from a containment building to the

environment.

In general, releases will in most cases occur over an extended period of time. The release rate will

generally vary as a function of time. The time dependence of the release is treated by estimating the

activity release rate averaged over discrete time steps that have a duration of 15 minutes.

Core inventories

For nuclear power plant source terms based on core damage, the radionuclide inventories assumed to be

in the reactor core are shown in Table 1.

The values in Table 1 are for low-enriched uranium fuel. The values were derived from Table 2.2 of

NUREG-1228 (McKenna and Giitter 1988). The derivation was done by dividing the fission product

inventories in NUREG-1228 by 3 to convert from Ci/MWe to Ci/MWt, and then rounding to 2 significant

figures. The inventories of nuclides with a half-life of more than one year were scaled up from a burnup

of 18,000 to 30,000 MWD/MTU. The inventories in NUREG-1228 were derived from the Reactor Safety

Study, WASH-1400. Table VI 13-1 of WASH-1400 ranked the nuclides in the core by importance to

early health effects. The nuclides with greater importance for early health effects were included in the

NUREG-1228 core inventory list. In addition, NUREG-1228 added noble gases that had lesser

importance for early health effects because noble gases are the most likely group of fission products to be

released to the environment by a nuclear power plant accident. According to Figure 2-4 of NUREG-1228,

the iodine and tellurium nuclides contribute almost two-thirds of the bone marrow dose for a major

nuclear power plant release. Krypton, cesium, strontium and barium are the other major contributors.
7

Table 1 Nuclear Power Plant Core Inventory During Operation for Low Enriched Uranium Fuel

(30,000 MWD/MTU burnup)

Nuclide Core Inventory Ci/MW(t) Nuclide Core Inventory Ci/MW(t)

Ba-140 5.30e+04 Ru-103 3.70e+04

Ce-144 2.80e+04 Ru-106 1.33e+04

Cs-134 4.17e+03 Sb-127 2.00e+03

Cs-136 1.00e+03 Sb-129 1.10e+04

Cs-137 2.67e+03 Sr-89 3.10e+04

I-131 2.80e+04 Sr-90 2.00e+03

I-132 4.00e+04 Sr-91 3.70e+04

I-133 5.70e+04 Te-129m 1.80e+03

I-134 6.30e+04 Te-131m 4.00e+03

I-135 5.00e+04 Te-132 4.00e+04

Kr-85 3.17e+02 Xe-131m 3.30e+02

Kr-85m 8.00e+03 Xe-133 5.70e+04

Kr-87 1.60e+04 Xe-133m 2.00e+03

Kr-88 2.30e+04 Xe-135 1.10e+04

La-140 5.30e+04 Xe-138 5.70e+04

Mo-99 5.30e+04 Y-91 4.00e+04

Np-239 5.50e+05

Reference: Derived from NUREG-1228, Table 2.2 (McKenna and Giitter 1988) which in turn derived

its table from WASH-1400

The inventories in Table 1 are based on a burn-up of 30,000 MWD/MTU. RASCAL adjusts the inventory

of radionuclides that have a half-life exceeding one year to account for burnup. The inventory for the

specified actual burnup, INVACTUAL, is calculated only for nuclides with a half-life of more than one year

using the equation below. There is no burnup adjustment for nuclides with a half-life less than one year.

INV INV BURNUP

MWD MTU

ACTUAL

ACTUAL

 30 000 

30 000

,

, /

If the reactor is shut down prior to the start of the release, the radionuclide inventories are adjusted to

account for radiological decay and ingrowth. In addition, at the end of each time step, the activities of the

nuclides present are adjusted to account for radiological decay and ingrowth. The minimum activity of a

nuclide allowed in a source term time step is 10-15 Ci.
8

Coolant Inventories

RASCAL uses coolant inventories for some accident types. The concentrations that RASCAL uses for

normal coolant are given in Table 2.

Table 2 Radionuclide concentrations in reactor coolant

Nuclide

PWR coolant

concentration

BWR coolant

concentration Nuclide

PWR coolant

concentration

BWR coolant

concentration

Ci/g Ci/g Ci/g Ci/g

Ba-140 1.30e-08 4.00e-10 Mo-99 6.40e-09 2.00e-09

Ce-144 4.00e-09 3.00e-12 Np-239 2.20e-09 8.00e-09

Co-58 4.60e-09 1.00e-10 Ru-103 7.50e-09 2.00e-11

Co-60 5.30e-10 2.00e-10 Ru-106 9.00e-08 3.00e-12

Cs-134 3.70e-11 3.00e-11 Sr-89 1.40e-10 1.00e-10

Cs-136 8.70e-10 2.00e-11 Sr-90 1.20e-11 7.00e-12

Cs-137 5.30e-11 8.00e-11 Sr-91 9.60e-10 4.00e-09

H-3 1.00e-06 1.00e-08 Tc-99m 4.70e-09 2.00e-09

I-131 2.00e-09 2.20e-09 Te-129m 1.90e-10 4.00e-11

I-132 6.00e-08 2.20e-08 Te-131m 1.50e-09 1.00e-10

I-133 2.60e-08 1.50e-08 Te-132 1.70e-09 1.00e-11

I-134 1.00e-07 4.30e-08 Xe-131m 7.30e-07 0

I-135 5.50e-08 2.20e-08 Xe-133 2.90e-08 0

Kr-85 4.30e-07 0 Xe-133m 7.00e-08 0

Kr-85m 1.60e-07 0 Xe-135 6.70e-08 0

Kr-87 1.70e-08 0 Xe-138 6.10e-08 0

Kr-88 1.80e-08 0 Y-91 5.20e-12 4.00e-11

La-140 2.50e-08 4.00e-10

Mn-54 1.60e-09 3.50e-11

Reference: ANSI/ANS 18.1-1999.

Those normal coolant concentrations are taken from ANSI/ANS 18.1-1999. During steady-state

conditions, iodine and other fission products may escape from fuel rods having clad defects and enter the

reactor coolant system. Since the internal pressure in the fuel rod is balanced with the coolant pressure

outside the fuel rod during steady-state conditions, the rate of escape is low. The fission products that do

escape into the reactor coolant system are continually removed by the reactor coolant system purification

cleanup resulting in a low equilibrium concentration.

However, if a reactor transient causes the pressure of the reactor coolant system to decrease rapidly, the

escape rate from fuel rods can increase and cause a temporary increase, or “spike,” in the coolant

concentrations. There is also a belief that coolant water can enter fuel rods through cladding defects. If

the reactor coolant system pressure suddenly decreases, this water could leach off iodine and cesium salts
9

deposited on the inner clad surfaces, increasing the iodine and cesium available for escape during the

transient.
10

Using RASCAL: Assessing a

PWR Core Damage Accident

This section of the workbook provides a detailed look at using RASCAL to develop a protective action

recommendation for a PWR core damage accident. It is a walk through the entire process from start to

finish.

The problems in this section should be worked in sequence as each depends on the previous work.
11

4 Source Term and Release

Pathway

Purpose

Discussion

To learn how to select source terms, release pathways and reduction mechanisms.

Here are a few facts that you should know:

• Almost all the radioactive material at a nuclear power plant is in the fuel rods. Therefore, only major

damage to fuel rods can cause a large release.

• The only plausible way to cause major damage to fuel rods is to remove the water covering the rods

so that the heat produced by radioactive decay can no longer be removed effectively.

• If water no longer covers the fuel rods, the fuel cladding will first start to melt. Later, the fuel itself

will start to melt. If the fuel remains uncovered, the molten fuel will eventually melt through the

reactor pressure vessel.

• Any accident that leaves the fuel rods uncovered is a very serious accident that will cause large

amounts of fission products to be released from the reactor core.

• It is a lot easier to predict when the uncovering of a reactor core will occur and how long the

uncovering will last than it is to predict how much core damage will occur (for example, what

percent of the fuel will melt). Therefore, RASCAL uses the time that the reactor core is uncovered as

its primary method to assess offsite consequences of accidents involving core damage.

• When you use the “time core is uncovered” source term type, RASCAL will calculate the timedependent release of fission products to the containment. The first fission products released from the

core are noble gases and volatile elements like iodine and cesium. Non-volatile materials do not

come out until later.

• The “time core is uncovered” source term option of RASCAL is likely to overestimate the speed and

magnitude of the release and thus also overestimate the projected radiological doses. RASCAL users

should inform decision makers of that fact.
12

Problem

Inputs: Step-by-step

You are provided with the following information:

• Arkansas Nuclear One, Unit 1 had been operating at full power

• At 10:00 A.M. the reactor scrammed due to a major rupture in the primary coolant system (loss-ofcoolant accident)

• Operators believe the core may become uncovered at 1:00 P.M. Further, they are concerned they may

not be able to provide enough makeup water to recover the core.

• Plant operators report they are unable to activate the containment spray system. However, they

expect the containment to remain intact and any release to the atmosphere will be at the design leak

rate.

Use RASCAL to estimate potential consequences from the accident.

If needed, start the Source Term to Dose model from the main RASCAL screen (see page 3). Then, input

the information provided into the Event Type, Event Location, Source Term, and Release Path screens of

the model.

We start with the main screen showing an undefined case and waiting for the event type to be selected.
13

Event Type

Selection of the event type is easy. First, click the Event Type button. Since the problem is at Arkansas

Nuclear and is a reactor accident - choose the option Nuclear Power Plant. Making this selection will

limit the choices you have further down the line.

Click the OK button to return to the main screen. The Event Type button now has a checkmark indicating

that the step has been completed. Also, the Event Location button color has now changed from grey to

blue indicating it is active.

Event Location

Specification of the event location is also easy in this case. Click the Event Location button to bring up

the Location and Plant Parameters screen.
14

1. Select the option to Load Existing Nuclear Power Plant Site from Database

RASCAL contains a database with information about all the commercial nuclear power plants in the

U.S. The database contains unit specific information such as power and volumes as well as location

and population information. The second option (Define a “Generic” Nuclear Power Plant Site) is

available if needed. It can be used to define a site anywhere in the world.

2. Select Arkansas - Unit 1 from the list of available site names

The drop-down list has all the nuclear power plants available in the database.

3. Leave all the plant parameters unchanged

This section displays some of the plant specific data from the database. The values can be changed if

needed. However, the problem states that the reactor had been at full power so leave the average

power set to the default. Leave the average fuel burnup at the default value of 30,000 MWD/MTU

because better information was not provided.

The average reactor power has units of megawatts thermal (MWt). The thermal power is a direct

measure of the energy produced by fission. Therefore, the fission product inventory will be

proportional to the thermal power. Changing the reactor thermal power level affects the release

quantity of all radionuclides.

(The electric power is the thermal power times the electrical generating efficiency of the plant.

Typical efficiencies are usually between 30% and 35%, giving a rough conversion factor of 3

between MWe and MWt. All plants have slightly different efficiencies and the efficiency of a single

plant can vary depending on operating conditions. Thus, fission product inventory is not exactly

proportional to electric power output. It is usually close, but not exact.)

Fuel burnup is a measure of how much fission energy has been produced by the fuel elements that are

currently in the core. The fission energy released per unit mass of the fuel has units of megawatt-days

per metric ton of uranium (MWD/MTU).

A brand new core will have zero burnup. After several reloads of reactor fuel (generally replacing

about one-third of the core per reload), the burnup will typically be about 20,000 MWD/MTU at the

start of the cycle and will steadily increase to about 40,000 MWD/MTU at the end of cycle when the

reactor shuts down to replace old fuel with fresh new fuel. The older fuel elements that are replaced

will typically have a burnup of about 50,000 MWD/MTU. The reactor control room can determine

the current fuel burnup at any point in the cycle, although this will not a have high priority during an

actual emergency.

Radionuclides with relatively short half-lives (less that a couple of weeks) reach a steady-state

equilibrium activity (quantity) fairly rapidly. Their activity in the core is largely unaffected by

burnup.

But, the activities of long-lived radionuclides (half-life greater than one year) steadily increase as the

reactor core produces power. Their activities never reach equilibrium. RASCAL uses average core

burnup to adjust the core inventory for the long-lived radionuclides in the core fuel that never reach

equilibrium. All long-lived radionuclides in the core inventory are scaled as needed based upon the

actual burnup value entered.

Click OK to return to the main screen.
15

Note that the case summary is filled in as you proceed through the definition of the problem. This

includes the information you enter as well as supplemental information pulled from the RASCAL

databases. For example, the 2000 Census population at 2, 5, and10 mile radii from the plant are shown.

Also shown are, the design pressure and design leak rate.

Source Term

Now select the Source Term button. This will display the Source Term Options for Nuclear Power

Plant screen. All the available source term types for a nuclear power plant accident are listed.
16

1. The top three options base the source term on an estimate of the amount of core damage.

2. The bottom five options base the source term on some form of measurement.

Select the Time Core Is Uncovered option on this screen and then click OK to proceed.

Enter the time of the reactor shutdown (10:00) and the time the core was uncovered (13:00).

There are two important things to understand here about times in RASCAL. First, RASCAL uses a 24

hour clock (instead of A.M. and P.M.). That is why we entered 13:00 instead of 01:00. Second, you should

always work in site time. All information received from the plant will be in their local time. Trying to

convert time zones can be confusing in an emergency and is not necessary if all parties have agreed to

work with site time.

Leave the option for Core recovered set to No. Click OK to complete the source term definition.

Release pathway

Now select the Release Pathway button on the main screen. This will display the PWR Release

Pathways screen.

Each source term type will have one or more available release pathway. As shown below, there are three

release pathway options for a PWR. Each option has an associated containment schematic which uses red

lines to show pathways to the atmosphere.
17

Select the option Containment leakage / failure and then click OK to display the containment release

pathway definition screen.
18

1. For the pathway description enter the text: Design leakage.

This user-entered description is not used in the calculations but will appear on the case summary

output. It should be used to clarify where or how the material is entering the atmosphere.

2. Leave the release point characterization set to: Not an isolated stack.

This will be a release from the reactor containment building and not from a stack. Only some BWRs

actually have isolated stacks.

3. Release height: 0.0 m

If known, the height above ground level at which the material enters the atmosphere should be

entered. This value may be adjusted upward if needed to represent an effective release height. For

example, if a fire is forcing the material higher you might use an estimate of the height of the smoke

as an effective release height. In our case we do not have a defined release point so leave the release

height at the default value of 0.0 m.

Consider building wake effects: Yes.

Historically, adjustments to the atmospheric dispersion parameters have been made to compensate

for releases from buildings. These adjustments have been based on building dimensions and have not

considered wind speed. RASCAL includes optional adjustments to the dispersion parameters that are

functions of building area, wind speed, and distance downwind (Ramsdell 1990). The adjustments,

which are inversely related to wind speed, start at zero at the release point and increase with distance

downwind until a limit, based on building area, is reached. (The adjustments are actually a function
19

Inputs

of travel time.) When the wind speed exceeds about 4 m/s the adjustments become negligible. The

adjustments have been referred to as building wake corrections. However, the adjustments are more

sensitive to wind speed than building area and are only significant at low wind speeds. Therefore, it

is more appropriate to refer to the correction as a low wind speed correction. More recent analysis of

the experimental dispersion data (Ramsdell and Fosmire 1998a, 1998b) has yielded adjustments that

are independent of building area.

4. Leave the Start of release to containment time as initially set to match the core damage time

(13:00).

This entry allows for the consideration of the holdup of material before it enters the containment

atmosphere. No information is provided on any delays in the radioactivity moving from the core to

the containment. Thus, assume that the material enters the containment immediately.

5. Leak rate to atmosphere described by: Percent volume

Leakage fraction for reactors can be described in two ways: 1) as a leak rate from containment in

percent volume per time, or 2) as a leak rate set by a pressure and containment hole size. Both

methods allow the leak rate to vary with time. The methods cannot be combined.

6. Leave the spray and leak rate events unchanged

The lower portion of the screen deals with describing the time dependent leakage of material to the

environment. A leak type is selected and then release events are entered into a table. The default is

for a leak rate type of percent volume, for there to be no active reductions (e.g. sprays, filters), and

for the leak rate to be at design. The event grid already has 2 events defined: sprays off and design

leak rate. The defaults are correct for the problem and do not need to be changed.

Click the OK button to accept the release pathway definitions.

In many of the later problems in the workbook the inputs are described in a much briefer format without

all the discussion. However, when appropriate, the rationale for an input will be provided.

Following is the abbreviated input summary for the problem up to this point.

Event Type Nuclear Power Plant

Event

Location

Arkansas - Unit 1

Source Term Time Core is Uncovered

Reactor shutdown: 10:00

Core uncovered: Yes, at 13:00
20

Core recovered: No

Release

Pathway

Containment Leakage / Failure

Pathway description: Design leakage from containment

Release point characterization: Not an isolated stack

Release height: 0.0 m

Consider building wake effects: Yes

Start of release to containment: 13:00

Leak rate to atmosphere described by: Percent volume

Release path events:

<date> 13:00 Sprays Off

<date> 13:00 Leak Rate Design
21

5 Entering Site Meteorological Data

Purpose

Discussion

Problem

To learn how to enter the basic meteorological observations obtained from the site.

Meteorological data is needed to model the behavior of the radioactive plume in the atmosphere. The

minimum required data is:

wind speed and direction defines the downwind transport

atmospheric stability governs plume horizontal and vertical growth

precipitation defines wet deposition (a very important removal process)

The first step in creating a meteorological data set for use with RASCAL is entering the meteorological

observations for the release point. The data can be obtained from a variety of sources. For nuclear power

plants, observations for the site itself would be obtained via the Emergency Response Data System

(ERDS) or by telephone from the licensee. We will start by entering that data.

ERDS has limitations:

- it provides no forecast meteorological information

- it may not be connected when needed

- the data is from a single location and may not be sufficient to describe winds in complex terrain

- there are no ERDS connections at facilities other than nuclear power plants

For purposes of this problem, we will assume that ERDS and the plant operators have provided the

following data:

Time Wind direction

(deg)

Wind speed

(mph)

Stability

class

Precipitation Air Temp

(deg F)

1100 10 6 B No precip 65

Note that ERDS does not provide information on precipitation. That information would need to be

acquired from another source.
22

Inputs: Step-by-step

Select the Meteorology button on the main screen. This will display the Select Meteorological Data Set

screen.

The default is to use Predefined Data (Non Site-specific). The available data sets portion of the screen

lists all the data distributed with the RASCAL program. These “generic” data sets are described further

in Topic 40.

Actual Observations and Forecasts

This data type is both site-specific and date/time-specific. That is, it can be used only for releases from

the site specified at the specified times. Since it is site-specific, it can correct for topographic effects. The

date and times of the meteorological data must closely match the release times. Meteorological data must

start within a 2 hour window before the release to the atmosphere starts. The data set can be comprised of

a mix of observations and forecast records. However, entering a set of observations for a station will

cause any forecasts for that station at an earlier time to be deleted.

1. Choose the Actual Observations and Forecasts data set type.
23

This will enable the buttons used to access the Meteorological Data Processor program. If no data

sets have been previously created for this site, then the Available Data Sets box will be empty.

2. Click the Create New button.

Since we have not yet entered any weather data for this event, we want to create a new set. Using

actual data requires that the times of the meteorological observations closely agree with the times of

the release to the atmosphere.

This will start the Meteorological Data Processor program and display the main screen.

1. The main steps of the program are controlled via the buttons on the left side; starting from the top

and working downward. The Location button is greyed out and unavailable because the program was

started from within the source term to dose model. At this point the location has already been defined

and thus doing it again is not necessary. The Location button is available only if the Meteorological

Data Processor program is started in a stand-alone mode. The Save and Process Data, View

Meteorology, and Export Data Set buttons are also unavailable since no data has yet been entered.

2. This is a list of the available weather stations surrounding the site. These are taken from the

RASCAL database. The display shows the distance and the direction of the station from the release

point.

The NWS is continuing to add observing stations. If you find other stations that you would like to use

they can be added. Refer to “Adding Weather Stations” on page 163 for the steps.

3. A simple map show the relative positions of the stations to the release point.

Click the Enter Data button to display the data entry screen.
24

Data Entry Screen

Note the following features of the data entry screen:

1. The default weather station (first in the drop-down list at the top) is the on-site meteorological tower.

For sites not in the RASCAL database, this station will be the release point. At least one observation

must be entered for this station. It should usually be at the first observation time. It is recommended

that you always begin by entering the data for the release point before entering data for other stations.

You can change the station by picking from the Enter data for list. Try this to see how it works.

Notice that the table of data will change as the station changes.

2. Use the Change units or methods button if the units of the data you are receiving do not match

those currently displayed in the data entry grid.

3. Weather data for each station is entered into a separate grid. Do not combine data from multiple

stations into one table. The table of data initially consists of a single, mostly blank record.

Data can be entered for any date or time. However, there must be data before or at the same time as

the start of the release to the atmosphere.

4. The Add record button is used to add records to the end of the data entry grid.
25

Entering Data

Now, enter the following data for station ARKA:

Column header User entry Comments

Type Obs This means that the record is an observation and represents an

actual set of measured values (in contrast to forecast)

Date today Use the default, which if the computer clock is correct, should be

today.

Time 11:00 Enter the time using a 24-hour clock. The program will round the

time to the nearest quarter-hour. For example, an entry of 12:07

would be changed to 12:00. Similarly, an entry of 14:22 would be

changed to 14:30.

Direction from

(deg)

10 This is the direction from which the wind is blowing. A wind from the

north is 0 degrees, from the east is 90 degrees, from the south is

180 degrees, and from the west is 270 degrees.

Speed (mph) 6

Stability B

Precipitation No precip

Air Temp (deg F) 65

Air Pressure (mb) <blank> This is needed only if the release contains UF6.

Dew Pt (deg F) <blank> This is needed only if the release contains UF6.

The record will look like this:

Now click the OK button to return to the main form.
26

Observation Summary

Note that the Observation Summary tab is active when the screen is redisplayed after doing data entry.

This summary shows in one place how much data has been entered. For each station, it shows the number

of observations (or forecasts) and the date and time of the first and last entries. In this case, a single

observation has been entered for the ARKA site.

Save and Process Data

The RASCAL transport and diffusion models require gridded wind fields for their calculations. Just

entering the observation data into the program is not enough. A final step is required to take the

information at these observation points and generate the gridded data. Each time additions or changes are

made to the data, the save and process step must be repeated.

The Save and Process Data button is now active. Click it to display the Save observations and

process data screen.
27

1. The field at the top of the screen is used to name the data set. This name should uniquely identify the

data set to you and to others who will share the data set. It should consist only of alphanumeric

characters. Punctuation characters (e.g. colons, commas, semi-colons) should be avoided.

For this first data set, use a name that indicates when the data set was created, for example:

ARKA 2007-03-15 1100 (Change the date in your name as needed)

2. The data set description is text that is displayed with the data set name in the data set selection

screen. It is recommended that you not use the automatically created description. It will not change if

the first data record stays that same (which is likely) and can be confusing.

Instead, select the User entered option and then type in the reminder text “Name indicates latest

data”. This will remind you that the naming scheme uses the time the data was entered and the latest

time should be the most current set of data.

3. Leave the Data processing options at the default settings

- Estimate missing stability using

This option allows the program to replace missing stabilities with an estimated value based upon

wind speed, time of day, and precipitation. If Persistence is selected, the stability will remain

the same as the previous observation.

- Adjust stability for consistency

This option allows the program to compare the user entered stabilities with ranges of stability

classes that would be expected given the time of day and meteorological conditions. Stability

values that are out of range are replaced with more likely values.
28

- Modify winds for topography

The RASCAL database contains topography data for each site. This data can be used by the

program to modify the wind fields so wind flows around mountains instead of through them.

Click the OK button. When the calculations are completed you will be returned to the main screen on the

Observation Summary tab.

1. The View Meteorology button will launch a separate program for viewing both the entered data and

the generated gridded data to be used by the models.

2. The Export Data Set button can be used to created a single file containing all the meteorological

information in the current data set. This file can be saved in any location and can be copied or

mailed. There is an import button on the meteorological data selection screen that allows this type

file to be imported. Then export/import functionality allows the jobs of dose analyst and weather data

collection and entry to be separated.

