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RASCAL 4.1 Radiological Assessment System for Consequence Analysis

RASCAL 4.1 National Radiological Emergency

Preparedness Conference Tuesday, April 19, 2011

Lou Brandon

NRC Radiological Assessment Code for Consequence Analysis (RASCAL) Version 4.1:

Updates, Perspectives, Initiatives, Resources, and Future Plans

• Version 4.0 released in June 2010 • Version 4.1 released in January 2011 • Presentation goals:

– Highlight the changes and new features – Discuss in more detail big changes – Discuss the ongoing and future work on RASCAL

Changes That Came in 4.0

Atmospheric Dispersion

• What is New? – RASCAL v4 has changed from distance-based

dispersion parameters to time-based parameters – Gone are the Pasquill-Gifford parameters – Dispersion is now a function of:

• time since release • wind speed • atmospheric stability • surface roughness

Atmospheric Dispersion – most significant change

• What are the Implications of the Changes? – The RASCAL v4 dispersion parameters tend to be

larger than the RASCAL v3.0.5 parameters – X/Qs and doses for ground-level releases will tend

to be lower – X/Qs and doses for elevated releases will tend to

be higher near the release point

Atmospheric Dispersion

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

0.1 1 10To

tal E

DE

(rem

) Distance (mi)

R3 Plume

R3 Puff

R4 Plume

R4 Puff

1.E-02

1.E-01

1.E+00

1.E+01

0.1 1 10

Tota

l ED

E (r

em)

Distance (mi)

R3 Plume

R3 Puff

R4 Plume

R4 Puff

Ground Level, D Stability, 3 m/s

Elevated, D Stability, 3 m/s

Thyroid dose to 10 miles for 4 mph - D stability

V3.0.5 V4.0

Conditions Ratio R4/R305 for thyroid dose at 5 miles

4 mph, D stability 27%

15 mph, B stability 31%

4 mph, G stability 16%

8 mph, D stability, Rain 24%

Model differences in thyroid doses for a core uncovered scenario with differing met conditions

3.0.5 (left) vs 4.0 TEDE 3.9 rem vs 1.2 rem at 2 mi

1.3 rem vs 0.38 at 5 mi

9

8 mph, E Stability

TEDE > 1 rem at 5 miles

TEDE > 1 rem at 2 miles

• Are the Dispersion and Deposition Changes Reasonable? – Regional Atmospheric Transport Code for Hanford

Emissions (RATCHET) developed in 1990s, now in RASCAL – The Hanford Environmental Dose Reconstruction Project

included an extensive validation effort – The development and application of the new algorithms

were extensively reviewed by leading experts including F. Gifford and scientific organizations including the National Academy of Sciences.

– The dispersion and deposition algorithms have been used in subsequent dose reconstruction projects (ORNL, INEL, Rocky Flats, and Mayak, USSR)

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Atmospheric Transport & Dispersion (ATD)

Rocky Flats – Sulfur Hexafluoride Tracer Study

• Evaluation of Atmospheric Transport Models for Use in Phase II of the Historical Public Exposure Studies at the Rocky Flats Plant (Risk Analysis, Vol 19, No. 4, 1999, Rood, Killough, Till)

• Involved 5 models; ISCST2, RATCHET, TRIAD, INPUFF2, and TRAC.

• “No one model outperformed the others in all modeling objectives… …overall performance of RATCHET was somewhat better than the other models.”

Atmospheric Deposition

• Why the Changes? – The RASCAL v3.0.5 parameters were developed

in the 1950s and early 1960s. – Research on atmospheric processes in the 1960s,

1970s, and 1980s provide better methods of estimating atmospheric deposition.

Atmospheric Dry Deposition

• What is New? – RASCAL v4 has changed from constant dry

deposition velocities to dry deposition velocities that are a function of atmospheric conditions including wind speed, stability, and surface roughness.

– RASCAL v4 treats iodine (halogens) as three species having different deposition characteristics for purposes of calculating deposition (I2, particles, and CH3I)

Atmospheric Dry and Wet Deposition

• What is New? – RASCAL v4 iodine speciation is 25% Particles,

30% I2, and 45% CH3I; CH3I is assumed not to deposit.

– RASCAL v4 uses a wet deposition velocity for wet deposition of gases and a washout model for wet deposition of particles. These parameters are functions of wind speed, atmospheric stability, surface roughness, and precipitation rate

Atmospheric Deposition

• What are the Implications of the Changes? – The RASCAL v4 deposition parameters, while not

constant, tend to be within a factor of 2 of the RASCAL v3.0.5 parameters.