3. The Return button exits the Meteorological Data Processor and returns control to the Source Term to

Dose model user interface.

Before returning to the model to use this data set, click the View Meteorology button.
29

Viewing the Meteorology

This is the Meteorological Data Viewer main screen.

The viewer program provides both text and graphics displays of both the entered data and the processed

data.

Click the Entered Data button.
30

This screen provides a set of pictures to summarize the entered data at each time.

1. The large image on the left shows the winds. Arrows represent the direction in which the wind is

blowing. In our case, the wind direction was 10 degrees (from the north). The length of the arrow is

proportional to the wind speed. Since we entered only data for the site, there is no other station data

to display and they are represented by an X.

2. The View topography check box controls whether a colored representation of terrain heights is

displayed beneath the wind arrows.

3. The viewer can cycle through the data in 15 minute time steps. Since we had only a single

measurement time there is only one time to display.

4. The 3 smaller images on the right reflect the data entered for stability, precipitation, and mixing

height.

Click Return to go back to the data selection screen.

Click the 10 mi radius gridded button.
31

Now displayed in the large box on the left are arrows representing the wind field generated by the

program from the single data record entered. Recall that the wind direction was 10 degrees. Wind

direction is given as the direction from which the wind is blowing. Thus, the arrows show the direction

material would be transported.

The three smaller boxes to the right show the stability, precipitation type, and mixing height. The first

two are as entered with the data. The mixing height was calculated by the program.

We now have a group of files that include the user entered data and the processed wind fields to be used

by the transport and diffusion models. This data set will work only with the Arkansas site and on the date

specified. This data set can be recalled at any time for editing. However, each time the data is changed,

you must again Save and Process Data.
32

Click the Return button to close the wind field display. Then, click the Exit button to close the

Meteorological Data Viewer. Finally, click the Return button of the Meteorological Data Processor. This

returns to the Meteorological Data Selection screen. Notice that the data set just created is selected for

use. Also, notice that the data set description entered when processing the data is shown along with the

date and time of the observation.

Click the OK button to return to the main screen.
33

6 Calculate Doses

Purpose

Discussion

Problem

Inputs

To learn how to calculate dose.

The last information to be entered before starting the calculations is the distance to which doses are to be

calculated and when to stop the calculations.

Setting the Distance of calculation determines which models are run and the locations for the model

receptors. In addition to defining the distance to which doses should be calculated, you also need to

specify when the calculations should be terminated. This is essentially the end-of-exposure. Doses are

accumulated up to this time (with the exception of 4-day groundshine which always goes to 4 days).

Setting this value is discussed more fully in Problem 11.

Recall that you have been asked to evaluate the appropriateness of the protective action recommendation.

In order to do this you will need to determine the projected total effective dose equivalent (TEDE) and

the thyroid dose (thyroid committed dose equivalent or thyroid CDE).

Calculation

Options

Distance of calculation: Close-in + out to 10 miles (16 km)

End calculations at: Start of release to atmosphere plus 6 hours

(We will look at this 6-hour assumption in greater detail later on)

Case description: Core uncovered, design leak rate
34

Inputs: Step-by-step

Click the Calculate Doses button on the main screen.

1. Distance of calculation: Close-in + out to 10 miles(16 km)

Always select close-in plus out to 10 miles for the initial run. If there is a subsequent interest in doses

at distances beyond 10 miles, run the calculations again selecting a greater distance. (Hint: if you

save the case after you run it the first time, you will not have to re-enter all the data. You will just

have to change a single entry on the Start the Calculations screen.)

2. End of calculations: Start of release to atmosphere plus 6 hours

The default of 6 hours is sufficiently long that, even if the wind speed was low (e.g. 2 mph), some

material would reach the default distance setting of 10 miles. You should always evaluate whether

this “end-of-calculation” provides enough time given the wind speed and final distance of interest for

the material transport. This issue is discussed in more detail in Problem 11.

3. Case description: Core uncovered, design leak rate

This text will be shown on all output products and should uniquely describe the case you are running.

Click the OK button to start the calculations.
35

Status windows will indicate the progress of calculations. The sequences of calculations is: source term,

close-in model, and if needed the puff model to the specified distance. (The transport and diffusion

models are described in Topic 7). At the end of the calculations, the Maximum Dose Values tab of the

main screen will be displayed.

SAVE THIS CASE!!

This is the time to save all your work so that it can be recalled later. Click the Save Case button in the

lower, left of the main screen or select File | Save Case from the menu. Enter a name for the file and

click OK.

For consistency in the workbook, use the name: Using RASCAL - Case 1

All the input information and all the results will be saved in a single file that can be backed-up, copied,

and distributed.
36

7 Transport and Diffusion

Models

Purpose

Discussion

To learn about the two transport and diffusion models used in RASCAL.

There are two transport and diffusion models in RASCAL used for radiological releases (a separate

plume model handles UF6releases). Close to the release point a straight-line Gaussian plume model is

used. This model is characterized by the following features:

- A polar grid of receptors is used. As shown in

Figure 1, this grid consist of 8 concentric

circles with receptors located every 10

degrees around the circles. There are default

distance settings (see Table 3) for the circles

or the 8 distances may be set by the user.

- The model is steady-state. That is material is

transported “immediately” to all distances.

There is no need to allow for transport time

on this grid. The disadvantage is that the

receptors may report doses before the

material has had time to be transported to the

receptor.

- The release point is always at the center and

space between the receptors on a circle

increases with distance from the release.

Figure 1 Polar receptor grid for the plume model
37

Miles East-West from Center

-10 -5 0 5 10

Miles North-South from Center

-10

-5

0

5

10

Table 3 Default distances for close-in polar grid

Calculation

distance setting

Distances in miles

Close-in only or

Close-in + 10 mile

0.1 0.2 0.3 0.5 0.7 1.0 1.5 2.0

Close-in + 25 mile 0.25 0.5 1.0 1.5 2.0 3.0 4.0 5.0

Close-in + 50 mile 0.5 1.0 1.5 2.0 3.0 5.0 7.0 10.0

Further away from the release point, RASCAL switches to a Lagrangian puff model. This model has

the following characteristics:

- It uses a uniformly spaced Cartesian grid of 41 x 41 receptor points. Figure 2 illustrates this grid. The

release point is always at the center.

- The grid spacings are set by the user

selecting from 3 different distances:

10, 25, or 50 miles. The resolution of

the grid decreases as the calculation

distance selected is increased. The

distance between receptors for each

calculation distance is shown Table 4.

- Time must be allowed for material

transport time. For example, with a 4

mph wind speed, if the calculations

are ended after only 2 hours, the

material will not have had time to be

transported to the 10 mile edge of the

modeling area.

Figure 2 Cartesian receptor grid for

the puff model

Table 4 Distances between Cartesian grid receptors

Calculation distance Distance between receptor points

10 miles 0.50 miles

25 miles 1.25 miles

50 miles 2.50 miles

These receptor grids are evident when looking at dose footprints. With the closein polar grid, the

footprint consists of wedge-shaped pieces representing the area around a receptor point as shown in the

example below.
38

With the puff model, the footprint is represented by squares drawn around each receptor.

Remember:

The close-in calculation uses a straight-line Gaussian model. This is a steady-state calculation. That is,

material is transported “immediately” to all distances. There is no consideration of the calculation

duration. Receptors may report doses before the material has had time to be transported to the receptor.

Use care when interpreting the results from the close-in model especially when using distances beyond 2

miles.
39

8 Using the Maximum Dose Values

Purpose

Discussion of PAGs

To learn how to use the RASCAL maximum dose values tables.

Chapters 2 and 5 of the EPA Manual of Protective Action Guides and Protective Actions for Nuclear

Incidents (EPA 400-R-92-001) discuss the protective action guides (PAGs) for the early phase. The

following material is from those chapters.

Protective Action PAG (projected dose) Comments

Evacuation

(or sheltering)

TEDE 1-5 rem

Thyroid CDE 5-25 rem

Evacuation (or for some situations, sheltering)

should normally be initiated at 1 rem TEDE or

5 rem thyroid CDE.

TEDE is the sum of inhalation dose and the external doses from cloudshine and 4-days of

groundshine.

“Although the PAG is expressed as a range of 1-5 rem, it is emphasized that, under normal conditions,

evacuation of members of the general population should be initiated for most incidents at a projected

dose of 1 rem.” (page 2-5)

“Sheltering may be preferable to evacuation as a protective action in some situations. Because of the

higher risks associated with evacuation of some special groups in the population (e.g. those who are not

readily mobile), sheltering may be the preferred alternative for such groups as a protective action at

projected doses up to 5 rem. In addition, under unusually hazardous environmental conditions, use of

sheltering at projected doses up to 5 rem to the general population (and up to 10 rem to special groups)

may become justified.” (page 2-5)

“Illustrative examples of situations or groups for which evacuation may not be appropriate at 1 rem

include: a) the presence of severe weather, b) competing disasters, c) institutionalized persons who are

not readily mobile, and d) local physical factors which impede evacuation.” (page 2-6)

“No specific minimum level is established for initiation of sheltering. Sheltering in place is a low-cost,

low-risk protective action that can provide protection ...” (page 2-7)

“The projected dose comparison to the early phase PAGs is normally calculated for exposure during the

first four days following the projected (or actual) start of a release. The objective is to encompass the

entire period of exposure to the plume and to deposited material prior to implementation of any further,

longer-term protective action, such as relocation. Four days is chosen here as the duration of exposure to

deposited materials during the early phase because, for planning purposes; it is a reasonable estimate of

the time needed to make measurements, reach decisions, and prepare to implement relocation.” (page 5-

6)
40

Problem

Inputs

Fill in the answers in the table below.

Question Your answer

What are the TEDE’s at 2 and 5 miles?

What are the thyroid doses at 2 and 5

miles?

To what distance does the TEDE

exceed the PAG?

To what distance does the thyroid dose

exceed the PAG?

At what time does the plume first reach

5 miles? (Hint: what was the wind

speed?)

At what time have you assumed the

release to end? (Hint: On the “calculate

doses” screen, look at the “end

calculation at ...” entry)

What was the time for the latest

weather data that you entered?

Optional question

RASCAL model results may be used to prepare briefings for decision makers. The information that goes

into a briefing is discussed in more detail in Problem 16.

Should the results of this RASCAL run

be used to prepare the briefing?

No new inputs are required.
41

Results

The first results screen displayed is the Maximum Dose Values table.

1. Use the Value displayed options to select which set of doses you want to see. The sample screen

shown above is for the doses beyond the close-in area. A sample screen of close-in doses in shown

on the next page.

The doses shown are the highest doses at fixed distances from the release. The screen only shows at

one time the “close-in” doses or the doses beyond the close-in area. The “close-in” doses are the

doses calculated by the straight-line Gaussian plume. The doses beyond the close-in area are

calculated using a Lagrangian puff model.

2. The tab contains a Print button to be used to send the dose table to the currently selected printer.

Both sets of dose values are printed along with a complete description of all the data you have

entered. Changing the printer is done using the File | Print Setup ... item on the menu bar.

The early phase (plume phase) doses that RASCAL calculates are for people who are outdoors during

plume passage and who remain outdoors exposed to ground shine from deposited radionuclides for four

days after the radionuclides have been deposited. Thus, the early phase doses that RASCAL calculates

are larger than the doses that would be expected for people engaged in normal activities (spending much

time indoors). In addition, people who evacuated or relocated within four days after plume passage

would receive lower doses than RASCAL calculates.

This overestimation of the early phase doses by RASCAL is intentional. The purpose of the RASCAL

dose calculation is to determine if protective actions are needed, not to provide realistic estimates of the

doses that people would actually receive. The need for protective actions is based on the doses that would

be received if no protective actions of any type were taken, even actions such as simply spending some
42

time indoors. The RASCAL dose estimates should not be used as an estimate of the doses that would be

received by people who did not intentionally take protective actions because even performing normal

everyday activities will reduce doses to below those estimated by RASCAL.

The TEDE and Thyroid CDE numbers will appear underlined if the value exceeds the lower end of the

EPA PAG range. Following the table of numbers is a “notes” section which defines the PAG thresholds

and provides other information about the values shown. The maximum values table has a minimum dose

of 0.1 mrem. Doses falling below that threshold are not shown. However, these low numbers can be

examined by using the numeric values option for display under Detailed Results.

Use the Close-in doses and Doses to 10 miles views of the Maximum Dose Values screen to answer

the first 4 questions that you were asked.
43

Did you get the answers below?

Question Your answer

What are the TEDE’s at 2 and 5 miles? 0.21 and 0.042 rem

What are the thyroid doses at 2 and 5

miles?

2.6 and 0.52 rem

To what distance does the TEDE exceed

the PAG?

To between 0.7 and 1.0 miles

To what distance does the thyroid dose

exceed the PAG?

To almost 1.5 miles

At what time does the plume first reach 5

miles?

About 2 P.M.

(1hr after release start with 6 mph winds)

At what time have you assumed the

release to end?

7 P.M.

(Release start time of 1 p.m. plus 6 hours)

What was the time for the latest weather

data that you entered?

11 A.M.

Answer to optional question

Should the results of this RASCAL run be

used to prepare the briefing?

No. You can’t use 11 A.M. weather to model plume

behavior at 7 P.M. (8 hours later)
44

9 Obtaining Observed Weather

Data from the Internet

Purpose

Discussion

To learn how to obtain observed weather data from the Internet.

Weather data from only the release point is not really good enough for dose projections to 10 miles.

As discussed earlier, site meteorological towers (e.g. those required at nuclear power plants) provide the

best initial weather data for use by the RASCAL models. To supplement the on-site data and improve the

representation of wind fields, we should use additional sources of weather data. The more data you have

to represent the meteorological conditions in the modeling area, the better the wind field representation.

Whenever possible, use data from multiple stations, especially stations downwind of the release point.

This becomes especially important at greater distances (25 and 50 miles).

To obtain observed weather data:

- For sites in the RASCAL database, go to the website:

weather.noaa.gov/weather/current/K???.html

where you replace ??? with the three letter code for the weather station that you want. The station

identifiers are case sensitive and must be all capital letters. The “html” must be lowercase. (The

NWS website is picky).

For example, the page with the current weather for Dulles airport would be KIAD.html.

- For sites not in the RASCAL database, go to the website: weather.gov

Navigate to the area of interest using either the map or entering the city and state. The current

weather observations at a nearby weather station are shown.

The National Weather Service is prepared to offer direct assistance if requested. They can provide

observations as well as detailed forecasts. They will be able to give you additional insights on the data

and tell you how reliable they think it is. In addition, they can provide stability class predictions and

more exact information on precipitation.

The NWS requests that NRC staff contact the local forecast office (LFO) nearest the release. NRC

Protective Measures Team procedures provide details on how to make contact and a list of offices and

telephone numbers. The old procedure of first contacting the Senior Duty Meteorologist has been

discontinued.

Non-NRC responders will need to establish their own relationship with the NWS.
45

Problem

Do the following if you have an Internet connection, otherwise skip down to the workbook data.

To supplement the weather data from the Arkansas site, obtain the current weather observations for RUE

(Russellville) and MWT (Mount Ida). The Russellville station is 8.5 miles from the plant and will

provide good additional data for computations to 10 miles. The Mount Ida station is 56 miles away but at

least is in the downwind direction (currently).

If the wind speed units are not given, assume that they are in miles per hour (mph). You will find that the

NWS does not provide stability on their web pages. You will need to get it from the NWS directly (call

the LFO) or just enter “unknown” and let the code estimate it.

Fill in the table below with the current data obtained from the Internet:

Station Type Date Time Direction

(from)

Speed Stability Precipitation

RUE Obs

MWT Obs

Workbook data to be used in working the problem

Normally, you would enter the information, as recorded above, into RASCAL. However, to avoid an

inconsistency with the previous data, enter the data below.

Station Type Date Time Direction

(from)

Speed

(mph)

Stability Precipitation

RUE Obs today 1100 340 5 unknown No precip

MWT Obs today 1100 320 3 unknown No precip
46

Begin, by clicking the Meteorology button to display the screen for selecting the data set.

Click the Edit Existing button this time as we want to make additions to the data set not create a brand

new one.

When the Meteorological Data Processor has started, select Enter Data. You will see that the single

ARKA observation entered previously is still there. Now, we want to add the observations from the two

NWS stations.

Remember that each station has its own data table. Select from the Enter data for choices to switch

between the data tables.

When both the RUE and MWT data has been entered, click the OK button. The Observation Summary

tab now shows that data for 3 locations has been entered.

Remember that the final step after changing any data is to process and save. Click the Save and Process

button. Since we are editing the 1100 data set, we will get a warning asking whether we want to overwrite

the existing file.
47

We do not want to overwrite the file so click the No button.

For this exercise, continue the naming scheme using the site ID and the date and time the data is updated.

Assume that we are updating this data about half an hour later than before. Thus, use a name such as

ARKA 2007-03-15 1130. By updating the time in the name we can always tell which data set was created

last and presumably contains the “best” estimate of the conditions.

Recalculate the doses using this new data set to see if including more meteorological data makes a

difference. Provide a new set of answers to the questions below.

Question Previous answer

(single station)

New Answer

(3 stations)

What are the TEDE’s at 2 and 5 miles? 0.21 and 0.042 rem

What are the thyroid doses at 2 and 5

miles?

2.6 and 0.52 rem

To what distance does the TEDE exceed

the PAG?

To between 0.7 and 1.0

miles

To what distance does the thyroid dose

exceed the PAG?

To almost 1.5 miles

SAVE THIS CASE!!

For consistency in the workbook, use the name: Using RASCAL - Case 2. You do not want to overwrite

the previous case.
48

Results

Question Previous answer

(single station)

New Answer

(3 stations)

What are the TEDE’s at 2 and 5 miles? 0.21 and 0.042 rem 0.21 and 0.049

What are the thyroid doses at 2 and 5

miles?

2.6 and 0.54 rem 2.6 and 0.61

To what distance does the TEDE exceed

the PAG?

To between 0.7 and 1.0

miles

To between 0.7 and 1.0

miles

To what distance does the thyroid dose

exceed the PAG?

To almost 1.5 miles To almost 1.5 miles

There are no significant changes to either the doses or the distances.
49

10 Obtaining Forecast Weather

Data from the Internet

Purpose

Discussion

To learn how to obtain forecast weather data from the National Weather Service.

Observed data is of course the best to use as input to the models. These are conditions that have actually

been measured. This is fine if the release has already occurred and your job is to estimate where the

material went. However, you may be doing an assessment of potential consequences at some future time.

The release may not yet have taken place but you want to run scenarios based on possible future

meteorology. Or, the release may be occurring now and you want to predict the movement of the plume

for the next few hours.

Over short periods of time (a couple of hours) assuming the current observed conditions will persist may

be adequate. For longer times, the uncertainty increases. Therefore, you should add forecasts to the

meteorological data set.

Note that RASCAL will delete any forecast records that are followed by a later observation. Forecast

records are only used for times later than the last observation.

To obtain forecast data,

1. Go to the website: weather.gov

2. Navigate to the site area by entering the city and state or by clicking on the map. Using the

Detailed Point Forecast map, click as close to the site as possible.

3. Select Tabular Forecast under the heading Additional Forecasts & Information.

4. Record relevant information: time, wind direction, wind speed, probability of precipitation, and

precipitation type and likelihood.

5. If there is precipitation in the forecast, you will also have to go to the Hourly Weather Graph to

get the amount of precipitation during each 6-hour interval.
50

Problem

Do the following if you have an internet connection, otherwise skip down to the workbook data.

Obtain the weather forecast for the Arkansas plant for 1 P.M., 4 P.M., and 7 P.M. Record the forecast data

in the table below.

Hour Wdir Wspd PoP Precip type Precip

likelihood

Precip

amount

compass degrees

1300

1600

1900

The National Weather Service gives wind direction in terms of compass directions (for example, N, NNE,

NE, etc.) that the wind comes from. You will have to convert these to degrees.

N = 000 E = 090 S = 180 W = 270

NNE = 023 ESE = 112 SSW = 202 WNW = 292

NE = 045 SE = 135 SW = 225 NW = 315

ENE = 067 SSE = 158 WSW = 248 NNW = 338

Workbook data to be used in working the problem

For consistency, we will enter the data below into RASCAL. Modify the latest data set to add to the

Arkansas data the three forecast records shown below:

Type Date Time Direction Speed Stability Precip Air temp

Fcst today 13:00 315 8 mph B None 68 F

Fcst today 16:00 270 5 mph D None 76 F

Fcst today 19:00 225 3 mph E None 75 F

Remember, you are adding 3 forecast records to the already existing observation for ARKA. On the data

set selection screen, use the Edit existing button again with the 1130 data set selected. Then, in the

meteorological data processor, click the Enter data button and add the forecast records.

The data grid for Arkansas will look like this:

Process the data set and save with a new name (do not overwrite the previous file). In this case, use a time

in the name of 1200.
51

Use the View Meteorology button to start the viewer program.

Note that there are now 33 dates and times shown. The processor has filled in the gaps between the hours

with additional data.

Click the Entered data button to examine the data.

Step through the data using the control buttons and observe the wind arrow. Note that the arrow direction

changes abruptly on the hour. This is because there is no interpolation between an observation and the

forecast records.

Exit the Meteorological Data Viewer program and then return from the Meteorological Data Processor

program into the Select Meteorological Data Set screen. The data set just created should be highlighted.

Run the calculations using this new data set to estimate doses using the following settings:

- Distance of calculation: Close-in + out to 10 miles

- End calculations at: Start of release to atmosphere plus: 6 hours

Answer the set of questions again based on your results using observed and forecast weather.
52

Question Previous answer

(3 stations - obs only)

New Answer

(3 stations- obs & fcst)

What are the TEDE’s at 2 and 5 miles? 0.21 and 0.045 rem

What are the thyroid doses at 2 and 5

miles?

2.7 and 0.56 rem

To what distance does the TEDE exceed

the PAG?

To between 0.7 and 1.0

miles

To what distance does the thyroid dose

exceed the PAG?

To almost 1.5 miles

Optional question

Should this new RASCAL run be used to

prepare the briefing?

SAVE THIS CASE!!

For consistency in the workbook, use the name: Using RASCAL - Case 3
53

Results

Question Previous answer

(3 stations - obs only)

New Answer

(3 stations - obs & fcst)

What are the TEDE’s at 2 and 5 miles? 0.21 and 0.045 rem 1.2 and 0.29 rem

What are the thyroid doses at 2 and 5

miles?

2.7 and 0.56 rem 14 and 3.4 rem

To what distance does the TEDE exceed

the PAG?

To between 0.7 and 1.0

miles

~ 2.5 miles

To what distance does the thyroid dose

exceed the PAG?

To almost 1.5 miles To 4 miles

Adding the forecast information has resulted in increases in the projected doses. However, you are not

seeing what direction the plume is moving.

Answer to optional question

Should this new RASCAL run be used to

prepare the briefing?

No. You still do not have the information you need for your

briefing. Continue with the next problem.
54

11 Time for End of Calculation

Purpose

Discussion

To show how to select an appropriate time for the end of the calculations.

On the start calculations screen you must specify the time after the start of the release at which you want

to end the calculations.

The time can be specified as a number of hours after the start of the release to the atmosphere or as a

specific date and time.

This is what happens at the time that the calculations end:

1. The release of material to the atmosphere ends (if it has not already ended).

2. The plume movement stops outside the close-in area.

3. Direct cloudshine dose from the plume stops.

4. Inhalation of radionuclides stops, but the full committed dose equivalent from radionuclides already

inhaled is calculated.

5. Deposition of radionuclides on the ground stops, but the dose from 4-days of exposure to the

radionuclides already deposited before the end of calculations is calculated.

Thus, if you end the calculations too early, projected doses may be too small because you have ended the

calculations before the plume has delivered its dose. Conversely, if you end the calculations unnecessarily

late, the computer run time will be unnecessarily long.
55

10 20 30 40

Miles from release point

Plume location at hour H

H=1 H=2 H=4 H=10

0

Calculation Duration  Release Duration 

Calculation Distance

Wind Speed

Problem

The diagram below illustrates the problem. Assume you have had a 1 hour release with a 4 mph wind

speed. The ellipses represent the position of the plume in the air at various hours (H) after the release. The

plume stretches for 4 miles. At H=1 the release has just ended. The leading edge of the plume has reached

4 miles (1 hr x 4 mph = 4 miles) and the trailing edge had just left the release point.

If you end the calculations 1 hour after the release starts, doses at 5 miles and beyond will all be zero.

They will be zero not because no dose would be received but because insufficient time was allowed for

material to be transported to those distances.

There is a simple rule of thumb that can be used for setting the calculation duration as long as the wind

direction and speed and not going to vary too much over the model period.

Round the calculation duration up to the nearest hour. However, be careful not to set a time much longer

than necessary because it will increase the calculation time unnecessarily. Also, increase the duration if

the wind directions are changing significantly and especially if they reverse directions. Remember not to

mix incompatible units; use mph with miles or m/s with meters.

Remember:

As discussed in the earlier section on transport and diffusion models, the close-in calculation uses a

straight-line Gaussian model. This is a steady-state calculation. That is, material is transported

“immediately” to all distances. There is no consideration of the calculation duration. Receptors may report

doses before the material has had time to be transported to the receptor. Use care when interpreting the

results from the close-in model especially when using distances beyond 2 miles.

Assume that after 12 hours, the pressure in the containment will be reduced to zero. This will effectively

end the release to the atmosphere.

Recompute the doses based on these assumptions. You will need to make changes on the release pathway

screen to end the release, enter more forecast weather data, and increase the duration of the calculation.
56

Inputs

Modify the latest meteorological data set to add to the Arkansas data the two additional forecast records

shown below:

Type Date Time Direction Speed Stability Precip Air temp

Fcst today 23:00 230 2 mph E None 63 F

Fcst next day 02:00 270 4 mph E None 59 F

Save the meteorological data set under a new name using the time: 1230.

Run the calculations again and then fill in the table below:

Question Your answer

What are the TEDE’s at 2 and 5 miles?

What are the thyroid doses at 2 and 5

miles?

To what distance does the TEDE

exceed the PAG?

To what distance does the thyroid dose

exceed the PAG?

Event Type Nuclear Power Plant

Event Location Arkansas - Unit 1

Source Term Time Core Is Uncovered

Reactor shutdown: 10:00

Core uncovered: Yes, at 13:00

Core recovered: No

Release Path Containment Leakage / Failure

Release point characterization: Not an isolated stack

Release height: 0.0 m

Consider building wake effects: Yes

Start of release to atmosphere: 13:00

Release path events:
57

Results

<date> 13:00 Sprays Off

<date> 13:00 Leak rate Design

<date+1> 01:00 Leak rate 0% per day

Meteorology Data set type: Actual

Data set: ARKA <date> 1230

Calculation

Options

Distance of calculation: Close-in + out to 10 miles.

End calculations at: Start of release to atmosphere plus: 15 hours.

Rationale: This is the 12 hour release duration plus 3 hours for plume travel time

to 10 miles.

Question Your answer

What are the TEDE’s at 2 and 5 miles? 1.4 and 1.1 rem

What are the thyroid doses at 2 and 5

miles?

16 and 13 rem

To what distance does the TEDE

exceed the PAG?

A little farther than 5 miles

To what distance does the thyroid dose

exceed the PAG?

Between 7 and 10 miles

For very long release times

You may wonder how to handle a situation in which the release time is very long. For example, consider a

reactor containment leaking at the design basis leak rate, which is likely to be under 1%/day. The leak rate

is so small that the leakage will effectively be nearly constant over many weeks. Thus, you might think

that you should end the calculations many weeks or even months after the start of the release. However,

this is not the case. First, there is a limit of 48 hours on the calculation duration.

In addition, two other factors should be considered. First, the pressure in the containment will decrease

with time as heat is removed. This will cause the release rate to decrease to lower than the rate used in

RASCAL. Second, the projected doses being calculated by RASCAL are being used for early decisions on

protective actions. When a release continues beyond a day it is no longer in the early phase of the

emergency. RASCAL is designed primarily for early decisions that can be implemented before a release

starts. Decisions about protective actions for long term releases can be made later as the situation becomes

better understood and field measurements become available.

In conclusion, for the projected doses to be properly applied, the end of calculations for RASCAL should

seldom exceed 24 hours from the start of the release. In fact, there is a limit on the calculation duration of

48 hours after the start of the release to the atmosphere.

SAVE THIS CASE!!

For consistency in the workbook, use the name: Using RASCAL - Case 4
58

12 Displaying Plume Footprints

Purpose

Problem

Results

To learn how to obtain a picture so that plume direction and area exceeding PAGs can be evaluated.

Now we would like to see the spatial extent of the doses and the direction of the maximum doses.

To do this we need to generate plume plots. Begin by selecting the Detailed Results button on the left

side of the screen.

This will display the Detailed Results of Dose Calculations screen. The screen is divided into four main

sections: Display Format, Result Type, Time Period, and Display Units.

Look first at the Display Format section:
59

This section controls how the information is presented. Results can be displayed as either a numeric table

or as a graphic “footprint”. We must also choose whether we want to see the results from the close-in

calculation or from the 10-mile calculation. We must look at them separately.

The Result Type section contains an option button for each of the 14 results calculated by RASCAL.

Note that we have additional result types not shown in the maximum dose values table.

To get a footprint of the thyroid CDE from the close-in calculation, select the following options:

- Display format: From close-in calculation - Footprint

- Result type: Thyroid

- Time period: Start of release to end of calculation

- Display units: English

Select the Display Selected Result button.
60

Note that the close-in footprint shape reflects the type of receptor grid used by the straight-line Gaussian

plume model. Each colored area represents the dose at a model receptor point on the polar grid.

Click OK to return to the Detailed Results screen. Now display the thyroid dose footprint for the 10-mile

calculation. The footprint for the 10-mile distance reflects the rectangular grid used by the puff model.
61

Answers the question:

Question Your answer

In which compass direction from the

release point are the doses greatest?

Now, let’s use the cursor to get some more detail about one of the individual cells on the footprint. You

can see the location information and exact dose at any point and also examine the time history of the dose

at a point.

Put the cursor in a colored cell of either footprint and note that the dose and location are displayed at the

upper right of the screen. Follow the “centerline” out from the release point until you see:

Here is the thyroid CDE of 7.56 rem at 7.1 miles northeast (45o) of the release

point.

Click the mouse while the cursor is positioned over that cell to display a rate plot.
62

These graphs show us that 7.1 miles from the release point: the thyroid dose does not start to be delivered

until about 8 hours after the start of the release, and continues to deliver the dose until about 12 hours

after the start of release.

Did you get the answers below?

Question Your answer

In which compass direction from the

release point are the doses greatest?

To the northeast
63

13 Comparing Field

Measurements with

RASCAL Results

Purpose

Discussion

Problem

To learn how to determine if the RASCAL results are consistent with a field measurement.

Detailed results allow not only varying the result type but examining doses and dose rates at intervals

during the modeling duration. For example, instead of looking at thyroid doses for the entire 15 hour

period of the previous case, you could look at the thyroid dose over an interval in the middle of that 15

hour block.

RASCAL calculates external dose rates for both open and closed window meters. These are useful for

comparison with field readings.

Assume that the accident has unfolded as expected. We are in the middle of the release and a field team

reports a closed-window (gamma) meter reading of 1.0 mR/h at 5:30 P.M. The measurement was made on

the approximate plume centerline at a distance of 5.5 miles east of the release point.

How does this measured value compare to the value predicted by the RASCAL source term to dose

model?
64

Results

To get the reading we need for comparison with the field data, make the following 2 selections on the

detailed results screen.

1. For result type, select External Dose Rate - Closed Window. This will display the gamma dose rate.

2. For time period, only the single time option is available. Select the time to match the field reading

(17:30).

Click the Display Selected Result button.
65

We are interested in the gamma rate at a point 5.5 miles east of the release. Move the cursor over the

colored cells and watch the display in the upper right. As you traverse the yellow cells at some point the

box will show 90o at 5.5 miles.

The 4.00 is the gamma dose in mR/h at that location.

Conclusion

These results are pretty close considering all the uncertainties involved. Be sure to confirm with multiple

readings. However, we should feel comfortable about the modeling run. Tell supervisors and decision

makers that the field readings are consistent and add confidence to the model results.
66

14 Normalizing the Model to Match

Field Team Data

Purpose

Discussion

To learn how to normalize RASCAL Source Term to Dose model results to match field team data.

The basic method for normalizing the model results consists of two parts: obtaining the field

measurements and then adjusting the model runs.

Obtain field measurements

1. Use 1 or 2 field teams to traverse the plume at least once and preferably twice. It is necessary to

actually traverse the plume. Field measurements that do not include measurements near the plume

centerline are essentially useless. If all the measurements are near the plume edge, you will learn if

there is something there or not but you cannot estimate the magnitude of what is there. You cannot

determine if your RASCAL results are too large, too small, or about right.

2. The easiest type of measurement to get is a gamma (closed-window) exposure rate reading in mR/hr.

The gamma rays will come from two sources: radionuclides in the plume and radionuclides that have

been deposited on the ground. Early in the release most of the gamma rays will come from airborne

radionuclides in the plume. Late in the release, gamma rays from radionuclides deposited on the

ground may predominate. Your meter will not be able to distinguish the two gamma ray sources.

3. Measured gamma dose rates are expected to vary greatly over brief time intervals and over short

distances. Our models represent airborne concentrations as slowly and steadily decreasing with

distance from the plume centerline. The model is a good representation of reality only if measured

concentrations are averaged over some time, for example 5 to 10 minutes. To avoid being misled by

very short-term fluctuations, you must do one of two things. You must note the dose rate over a period

of several minutes and record the average dose rate during that time interval, or you must make

several (at least 4 or 5) nearby measurements and average them. Making several nearby measurements

separates your measurements in both time and space.

4. Assuming that your gamma measurements have been taken so that the appropriate averaging has been

done, you will still need measurements for several locations near the plume centerline. In addition,

you should take measurements to roughly estimate the location of the edge of the plume.

5. At each measurement point, record:

a. - the closed-window meter reading in mR/h

b. - the time the measurement was taken

c. - the location of the measurement point so that you can locate it on a map.

6. Another type of measurement that you can get is an air sample. Air samples are normally taken over

some time interval such as 5 minutes so they do average the concentration over a time interval.
67

However, air samples are harder to get than gamma rate measurements and they take longer to

analyze.

RASCAL Modeling Runs

1. Make a RASCAL run using the best estimate of source term, release, and meteorology. Your run

should be a best estimate. You will learn very little if you do a worst case run and find that the worst

case RASCAL case gives larger doses than the field measurements. Run the calculations until plume

passage would be complete.

2. Select the Detailed Results button. You will get the screen shown below.

3. For Result Type, select External Dose Rate - Closed Window. For the Time Period, only the “Single

time” option will be available to you (because dose rate must be associated with a single time). Select

the time that most closely matches the field measurement time. (If your field measurements were

taken over widely varying times, you will have to look at several sets of RASCAL results, each

corresponding to the appropriate field measurement time.)

4. Under Display Format, determine if your field measurement location is “close-in,” usually less than 2

miles, or further out. You have the choice if you want to see the External dose rate - closed window

results as a “Footprint” (picture) or as a numeric table. Either will work, but we recommend the

Footprint because it shows the map background, which will make your job easier.

5. With the footprint displayed, place your cursor on the displayed plume at the distance and direction

from the release point corresponding to your field measurement. The exposure dose rate, the distance,
68

Problem

and the direction are displayed in the box at the upper right. The dose units are in the legend. Record

the RASCAL exposure dose rate. Repeat for each measurement.

6. Compare the RASCAL footprint results with the field measurements. Which is larger and by how

much? Is the location of the plume centerline from the footprint and the field measurements about the

same? Are the edges of the plume in about the same place?

Assume that the accident is unfolding as expected. Make sure that Case 4 calculations are loaded.

Field teams have traversed the plume. The roads used were 5-6 miles away from the release point and

were to the east of the release.

The following measurements of gamma exposure rate were reported.

ID Time Direction from

release point

Distance Measured RASCAL

result

degrees mi mR/h mR/h

S1 17:18 79 6.0 0.05

S2 17:22 86 5.5 0.7

S3 17:25 91 5.7 8.2

S4 17:30 94 5.1 4.9

S5 17:34 99 5.9 1.9

S6 17:41 105 6.1 0.12

Recording RASCAL Results

We are going to first direct our attention to the centerline dose, which is measurement S3 with a reading

of 8.2 mR/h. Seeing a reading of 4.9 mR/h for measurement S4, which is about the same magnitude gives

us confidence that our highest measured dose is not an outlier.

Use the Detailed results screen to select the dose type, distance, and time period. The dose type should be

the External Dose Rate - Closed Window to see the needed gamma exposure rate projections. The

Footprint format will provide an easy to use method for picking off doses. Since we are interested in

doses at a distance of 5-6 miles we need to use the From 10-mile calculation display format. Set the time

period to Single time 17:30 to correspond to the general time when the measurements were taken.

Click Display Selected Results. Now use the cursor (as described in the previous problem) to obtain the

doses from cells on the footprint display that are closest to the measurement locations. Fill in the table

above with the model results.
69

Results

The following RASCAL results could be picked off the footprint display.

ID Time Direction from

release point

Distance Measured RASCAL

result

degrees mi mR/h mR/h (deg,

distance)

S1 17:18 79 6.0 0.05 0.0027 80.5, 6.1

S2 17:22 86 5.5 0.7 0.81 84.8, 5.5

S3 17:25 91 5.7 8.2 4.0 90, 5.5

S4 17:30 94 5.1 4.9 2.1 95, 5.5

S5 17:34 99 5.9 1.9 0.25 100, 6.1

S6 17:41 105 6.1 0.12 0.05 104, 6.2

Interpretation of the Comparison

These are our recommendations for interpreting the comparison:

1. Don’t put too much weight on just a few field measurements taken within a short time interval and

from a few locations in close proximity. If one set of field measurements is not matching the model,

get additional sets of measurements before you draw strong conclusions.

2. If the centerline doses are within a factor of 2 or 3, that is dead on. You can say that the field

measurements agree with the model results.

3. We would start to get a little concerned if the field measurements were more than 3 times higher than

the model predictions. RASCAL is designed to give a somewhat conservative (over-estimate) of

doses. If field measurements were 3 times higher than predicted, we would start to worry that perhaps

we are not understanding what is happening and perhaps recommended protective actions are not

adequate.

4. If the field measurements are a factor of 3 to 10 lower than the model results, we would probably not

adjust the model inputs to rerun the model nor would we change a prior protective action

recommendation. We would probably tell the decisionmaker that the field measurements were a little

lower than the model predictions, but are roughly consistent. We would definitely not quantify the

size of the difference to the decisionmaker because we don’t want to get caught up in details and

trivia.

5. If the field measurements are coming in more than a factor of 10 lower than the model predictions,

this indicates that our model inputs need to be adjusted. (This assumes that we have confidence in the

field measurements.) We would ask, where could we have gone wrong? We would probably adjust

the model inputs and rerun the RASCAL model.
70

6. If the direction of the maximum doses (presumably the plume centerline) don’t agree (meaning more

than 10 degrees), it means the model wind direction may be off from the actual wind direction. We

would not try to adjust the meteorology, but we would add a qualifier to the results describing the

difference.
71

15 Field Measurement to Dose

Purpose

Discussion

Problem

To learn how to use the Field Measurement to Dose model to calculate intermediate phase doses based on

measured ground concentrations.

The Field Measurement to Dose model would normally be used after releases had ended to determine

whether the area is habitable or do residents need long-term relocation. The model estimates doses based

upon measurements of ground contamination. Within the NRC, the site team is the most likely user. The

calculations can also be done using the Turbo-FRMAC code.

Two EPA pathways are considered: groundshine and inhalation due to resuspension. Both pathways are

affected by weathering. The material becomes less accessible through time as natural processes work. The

EPA sets the following limits:

1

st year PAG = 2 rem

2

nd year objective = 0.5 rem

50 year objective = 5 rem

The release from Arkansas Nuclear One has stopped. Field teams have been dispatched to determine

where and how much radioactive material was deposited. The first report to come in provides:

Sample ID: ABC123

Location: a street corner in a subdivision downwind of the plant

Sample analyzed: day after accident at 13:55
72

Inputs: Step-by-step

Sample data

Nuclide Concentration

microcuries/meter2

Ba-140 1.4

Cs-134 0.6

Cs-137 0.35

I-131 1.7

I-132 1.3

La-140 1.3

Sr-89 1.0

Te-132 1.2

The residents were evacuated early in the accident. Is it now safe for them to return to their homes?

Start the Field Measurement to Dose model from the main RASCAL screen.

Operation of the user interface is similar to the Source Term to Dose model; buttons on the left, top to

bottom. A tab area shows the summary of inputs and the results of the calculations
73

Begin by selecting the Event Description button on the main screen. That will display the following:

1. Event name: Arkansas Nuclear One

An entry is required but the text is used for labeling only; it has no impact on the calculations.

2. Release started: put a check in the box, change the date if needed, and enter a time of 13:00

This information is optional and is used only for labeling purposes.

3. We could also enter the latitude and longitude of the release point. For this case it would be the

information reported in the Source Term to Dose model case summary for Arkansas.

Click OK to return to the main screen. Note that the Event Description button now has a checkmark and

the case summary has been expanded.
74

Next, select the Sample Data button.

1. Type in the sample ID provided: ABC123

This entry is required and should uniquely identify the sample. It will be used to label the results.

2. Set the date and time the sample was analyzed: <date+1> 13:55

3. If provided, you may optionally describe the location of the sample and/or the type of sample.

4. The default ground concentration units of μCi/m2 are correct so no change is needed.

5. Enter the nuclide names and concentrations for the sample.

You can speed up the data entry process by typing in the nuclide name without using the drop-down

list and then tabbing to the next column to enter the concentration. Tabbing again gets you to the next

row ready for the next nuclide name.

When the sample data is complete, click the OK button.

Finally, from the main screen, click the Calculation Options button.
75

1. Leave the reentry delay at 0 days. Select Cs-137 as the DRL marker nuclide.

The reentry delay is used for areas in which people have evacuated. For example, consider a case in

which the measurements and analysis needed to define a relocation area will take a week. The EPA

PAGs are based on the concept of averted dose - the dose that can be avoided by taking an action. To

determine if an area is suitable for reentry a week after the accident, the dose that could be averted by

not reinhabiting the area is compared to the EPA IP protective action guides. Thus, the first year PAG

would be compared to the dose not including the first week.

In some instances it may be difficult to use the exposure rate DRL to identify areas where doses

might exceed the protective action guides. Examples are when the exposure rate is near background

levels or when there are no gamma-emitting radionuclides in the mix. In those instances, it may be

easier to measure the surface concentration of a particular marker radionuclide rather than the

exposure rate. You may select the marker nuclide to be used from the list of measured nuclides on the

ground.

2. Leave the four factors at their defaults.

The ground roughness correction factor accounts for the fact that the ground surface is not perfectly

smooth. Some of the ground shine radiation will be intercepted by this uneven surface and cannot

contribute to the dose. EPA used to use a value of 0.7 but now we use 0.82.

Intermediate-phase inhalation doses are calculated assuming activity on the ground is resuspended and

then inhaled. The resuspension process in the model begins with the user entered resuspension factor

and decreases with time. The default initial resuspension factor is 1.00E-06 /m and represents normal

conditions for a temperate climate area. The value should be changed only if there is reasonable

confidence that resuspension rates will be different. For example, with a very dry and windy area, the

factor might be increased.

Inadvertent ingestion is the accidental ingestion of radioactive material from contamination on

surfaces. This can happen for example if a person touches a contaminated surface picking up a small
76

amount of radioactive material on their hands. If they then hold a sandwich, some of the material will

transfer to the sandwich and be eaten with the sandwich. The default inadvertent ingestion rate is 0.0,

assuming no contribution to the intermediate-phase dose. Neither EPA or FRMAC will consider

inadvertent ingestion in their calculations.

The occupancy time describes how long a person would be exposed. The default of 168 hours per

week assumes the worst case - they are there the entire time.

3. Set the dose units to whatever is most useful. SI units can be used if desired.

Click the OK button to return to the main screen again.

Now the problem is fully defined and the program is ready to calculate the intermediate-phase doses.

Click the Compute Doses button. The results will automatically be displayed.
77

Results are far below the EPA PAGs for the intermediate phase. Based on that single result, people can

immediately return to their homes in the area. However, measurements at only one location and/or only

one sample is not enough data to make a decision.

For a typical “reactor mix” of radionuclides, if the first year dose is below the PAGs then the second and

fifty years doses will be below PAGs as well. Also, the groundshine dose will usually dominate.
78

16 Briefing for Non-Technical

Decision Maker

Purpose

Discussion

Problem

To learn how to prepare a briefing for a non-technical decision maker.

Whether you will ever brief a non-technical decision maker or not, you need to understand the information

that should be in the briefing. Until you know which information is important to convey and which

information is not useful, you will not be able to do a good job of explaining your RASCAL results.

In the briefing of a non-technical decision maker, the numbers and the technical terms that we have been

using in this course are not appropriate for the briefing. That information is too technical and detailed. The

decisionmaker needs the big picture. The public needs to be told what it needs to do to escape from

danger. They do not want and will not understand technical details.

We are going to give you insight into what information should be conveyed and what information will just

confuse the message.

Arkansas Nuclear One, Unit 1, declared a General Emergency at 10:20 A.M. Assume that the standard

protective action recommendation for a General Emergency is evacuation to 2 miles full circle and to 5

miles downwind in a 45° sector.

Your job is to evaluate the appropriateness of this standard protective action recommendation and

prepare a briefing for a non-technical decision maker that describes the adequacy and

appropriateness of the standard protective action recommendation for the specific accident being

evaluated.

Assume that the person making the public statement will be the Governor of Arkansas. Your briefing

should prepare him to make a public statement. Therefore, your briefing should include the basis for the

decision in language that is understandable to a non-technical person.

Assume that there are no site-specific protective action sectors or factors that must be considered.
79

Points to Include in Briefing the Decision Maker

The points below should probably be included in the briefing. The problem you have been working did

not include detailed information of the approved emergency plan for the site or site-specific information

so you cannot include that information in this exercise briefing. However, in a real event, that information

should also be included.

Topic Rationale

Existing emergency plan: There is an existing State

emergency plan for handling accidents of this type. The

plan was carefully thought out and reviewed and

approved by many state departments and by federal

agencies.

You want to reassure both the decision

maker and the public that you know what

you are doing. The fact that you have an

existing plan that was carefully thought out

is a big plus for credibility.

The plan has a solid basis: The emergency plan is

based on careful consideration of the potential

consequences of nuclear power plant accidents and on

guidance established by the U. S. Environmental

Protection Agency (Manual of Protective Action

Guides and Protective Actions for Nuclear Incidents,

USEPA, 1992).

The public will be reassured if they believe

that the situation was carefully analyzed

beforehand. The EPA is an agency with

credibility for protecting the health and

safety of the public.

Balancing benefits against detriments: The radiation

dose levels for taking protective actions that are

established in the EPA guidance were developed by

balancing the potential benefits achieved by taking the

actions against the potential detriments of taking the

actions.

The decision maker should realize that the

PAGs balance benefits against detriments.

Any political decision maker will be aware

of the detriments to a large scale evacuation.

The decision maker needs to be assured that

those detriments were considered in

establishing the PAGs.

You are following the plan: Recommend that the

decision maker follow the existing plan and order an

evacuation as specified in the plan. In this problem that

calls for evacuation to 2 miles full circle and 5 miles

downwind.

Both the decision maker and the public will

be reassured that the response actions were

carefully thought out and planned in

advance.

Maps of evacuation areas: Have a map of the areas

showing the areas that you think should be evacuated.

Do NOT show a plume plot to the decision maker.

You need a map. Trying to describe an

evacuation area without a map would be

incomprehensible to anyone.

Maps showing plume plots: NEVER, NEVER, EVER

show a plume plot to a decision maker.