– RASCAL v4 deposition velocities for iodine tend to be lower than the RASCAL 3.0.5 value in low wind speed conditions and higher in high wind speeds.

– Deposition of iodine is generally lower in RASCAL v4 because 45% of the iodine does not deposit.

Updated Core Inventory

• Old core inventory – RASCAL 3 – Taken from NUREG-1228 / WASH-1400 – Selected for early health effects + likely noble

gases

• New core inventory – RASCAL 4 – Based on normalized SCALE/ORIGEN run – Increased number of nuclides from 33 to 58 – No longer select for early health effects

• Impact – small changes to source term

Updated Coolant Inventory

• From ANSI/ANS 18.1-1999 • Old inventory (RASCAL 3) excluded:

– nuclides with half-life < 50 minutes, and – noble gases for BWRs

• New inventory (RASCAL 4) includes all • A more complete set; nuclide number

increased from 36 to 63 • Impact – small changes to source term

Radioactive Decay: What Is New?

• The decay scheme has been revised in the source term, environmental and dose calculations

• The decay scheme uses simplified chains that include short-lived daughters implicitly and are truncated at long-lived daughters

• Decay calculations are made using the Bateman Equations for 0 to 3 daughters and include branching.

• Nuclides with implicit daughters have a ‘*’ after the name; e.g. Cs-137*

Radioactive Decay

• Why the Change? – Consistency

• RASCAL v3.0.5 uses 3 different decay schemes • RASCAL v 4 uses just one

– Traceability • RASCAL v4 decay schemes are documented • Appendices in the technical documentation list the

chains, decay parameters and implicit daughters

Radioactive Decay

• What are the Implications of the Change?

– The changes in decay schemes should not result in any significant changes in dose estimates; however, they significantly alter DRL estimates.

– Truncation errors have been evaluated and are generally << 1%

– Addition of implicit daughters and simplification of chains that include branching increases doses slightly at short times

Monitored Release

• Assumptions – Monitored pathway – Monitor capable of distinguishing between

particle and noble gas activity – Reactor is shutdown with core damage – Particles are CsI

Monitored Release

• Why the Change? – RASCAL 3.0.5 significantly overestimated the

long-term consequences of a release by exaggerating the Cs-137 activity

– RASCAL 3.0.5 significantly underestimated the short-term consequences of a release by minimizing the I-131 activity

Monitored Release

Isotope RASCAL v3.0.5 RASCAL v4

I-131 0.500 0.115

I-132 0.167

I-133 0.233

I-134 0.258

I-135 0.223

Cs-134 0.00193

Cs-136 0.000613

Cs-137 0.500 0.00134

Monitored Release Particle Activity Fraction

BWR release options

SGTR Changes

Spent Fuel Pool Uncovered

Changes in SF Pool

• New version requires only age of newest batch, total batch count, and times for cooling lost and regained

• Assumes a 18 month refuel interval and cladding fire if not cooled for 2 hours

• Release over 24 hours unless re-cooled • Impact – generally smaller source terms due to

better characterization of newest batch

Intermediate Phase Doses

• Have been added to the Source Term to Dose model; previously only in Field Measurement to Dose

• Based on the projected deposition • Allows early “look” as relocation issues

IP Doses Available in 2 Places

Maximum Values Summary Detailed Results

Values provided for any location.

Ground Concentration - Total

Surface Concentration - Deposited Nuclides

Nuclide Mix on Ground at Specific Location

Millstone – Thyroid CDE 5.6 rem @ 0.2 mi

This is a low dose impact scenario with PAGs exceeded less than 0.25 miles out.

FDA DRL 9600 pCi/m2 (prod) ~ 0.01 uCi/m2

So, DIL possibly exceeded beyond 50 miles. Sample before embargoing.

Lowest RASCAL scale now about I-131 DRL limit for produce.

Export Footprint to Shapefile

• Shapefile is a geospatial vector file format • Export function requires the MapWindow GIS

open source software • www.mapwindow.org • Separate installation required for this feature

to work • MapWinGIS installer available with RASCAL

installation

Export to GIS from Footprint Display

Advantages of Plume in GIS

• Can perform spatial analysis; answer questions about geographic features in relation to the plume

• Have more control over the display – Emphasize features of interest – Add or subtract layers,i.e. change background

• Plot other information such as field team readings

Use the conversion tool “Layer to KML” in the ArcToolbox Create a file from the “plume” layer Drag the new file into Google Earth

ArcMap to Google Earth

Plume Displayed in 3 Programs

RASCAL ArcMap Google Earth

Changes New in 4.1

Effluent Releases - by Mixtures Release Rate Calculator

Release Rate Calculations

Gross concentration and flow rate are used to calculate a release rate in the units specified on the previous screen. The is a “one-way” tool. It only inserts the calculated value. Nothing is saved.