Plume plots are too technical and confusing

for a non-technical decision maker. They are

for you, not the decision maker. You already

translated the plume plot into a

recommended evacuation area. That’s all you

have to tell the decision maker.
Topic Rationale

80

Description of evacuation area: Say something like:

the downwind direction is ______. The width of the

downwind evacuation should be (select whichever is

appropriate) (1) 45 degrees because the wind direction

is well-known and persistent, or (2) ____ degrees

because the wind direction is expected to change

during the release or the wind direction is uncertain.

Use the results that you have from the

problem.

Put the calculated dose plots in their proper

context: Say something like: our calculations of

projected doses suggest that the above evacuation is

significantly larger than would be needed based on the

EPA guidance. Thus, a smaller evacuation could be

justified. However, we believe that, as a general

principle, existing plans should be followed. According

to our dose projections, the evacuation according to the

plan is more than adequate to protect public health and

safety.

The decision maker should understand the

basis for your recommendation, but he does

not need all the technical details. Avoid

technical jargon. Talking about TEDE, rems,

curies/square meter, projected doses, and 4-

day groundshine will just confuse him.

Real measurements: We have sent radiation

monitoring teams into the field to measure radiation

levels. At this time no release of radiation has been

detected. We will continue to have monitoring teams in

the field to measure radiation levels.

Real measurement data beat theory any day.

The fact that you are really checking what is

really happening is reassuring. Even zeros as

results are great.

Describe the current situation: For this problem you

might say something like: there has been no significant

radiological release at this time. The evacuation being

ordered is a precautionary measure to guard against the

possibility of a significant radiological release.

Be very careful about how you describe the

release and the reason that the evacuation is

recommended.

Urgency: For this problem, you might say something

like: the evacuation should be prompt but orderly.

Current conditions are not dangerous.

The public needs to be told the truth about

the degree of urgency needed for their

actions.

Return to homes: Inform the decision maker that there

is a possibility that residual radioactive contamination

in some areas may (or may not) make those areas

uninhabitable in the future, but that cannot be

determined until the incident is over and measurements

of deposited radioactivity have been made. The

decision maker should say that a decision on return will

be made when we are sure it is safe to return. We need

to determine that the plant is stabilized and that

radiation levels, if any, are below established

guidelines.

People need to be informed of the possibility

of long term relocation. If they become

aware of that only later, they will feel they

were not told the whole truth.

Children in school: Describe how the state plan deals

with the issue of children in school.

This will be of great concern to parents. It

must be described in public announcements.
Topic Rationale

81

Use of potassium iodine: If you expect that people

will evacuate before the plume reaches them say

something like: the use of potassium iodine for the

public is not recommended at this time because the

evacuation should keep thyroid doses well below the

levels for which the FDA recommends use of

potassium iodine.

The FDA has established criteria for the use

of KI. The state plan will have considered

the FDA recommendations. Follow the state

plan.

Pets: Inform the decision maker on how the plan deals

with the issue of people’s pets.

People will be concerned about their pets.

They must be told what they should do. They

will be reassured if they are aware that it has

been considered.
82

Nuclear Power Plants

The section “Using RASCAL: Assessing a PWR Core Damage Accident” ran through the entire code for

one particular reactor core damage accident to teach you many of the details of the code. This section on

Nuclear Power Plant Problems has short problems, each illustrating some specific aspect of the code.

These problems primarily explore reactor source terms and release pathways.
83

17 Examining the RASCAL Source

Term

Purpose

Discussion

Problem

Results

To learn how to look at the details of the source term generated by RASCAL and how to export the source

term information to the IMAAC.

Section 3 described how RASCAL calculates the source term used in the analysis.

The October 2004 Nuclear/Radiological Incident Annex of the National Response designates the

Interagency Modeling and Atmospheric Assessment Center (IMAAC) as the single source for atmospheric

dispersion and consequence prediction. During a radiological Incident of National Significance in which

the NRC is the Coordinating Agency, RASCAL may be used to supply a source term to the IMAAC.

Source terms should be sent to IMAAC only from NRC Headquarters, not from the NRC Regions or the

NRC site teams.

Using the case saved at the end of Problem 6 (should be Case 1),

1. Answer the following questions about the source term:

Of the total activity released to the atmosphere, what fraction is noble gases?

Iodines are always a concern in a release. Describe the time dependence of the iodine release. At what

time is the iodine release rate the greatest?

2. Prepare a source term export file for sending to the IMAAC.

Load the saved case from problem 6, the suggested name was Using RASCAL - Case 1. You can do this

by selecting File | Open Case from the menu bar and then selecting the file name from the list.

Select the Source Term Summary tab.
84

The total activity (1.5E+05) is given at the top of the summary. To get the noble gas activity fraction, you

will have to manually add up the activities for all the noble gases and then divide by the total activity

released to the atmosphere.

Noble gas Activity (Ci)

Kr-85 3.4E+02

Kr-85m 3.3E+03

Kr-87 7.4E+02

Kr-88 5.6E+03

Xe-131m 3.5E+02

Xe-133 6.1E+04

Xe-133m 2.1E+03

Xe-135 2.0E+04

Xe-135m 3.0E+03

Xe-138 1.0E-01

Total 9.64E+04 9.64E+04 / 1.5E+05 = 64.3 %
85

For reference, the radionuclide releases from TMI and Chernobyl are show below.

Nuclide group TMI (Ci released) Chernobyl (Ci released)

noble gases 2.5 million 170 million

radioiodines 15 48 million

others negligible 72 million

TMI reference: Table II-1 of “Three Mile Island: A Report to the Commissioners and to the Public,”

Nuclear Regulatory Commission Special Inquiry Group, Mitchell Rogovin, Director, 1980.

Chernobyl reference: Table 1 of “Chernobyl - Assessment of Radiological and Health Impacts,”

Nuclear Energy Agency, Organisation for Economic Co-Operation and Development, 2002.

To see the time dependence, select the Details button on the tab.

This shows the activity of each radionuclide released to the atmosphere each 15 minute time step.

Examination of the iodine rows shows the amount released each time period increasing.

Next, click the Plot button. In the selection boxes on the right, select I-131, I -132, and I-133. Then, click

the Update Plot button.
86

The graph shows the release rate of the selected iodines in units of curies per 15-minute time step.

From the graph, the rate is greatest at about 16:30.

To create the IMAAC export file

1. Return to the “details” view of the source term.

2. Click the Export button to the right of the nuclides table.

3. The message explains that you are creating a comma-delimited text file. Click the Yes button to

continue.

4. Navigate to the folder where you want to save the file. Enter a unique file name. Click the Save

button.

5. The file can now be attached to an e-mail and sent to the IMAAC.

NRC staff - Refer to Protective Measures Team procedures for IMAAC notification and additional

information that needs to be in the e-mail. Source terms should be sent to IMAAC only from

Headquarters, not from the NRC Regions or NRC site teams.
87

18 Release Pathway Reduction

Mechanisms

Purpose

Discussion

RDF e

T 

Problem

To study how to use release pathway reduction mechanisms to obtain an appropriate release.

The magnitude of the leakage rate of radioactive material to the atmosphere is an important consideration

when estimating doses. One way to define leakage is by a containment pressure and a containment hole

size. Reducing either will reduce the rate at which material enters the atmosphere.

Various reduction mechanisms are modeled by RASCAL. The reduction of the source term by sprays is

treated as an exponential function with time. There is an initial effectiveness that is applied for the first 15

minutes that radionuclides are in the containment atmosphere and then a reduced effectiveness acting after

15 minutes. The reduction factor (RDF) is calculated as:

where T is the total amount of time (h) that the sprays have been operating and lambda (λ) is 12/h for the

first 15 minutes and 0.2/h after 15 minutes.

Some PWRs use ice bed condensers to allow for smaller containment volumes. Such containments route

hot gases through large ice baskets to condense steam and lower containment pressure. Factors to consider

with this type of containment are whether the ice has been exhausted and whether the recirculation fans

are available to provide multiple passes of the hot gases through the ice beds.

The Catawba Nuclear Plant, Unit 1 (a PWR with an ice condenser containment) had been operating at full

power. The reactor scrammed at 10:45 A.M. local time. At 1:30 P.M. local time the core was uncovered. It

was recovered after 45 minutes but there was a direct release path (e.g. PORV) to the containment.

We will first run this problem with none of the active reduction mechanisms operating and with a 4-inch

diameter opening in the containment with the containment at the maximum design pressure of 15 lb/in2.

Then we will change release pathways to reduce the size of the release. It is assumed the opening will

remain open for 3 hours (until 16:30) and then be completely closed. (Hint: you need to set the diameter to

zero.)

Run the following six cases and fill in the source term and doses in the table.

Case 1: Initial case described above (with sprays off, ice bed exhausted, and fans off)
88

Case 2: Reduce the containment pressure by a factor of 3; from 15 lb/in2down to 5 lb/in2.

Case 3: Reduce the hole size to 2 inch diameter.

Case 4: Assume that the ice bed is not exhausted

Case 5: Turn on the recirculation fans

Case 6: Turn on the sprays

Use the predefined Standard Meteorology dataset.

Case 1 Case 2 Case 3 Case 4 Case 5 Case 6

Sprays Off Off Off Off Off On

Recirculation fans Off Off Off Off On On

Ice bed exhausted Yes Yes Yes No No No

Hole size @ 13:30 4" dia 4" dia 2" dia 2" dia 2" dia 2" dia

Containment

pressure @ 13:30

15 lb/in25 lb/in25 lb/in25 lb/in25 lb/in25 lb/in2

Total source term

(Ci)

TEDE at 1 mile

(rem)
89

Inputs

Event Type Nuclear Power Plant

Event Location Catawba - Unit 1

Leave the average reactor power and the average fuel burnup at the default values.

Source Term Time Core is Uncovered

Reactor shutdown: 10:45

Core uncovered: Yes, at 13:30

Core recovered: Yes, at 14:15

Release Path Containment Leakage / Failure

Release point characterization: Not an isolated stack

Release height: 0.0 m

Consider building wake effects: Yes.

Start of release to containment: 13:30

Rationale: The problem specified no holdup in containment. Set the time to

match the core uncovered time (13:30).

Leak rate to atmosphere described by: Containment Pressure / Hole size

Leak events:

<date> 13:30 Sprays Off

<date> 13:30 Recirc fans Off

<date> 13:30 Ice bed exhausted: Yes

<date> 13:30 Leak rate 15 lb/in2, 4 inch dia

<date> 16:30 Leak rate 15 lb/in2, 0 inch dia

(terminates the release)

Rationale: The leak rate event at 16:30 is added to close the major release path.

The leak events shown above are for Case 1. Modify the leak events as needed for

each of the other cases (2 - 6).

Meteorology Data set type: Predefined data (non site specific)

Data set: Standard Meteorology

Calculation

Options

Distance of calculation: Close-in only.
90

Results

End calculations at: Start of release plus 6 hours

Case 1 Case 2 Case 3 Case 4 Case 5 Case 6

Sprays Off Off Off Off Off On

Recirculation fans Off Off Off Off On On

Ice bed exhausted Yes Yes Yes No No No

Hole size 4" dia 4" dia 2"dia 2" dia 2" dia 2" dia

Containment

pressure

15 lb/in25 lb/in25 lb/in25 lb/in25 lb/in25 lb/in2

Total source term

(Ci)

3.2E+07 2.4E+07 6.5E+06 5.7E+06 5.3E+06 4.9E+06

TEDE at 1 mile

(rem)

270 200 53 27 14 2.9
91

19 Monitored Mixtures

Purpose

Discussion

To show how to determine projected doses based on effluent monitor readings.

When a nuclear power plant effluent monitor detects a release, the release is likely to be a mixture of

many radionuclides (fission products) rather than just a single radionuclide. However, the effluent monitor

cannot identity the specific radionuclides present. Instead, the effluent monitor will usually be able to

provide only the noble gas activity release rate, the radioiodine activity release rate, and sometimes a

particulate activity release rate.

The effluent monitor may provide a reading in terms of some number of counts per second. The counts per

second reading cannot be used by RASCAL because RASCAL does not know the efficiency of the

effluent monitor. Therefore, RASCAL cannot convert the count rate in terms of counts per second to a

concentration in terms of curies per second. However, every plant has a conversion factor that will permit

the conversion of counts per second to curies per second.

Sometimes, the plant may use this conversion factor and report the release rates to you directly in terms of

curies/second. Other times it may not be easy to obtain this conversion factor from the plant because the

factor has been buried in the plant’s dose projection software, and the users of the software may enter the

monitor reading in terms of counts per second without knowing the value of the conversion factor that is

being used. Nevertheless, the plant has this conversion factor, and you should be able to get it if you are

persistent. Once you have the conversion factor, you can convert counts per second to curies per second.

If the plant provides you with an effluent concentration in terms of curies per unit volume and the effluent

flow rate, you can multiply these two numbers together to determine the effluent activity release rate in

terms of curies/second.

Monitored releases will be filtered so they should be mostly noble gases but with a small proportion of

iodines and particulates. RASCAL estimates the composition of the noble gas component of the release by

starting with the equilibrium proportions of each noble gas radionuclide that will be present in the reactor

core while it is operating. Then the proportions of each that will be present at the start of the release will

be determined by multiplying the initial proportion by the radiological decay factor and renormalizing the

proportions to the time of the release start. The same is done for radioiodines.

For particulates a different technique is used because there is really no practical way to determine the

composition of the particulate mixture. Particulates are assumed to be entirely composed of cesium iodide

(Cs-137 + I-131). This is a very conservative assumption. It assumes that particulates are entirely made up

of radionuclides that have relatively long half lives and are biologically among the most hazardous.

However, the overestimate of the dose for particulates in not expected to have a significant impact on

protective action decisions because the particulate release rate should be very low.
92

Problem

Inputs

A malfunction at the North Anna, Unit 2 nuclear power plant caused the plant to shut down at 3:50 P.M.

Shortly thereafter (4:00 P.M.) , an effluent release through a monitored pathway was detected.

The effluent release rate was reported to be 95 Ci/s for noble gases, 1.2 Ci/s for radioiodines, and 0.03

Ci/s for particulates. The plant’s technical specifications state that the release duration must be limited to

no more than 30 minutes.

Determine the projected TEDE and Thyroid CDE at 1 mile.

Dose type Distance from release

1 mile

TEDE (rem)

Thyroid CDE (rem)

Event Type Nuclear power plant

Event Location North Anna - Unit 2

Assume 100% power and default burnup

Source Term Monitored Releases - Mixtures

Reactor shutdown: Yes, at 15:50

Sample taken: 16:00

Release rates:

Noble gases 95 Ci/s

Iodines 1.2 Ci/s

Particulates 0.03 Ci/s

Release Path Direct to Atmosphere

Release point characterization: Not an isolated stack

Release height: 0.0 m

Consider building wake effects: Yes
93

Results

Start of release to atmosphere: 16:00 ( to correspond to the sample time)

End of release to atmosphere: Release duration - 00:30

Meteorology Data set type: Predefined data (non site specific)

Data set: Standard Meteorology

Calculation

Options

Calculation distance: Close-in only

End calculations at: Start of release to atmosphere plus, 6 hours

The following results are available from the Maximum Dose Values tab displaying the close-in doses.

Dose type Distance from release

1 mile

TEDE (rem) 1.3E-01

Thyroid CDE (rem) 1.2E+00
94

20 Containment Radiation Monitor

Purpose

Discussion

1e+6

1e+5

1e+4

1e+3

1e+2

1e+1

1e+0

1e-1

1e-2

1e-3

Containment Monitor Reading - Unshielded (R/h)

1h 24 h

Normal Coolant

1h 24 h

Spiked Coolant

1h 24 h

Cladding Failure

1h 24 h

Core Melt

Damage State and Time After Reactor Shutdown

100%

10%

1%

100%

10%

1%

Sprays

Off

Sprays

On

Key to Spray Status and

Damage Amount

To learn how a containment radiation monitor reading can be used to generate a source term.

RASCAL can use a reading from a containment radiation monitor to estimate the amount of core damage.

For example, RASCAL might calculate that the monitor reading you entered corresponds to 37% core

melt. RASCAL will then use 37% core melt to calculate the activity released to the containment based on

the core inventory and the core release fractions.

The factors that RASCAL uses to estimate core damage

consider whether the sprays are on or not. If the sprays

are operating, they will wash out most of the particulates

so that a given monitor reading would correspond to

more core damage than if the sprays were off. Figure 3

shows the containment dome monitor response for a

PWR.

Figure 3 PWR containment monitor response
95

Auxiliary Building Containment Turbine Builiding

Low Pressure System

Sprays

Reactor

Vessel

Steam

Generator

Pressurizer

Relief Tank

Sprays

Condenser

Safety Relief

Valve

Steam Jet

Air Ejector

Exhaust

Filter

The advantage of this method is that the core damage estimate is based on real measured data instead of a

calculation of how much core damage is likely to occur based on how long the core is uncovered. Used

together, the two methods can compliment each other and allow a better understanding of what is really

happening.

There are several cautions in using this method. First, the monitor must “see” more than 50% of the area

being monitored (see Figures A-3 and A-4 in the RTM). If the monitor does not see this much, do not use

this method.

Second, in interpreting the RASCAL results, remember that there will be a time delay before fission

products released from the core can affect the monitor reading. When there is a delay in the movement of

fission products from the core to the containment or a delay in mixing within the containment,

containment radiation monitor readings may start out low and then steadily increase with time. Thus, the

maximum reading will give the best estimate of true core damage.

Third, the actual radionuclide mix in the containment may be different from that assumed in the

calibration of the monitor. This can be especially significant for high dose rates when a shielded detector

is used.
96

Problem

Inputs

An accident occurred at Waterford Unit 3. The reactor scrammed at 12:00 P.M. By 12:45 P.M. some of the

core was uncovered. The release from the core passed into the containment building. Release from the

containment was via design leak rate.

During the course of the event, you receive periodic readings from the containment dome radiation

monitor. Perform a RASCAL calculation (with Standard Meteorology) based on the containment radiation

monitor readings in the table below:

Time PWR containment

monitor reading, R/h

12:45 P.M. 14

1:30 P.M. 50,000

3:00 P.M. 300,000

Look at the Source Term Summary tab and fill in the table below.

Containment radiation

monitor reading

Indicated core

damage

12:45 P.M.

1:30 P.M.

3:00 P.M.

Event Type Nuclear power plant

Event Location Waterford - Unit 3

Source Term Containment Radiation Monitor

Reactor shutdown: 12:00

Monitor location: PWR Containment Dome (not user selectable)

Containment radiation monitor readings (R/h):

<date> 12:45 14

<date> 13:30 50000

<date> 15:00 300000
97

Results

Release Path Containment Leakage / Failure

Release point characterization: Not an isolated stack

Release height: 0.0 m

Consider building wake effects: Yes

Start of release to containment: 12:45 to correspond to first monitor reading

Leak rate events:

<date> 12:45 Leak rate Design

<date> 12:45 Sprays Off

Meteorology Data set type: Predefined data (non site specific)

Data set: Standard Meteorology

Calculation

Options

Calculation distance: Close-in only

End calculations at: Start of release to atmosphere plus, 6 hours

Examine the Source Term Summary to see what amount of core damage was estimated based on the

radiation monitor readings.

Containment radiation

monitor reading

Indicated core damage

12:45 P.M. 1.92 E-02% cladding failure

1:30 P.M. 7.2% core melt

3:00 P.M. 43.2% core melt
98

21 Containment Bypass

Purpose

Discussion

Problem

To learn how to estimate projected doses when there is a release of coolant and when the release pathway

bypasses the containment.

We have to distinguish between “source term” and “release pathway.” A “bypass accident” means we

have specified the release pathway. The release pathway for a bypass accident is one in which coolant

escapes to the atmosphere without going through the containment.

There are three source term types that can be used for coolant releases. The “time core is uncovered”

source term type can estimate the activity entering the coolant if the core is uncovered. The “ultimate core

damage state” source term type can estimate coolant activity for normal coolant, for spiked coolant, and

for accidents in which there is cladding damage. The “coolant sample” source term type can estimate

coolant activity based on the sample data.

The Peach Bottom Unit 2 nuclear power plant experienced a leak in a containment penetration pipe that

could not be isolated (closed). The resulting drop in reactor coolant system pressure and water level

caused the reactor to automatically shut down at 11:45 A.M., but some fuel damage occurred. The

indication is that the fuel suffered 4% cladding failure.

The pumps being used to maintain the water levels in the reactor coolant system are injecting 300

gallons/minute.

The leak is into an auxiliary building where the coolant immediately flashes into steam. The steam can

escape the building to the atmosphere without any filtering.

Calculate the projected TEDE and thyroid CDE at 2 miles.

Dose type Distance from release

2 miles

TEDE (rem)

Thyroid CDE (rem)
99

Inputs

Results

Event Type Nuclear power plant

Event Location Peach Bottom - Unit 2

Assume 100% power and default burnup

Source Term Ultimate Core Damage State

Reactor shutdown: 11:45

Ultimate core damage state: Cladding failure - 4 percent

Completion of cladding failure: 11:45

Release Path Bypass secondary containment

Release point characterization: Not an isolated stack

Release height: 0.0 m

Consider building wake effects: Yes

Release events:

<date> 11:45 Leak rate 300 gal/min

<date> 11:45 Filters Off

Meteorology Data set type: Predefined data (non site specific)

Data set: Standard Meteorology

Calculation

Options

Calculation distance: Close-in only

End calculations at: Start of release to atmosphere plus, 6 hours

The following results are available from the Maximum Dose Values tab displaying the close-in doses.

Dose type Distance from release

2 miles

TEDE (rem) 1.0E+01

Thyroid CDE (rem) 2.0E+02
100

22 Steam Generator Tube Rupture

with Coolant Release

Purpose

Discussion

To learn how to determine projected doses due to a steam generator tube rupture and to understand

coolant spiking.

A steam generator tube rupture (SGTR) in a PWR allows primary system coolant to escape rapidly to the

secondary system. The rapid loss of coolant causes the pressure to drop in the primary system, which in

turn causes the reactor to automatically “scram” (shutdown).

Coolant “spiking”

The rapid drop in pressure in the primary system causes an increase in the rate at which the radioactive

fission products in the fuel rod cladding gap escape to the coolant. The concentration of fission products

in the coolant rises rapidly. Originally, it was noticed that radioiodine concentrations rose and the

phenomenon was first called “iodine spiking.” Later it was found that the concentrations of all

radionuclides rose with the possible exception of noble gases. Now we call this phenomenon “coolant

spiking” or simply “spiking.” RASCAL assumes that the concentrations of only the halogens and alkali

metals fission products in the coolant increase by the spiking factor.

The RASCAL user must specify the “spiking factor” using the Ultimate core damage state screen. At the

start of an accident there will be no way to determine what the actual spiking factor is. After some time, it

should be possible to analyze a coolant sample and estimate the spiking factor be comparing its activity to

normal coolant activity. Thus, we recommend running RASCAL initially using the spiking factor default

value of 100 and then adjusting the spiking factor after a primary coolant sample has been analyzed.

Partitioning

The RASCAL user must specify whether the radionuclides that leak into the steam generator are

“partitioned” or “not partitioned.” “Partitioning” occurs when the leak is below the water level on the

secondary side of the steam generator. The water from the primary system that leaks into the steam

generator mixes with the water in the steam generator. When the radionuclides are “partitioned,” the

concentration of radionuclides in the steam will be less than their concentration in the steam generator

water by a partitioning factor.” “Not partitioned” occurs when the leak is above the steam generator water

level. Then, most of the primary coolant will flash into steam and most of the radionuclides will be

available for release.

Partitioning is assumed to have no effect on noble gases. Noble gases in the primary coolant leakage are

assumed to immediately be available for release without any reduction or holdup. If the user selects

“partitioned,” RASCAL reduces the release of all radionuclides that are not noble gases by a factor of 50.

If the user selects “not partitioned,” RASCAL reduces the release of all radionuclides that are not noble

gases by a factor of 2.
101

How does the RASCAL user know whether to select “partitioned” or “not partitioned”? Although the

actual tube break location may be unknown, the steam generator water level relative to the top of the tube

bundle should be available. If the water level is near or above the top of the tubes, the user should select

“partitioned.” If the reactor has a once-through steam generator, RASCAL does not allow “partitioning”

because most of the tube length in a once-through steam generator is not covered by water.

Setting the leak rate

The RASCAL user must also specify the rate of primary coolant loss to the secondary system. This can be

done in one of two ways.

One method is to specify the actual rate of coolant loss from the ruptured tubes. This loss can be estimated

by the amount of water being added to the primary, from whatever source, to try and balance the flow into

the secondary system. For a typical steam generator leak, the normal charging system flow may be enough

to keep up with the leak. In this case, the difference between the letdown flow rate and the charging flow

rate is the rate of leakage. Some plants have an “excess makeup flow rate” meter that displays this

difference.

The other method is by specifying the number of steam generator tubes that have ruptured. RASCAL then

assumes that the rate of primary coolant loss is the number of tubes that have failed multiplied by 500

gpm/tube. It is reasonable to select one tube unless the coolant makeup rate is so large that it indicates that

more than one tube might be ruptured.

If the tube leak exceeds the normal charging capacity, then safety injection may actuate when the

pressurizer pressure decreases. The operators can estimate the coolant makeup rate from the safety

injection flow meter. Note that there was an event at a plant a few years ago, in which the operator

detected the leak and started a second charging pump. This prevented the automatic actuation of safety

injection and the reactor trip as the two pumps kept up with the leakage.

The bottom line is to enter the rate at which water is being added to the primary coolant system, from

whatever source. The program labels it “charging flow” but it might be more aptly labeled “makeup flow”.

Release pathways

The RASCAL user must also specify whether the release to the atmosphere is through the steam jet air

ejector or the safety relief valves on the secondary system that are used to relieve high pressure. Usually

the release will be through the steam jet air ejector.

The primary-to-secondary leakage may cause pressures to briefly exceed the safety relief valve set-point,

but the main steam dump valves should quickly relieve the pressure. The response of the steam dump

valves may not be quite fast enough to handle a load rejection without a little steam release through the

safety relief valves, but this release is generally less than a minute, which is negligible.

When the release is through the steam jet air ejector, RASCAL assumes a reduction factor of 20 for nonnoble gases. When the release is through the safety relief valves, there is no reduction. A release through

the steam jet air ejector is likely to be a monitored release. In that case, it would be useful to do another

RASCAL run using the “Monitored Releases - Mixtures” source term option.

If the main condenser is not available, for example, because of loss of offsite power, the secondary system

pressure will increase until the safety relief valves open. Thus, if the main condenser is not available, the

RASCAL user should assume the release is through the high-pressure safety relief valves.
102

Problem

Inputs

As time progresses, the pressure difference between the primary and secondary will decrease and the

movement of fission products to the secondary will stop after several hours. Thus, the release is

essentially self-terminating.

The Crystal River Unit 3 nuclear power plant experienced a sudden drop in primary system pressure and a

sudden rise in secondary pressure at 12:36 A.M., shortly after midnight. The reactor immediately

scrammed (shut down) in response to the sudden drop in primary system pressure.

The operators assumed that a steam generator tube rupture had occurred. The operators estimated that the

makeup flow (including safety injection) was about 500 gpm. Assume that the sudden drop in primary

system pressure will cause coolant spiking. Use the default spiking factor of 100.

The increase in pressure on the secondary side caused the high-pressure safety relief valves to open

briefly, but after that the release was through the steam jet air ejector.

The release point is 30 meters above ground level.

Determine the TEDE and the thyroid CDE at 1 mile.

Dose type Distance from

release

1 mile

TEDE (rem)

Thyroid CDE (rem)

Event Type Nuclear Power Plant

Event Location Crystal River - Unit 3

Leave the average reactor power and the average fuel burnup at the default values.

Source Term Ultimate Core Damage State

(because only this source term type calculates coolant spiking)

Reactor shutdown: 00:36

Core damage endpoint: Increased fuel pin leakage, with coolant contamination

spike by factor of 100

Time of increased fuel pin leakage: 00:36

Release Path Steam Generator Tube Rupture
103

Results

Conclusion

Release point: Steam jet air ejector

Effective release height: 30.0 m

Rationale: This is assumed to be the height of the steam jet air ejector above

ground level.

Consider building wake effects: Yes

SG water mass: 9.3E+04 lb

Steaming rate: 7.50E+04 lb/h

Release events:

<date> 00:36 SG Condition Not partitioned

<date> 00:36 Leak rate into SG 500 gal/min

Meteorology Data set type: Predefined data (non site specific)

Data set: Standard Meteorology

Calculation

Options

You are asked for doses at 1 mile so you could set the distance of calculation to

Close-in only.

End calculations at: Start of release plus 6 hours

Dose type Distance from

release

1 mile

TEDE (rem) 2.0E-03

Thyroid CDE (rem) 1.5E-02

Offsite doses from a steam generator tube rupture accident are low compared to offsite doses from core

damage accidents. A steam generator tube rupture accident without core damage releases only coolant

activity. The curie content in coolant without core damage is low compared to the activities that might be

present if there were core damage.
104

23 Coolant Sample

Purpose

Discussion

Problem

Inputs

To show how to use radionuclide activities measured in a coolant sample to determine the source term.

The coolant sample source term option can be used only when coolant is being released directly to the

environment. Thus, this source term option can be used for containment bypass release paths and steam

generator tube rupture release paths.

The analysis of coolant activities will normally take a couple of hours to complete. Thus, the coolant

sample source term option cannot be run early in the accident sequence. Since our objective is to make

protective action decisions as early as possible, the coolant sample source term option is not likely to be

available in time to be used for making protective action decisions. Other source term options will have to

be used instead. However, the coolant sample source term option can be used as a way to improve the

accuracy of previous estimates of release size. But, coolant sampling systems are designed for routine

sampling and may not be able to measure the high activity concentrations that might result after

significant core damage.

For the previous SGTR problem, assume that the post-accident sampling system (PASS) collected a

coolant sample 15 minutes after reactor shutdown. The activity in the coolant was measured as the

equivalent to 311 μCi of I-131 per milliliter (after being corrected for radiological decay back to the time

the sample was collected).

Determine the TEDE and the thyroid CDE at 1 mile.

Dose type Distance from

release

1 mile

TEDE (rem)

Thyroid CDE (rem)

Compare the source term results with the previous SGTR problem. What conclusions can be drawn?

Event Type Nuclear Power Plant
105

Results

Event Location Crystal River - Unit 3

Leave the average reactor power and the average fuel burnup at the default values.

Source Term Coolant Sample

Time sample taken: 00:51 (Shutdown time of 00:36 + 15 minutes)

Sample activity units: μCi/ml

Nuclide and activities:

I-131 3.11E+02

Release Path Steam Generator Tube Rupture

Release point: Steam jet air ejector

Effective release height: 30.0 m

Rationale: This is assumed to be the height of the steam jet air ejector above

ground level.

Consider building wake effects: Yes

SG water mass: 9.3E+04 lb

Steaming rate: 7.50E+04 lb/h

Release events:

<date> 00:51 SG Condition Not partitioned

<date> 00:51 Leak rate into SG 500 gal/min

Meteorology Data set type: Predefined data (non site specific)

Data set: Standard Meteorology

Calculation

Options

Distance of calculation: Close-in only.

End calculations at: Start of release plus 6 hours

Dose type Distance from

release

1 mile

TEDE (rem) 2.1E-01

Thyroid CDE (rem) 6.1E+00
106

24 Ultimate Core Damage State

Source Term

Purpose

Discussion

Problem

To learn how to use the Ultimate Core Damage State source term.

The Ultimate Core Damage State source term option allows you to specify how much spiked coolant or

cladding damage you expect and when that “maximum” amount of damage will have been reached.

In RASCAL 3.0.5, the user can no longer select core melt or vessel melt-through as could be done in

previous versions of RASCAL. For accidents proceeding to core melt, the user interface screen tells the

user to use the “time core is uncovered” source term type. For accidents with core melt, the timing of the

release would not be at all realistic using the ultimate core damage state source term option. In addition,

while the user may have a relatively good idea of when core damage may begin, he may have less

knowledge of when the maximum damage will occur. For these reasons, it is required that for accidents

that are expected to proceed into core melt, the use of the “time core is uncovered” source term type

should give more realistic results.

At 8:30 p.m. the Comanche Peak Unit 1 nuclear power plant reactor scrammed when it experienced a

sudden drop in primary system pressure. A sudden rise in containment pressure and containment radiation

levels indicate that a leak of coolant to the containment atmosphere had occurred. Failure of a pump

supplying coolant caused that water level to drop temporarily causing some fuel rods to overheat.

At 09:00 p.m. a coolant radiation monitor indicated that the cladding on 4% of the fuel rods had been

damaged.

Assume that the containment sprays were not activated. There is no reason to believe that the containment

will not remained intact. Estimate off-site doses.

Dose type Distance from

release

0.1 mile

TEDE (rem)

Thyroid CDE (rem)
107

Inputs

Event Type Nuclear Power Plant

Event Location Comanche Peak - Unit 1

Leave the average reactor power and the average fuel burnup at the default values.

Source Term Ultimate Core Damage State

Rationale: This is the appropriate source term type since we have an estimate of

the total amount of fuel damage that occurred.

Reactor shutdown: 20:30

Core damage endpoint: Cladding failure - 4%

Time of cladding failure: 21:00

Release Path Containment Leakage/Failure

Release point characterization: Not an isolated stack

Effective release height: 0.0 m

Consider building wake effects: Yes

Start of release to containment: 21:00

Release events:

<date> 21:00 Sprays Off

<date> 21:00 Leak rate Design

Rationale: We assume that the sprays were not activated and with an intact

containment the leak rate will be at design.

Meteorology Data set type: Predefined data (non site specific)

Data set: Standard Meteorology

Calculation

Options

Distance of calculation: Close-in only.

End calculations at: Start of release plus 6 hours
108

Results

Dose type Distance from

release

0.1 mile

TEDE (rem) 2.4E-02

Thyroid CDE (rem) 4.7E-01
109

Spent Fuel

There are three possible spent fuel source terms from spent fuel accident types: cold gap, hot gap, and

cladding fire. For all three, the inventory available for release is computed the same way. The number of

assemblies per core is specific to each plant and is part of the plant parameters in RASCAL. The activity

of a full core can be computed from the reactor power and the core inventory adjusted for burnup. The

spent fuel source term inventory is then the full core inventory scaled as needed for the portion of a full

core represented by the number of spent fuel assemblies involved in the accident. Where the spent fuel

amount is specified in batches, a batch is defined as one-third of a core. The burnup value used to adjust

the inventory is the average burnup of the fuel in storage not the fuel currently in the reactor core.

Cold gap release

A “cold gap release” occurs when spent fuel elements are mechanically damaged but the temperature is

low enough that the cladding does not suffer any thermal damage. Examples include mechanical damage

to fuel elements damaged underwater in a fuel pool and mechanical damage to fuel elements in a dry cask

storage. Radionuclides in the gap between the cladding and the fuel pellets will be released. The fractions

of the inventory in the fuel element that will be released in a “cold gap release” are given in Table 5 for

each radionuclide group.

Hot gap release

A “hot gap release” occurs when the fuel cladding ruptures due to heat build up releasing the gap

inventory. If the spent fuel elements in a pool become uncovered, their temperature will rise. If the

temperature reaches 1200 oF, the fuel cladding will rupture due to the buildup up of internal pressure and

will release the radioactivity in the gap between the cladding and the fuel pellets. The fractions of the

inventory in the fuel element that will be released in a “hot gap release” are given in Table 5 for each

radionuclide group.

Cladding fire

A “cladding fire release” occurs when the fuel elements remain uncooled and the temperature becomes

high enough to cause the cladding to burn. The fractions of the inventory in the fuel element that will be

released in a “cladding fire release” are given in Table 5 for each radionuclide group.
110

Table 5 Fuel activity release fractions used in spent fuel accidents

Nuclide group Cold gap Hot gap Cladding

fire

Noble gases (Xe, Kr) 0.4 0.4 1

Halogens (I, Br) 0.003 0.03 0.7

Alkali metals (Cs, Rb) 0.003 0.03 0.3

Tellurium group (Te, Sb, Se) 1×10-4 0.001 0.006

Barium, strontium (Ba, Sr) 6×10-7 6×10-6 6×10-4

Noble metals (Ru, Rh, Pd, Mo, Tc, Co) 6×10-7 6×10-6 6×10-6

Cerium group (Ce, Pu, Np) 6×10-7 6×10-6 2×10-6

Lanthanides (La, Zr, Nd, Eu, Nb, Pm, Pr, Sm, Y, Cm, Am) 6×10-7 6×10-6 2×10-6

Reference: from Table 2.1 in NUREG-1887; originally from NUREG/CR-6451

Caution: The release fractions for spent fuel are for oxides, not metal.

RASCAL can analyze three types of spent fuel accidents as seen in the Source Term Options for Spent

Fuel screen below:

Pool Storage - Uncovered Fuel

RASCAL can analyze spent fuel pool accidents in which spent fuel pool water is lost and the fuel

elements become uncovered. When spent fuel pool water is lost, it is assumed that the fuel must be

uncovered for more than two hours before sufficient heating can occur to reach 1200 oF, the temperature

at which cladding is expected to fail. After two hours, the fuel cladding ruptures due to the build up of

internal pressure releasing the hot gap fraction of the fission products (see Table 6). Only fuel that has

been irradiated within the past year (for a PWR) or the last 180 days (for a BWR) is assumed to be able to

reach 1200 oF after the loss of cooling water. Loss of cooling for older fuel will not result in a release. If

the release is filtered, a reduction factor of 0.01 is applied to all radionuclides except noble gases.
111

Table 6 Spent fuel damage estimates based on storage duration and time fuel is uncovered

Type of release

Storage

duration

PWR fuel stored less than 1 year

- or -

BWR fuel stored less than 180

days

PWR fuel stored 1 year or longer

- or -

BWR fuel stored 180 days or longer

Pool not fully

drained or

drained for less

than 2 hours

Hot gap release No release

Pool fully

drained for 2

hours or longer

Cladding fire release Hot gap release

Pool Storage - Damaged Assembly Under Water

RASCAL can analyze mechanical damage to spent fuel in a fuel pool in which the fuel remains

underwater and adequately cooled. Fuel that is damaged underwater is assumed to remain cold but suffers

cladding failure resulting in a cold gap release (see Table 5). Pool scrubbing removes 99% of the nonnoble fission products released from the damaged fuel. If the release to the environment is filtered, a

further reduction factor of 0.01 is applied to all radionuclides except noble gases.

Dry Storage - Cask Release

RASCAL has the capability to model an accident in which there is damage to the cladding of fuel

assemblies stored in a cask and the integrity of the fuel cask is lost. Only one cask can be involved but the

user may vary the number of assemblies damaged. If the assemblies are damaged but have not lost cooling

for greater than the thermal limit, a cold gap release fraction is used (see Table 5). If cooling has been lost

long enough to allow the cladding to melt, then the hot gap release fraction is assumed. No release is

assumed if the cladding does not melt or if the cask is engulfed in a fire.

Decay Since Last Irradiation

RASCAL decays the stored fuel based on the specified “time since last irradiation”. Both the damaged

assembly underwater and the dry storage cask releases assume that all the damaged fuel is of the same

age. In these two cases, decay is from the user entered date or for the user entered time in storage. The

pool storage with uncovered fuel scenario allows specification of different ages. In this case the decay is

done as follows:
112

Time since last irradiation

PWR BWR Decay applied by

the model

< 1 year < 180 days 1 week

1-2 years 180+ days 1 year

> 2 years NA 2 years

Caution

The current version of the model (v3.0.5) applies only 1 week of decay to any spent fuel in the first age

category (< 1 yr PWR, < 180 days BWR). For fuel whose age is toward the higher side of this interval,

this can significantly overestimate the activity available for release and thus overestimate the projected

dose. This limitation will be changed in a future version of the code.
113

25 Assembly Damaged Underwater

Purpose

Discussion

Problem

Inputs

To learn how to assess a spent fuel accident where the damaged fuel remains underwater.

See the introduction to spent fuel source terms at the beginning of this section (page 109).

You are asked to make a dose projection for a fuel handling accident at the Crystal River nuclear power

station. You are told that at 12:49 A.M., a fuel assembly that was being removed from the reactor to the

fuel pool was smashed against another assembly in the pool and that both were severely damaged. The

reactor had been shut down for 6 days. The assembly already in the pool had been there for over a year.

The fuel pool building is 20 meters high and has a filtered exhaust vent near the top. The building

ventilation rate is 10 air changes/hour.

Calculate the TEDE and thyroid CDE at 0.1 and 0.2 miles. How many total curies were released? How

many radionuclides were represented in the source term?

Fill in the following tables:

Total activity released to atmosphere curies

Dose type Distance from release

0.1 mi 0.2 mi

TEDE (rem)

Thyroid CDE (rem)

Event Type Spent Fuel

Event Location Crystal River - Unit 3
114

Leave the average reactor power and average fuel burnup at the default values

because better information was not provided.

Source Term Pool Storage - Damaged Assembly under Water

Number of fuel assemblies damaged: 1

Rationale: Although 2 assemblies were damaged, one had been recently

irradiated and the other had been out of the reactor for much longer. The source

term will be dominated by the recently removed fuel. If you want to compare the

relative source terms you can run RASCAL separately for each assembly.

Age of damaged fuel assemblies: Use the option for How long in storage and set to

6 days.

When did the damage to the fuel occur: 00:49

Release Path Release height: 20.0 m

Release point characterization: Not an isolated stack

Consider building wake effects: Yes

Start of release to atmosphere: 00:49.

Rationale: The release cannot start until the fuel has been damaged.

End of release to atmosphere: Release duration: 02:00 hh:mm

Rationale: You might think you should put in 1 hour because at a rate of

100%/hour, all the fission products will have been released. But this is not true.

The release rate is a rate, and like with radioactive decay, some always remains

within the building. Using 2 hours as the time will get essentially all the fission

products out of the building.

Filtered?: Yes

Leak rate to atmosphere: Total failure (100% per hour)

Rationale: This is tricky. Since there are 10 air changes per hour, you might

assume that you should set the percent volume to 1000% / hour. If you do this,

the code will report that the maximum allowed value is 100% / hour. A value of

1000% / hour would be correct if the fission products released from the fuel

instantaneously got into the air and were perfectly mixed. But that really takes

time. As a practical matter, roughly 100% / hour is about the fastest rate at which

the fission products can escape the building.

Meteorology Data set type: Predefined data (non site specific)

Data set: Standard Meteorology

Calculation

Options

Distance of calculation: Close-in only.
115

Results

Rationale: For non-reactor accidents there is rarely a need to calculate beyond 2

miles, and the code will complete the calculations faster.

End calculations at: Start of release plus 4 hours.

Rationale: You want enough time for all the material to be released.

The following results can be compiled from the source term summary and maximum values tables after

the completion of the calculations:

Total activity released to atmosphere 1.7E+05 curies

Dose type Distance from release

0.1 mi 0.2 mi

TEDE (rem) 2.5E-02 1.4E-02

Thyroid CDE (rem) 5.7E-03 2.1E-03
116

26 Pool Drained

Purpose

Discussion

Problem

Inputs

To learn how to model a spent fuel accident where the storage pool loses water and the fuel is uncovered.

See the introduction to spent fuel source terms at the beginning of this section (page 109).

The plant staff are calling you from San Onofre, Unit 2 because there has been an earthquake in the

vicinity. The spent fuel pool has lost much of its water due to a large crack possibly flowing into a sink

hole. Due to a malfunctioning pump, it has not been possible to provide enough water to make up for the

loss. The water dropped to the top of the fuel at 8:49 A.M., and appears likely to continue dropping.

Estimates are that the fuel will be fully uncovered by 11:00 A.M. The pool has high density racking and

contains one batch of fuel that was unloaded from the reactor only 2 weeks earlier. (A batch is defined as

one-third of a core) Another batch was unloaded about a year before that, and 8 batches have been in the

pool for longer than 2 years. The spent fuel building has been severely damaged and is in many places

directly open to the atmosphere.

Estimate TEDE and thyroid CDE at 1, 5 and 10 miles and summarize the source term. Fill in the following

tables:

Total activity released to atmosphere curies

Dose type Distance from release

1 mi 5 mi 10 mi

TEDE (rem)

Thyroid CDE (rem)

Event Type Spent Fuel

Event Location San Onofre - Unit 2
117

Source Term Pool Storage - Uncovered Fuel

Density of fuel pool racking: High

Amount of fuel in the pool: Use the Number of batches option

< 1 year: 1 batch

1 - 2 years: 1 batch

> 2 years: 8 batches

Fuel uncovered: 08:49

Pool is totally drained: Yes, at 11:00

Fuel is recovered: No

Release Path Release height: 0.0 m.

Release point characterization: Not an isolated stack

Consider building wake effects? Yes

Start of release to atmosphere: 10:49.

Rationale: The release cannot start until at least 2 hours after the fuel has been

uncovered.

End of release to atmosphere: Release duration: 0 days 02:00 hh:mm

Rationale: You might think you should put in 1 hour because at a rate of

100%/hour, all the fission products will have been released. But this is not true.

The release rate is a rate, and like with radioactive decay, some always remains

within the building. Using 2 hours as the time will get essentially all the material

out of the building.

Filtered?: No.

Rationale: Since the problem states that the building is open to the atmosphere

any filters are likely being bypassed or having very limited effectiveness.

Leak rate to atmosphere: Total failure (100% per hour)

Rationale: As a practical matter, roughly 100%/hour is about the fastest rate at

which the fission products can escape the building. This is a good value to use

for catastrophic failure of a building.

Meteorology Data set type: Predefined data (non site specific)

Data set: Standard Meteorology

Calculation

Options

Distance of calculation: Close in + to 10 miles

End calculations at: Start of release plus 6 hours
118

Results

After the run, the results can be summarized as follows:

Total activity released to atmosphere 8.6E+07 curies

Dose type Distance from release

1 mi 5 mi 10 mi

TEDE (rem) 5.2E+03 1.2E+03 4.5E+02

Thyroid CDE (rem) 3.9E+04 8.9E+03 3.5E+03

Both TEDE and thyroid PAGs are exceeded at 10 miles. The model should be run again with a calculation

radius of 25 miles. However, don’t delay making protective action recommendations waiting for these

additional model runs.
119

27 Dry Cask Rupture

Purpose

Discussion

Problem

To learn how to a spent fuel accident where a dry cask storage unit is ruptured.

See the introduction to spent fuel source terms at the beginning of this section (page 109).

The RASCAL database contains a information of a variety of dry storage casks. The user may select from

the list of cask types to set the number of assemblies or manually enter a value. Table 7 lists the cask types

defined and the number of fuel assemblies stored in each.

Table 7 Spent Fuel Dry Storage Cask Types

Cask name # fuel assemblies Cask name # fuel assemblies

CASTOR V/21 21 NAC-STC 26

CASTOR X/32S 32 NAC-UMS 24

FuelSolutions 21 NUHOMS-24P 24

Hi-Storm 100 24 NUHOMS-32P 32

Holtec Hi-Star 100 24 SNC Transtor 24

NAC-C28 S/T 28 TN-24 24

NAC-I28 S/T 28 TN-32 32

NAC-MPC 24 GTCC 24 TN-40 40

NAC-MPC 36 Yankee 36 VSC-24 24

NAC-S/T 26

In the late night hours and under cover of a heavy snowstorm, a terrorist entered the plant grounds of the

Prairie Island Nuclear Power Station. Unable to gain access to the reactor buildings, he has barricaded

himself in the dry cask storage yard. Law enforcement officials are in contact with him and believe he has

attached some explosive device to one of the casks.

The current local time is 4:15 A.M. You are asked to make an assessment of the potential consequences of

the explosive breaching of a single cask. The cask involved has been identified as a Castor V/21. This is a

vertical metal cask on a concrete pad. The experts predict that the explosion will partially rupture the cask

and estimate that roughly three-quarters of the assemblies within will be damaged by the shock. The

snowstorm has stopped and current winds are reported as light.
120

Inputs

Make your calculations and then fill in the tables below. Use an appropriate predefined meteorological

data set other than the standard one.

Total activity released to atmosphere curies

Dose type Distance from release

0.1 mi 0.2 mi

TEDE (rem)

Thyroid CDE (rem)

Event Type Spent Fuel

Event Location Prairie Island - Unit 1 (could use either unit as fuel storage area serves both and as

long as the fuel burnup value is appropriate)

Source Term Dry Storage - Cask Release

Type of cask: Known: CASTOR V/21

This sets the number of PWR assemblies in the cask to 21.

Age of damaged fuel assemblies: How long in storage: 5 years

Rationale: This is unknown at this time but the worst case would be the

minimum cooling time value of 5 years. This information would be available

from technical staff.

Type of event: Major damage with 75% fuel elements damaged

Release Path Release point characterization: Not an isolated stack

Release height: 0.0 m

Consider building wake effects? Yes

Start of release to atmosphere: 04:15

End of release to atmosphere: Release duration: 02:00 hh:mm

Rationale: We are going to assume that the explosion ruptures the cask but has

little effect on dispersing the material. Thus, a release duration of 2 hours

provides enough time for the material to leave the cask.
121

Results

Filtered?: No (not an option with dry cask storage releases)

Leak rate to atmosphere: Total failure (100% per hour)

Rationale: This will be the rate at which the material exits the ruptured cask and

enters the atmosphere. The worst case option would be total failure.

Meteorology Data set type: Predefined data (non site specific)

Data set: Winter - Night - Calm

Calculation

Options

Calculation distance: Close-in only.

Rationale: For non-reactor accidents there is rarely a need to calculate beyond 2

miles, and the code will complete the calculations sooner.

End calculations at: Start of release to atmosphere plus 4 hours.

Rationale: You want a little longer than the end of the release so that all the

material can exit the cask.

The following results are available after the completion of the calculations. The total activity released is

from the top of the source term summary.

Total activity released to atmosphere 3.4E+04 curies

Dose type Distance from release

0.1 mi 0.2 mi

TEDE (rem) 5.3E+00 2.6E+00

Thyroid CDE (rem) 4.0E+00 1.9E+00
122

Fuel Cycle / UF6/ Criticality

For fuel cycle facilities, RASCAL can calculate doses from: accidental criticalities, UF6releases, and

releases caused by fires and explosions. The following problems show how to use RASCAL to analyze

these types of accidents.

Because we want to focus on the fuel cycle accidents themselves and not meteorology, we will use the

predefined Standard Meteorology data set for all problems. This is easy to do and eliminates variability

caused by differing meteorological conditions.
123

28 Uranium Process Fire

Purpose

Discussion

To learn about the options for modeling a fire at a uranium processing facility.

Under the Event Type: Fuel Cycle / UF6 / Criticality, it is possible to model the release of uranium oxide

resulting from a fire. Five separate fire scenarios are modeled: production process (wet and dry), HEPA

filter, incinerator exhaust, waste, and milling. Each scenario may require further refinement of fire

conditions by the user. Each combination of fire type and condition has a default airborne release fraction

(ARF) and inhalation fraction (IF) as shown in Table 8. These values may be changed by the user.

Table 8 Airborne release fractions and inhalation fractions used in uranium oxide fires

Type of fire Condition ARF

(Fuel cycle)

ARF

(Other radioactive

material fires)

IF

Production

process

Dry process 0.001 0.001 1

Wet process 3×10-5 0.001 1

HEPA filter At high temperature 1×10-4 0.001 1

Failure 1 NA 1

Incinerator

exhaust

0.4 NA 1

Waste fire Solid packaged in drums 5×10-4 NA 1

Solid loosely packed 0.05 0.001 1

Combustible liquid 0.03 0.005 1

Non-combustible liquid 0.002 0.001 1

Uranium mill Drum in a fire 0.001 0.001 1

Solvent extraction 0.03 0.005 1

Reference: from Table 3.7 of NUREG-1887 taken from Airborne Release Fractions/Rates and Respirable Fractions for NonReactor Nuclear Facilities: DOE Handbook. Vol. 1, 1994

It is also possible to model uranium release from fires using the Event Type: Other Radioactive Material

Releases. The default airborne release fraction (ARF) for uranium is 0.001 based on the most commonly

encountered forms of the material. However, a table gives alternate airborne release fractions based on the

physical form of the material. For comparison of the two approaches, Table 8 also shows ARFs based on

that table. In general, the two sets of ARFs are reasonably consistent considering that they came from two

different sources and are based on different scenario descriptions and experimental data.
124

Problem

Inputs

The differences do indicate that some judgement should be used when selecting ARFs. For fuel processing

facilities, it is probably more appropriate to use the fire ARFs in the Event Type: Fuel Cycle / UF6 /

Criticality than those in the Event Type: Other Radioactive Material Releases. The ARFs used for Fuel

Cycle fires were generated specifically for uranium oxide processing. The ARFs for Other Radioactive

Materials were generated on a more generic basis.

The source term is calculated using the airborne release fraction and the user specified material at risk

(mass of uranium oxide). The mass of uranium oxide is converted to a mass of uranium by multiplying by

0.88. Then the mass of uranium is converted to an activity based on the user specified enrichment value.

The inhalation fraction is used during the dose calculations to reduce the amount of material inhaled and

contributing to the inhalation dose.

A fire occurred at 9:47 A.M. in the powder preparation area of the UO2 Building at the AREVA NP

Richland facility. The fire lasted for 20 minutes and breached the building containment. Approximately

12,000 kg of UO2/U3O8 powder (4% enriched) is located in the powder preparation area. All of the

airborne material is assumed to be released through the airlock doors.

Fill in the following table:

TEDE at 0.1 mile

Predominant dose pathway

Event Type Fuel Cycle / UF6 / Criticality

Event Location AREVA NP Richland

Source Term Fire Involving Uranium Oxide

Type of fire: Production process

Uranium enrichment level: 4%

Production process: Dry Process

Material at risk: 12,000 kg.

Airborne release fraction: 0.001 (default)

Inhalation fraction: 1.0 (default)

Rationale: It would also be reasonable to lower the ARF. Experiments involving

surface contamination on flammable material (wood) had ARFs of roughly
125

Results

0.001. When the mass of the uranium is large relative to the mass of the

flammable material, lower ARFs can be expected. For this problem an ARF of

10-4 or even 10-5 might not be unreasonable.

Release Path Release point characterization: Not an isolated stack

Release height: 0.0 m

Consider building wake effects? Yes

Rationale: We have treated this plume as though it will be entrained in the

building wake and not rise due to buoyancy which might occur with a heated

plume release from a fire. If observers from the site reported that the plume was

rising and not being entrained in the building wake, it would be reasonable to

select isolated stack and use the release height as the plume rise height estimated

by the observers. Building wake would not be used in this case.

Pathway condition: Inside building , Pathway filtered: No

Rationale: If you expected that there would be significant deposition of the

uranium oxide in the building you could decrease the available amount by

assuming that the release was filtered.

Release timings

Start of release to atmosphere: 09:47

End of release to atmosphere: Duration 0 days 01:00 hh:mm

Rationale: The release time affects only the rate at which material escapes, not

the magnitude. Increasing the release time will leave the release magnitude

unchanged, but will decrease the release rate. Remember not to end the

calculations before the release has been completed.

Meteorology Data set type: Predefined data (non site specific)

Data set: Standard Meteorology

Calculation

Options

Distance of Calculation: Close-in only.

End calculations at: Start of release plus 1 hour.

Rationale: We want to make sure the calculations run for the entire duration of

the release. The close-in plume model transports material instantaneously so we

don’t need to add extra time for transport.

TEDE at 0.1 mile 6.5E-02 rem

Predominant dose pathway inhalation CEDE
126

29 Explosion Involving Uranium

Oxide

Purpose

Discussion

To learn about the options for modeling an explosion involving uranium oxide.

RASCAL can model the release of uranium oxide from an explosion. First the user must characterize the

explosion as one of the following:

– detonation; a shattering such as from a high explosive

– deflagration; enveloping with no shattering such as from a propane explosion

– venting; a result of over-pressurization such as a container rupture from high internal pressure

Next, the form of the uranium oxide material must be specified as liquid, solid, powder, or surface

contamination. Each combination of type and form has a default airborne release fraction (ARF) and

inhalation fraction (IF) as shown in Table 9. These values may be changed by the user.

Table 9 Airborne release fractions and inhalation fractions for explosions involving U oxide

Explosion characteristics Material form ARF IF

Detonation (high explosive) Liquid 1 1

Solid 1 0.2

Powder 1 0.2

Surface

contamination

0.001 1

Deflagration (fire) Liquid 1×10-6 1

Solid 0 0

Powder 0.005 0.3

Surface

contamination

0.001 1

Venting (sudden pressure change) Liquid 0.002 1

Solid 0 0

Powder 0.1 0.7

Surface

contamination

0.001 1

Reference: from Table 3.8 of NUREG-1887, corrected and taken from Airborne Release Fractions/Rates and Respirable

Fractions for Non-Reactor Nuclear Facilities: DOE Handbook. Vol. 1, 1994
127

Problem

Inputs

The source term is calculated using the airborne release fraction and the user specified mass of material at

risk (mass of uranium oxide). The mass of uranium oxide is converted to a mass of uranium by

multiplying by 0.88. Then the mass of uranium is converted to an activity based on the user specified

enrichment value. The inhalation fraction is used in the calculation of inhalation dose.

You are asked to respond to an accident in the Research and Test Reactor Fuel Element area of Bay 15 at

BWX Technologies. At 3:35 P.M. local time, a boxline containing 3.6 kg of U3O8 explodes due to a loss of

the inert atmosphere and a combination of aluminum and uranium which ignited. The explosion has

destroyed the boxline and breached the roof of the building (estimated to be 12 meters above the ground

level). The enrichment of the material is 93%.

How many total curies of activity were released to the atmosphere? Estimate the possible doses at the site

boundary (540 m away) and to the nearest resident (1100 m away).

Event Type Fuel Cycle / UF6 / Criticality

Event Location BWX Technologies

Source Term Explosion Involving Uranium Oxide

Characterize the explosion: Deflagration

Rationale: This is the appropriate explosion type for the ignition of aluminum

and uranium.

Material form: Powder

Material at risk: 3.6 kg

ARF and IF: 5.00E-03 and 3.00E-01

Rationale: Leave at defaults since have no reason to change.

Uranium enrichment: 93%

Release Path Pathway description: Breached roof

Release point characterization: Not an isolated stack

Release height: 12 m

Consider building wake effects: Yes

Pathway condition: Inside building, Pathway filtered: No
128

Results

Rationale: The explosion occurred inside the building but since the roof has been

breached assume that the release will not be filtered or sprayed. A 50% reduction

will be applied due to the retention of material within the structure. Thus, you

cannot just set the release as being outside to get the same effect.

Release timings:

Start of release to atmosphere: 15:35

End of release to atmosphere: 15:50

Rationale: Start was at 15:35. Since it was an explosion, assume that the

energetic release got everything out in 15 minutes. Either set the end time to

15:50 or the duration to 00:15.

Meteorology Data set type: Predefined data (non site specific)

Data set: Standard Meteorology

Calculation

Options

Select Close-in only. Then, select to use User defined close-in distances. Click the

Set Close Distances button. Then, edit the settings to change from units of miles to

kilometers. Also, change two of the default distances to match the two distances of

specific interest. For example, change 0.5 to 0.54 and 1.0 to 1.1 km.

End calculations at: Start of release to atmosphere + 1 hour

The following results are available after the completion of the calculations:

Total source term (curies) 8.7E-04

Dose type Distance from release

0.54 km 1.1 km

TEDE (rem) 2.4E-04 1.3E-04

You will note that the doses are very small - so small that some are not shown on the Maximum Dose

Values table. However, by selecting Detailed Results and then selecting the option of a Numeric Table

for the Close-in Calculations these lower doses can be seen. Doses are small because the size of the

release was very small. There was relatively little uranium involved and uranium has a low specific

activity. Also, since uranium is not volatile, relatively little becomes airborne (recall the airborne release

fraction was 0.005).
129

30 UF6 Cylinder Rupture

Purpose

Discussion

To learn about the result types available from the UF6 plume model and how to model a release from a

UF6 cylinder.

RASCAL can model the release of UF6from a cylinder (or other container). The user must specify the

amount of UF6 contained or the number and type of cylinders. The user must also specify a UF6release

rate and the fraction ultimately released. The exception to this is for liquid UF6in a cylinder with a

damaged valve. In this case, RASCAL estimates the fraction released based upon the position of the valve.

RASCAL uses a special model when treating the transport and diffusion of a UF6release. The model

considers both the buoyancy of the plume due to the heat generated by it’s reaction with water vapor and

the slumping of the plume caused by its high density. The model is described in detail in Chapter 5 of the

RASCAL technical manual.

For UF6releases, only one meteorological observation can be entered. In other words, the weather cannot

change during the release. This is only true for UF6releases and not for any other types of releases.

The model calculates 7 different types of results for UF6releases. The types are described below:

HF Concentration - 1-hour equivalent

The damage done by exposure to HF is not strictly proportional to its concentration times the time of

exposure as it is for many other toxic gases. Instead, exposure to high concentrations of HF for short

times has more effect than the same exposure spread out over a longer time. The HF concentration

1-hour equivalent provides a means of comparing the health effects of exposures by using a common

time of exposure. (Reference: S. McGuire, NUREG-1391, Chemical Toxicity of Uranium

Hexafluoride Compared to Acute Effects of Radiation, 1991). The 1-hour equivalent concentration

C1 hr is a measure of the degree of acute lung edema that may result and cause death. It is calculated in

terms of the concentration C during the time of exposure t in hours:

C1 hr = C x t 0.5

The implications of this relationship are that a doubling of concentration would require 1/4 the

exposure time to maintain the same toxic load level. Or, to double the exposure duration would

require the concentration to be about 71% of the original level to maintain effect.

Table 10 lists the health effects and ERPG levels for HF 1-hour equivalent concentrations.
130

Table 10 Health effects due to HF exposure

Health effect due to HF exposure HF concentration -

1 hr equivalent

50% fatality without emergency medical treatment 1070 mg/m3(1264 ppm)

ERPG-3: American Industrial Hygiene Association Emergency

Response Planning Guideline -3: The maximum airborne

concentration below which it is believed that nearly all individuals

could be exposed for up to one hour without experiencing or

developing life-threatening health effects.

41 mg/m3(48 ppm)

ERPG-2: The maximum airborne concentration below which it is

believed that nearly all individuals could be exposed for up to

one hour without experiencing or developing irreversible or other

serious health effects or symptoms which could impair an

individual’s ability to take protective action.

16.4 mg/m3(19 ppm)

ERPG-1: The maximum airborne concentration below which it is

believed that nearly all individuals could be exposed for up to

one hour without experiencing other than mild, transient adverse

health effects or without perceiving a clearly defined

objectionable odor.

4.1 mg/m3(4.8 ppm)

HF Concentration - Average

The HF concentration averaged over the duration of the exposure.

HF Deposition

The HF concentration (g/m2) deposited on the ground. This result provides a measure of the potential

hazard from contact with exposed surfaces. It may be used to reconstruct the path of the plume and the

HF concentration in the plume. A dry deposition velocity of 0.3 cm/s is used in the calculations.

Uranium Exposure

The uranium exposure (g-s/m3) equal to concentration times the time of exposure.

Uranium Intake

The uranium intake (mg) by inhalation. Uranium intake provides the best measure of potential acute

kidney damage due to heavy metal poisoning as shown in Table 11. There are no known long term

chemical injuries from uranium intakes that are sub-lethal.
131

Problem

Table 11 Health effects due to uranium intake by inhalation

U intake by

inhalation

Health effect

below 5 mg none

8 mg threshold for clinically observable transient

chemical changes in urine indicating renal distress

50 mg threshold for permanent renal damage (speculative

- never observed in humans)

230 mg 50% fatality without medical treatment

(From: S. McGuire, NUREG-1391).

Uranium CEDE

The committed effective dose equivalent (CEDE) from inhaled uranium (rem) provides the radiation

dose to people in the plume. It is a measure of the long-term risk due to radiation exposure. There is

essentially no external radiation exposure from airborne uranium so the CEDE will also be the TEDE.

The dose conversion factor is 2.73 rem/μCi intake. This value is for soluble uranium.

Uranium Deposition

The uranium concentration (g/m2) deposited on the ground. This result provides a measure of the

potential hazard from contact with exposed surfaces and from resuspension of uranium. It may be

used to reconstruct the path of the plume and the uranium concentration in the plume. A dry

deposition velocity of 0.3 cm/s is used in the calculations.

At 9:30 A.M. workers at AREVA NP Richland were moving a Model 30 cylinder full of hot, liquid, 4%

enriched UF6to an outdoor storage area. The cylinder was dropped resulting in the rupture of the cylinder.

Evaluate the impact of this release on a person standing on the plume centerline, at a distance of 0.2 miles.

Using the results shown in the maximum dose values table and Tables 10 and 11, fill in the table below:

Result type Result at 0.2 miles

Value and units Impact

HF conc 1 hr

equivalent

Uranium intake

Radiation dose

(U CEDE)
132

Inputs

Event Type Fuel Cycle / UF6 / Criticality

Event Location AREVA NP Richland

Source Term UF6 Release From Cylinder

Amount of UF6involved: Since the cylinder type is known, leave the option selected

for Type and number of cylinders. Then, set the number of 21⁄2 ton cylinders to 1.

Form of UF6: Liquid

Cylinder damage type: Cylinder rupture

Release fraction: 0.65

Release rate: 32 kg/s

Rationale: Given no other information, leave the release fraction and release

rates as defaults.

Start of release: 09:30

Uranium enrichment level : 4%

Release Path Effective release height: Fixed at ground level.

Rationale: There is no option to enter an elevated release as the UF6 model

handles only releases at ground level.

Consider building wake effects: Yes

Release pathway to atmosphere: Direct

Rationale: The problem description says the cylinder is outside so the pathway

should be direct to the atmosphere.

No other information is needed to define the release pathway.

Meteorology Data set type: Predefined data (non site specific)

Data set: Standard Meteorology

Calculation

Options

For setting the distance of calculation, notice that Close-in only is selected and other

choices are unavailable. For releases of UF6, RASCAL automatically switches to the

UF6 plume model. The user may set specific distances at which doses are calculated.

End the calculations at: Start of the release to atmosphere + 1 hour
133

Results

The following values are available in the Maximum Dose Values table:

Result type Result at 0.2 miles

Value and units Impact

HF conc 1 hr equi. 4.0 ppm None. Below level where symptoms are

observed

Uranium intake 2.0 mg None. Below threshold for any observable

transient effect

Radiation dose

(U CEDE)

0.013 rem None. Below EPA PAGs and public dose

limit
134

31 UF6 Cascade Release

Purpose

Discussion

Problem

To learn how to model an accident in a cascade at one of the gaseous diffusion plant buildings.

The UF6 cascade release accident type is available only for the Portsmouth and Paducah gaseous diffusion

plants. In addition, the cascade release source term option is available only for certain buildings of those

facilities. Tables 12 and 13 list the building names and information about the default inventories and

release rates.

Table 12 Paducah GDP buildings and default inventory and release rates

Building name Cells per unit Number of units Avg cell

inventory (lbs)

Release rate

(lbs/sec)

C-331 10 4 4,400 130

C-333 10 6 9,500 130

C-335 10 4 4,600 130

C-337 10 6 8,400 130

C-310 10 1 150 130

Table 13 Portsmouth GDP buildings and default inventory and release rates

Building name Cells per unit Number of units Avg cell

inventory (lbs)

Release rate

(lbs/sec)

X-326 20 2.5 1,000 130

X-330 10 11 5,000 130

X-333 10 8 5,000 130

You are called upon to make a dose assessment for an accident at the U.S. Enrichment Paducah gaseous

diffusion plant. At 12:45 P.M. a block valve control failure resulted in a pressure increase which ruptured

the primary containment of a cell. The problem occurred in the C-333 process building and operators have

been unable to isolate the cell. The enrichment level is 5%.

It is a windy, summer afternoon with the process building operating in its summer flow configuration.

What are the potential radiation and chemical doses to persons 2 miles downwind of the building?
135

Inputs

Fill in the following table with values from the model and impacts taken from Tables 10 and 11.

Result type Results at 2 miles

Numerical value Impact

Radiation dose

(U CEDE)

Uranium intake

HF conc 1 hr equi.

Event Type Fuel Cycle / UF6 / Criticality

Event Location U.S. Enrichment - Paducah

Source Term Building: C-333 Cascade / Process

UF6 Release From Cascade System

Release described by: 1 cell with 9,500 pounds per cell

Rationale: We are told that a single cell containment failed. Since we do not

have information on the cell inventory, accept the default value.

Start of release: 12:45

Release rate to building: 130 pounds per second

Rationale: Since we have no additional information, accept the default value for

the release rate.

Release fraction: 1.0

Rationale: The worst case is for all the material to move from the cascade cell

into the building so leave the default value unchanged.

UF6 Enrichment level: 5%

Release Path Cascade building flow configuration: Summer

Meteorology Data set type: Predefined data (non site specific)

Data set: Summer - Afternoon - Windy

Rationale: Problem states a windy, summer afternoon and no onsite weather data

is available at this time.
136

Results

Calculation

Options

There is no option for calculation distance with UF6releases. The UF6 plume model

is always selected. You may however adjust the distances of the 8 receptor rings if

needed. In this problem, leave the distances as set.

End of calculations: Start of the release to atmosphere + 2 hours

Result type Result at 2 miles

Numerical value Impact

Radiation dose

(U CEDE)

2.3E-03 rem None. Below EPA PAGs and public dose

limit.

Uranium intake 0.28 mg None. Below soluble uranium intake limit of

10 mg in 10CFR Part 20

HF conc 1 hr equi. 0.46 ppm None. Below ERPG-1

The distance at which 100% of the UF6 has reacted with the moisture in the atmosphere is 96.6 meters.

(This is shown on the Maximum Dose Values tab of the main screen).

Essentially, the radiation dose (U CEDE) is a TEDE since the cloudshine and groundshine doses are

effectively zero. Thus, the U CEDE can be compared to the EPA TEDE PAG (see page 39).
137

32 Criticality

Purpose

Discussion

To learn how to use RASCAL to estimate consequences from a criticality accident.

To estimate doses from a criticality accident, RASCAL first establishes the number of fissions that will

occur. The user may either enter the number of fissions directly or may select the type of system being

modeled, allowing RASCAL to determine the fission yield. The systems available and their assumed

fission yields are shown in Table 14. The total yield assumes multiple bursts over 8 hours.

Table 14 Fission yields used in criticality calculations

System modeled in the

scenario

Initial burst yield

(fissions)

Total yield

over 8 hours

(fissions)

Solution <100 gal 1×1017 3×1018

Solution >100 gal 1×1018 3×1019

Liquid/powder 3×1020 3×1020

Liquid/metal pieces 3×1018 1×1019

Solid uranium 3×1019 3×1019

Solid plutonium 1×1018 1×1018

Large storage arrays below

prompt critical

Steady state 1×1019

Large storage arrays above

prompt critical

3×1022 3×1022

Reference: from Table 3.9 of NUREG-1887 which were taken from NUREG/CR-6410

From the fission yield, RASCAL determines the fission product release to the atmosphere, the

atmospheric dispersion of those fission products, and the doses from the plume. RASCAL also calculates

the direct gamma and neutron shine dose. The user can reduce the amount of material released to the

atmosphere by specifying release fractions for noble gases, iodines, and other radionuclides. Further

reductions can be specified by having a filtered release pathway. The user can also specify shielding to

reduce the direct shine dose.
138

Problem

Inputs

At 1:45 P.M., criticality alarms sound at the AREVA NP Richland facility. The operators determine that a

criticality excursion is occurring in a 125 gallon tank holding a solution of enriched UO2 and water.

Subsequently, radiation monitors detect a second burst indicating that the criticality is on-going. The room

air is vented through an 18 meter high exhaust stack on the building roof.

1. How many total fissions will occur?

2. Fill in the following table:

Dose (rem)

Distance

150 m 300 m 3,000 m

TEDE from plume

TEDE from criticality shine

Total TEDE

3. To what distances are the EPA PAGs exceeded?

4. What early health effects would we expect to a person standing 50 m from the criticality when it

occurred?

Event Type Fuel Cycle / UF6 / Criticality

Event Location AREVA NP Richland

Source Term Criticality Accident

Start of criticality: 13:45

Criticality consists of: Multiple bursts

Rationale: This an appropriate choice since measurements suggest that the

criticality is continuing.

Define fission yield by: Type of system with Solutions over 100 gal

Airborne release fractions: 1.0, 0.25, and 0.0005 (defaults)

Rationale: There is no other information that would cause us to change the

default settings.

Shielding thickness: 0.0 for steel, concrete, and water
139

Rationale: There is no information to cause a change from the defaults. You

could assume no shielding which would be the worst case.

Release Path Pathway description: Room air vented through exhaust stack

Release point characterization: Not an isolated stack

Rationale: Even though the description calls for the release to be through an

exhaust stack, this is not an isolated stack. For RASCAL and emergency

response, a stack should be considered “isolated” if it is more than 2 times the

height of a building that is within a distance of 5 stack heights. Short stacks on

roofs should not be treated as isolated.

Release height: 18 m

Consider building wake effects: Yes

Release timings:

Start of release to atmosphere: 13:45

End of release to atmosphere: Duration 0 days 10:00 hh:mm

Rationale: The start of the release would be the start of the criticality. For the

duration, the worst case would be if the criticality continues for the full 8 hours.

The additional 2 hours will allow most fission products to escape the building.

Stopping the release early effectively stops the criticality since the material can

no longer be released.

Reduction factors: 1.0 for all 3 groups

Rationale: If you thought there would be some plate-out and deposition within

the building and exhaust system, you could assume 50% reduction of non-noble

gases during passage through the building and the exhaust system.

Leak rate: 100%/h (ordinary ventilation)

Rationale: Pick the worst case since there is no information about the flow rates

of the exhaust fan.

Meteorology Data set type: Predefined data (non site specific)

Data set: Standard Meteorology

Calculation

Options

You are asked for doses only to 3,000 meters (~2 miles). Select Close-in only.

To get the doses calculated at 150, 300, and 3,000 meters exactly, select the option

to use User defined close-in distances. Then select the Set Close Distances

button. In the section to the left labeled “For non-UF6 releases”, select the

Kilometer option and then make the following changes to distances:

Change distance 1 to: 0.15

Change distance 8 to: 3.0
140

Results

End calculations at: Start of release plus 10 hours.

Rationale: We want to make sure the calculations run for the entire duration of

the release. We added 2 hours to allow material to escape the building. That

would also allow time for most of the material to reach 2 miles.

1. From the Criticality shine dose option on the Maximum Dose Values tab, you can see that there

were 3.0E+19 fissions during the release period.

2 The close-in dose table of the Maximum Dose Values section will show the TEDE from the passing

plume. The table will include the distances set earlier before the calculations. Select the option to see

the criticality shine doses. Now, to get the distances in meters requires a shift to the metric units. This

however, also changes the dose units to Sv. Simply convert the Sv to rem by multiplying by 100 (1 Sv

= 100 rem).

As you can see from the table you filled out, the dose is dominated by the direct neutron shine dose.

Dose from the exposure to the plume is negligible by comparison. RASCAL does not provide shine

doses beyond 300 meters. To obtain the dose at 3,000 meters, the inverse square law can be used

(divide 300 m dose by 102). This approximation neglects attenuation in air and will therefore be an

overestimate.

Dose (rem)

Distance

150 m 300 m 3,000 m

TEDE from plume 0.35 0.15 0.019

TEDE from criticality shine 140 34 0.34

Total TEDE 140 34 0.36

3. If you consider the total dose delivered, the 1-rem PAG is exceeded to roughly 2,000 meters.

However, the PAG refers to projected dose that is potentially avoidable if protective actions are taken.

Once the first burst has occurred, its shine dose is no longer part of the projected dose. Thus, it could

legitimately be subtracted from the projected dose. But doing that would not change the distance

significantly.

4. At a distance of 50 meters, the shine TEDE from all the bursts over 8 hours is 1,200 rem. However, it

is reasonable to assume that after the initial burst, the individual would leave the area. Return to the

source term screen to redefine the criticality accident to consist of a single burst instead of the

multiple bursts. In that case, the shine dose from the first burst would be 37 rem neutron and 3.7 rem

gamma. No early health effects would be expected from that dose.
141

Other Radioactive Material Releases

RASCAL can calculate doses from the release of radioactive materials from other types of facilities.

Source terms can be produced for radioactive materials involved in fires or by measured or estimated

radionuclide release rates or release concentrations.

Five licensed sites are included in the RASCAL facilities database. In addition, the user can describe a site

not in the database.

All radioactive material licensees have much smaller radioactive material inventories than reactors. Thus,

the size of potential releases is vastly less. In addition, reactor accidents generally take a long time to

progress to a release. This is not always true at materials facilities. Thus, the RASCAL operator may be

trying to estimate what did happen rather than what will happen.
142

33 Radioactive Material in a Fire

Purpose

Discussion

To learn how to use RASCAL to model the consequences of radioactive material dispersed in a fire.

The Sources and Material in a Fire source term option is used to model the consequences of radioactive

material dispersed as a result of a fire. The user must specify the amount of material at risk and for each

radionuclide set an airborne release fraction and inhalation fraction. A default release fraction (see Table

15) is set by the code for each nuclide selected. These release fractions assume the material is on a

completely combustible surface. For example, they would be appropriate for materials on a wooden

laboratory bench. They would overestimate the airborne release fraction for material sitting on concrete or

steel.

Table 15 Fire activity release fractions by element (based on the likely form of the compound)

Element

Activity

Release

Fraction

Element

Activity

Release

Fraction

Element

Activity

Release

Fraction

Element

Activity

Release

Fraction

H(gas) 0.5 Se 0.01 I 0.5 W 0.01

C 0.01 Kr 1.0 Xe 1.0 Ir 0.001

Na 0.01 Rb 0.01 Cs 0.01 Au 0.01

P 0.5 Sr 0.01 Ba 0.01 Hg 0.01

S 0.5 Y 0.01 La 0.01 Tl 0.01

Cl 0.5 Zr 0.01 Ce 0.01 Pb 0.01

K 0.01 Nb 0.01 Pr 0.01 Bi 0.01

Ca 0.01 Mo 0.01 Pm 0.01 Po 0.01

Sc 0.01 Tc 0.01 Sm 0.01 Ra 0.001

Ti 0.01 Ru 0.1 Eu 0.01 Ac 0.001

V 0.01 Rh 0.01 Gd 0.01 Th 0.001

Cr 0.01 Ag 0.01 Tb 0.01 Pa 0.001

Mn 0.01 Cd 0.01 Ho 0.01 U 0.001

Fe 0.01 In 0.01 Tm 0.01 Np 0.001

Co 0.001 Sn 0.01 Yb 0.01 Pu 0.001

Zn 0.01 Sb 0.01 Hf 0.01 Am 0.001

Ge 0.01 Te 0.01 Ta 0.001

Reference: NUREG-1140
143

Problem

Guidance is provided in Table 16 for resetting the airborne release fraction if the element is in some other

form.

Table 16 Fire activity release fractions by form of compound

Form of compound Activity

release

fraction

Noble gas 1.0

Very mobile form 1.0

Volatile or combustible compound 0.5

Carbon 0.01

Nonvolatile compound / dispersible 0.01

Nonvolatile compound / less dispersible 0.001

U and Pu metal 0.001

Nonvolatile in a flammable liquid 0.005

Nonvolatile in a non-flammable liquid 0.001

Nonvolatile solid 0.0001

Reference: NUREG-1140

The release pathway settings control only the start and stop of the release to the atmosphere. It is assumed

that all the material will be released from the facility. There are no provisions with this source term option

for the application of sprays or filters.

You are tasked with estimating the doses resulting from a fire-induced release from a laboratory at the

E.R. Squibb radiopharmaceutical facility. At 8:00 A.M. this morning, an electrical short apparently ignited

some stored materials in the building and the fire has spread. It is reported that the laboratory may contain

as much as 100 curies of I-131.

What is the source term? That is, what is the total activity of I-131 released to the atmosphere?

Estimate doses to persons within a 1 mile radius of the fire and then fill in the following table:

Dose type Distance from release (miles)

0.1 1.0

TEDE (rem)

Thyroid CDE (rem)
144

Inputs

Event Type Other Radioactive Materials Release

Event Location E.R. Squibb

Source Term Sources and Material in a Fire

Fire location: Laboratory

Activity units for material at risk: Ci

U enrichment level: any value is OK

Rationale: The uranium enrichment value is used only if enriched uranium is

added to the list of material at risk.

List of material at risk in the fire: I-131 and 100.0 Ci

Rationale: When the I-131 is added, the default values for airborne release

fraction and inhalation fraction are entered automatically. These could be

changed if you had additional information to support different values. For now,

leave the ARF and IF for iodine (0.5 and 1.0) unchanged. Later credit could be

given for other reductions such as fire suppression sprays or hold up in the

structure.

Release Path Release point characterization: Not an isolated stack

Release height: 0.0 m

Consider building wake effects: Yes

Rationale: We have treated this plume as though it will be entrained in the

building wake and not rise due to buoyancy which might occur with a heated

plume release from a fire. If observers from the site reported that the plume was

rising and not being entrained in the building wake, it would be reasonable to

select isolated stack and use the release height as the plume rise height estimated

by the observers. Building wake would not be used in this case.

Release timings:

Start of release to atmosphere: 08:00

End of release to atmosphere: Release duration option and 01:00

Rationale: We don’t know how long the fire burned. For simplicity, until better

information is available, assume the fire burns for one hour.

Meteorology Data set type: Predefined data (non site specific)

Data set: Standard Meteorology
145

Results

Calculation

Options

Distance of calculation: Close-in only

End the calculations at: Start of release to atmosphere + 1 hour

Rationale: Because we are using only the close-in model, there is no need to add

time for plume transport. The close-in model transports the plume

instantaneously.

The reported source term is 50 Ci of I-131. That is what would be expected given the release fraction of

0.50.

The following doses are projected:

Dose type Distance from release (miles)

0.1 1.0

TEDE (rem) 7.0E-02 5.6E-03

Thyroid CDE (rem) 2.1E+00 1.6E-01

The thyroid dose at a tenth of a mile is less than 50% of the PAG of 5 rem. Persons closer may receive a

dose which exceeds the PAG. However, to receive this dose the plume could not rise due to buoyancy and

an individual would have to remain on the plume centerline (in the heaviest smoke) for the duration of the

release. It is more likely that people would move out of heavy smoke.
146

34 Transportation Accident

Purpose

Discussion

Problem

Inputs

To learn how to do an assessment for an accident location not in the RASCAL database.

A unique feature of a transportation accident is that its location will not be in the RASCAL database.

Thus, the RASCAL operator must enter a new site. This will also be true of accidents at smaller licensed

facilities which are not in the RASCAL database. Another unique feature is that information from the site

is likely to come from emergency responders with only limited knowledge of radioactive materials.

Most transportation accident scenarios will use the Other Radioactive Material Releases event type.

However, for spent fuel transportation accidents, select the Spent Fuel event type instead.

At 2:00 A.M. a tractor trailer truck jack-knifed in central Pennsylvania near the intersection of I-80 and

I-180 when the driver lost control on the icy road. The truck manifest says it was carrying 150,000 Ci of

tritium gas and was bound for the Safety Light facility in Bloomsburg, PA. State highway patrol reports

that the trailer slid at high speed into a bridge support and split open.

Make a preliminary assessment of the risk to persons in the immediate vicinity of the crash. What doses

may the first responders have received? What doses might nearby residents have received?

Dose type Distance from release (miles)

0.1 0.2 0.5 1.0

TEDE (rem)

Thyroid CDE (rem)

As you probably understand, RASCAL results will play only a small part in answering those questions.

Many other factors must be considered, some technical and some political. Nevertheless, RASCAL results

can still be valuable.

Event Type Other Radioactive Material Release
147

Event Location Select the option Describe a Material Site not in the Database and then fill in the

known information about the location.

The exact location may or may not be important depending on how you will handle

the meteorology. You can use “generic” weather (as will be described in the

Meteorology section) or you may want the best weather data available. Most likely

you will make the first RASCAL run with appropriate “generic” weather and then

switch to obtaining actual observations as time permits and they are available.

Initially, people will want your RASCAL results as soon as possible. Then, when

they have your first results, they will start to ask how accurate the results are. At this

point, generic weather is unlikely to be acceptable.

A good way to locate nearby weather stations is by knowing the latitude and

longitude of the release point. At the NRC, this information should be readily

available from a GIS Mapping Operator on the response team. Alternatively,

identifying close cities will help.

For this problem, assume that the GIS operator has given you the following site

information:

latitude = 41.0495o N

longitude = 76.8400o W

elevation = 153 meters

time zone = Eastern

Enter the above information to describe the physical location of the release. Note

that you will need to enter the longitude as a negative number since you cannot

specify ‘west’.

Name: Truck accident I-80 and I-180

City, county, state: Consulting a road map you see that the town of Milton is close

by. Enter the town and state names.

Source Term Isotopic Release Rates

In order to know how to handle the source term you will have to get a lot of

information from other people. Communicators in contact with response personnel at

the site will be obtaining information on the extent of the damage to the truck and its

contents. Transportation and radioactive material experts will be determining the

likely form of the material and how much might escape. Let us assume that they tell

you that they estimate that 10% of the containers may have ruptured and that most of

their contents are likely to leak out within an hour or two and would quickly

volatilize and become airborne. From this information we can estimate a release

quantity and release time. This means we can select Isotopic Release Rates as the

source term method.

Sample rate units: Ci/min

Rationale: These units are used for convenience to make it easy to

characterize the release.
148

Period start: 02:00

Rationale: We were told the accident happened at 2 a.m.

Period stop: 02:10

Rationale: Assume it took 10 minutes for all the gas to escape.

Nuclide: H-3 and the release rate is 1500.

Rationale: That gets all 15,000 Ci (10% of the total inventory) out in the 10

minutes.

Release Path Direct to atmosphere

Rationale: The accident occurred outside with no holdup or reduction by other

structures. The isotopic source term type being used assumes that the measured

release rates are the rate the activity enters the atmosphere.

Release height: 0.0 m

Consider building wake effects: Yes

Start of release to atmosphere: 02:00

End of release to atmosphere: Release duration, 0 days 00:10 hh:mm

Meteorology Predefined Data (Non Site-Specific) – Winter - Night - Calm

Rationale: Not much is known. However, it is the middle of the night and the

roads are icy so winter, night calm seems likely.

Calculation

Options

Distance of calculation: Close-in only.

End calculations: Start of release to atmosphere + 1 hour
149

Results

The source term summary confirms that all 15,000 Ci of tritium were released.

The following doses are projected:

Dose type Distance from release (miles)

0.1 0.2 0.5 1.0

TEDE (rem) 3.9E-02 1.9E-02 7.6E-03 4.6E-03

Thyroid CDE (rem) 3.9E-02 1.9E-02 7.6E-03 4.6E-03

The TEDE and thyroid CDE values are well below the EPA PAGs even at 1/10 of a mile from the release

point.

It seems curious that the TEDE and Thyroid CDE values are identical. Use the Nuclide Data Viewer to

check the dose factors.

You will see that the dose factors for Inhalation CEDE and Thyroid are identical for H-3 (tritium). Tritium

is unique in that it distributes uniformly through the body and all tissues receive the same dose. Also,

tritium has no gamma, i.e. no cloud or groundshine dose, and thus the CEDE dose factor is the same as the

thyroid dose factor.

The TEDE is the sum of the external dose and the inhalation CEDE. In this case, the external dose is zero.

The inhalation CDE is the sum of the CDE for each organ times a weighting factor for each organ. The

sum of the weighting factors is 1. And, since the tritium is evenly distributed all organs have the same

CDE. Thus, the TEDE and thyroid CDE are the same.
150

Meteorology

This section presents a series of problems to provide more practice with the meteorological data processor

and to illustrate how various meteorological conditions can affect resultant doses.

To simplify things, the following source term and release pathway will be used for all the problems:

Event Type Nuclear Power Plant

Event Location James A. Fitzpatrick

Source Term Time Core is Uncovered

Reactor shutdown: 03:30

Core uncovered: 06:00

Core recovered: No

Release Path Through the dry well wall

Not an isolated stack

Release height: 0.0 meters

Consider building wake effects: Yes

Release to containment: 06:00

Release events: all at 06:00

Sprays off

Filters off

Leak rate - 5% / d
151

35 Precipitation

Purpose

Discussion

To understand how to deal with precipitation.

Precipitation has a significant impact on projected dose. Precipitation washes particulates from the plume

causing higher groundshine doses where the plume first encounters the precipitation. As the plume travels,

depletion of the plume caused by precipitation will lower plume concentrations downwind. Thus, at

greater distances, precipitation will cause lower cloudshine, groundshine, and inhalation doses.

RASCAL understands only seven precipitation types: none and 3 types each of liquid and frozen

precipitation. The two classes are called rain and snow for simplicity. The precipitation in each class may

be light, moderate, or heavy. The National Weather Service reports precipitation rates, but the format is

not always uniform across the country. Rain includes drizzle, freezing rain, and freezing drizzle. Snow

includes snow grains, snow pellets, ice pellets, ice crystals, and hail.

Precipitation Intensity

Precipitation intensity may be used if available. Some observations will report the rainfall rate. Forecasts

normally include the predicted amount over 6 hour periods. Divide by 6 to get the hourly rate. Table 17

shows the appropriate conversion from rainfall rate to RASCAL precipitation class.

Table 17 Converting rainfall intensity to RASCAL precipitation class

Rainfall rate (intensity) Equivalent RASCAL precipitation class

< 0.04 in/h ( < 1 mm/h ) Light rain

0.04 in/h - 0.2 in/h ( 1 - 5 mm/h ) Moderate rain

> 0.2 in/h ( > 5 mm/h) Heavy rain

Doppler Radar

Doppler radar (NEXRAD) products display echo intensities in units of dBZ. These values correlate with

precipitation type and intensity. However, the conversion varies by the area of the country and the type of

precipitation that is occurring. Consult with a meteorologist if you wish to try and use these types of

products as input to RASCAL.

Probability of precipitation

The probability of precipitation (PoP or POP) is described as the probability that a measurable amount of

liquid precipitation (or the water equivalent of frozen precipitation) will occur. Measurable precipitation is

defined as greater than 0.2 mm or 0.01 inch. The PoPs do not necessarily indicate precipitation intensity.
152

Problem

Forecasters often use the following worded qualifiers to express uncertainty or to qualify the area.

PoP percent Expression of uncertainty Equivalent areal qualifiers

10 percent --- isolated or few

20 percent slight chance widely scattered

30 - 50 percent chance scattered

60 - 70 percent likely numerous

80 - 100 percent definite (none used)

The following is general guidance on using the PoP information in making RASCAL runs.

Probability of Precipitation (POP) What to do in RASCAL

Slight chance of less Set the precipitation class to “No Precip” and don’t worry about it.

Chance or likely Create two meteorological data sets, one without precipitation

and the other with precipitation. Run the RASCAL scenario with

both data sets and compare the doses. It is not appropriate to

average the doses from the two runs. Either precipitation will

occur or it won’t but you will have considered both cases.

Definite Enter the predicted precipitation

If needed, enter the initial conditions described on page 150 for source term and release path.

A. Create a meteorological data set with the following conditions:

Time Wind direction

(deg)

Wind speed

(mph)

Stability

class

Precipitation Air Temp

(deg F)

0600 210 6 B none 50

Process the data and save with the new name: FITZ No Rain

Then, run the calculations using the following settings:

- Distance of calculation: Close-in + out to 10 miles

- End calculations at: Start of release to atmosphere plus: 6 hours

Record the cloudshine and 4-day groundshine doses at 1, 5, and 10 miles in the tables provided.
153

Results

Precipitation

Cloudshine (rem) at distance of:

1 mi 5 mi 10 mi

No rain

Rain

Precipitation

4-day groundshine (rem) at distance of:

1 mi 5 mi 10 mi

No rain

Rain

B. Now, lets assume that the 06:00 observation included rain. Edit the meteorological data set to change

the precipitation type to Rain. Reprocess the data and save the data set under a new name: FITZ Rain.

Recalculate doses and again record the cloudshine and 4-day groundshine doses in the tables.

A comparison of the 2 shine doses at the selected distances:

Precipitation

Cloudshine dose (rem) at distance of:

1 mi 5 mi 10 mi

No rain 8.8E-01 8.4E-02 2.8E-02

Rain 6.9E-01 4.0E-02 1.0E-02

The cloudshine doses are higher at all distances for the “no rain” case. Why?

Precipitation

4-day groundshine dose (rem) at distance of:

1 mi 5 mi 10 mi

No rain 5.6E+00 2.6E-01 8.2E-02

Rain 1.1E+02 1.5E+00 2.7E-02

The 4-day groundshine dose at 1 mile is higher for the rain case, but at 10 miles the 4-day groundshine for

the rain case is lower. Why?

Rain washes the material out of the air and deposits it on the ground. When there is more material on the

ground, groundshine dose increases. When there is less material in the air, cloudshine decreases.
154

Summary

If the rain does not start until after the material has moved away from the release point, "hot spots" could

be created.

1. Moderate rain removes most of the non-noble gases in about an hour.

2. Rainfall decreases cloudshine doses by washing material out of the plume.

3. Rainfall increases groundshine dose close-in but decreases groundshine dose farther out.

4. RASCAL dose not model isolated precipitation events (e.g. thunderstorms) well.
155

36 Calm and Variable Winds

Purpose

Discussion

Problem

To learn how to deal with calm or variable winds.

Calm is defined in the Glossary of Meteorology as “the absence of apparent motion of the air”. It may be

quantified as a wind speed of less than 1 mile per hour. It does not however mean that there is no motion

of the air. Instead the air moves at low speed with lots of meander and no defined direction. Calm

conditions present a problem for dispersion modeling. Since there is no defined direction and the wind

speed is very low, the dispersion calculations cannot be based on plume movement. Instead, the models

switch to dispersion based on time.

The 3 models within RASCAL each treat calm conditions differently. The straight-line Gaussian plume

model (used close-in) and the puff model both switch to time based diffusion under calm conditions. The

plume model only “sees” the winds at the release point (site) and only the winds at the time of release.

The puff model (used for calculations to 10-50 miles) can encounter calm conditions anywhere within the

wind field. The UF6 plume model does not switch to a time-based diffusion. Instead, winds below 1 mph

are treated as 1 mph. This is important to note since it means that with the UF6 model the wind direction

for a zero wind speed will be used.

Care should be taken when making protective action decisions based upon model runs using calm wind

conditions. The low wind speeds and directional uncertainty cause high doses in areas not predicted by the

models. In some cases, a meteorologist may be able to provide a better value (speed and direction) by

examining data from surrounding weather stations.

A good approach is to go to the weather.gov tabular forecast tables. These will generally include

forecast wind speed and direction data for the current time. However, this data may be up to 12

hours old. It should not be used without first contacting the local forecast office..

Use the standard release scenario (page 150) for starting this problem.

Create a new meteorological data set with the following conditions:

Time Wind direction

(deg)

Wind speed

(mph)

Stability

class

Precipitation Air Temp

(deg F)

0600 130 0 B none 50

Process the data and save with the new name: FITZCalm
156

Results

Make a calculation run using this new data set and the following settings:

- Distance of calculation: Close-in + out to 10 miles

- End calculations at: Start of release to atmosphere plus: 6 hours

Examine the thyroid CDE footprints and also record the thyroid CDE values at 0.2, 1.0, and 2.0 miles.

Met data set

Thyroid CDE (rem) at distance of:

0.2 mi 1.0 mi 2.0 mi

Calm

The resulting thyroid CDE values for the three cases are:

Met data set

Thyroid CDE (rem) at distance of:

0.2 mi 1.0 mi 2.0 mi

Calm 9.8E+02 3.9E+01 9.7E+00

Here are the thyroid CDE footprints resulting when the wind speeds were really zero. A different pattern

emerges.

When the wind speed is less than 1 mph, diffusion coefficients are computed as a function of time. The

horizontal diffusion coefficient grows at a rate of 2300 feet (700 m) per hour. The vertical diffusion

coefficient grows as if the wind speed was 0.9 mph (0.4 m/s) in G stability. The material moves out in all

directions from the source. Note the similarity between the plume and puff patterns.

This problem indicates the difficulty in predicting the direction of material movement under low wind

speed conditions. The calm case is the extreme. Given no vector along which to move the material, the

model diffuses it equally in all directions. Even with a measured direction at low speeds that direction
157

tends to vary considerably. At low wind speeds the material can move in unexpected directions and since

it is moving slowly the concentrations can be high.
158

37 Elevated Releases

Purpose

Discussion

To see how elevated releases affect downwind inhalation doses.

Release Height

RASCAL characterizes the release point to the atmosphere as from either a non-isolated stack or an

isolated stack. For non-isolated stacks, release heights can range from ground level to 75 meters (250

feet). This option allows consideration of building wake effects. For isolated stacks, the release height

range is ground level to 200 meters (650 feet). The option does not consider building wake but can

consider plume rise and stack downwash.

Release Height Winds

The Meteorological Data Processor program generates wind fields for a height 10 meters above the

ground. If the actual release height of the material is greater than 10 meters a wind speed profile is used to

adjust the transport wind speed to the release height. This profile is dependent on atmospheric stability

and surface roughness. The equation and further discussion is provided in the RASCAL technical

documentation.

If the winds are measured at a height above 10 meters, they will be scaled

down to the 10 meter level. To properly use data from elevated

measurement heights you must make sure the “wind measurement height”

setting for the station is set correctly.

Mixing Layer Thickness

Heating of the surface and surface friction combine to generate turbulence

that mixes material released at or near ground level through a layer that

varies in thickness from a few meters to a few kilometers in thickness.

This layer is referred to as the mixing layer. The atmospheric models in

RASCAL use the mixing height (also referred to as the mixing-layer depth

or mixing-layer thickness) to limit vertical diffusion. Elevated releases

within the mixing layer disperse vertically and horizontally as the material

is transported by the wind. As shown in the Figure 4, the material is

reflected by the top of the mixing layer and the ground surface. At some

distance downwind the material becomes uniformly mixed through the layer. With elevated releases, it

may be some distance downwind before the actual plume of material intersects the ground surface.

10m

20m

30m

40m

50m

60m
159

Reflection from top of mixing

layer and from ground surface;

ultimately becomes uniformly

mixed.

Material passes downward and

becomes trapped in the mixed layer.

Vertical growth of plume

as if G-stability

Release above

mixing layer

Release within the

mixing layer

Problem

Figure 4 Plume interaction with the mixing layer

Since mixing heights are rarely measured at nuclear power plants, RASCAL provides two ways of

estimating the values: from current meteorological data or from climatological data. The first is the

preferred option.

Plume Rise and Stack Downwash

If an isolated stack is specified, the effective release height is the sum of three components: stack height,

plume rise, and stack downwash. Plume rise is caused by buoyancy due to density differences between the

effluent and the surrounding air and vertical momentum due to effluent flow rates. Both processes are

modeled by RASCAL. Stack downwash occurs when the stack exit velocity is less than or equal to the

wind speed at the stack exit. The downwash is an aerodynamic effect that reduces the release height by up

to 3 stack diameters.

Using the standard initial conditions (Page 150) for starting these meteorology related problems, edit the

release pathway to change the following:

- Release point characterization: Isolated stack

- Stack height: 60 meters

- Consider plume rise: No

Create a new meteorological data set with the following conditions:
160

Time Wind direction

(deg)

Wind speed

(mph)

Stability

class

Precipitation Air Temp

(deg F)

0600 340 3 F none 50

Process the data and save with the new name: FITZ Elevated

Make a calculation using the following settings:

.

- Distance of calculation: Close-in + out to 25 miles

- End calculations at: Start of release to atmosphere plus: 6 hours

Record the thyroid CDE and cloudshine doses in the following 2 tables in the rows labeled No plume

rise.

Calculation

Thyroid CDE (rem) at distance of:

0.5 mi 2 mi 10 mi 25 mi

No plume rise

With plume rise

Calculation

Cloudshine (rem) at distance of:

0.5 mi 2 mi 10 mi 25 mi

No plume rise

With plume rise

Next, go back into the release pathway section and change the option to Consider plume rise to Yes.

Then, click the Edit Plume Rise Settings button to access the Plume Rise Parameters screen. Enter the

following data:

- Effluent flow rate = 50,000 cfm

- Stack diameter = 3 ft

- Effluent temperature = 60 oF

Repeat the calculations and again record results in the tables in the With plume rise rows.
161

Results

The results for the two cases are shown below.

Calculation

Thyroid CDE (rem) at distance of:

0.5 mi 2 mi 10 mi 25 mi

No plume rise 5.8E-02 3.1E+02 6.5E+01 6.4E+00

With plume rise < 1.0E-04 5.5E+01 5.3E+01 8.6E+00

Calculation

Cloudshine (rem) at distance of:

0.5 mi 2 mi 10 mi 25 mi

No plume rise 2.0E+00 1.3E+00 1.2E-01 9.8E-03

With plume rise 1.4E+00 1.0E+00 1.3E-01 1.5E-02

Questions

For the calculation with no plume rise:

1. Why are the thyroid doses at 2 miles greater than those at 0.5 mile?

2. Why are there doses at 25 miles? With a wind speed of 3 mph and 6 hours of calculation time the

plume should only reach 18 miles.

For the calculation with plume rise:

3. Why are the thyroid doses higher at 25 miles than the case with no plume rise?

4. Why are the cloudshine doses lower at 0.5 and 2 miles than the case with no plume rise?

Answers to questions

1. Note that the thyroid inhalation dose at 0.5 miles is 0.058 rem. By 2 miles however this dose has risen

to 310 rem. The material was released 60 meters above the ground and in the stable F stability

conditions remained aloft for some distance downwind. It is only when the plume has had time to

grow vertically enough to intersect the ground that it begins to contribute to inhalation dose. Notice

that the cloudshine doses do not show the increase downwind.

2. Recall that the model will adjust the wind speed to the release height. In this case the wind speed of 3

mph at 10 meters above the ground was adjusted to about 5.5 mph at 60 meters above the ground.

With that wind speed the material would be transported 33 miles in the 6 hour calculation period.
162

3. The plume rise increases the effective release height. The material stays aloft longer and is able to

contribute more to the inhalation doses further downwind.

4. Again, the plume rise increased the effective release height. The material in the plume was higher

above the ground at any those distances downwind and thus contributed less to the cloudshine dose.

Click the 25 mi radius gridded button to view the wind field.
163

38 Adding Weather Stations

Purpose

Discussion

To learn how to add a meteorological station that is not in the RASCAL database.

The winds at Fitzpatrick and Syracuse have had the effect of transporting the material to the east and

northeast. Our assessment might be even better if we had some actual wind data downwind of the release.

After consulting a map, we see that there is the town of Watertown about 40 miles to the NE of the

Fitzpatrick site. This location was not listed as one of the stations for meteorological data in the RASCAL

database. However, data may be available.

If an internet connection is available, go see if you can find some current observations for Watertown,

New York.

One possible way to get the data for Watertown is as follows:

1. Go to the internet site: weather.noaa.gov

2. In the section United States Weather, select New York in the drop-down box and then click the Go

button.

3. In the section Current Weather Conditions, select Watertown in the list and then click the Go button.

An example of this type of report is shown below:

Having retrieved some current observations, we need a way to enter the data into the Meteorological Data

Processor. Watertown was not listed in the sites for Fitzpatrick so it will have to be added.
164

Select Stations | Add Station from the menu bar at the top of the main screen.

Fill in the information about the Watertown station.

1. The first two fields are used for labeling output products. They are not critical but should be accurate

to avoid confusion.

Station ID use either the 3 or 4 letter ID code ART or KART

Station Name Watertown International Airport

The station latitude and longitude are on the NWS page just below the site name. They are needed to

properly locate the weather station. They are shown in degrees-minutes-seconds and need to be

converted to decimal degrees (at least to the nearest 1/100 degree) before entering. Thus, the latitude

in decimal degrees will be:

43

59

60

31

3600

   43  0.9833  0.0086  43.9919

Station latitude (deg) 43.9919 N

Station longitude (deg) 76.0217 W

2. The station elevation is also shown in the NWS page after the latitude and longitude.

Station elevation 100 meters above sea level
165

3. For surface roughness, unless you have some other information about the station surrounding, you

should select a value from 0.1 to 0.2. This number is not critical to the calculations.

Station surface roughness 0.20 - Many trees, hedges (default)

4. Wind measurement height should be as accurate as possible. In this case we do not know the height so

enter the standard anemometer height of 10 meters.

Wind measurement height 10 meters above ground level

5. Wind speed units can be obtained by looking at the current weather conditions report. The decoded

version reports the wind speed in mph and in knots. Select the unit you will use for all the input of

speed for this station.

Wind speed measured in mph

6. Stability is not generally reported by the NWS with station observations. In this case, just leave the

selection at the default of Pasquill-Gifford stability class (A-G).

Click OK to return to the main screen.

If we always want Watertown to appear as a meteorological station for the Fitzpatrick site we will need to

do one more step. Select Stations | Update Station File from the menu bar. This will write a new copy of

the stations file into the Fitzpatrick data area. This new file will be used automatically in the future

whenever the Fitzpatrick site is selected.
166

39 Stability Classes

Purpose

Discussion

To learn about stability classes and how they are estimated by RASCAL.

Stability classes are determined on the basis of quantities that can be observed. For example, there is a

direct relationship between the temperature profile in the atmosphere and turbulence. As a result, NRC

has used temperature structure (ΔT/Δz) to define seven stability classes (see Table 18). Meteorological

towers at nuclear power plants measure ΔT directly. However, they may report the stability class instead

of the ΔT/Δz. ΔT/Δz is generally reported as C/100 m or F/100 ft.

At some nuclear power plants, ΔT is used to estimate the stability class for the vertical dispersion

parameter, and the standard deviation of wind directions, which is a direct measure of turbulence, is used

to determine a second stability class specifically for the horizontal dispersion parameter. RASCAL does

not have a provision for two stability classes. If two stability classes are available, the stability class for

the vertical dispersion parameter should be used.

Table 18 Selection of Pasquill-Gifford stability class by ΔT/Δz method

Stability class Temperature change with height **

(oC/100 m) (oF/100 ft)

A < -1.9 < -1.0

B -1.9 to -1.7 -1.0 to -0.9

C -1.7 to -1.5 -0.9 to -0.8

D -1.5 to -0.5 -0.8 to -0.3

E -0.5 to 1.5 -0.3 to 0.8

F 1.5 to 4.0 0.8 to 2.2

G > 4.0 > 2.2

** Negative values indicate a decrease in temperature with height

The National Weather Service does not include stability class in its reports, and they generally do not have

temperature profiles. Therefore methods have been developed to estimate stability classes on the basis of

more readily available weather variables such as wind speed, solar radiation, and sky cover along with

time of the day (see Table 19).
167

Table 19 Selection of Pasquill-Gifford stability class by meteorological conditions

Surface wind

speed

Daytime insolation ++ Nighttime conditions

m/s mph Strong Moderate Slight Thin overcast or

> 50% low clouds

<= 3/8 cloudiness

< 2 < 4 A A - B B

2 - 3 4 - 7 A - B B C E F

3 - 4 7 - 9 B B - C C D E

4 - 6 9 - 13 C C - D D D D

> 6 > 13 C D D D D

++ Insolation = incoming solar radiation; i.e. strength of sunlight at ground level. Use slight

insolation for mostly cloudy to overcast days or when it is near dawn or dusk. Use strong

insolation for no clouds at mid-day during the summer. At all other times and conditions during

daytime, assume moderate insolation.

The stability can be entered into RASCAL along with the other meteorological data. It may be entered

directly as a class (A to G) or as a temperature change with height (ΔT/Δz). There is an Unknown

selection if the stability is not known.

When the stability is unknown, RASCAL will estimate it based on the time of day, wind speed, and the

precipitation entered. Table 20 shows that estimated stability class for various conditions.

Table 20 How RASCAL estimates atmospheric stability class for missing stability classes

Wind speed (m/s)

No or light

precipitation

Moderate or heavy

precipitation

Daytime

 6.0 C C

> 6.0 D D

Nighttime

 3.0 F E

3.1 - 5.0 E E

> 5.0 D D

Reference: NUREG-1887, Section 6.3.2

Daytime is defined as one hour after sunrise to one hour before sunset. Nighttime is defined as one hour

before sunset to one hour after sunrise. The model computes the sunrise and sunset times based upon the

date and the release point latitude.

RASCAL also has the ability to adjust an entered stability class for consistency with other entered

information. Table 21 shows that allowed stability class ranges for a variety of conditions. If a stability

class is outside the range defined by the time of day, wind speed, and precipitation, it is set to the nearest

class within the range. For example, a value of F stability during the day with winds of 6 m/s and no
168

precipitation would be adjusted to a D class. Similarly, an A stability under the same conditions would be

set to C class.

Table 21 Limits of atmospheric stability classes based on time of day, wind speed, and precipitation

Wind speed (m/s)

No or light

precipitation

Moderate or heavy

precipitation

Daytime

 3.0 A - E C - E

3.1 - 5.0 B - D C - D

> 5.0 C - D C - D

Nighttime

 3.0 C - G C - E

3.1 - 5.0 D - F D - E

5.1 - 6.0 D - E D - E

> 6.0 D D

Reference: NUREG-1887, Section 6.3.2
169

40 Predefined Meteorological Data

Purpose

Discussion

To learn about the predefined meteorological data available with RASCAL.

Predefined Data (Non site-specific) is the default meteorological data set type when entering a new case.

RASCAL is distributed with 18 such data sets. They were developed to cover a range of common weather

conditions. These data sets have been given descriptive names such as Summer- Afternoon - Windy. Table

22 contains a summary of these data sets and their varying conditions.

There are pros and cons to using these predefined data sets.

Pros

- Each is a complete data set that can be used with any location and any date and time of release.

- They are quick and easy to use especially when no actual observations are available. They can be used

without needing to use the Meteorological Data Processor program.

Cons

- The wind fields are uniform in space as they are based on a single data record.

- They do not consider topography

- They have a fixed wind direction of 270 degrees

- They do not include any of the diurnal variations generally seen with actual conditions.

It is always better to use actual meteorological data.
170

Table 22 Summary of predefined meteorological data sets

Data set name Wind Stability Mixing Precip Air Air Relative

speed* class layer* code temp press humidity

mph m deg F mb %

Standard Meteorology 4 D 390 None 70 995 50

Summer - Afternoon - Calm 4 A 561 None 85 995 40

Summer - Afternoon - Rainy 8 C 884 Rain 70 995 95

Summer - Afternoon - Windy 15 B 1839 None 85 995 40

Summer - Morning - Calm 4 D 390 None 65 995 60

Summer - Morning - Rainy 8 D 780 Rain 60 995 95

Summer - Morning - Windy 15 D 1463 None 60 995 60

Summer - Night - Calm 4 F 123 None 55 995 80

Summer - Night - Rainy 8 E 333 Rain 50 995 95

Summer - Night - Windy 15 D 1463 None 50 995 85

Winter - Afternoon - Calm 4 C 442 None 35 995 75

Winter - Afternoon - Windy 20 D 1951 None 35 995 75

Winter - Morning - Calm 4 E 236 None 30 995 80

Winter - Morning - Windy 20 D 1951 None 30 995 80

Winter - Night - Calm 4 G 47 None 20 995 90

Winter - Night - Windy 20 D 1951 None 20 995 90

Winter - Rain 10 D 976 Rain 35 995 95

Winter - Snow 8 D 780 Snow 25 995 95

*Notes - Wind direction in all cases is from the west (270 degrees).

The mixing layer depths were calculated by the Meteorological Data Processor and were

not entered directly as observed data. If known, the mixing layer depth can be entered

directly by the user.
171

Purpose

Discussion

Problem

Decay Calculator

To learn how to calculate radiological decay using the Decay Calculator module.

The decay calculator can calculate the radiological decay of a single nuclide or a group of radionuclides

over any time period specified by the user.

Start with the sample from the Field Measurement to Dose problem. Assume that we want to know the

concentrations that will be present one year from the time the sample was taken. Our input data is in units

of μCi/m2, but the code can only accept activity, not activity per unit area. The way you deal with this is

by mentally remembering the area units. You enter μCi, get the results in μCi, but remember that the real

units are uCi/m2.

Which radionuclides are present in significant quantities after one year?

Nuclide Activity (μCi)

at time of sample

Activity (μCi)

after 1 year

Ba-140 1.4

Cs-134 0.6

Cs-137 0.35

I-131 1.7

I-132 1.3

La-140 1.3

Sr-89 1.0

Te-132 280
172

Inputs

Results

Enter the nuclide names and activities into the table. Set the decay interval to 1 year. Set the activity units

to μCi.

When completed, click the Compute button to decay the activities.

The results of the 1 year of decay are displayed as shown below.
173

The radionuclides present in significant quantities after one year of decay are:

Nuclide Activity (μCi)

Cs-134 0.43

Cs-137 0.34

Note that Ba-137m is also shown to be present by means of ingrowth. This is true, but not really

meaningful. When a laboratory reports that a sample contains Cs-137, they mean that it contains Cs-137 +

Ba-137m, the short-lived daughter of Cs-137.
174

References

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Radiation, NUREG-1391, U.S. Nuclear Regulatory Commission.

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McKenna, T.J. and J. Giitter. 1988. Source Term Estimation During Incident Response to Severe

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Vicinity of Buildings: Model Evaluation.”, Atmospheric Environment, 32:1679-1689.

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Analysis Handbook. NUREG/CR-6410, U.S. Nuclear Regulatory Commission.

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and PWR Permanently Shutdown Nuclear Power Plants. NUREG/CR-6451, BNL-NUREG-52498, U.S.

Nuclear Regulatory Commission.

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for Non-Reactor Nuclear Facilities: DOE Handbook. Vol. 1, DOE-HDBK-3010094, U.S. Department of

Energy.

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Risks in U.S. Commercial Nuclear Power Plants, WASH-1400 (NUREG-75/014), U.S. Nuclear

Regulatory Commission.

U.S. Nuclear Regulatory Commission, Division of Incident Response Operations, Office of Nuclear

Security and Incident Response. October, 2002. Response Technical Manual, Vol. 1, Rev. 5, U.S.

Nuclear Regulatory Commission.
175

Appendix 1: Lessons Learned from Radiological Emergencies

This is a summary of the major lesson learned from the Chernobyl, Goiania, and other radiological

emergencies. This list was adapted from work done by Tom McKenna of IAEA.

1. Failure to recognize severe emergencies

Problem: The severity of major nuclear emergencies that have occurred was not recognized or

comprehended by facility operators in the initial phase even when there were indisputable indications of

their severity. One reason is that severe emergencies were not considered in the preparedness process

because their occurrence was considered to be inconceivable.

Solution: Emergency preparedness should address severe emergencies including those of low probability.

2. The importance of having established protective action criteria and policies

Problem: Responses to Chernobyl, Goiania, and other radiological emergencies were delayed because

established criteria for taking protective actions were not in place and criteria could not be readily

developed after the start of the emergency during a period of heightened emotions and mistrust of public

officials and the scientific community.

Solution: Criteria and policies for taking protective actions and for the return to normalcy should be

established in advance as part of the preparedness process. These criteria should be complete enough to

apply to the entire conceivable range of emergency conditions and protective action decisions.

3. The destructiveness of “conservative assumptions”

Problem: The use of “conservative assumptions” led to actions that sometimes did more harm than good.

Unnecessarily conservative assumptions were often used because it was not clear how to deal with

uncertainties or whether existing guidance should be applied to the conditions that existed. There is a

general tendency to implement actions at levels below those recommended if it is unclear whether the

guidance addresses the situation at hand.

Solution: Actions should be taken based on realistic assumptions, and guidance should include clear

statements on the conditions under which it applies.

4. The need for plain language explanations of decisions

Problem: Following Chernobyl, Goiania, and other emergencies, the public took inappropriate and in

some cases harmful actions due to fear and misunderstandings concerning radiation risks and how to

reduce them. These fears were in part due to the use of cryptic technical terms and the reluctance of

technical experts to provide the definitive guidance needed and wanted by the public.

Solution: The criteria for taking protective actions should be accompanied by a plain language

explanation so that the public officials who make the decisions and who inform the public of those

decisions can understand the criteria and explain them to the public. The explanation must make clear
176

what actions are appropriate and what actions are inappropriate. The explanation must explain how the

recommended actions will insure the safety of the members of the public.

5. The need for planning to return to normalcy

Problem: Experience shows that after the emergency response there will be immense pressure from the

public to take actions to correct the problem and return the situation to normal. Experience shows that

officials, when under this intense pressure, take highly visible actions, even if those actions are only

minimally effective or even counterproductive.

Solution: Guidance and plans should include a full range of post-emergency countermeasures that are

both justified and optimized.
BIBLIOGRAPHIC DATA SHEET

(See instructions on the reverse)

NRC FORM 335

(9-2004)

NRCMD 3.7

U.S. NUCLEAR REGULATORY COMMISSION 1. REPORT NUMBER

 (Assigned by NRC, Add Vol., Supp., Rev.,

 and Addendum Numbers, if any.)

NUREG-1889

3. DATE REPORT PUBLISHED

MONTH

September

YEAR

2007

4. FIN OR GRANT NUMBER

R1110

2. TITLE AND SUBTITLE

RASCAL 3.0.5 Workbook

5. AUTHOR(S)

George F. Athey, Athey Consulting

Stephen A. McGuire, Nuclear Regulatory Commission

James Van Ramsdell, Pacific Northwest National Laboratory

6. TYPE OF REPORT

Technical report

7. PERIOD COVERED (Inclusive Dates)

NA

8. PERFORMING ORGANIZATION - NAME AND ADDRESS (If NRC, provide Division, Office or Region, U.S. Nuclear Regulatory Commission, and mailing address; if contractor,

Athey Consulting, P. O. Box 178, Charles Town, WV 25414-0178

9. SPONSORING ORGANIZATION - NAME AND ADDRESS (If NRC, type "Same as above"; if contractor, provide NRC Division, Office or Region, U.S. Nuclear Regulatory Commission, 

Office of Nuclear Security and Incident Response, U. S. Nuclear Regulatory Commission, Washington, DC 20555-0001

provide name and mailing address.)

and mailing address.)

10. SUPPLEMENTARY NOTES

11. ABSTRACT (200 words or less)

The code currently used by NRC's emergency operations center for making dose projections for atmospheric releases during

radiological emergencies is RASCAL version 3.0.5 (Radiological Assessment System for Consequence AnaLysis). This code

was developed by NRC. RASCAL 3.0.5 evaluates releases from: nuclear power plants, spent fuel storage pools and casks, fuel

cycle facilities, and radioactive material handling facilities. 

The workbook contains problems designed to familiarize the user with the computer-based tools of RASCAL through hands-on

problem solving. The workbook is primarily for use by students in a RASCAL training course supervised by a qualified instructor.

12. KEY WORDS/DESCRIPTORS (List words or phrases that will assist researchers in locating the report.)

RASCAL, emergency response, dose assessment, dose projections, plume modeling, student

workbook, training 14. SECURITY CLASSIFICATION

13. AVAILABILITY STATEMENT

unlimited

(This Page)

unclassified

(This Report)

unclassified

15. NUMBER OF PAGES

16. PRICE

NRC FORM 335 (9-2004) PRINTED ON RECYCLED PAPER

Office of Nuclear Security and Incident Response, U. S. Nuclear Regulatory Commission, Washington, DC 20555-0001

Pacific Northwest National Laboratory, P. O. Box 999, Richland, WA 99352