DRD Correction Factor Assist field teams by developing a correction factor for direct reading dosimeters that will estimate internal dose

Available Using Dose vs. Time Plot for Gamma Exposure Rate

See Help for derivations

DRD Correction Factor

Case 1: Monitored mixture source term – primarily noble gases and iodines

Gamma Rate

3 hours since release 2 miles downwind 15 minute DRD correction factor is 1.2. Low impact on total dose.

Case 2 - Core Uncovered

Gamma Rate 2

1.5 hours since release 2 miles downwind 15 minute DRD correction factor is 13.5. High impact on total dose.

DRD CF Summary

• If radionuclide mix in plume includes particulates, internal dose impact is from more than just iodines.

• DRD readings may need to be corrected by factors as high as 20.

• KI has much more limited effectiveness because it doesn’t limit dose, other than to thyroid.

• For various scenarios, dose and KI effectiveness for public populations, evacuating or stationary, can be analyzed.

Improved Interpolation of Meteorological Obs and Fcst

• Now interpolate between observations and forecasts; smoother transitions

• Persist both observations and forecasts for up to 2 hours, then interpolate

• Warn if asked to interpolate wind direction shift > 90 deg

• Warn if forecasts will be deleted

Calm Wind Modeling

• Calm wind model used for close-in calculations updated to improve consistency.

• Dispersion is a function of time after release. • If release stops, model will continue to

calculate doses and deposition. • Under calm conditions, wind speed not

extrapolated to release height.

Calm Conditions in the Plume Model

RASCAL 4.0 RASCAL 4.1

Calm Conditions in the Puff Model

RASCAL 4.0 RASCAL 4.1

Verification and Validation

• Work is ongoing in both areas • Examples shown for TurboFRMAC and NARAC

FMDose / TurboFRMAC

• FRMAC Assessment Workgroup • Compared results from RASCAL 4.0 & 4.1

Field Measurement to Dose model with TurboFRMAC 2010

• Found good agreement • Work ongoing • FRMAC proposing changes to resuspension

methods; RASCAL may follow

Figure 7.1 Comparison of Intermediate Phase TEDE Estimates From RASCAL 4 and TurboFRMAC2009 for Ground Contamination of 103 μCi/m2 for 25 Isotopes.

1.00E-04

1.00E-03

1.00E-02

1.00E-01

1.00E+00

1.00E+01

1.00E+02

1.00E+03

1.00E+04

1.00E-04 1.00E-03 1.00E-02 1.00E-01 1.00E+00 1.00E+01 1.00E+02 1.00E+03 1.00E+04

RASC

AL 4

TED

E

TurboFRMAC TEDE

1st Year

50 year

2nd Year

Figure 7.2 Comparison of Intermediate Phase Exposure Rate DRL Estimates From RASCAL 4 and TurboFRMAC2009 for Ground Contamination of 103 μCi/m2 for 25

Isotopes

1.00E-06

1.00E-05

1.00E-04

1.00E-03

1.00E-02

1.00E-01

1.00E+00

1.00E+01

1.00E+02

1.00E+03

1.00E+04

1.00E-04 1.00E-03 1.00E-02 1.00E-01 1.00E+00 1.00E+01 1.00E+02 1.00E+03 1.00E+04

RASC

AL 4

Dos

e Ra

te D

RL

TurboFRMAC Dose Rate DRL

1st Year

50 year

2nd Year

Table 7.2 Intermediate Phase Dose Radionuclide Exposure Period RASCAL 4 Turbo FRMAC 2009 Spreadsheet I-132 First Year 0.0801 0.0816 8.00E-2 Second Year NC NC NC Fifty Years 0.0801 0.0816 8.00E-2 Sr-90 First Year 0.679 0.689 NC Second Year 0.428 0.427 NC Fifty Years 8.16 8.16 NC Sr-90 + Y-90 First Year 0.685 NC NC Second Year 0.428 NC NC Fifty Years 8.17 NC NC Sr-90+ First Year 0.684 0.689 NC Second Year 0.428 0.427 NC Fifty Years 8.16 8.16 NC Am-241 First Year 70.2 71.9 70.2 Second Year 8.86 8.84 8.88 Fifty Years 297 2.98 306 I-129 First Year 2.29 2.23 2.29 Second Year 1.95 1.90 1.95 Fifty Years 55.5 54.0 55.1 U-232 First Year 103 104 NC Second Year 12.2 10.3 NC Fifty Years 425 323 NC U-232- First Year 100 104 NC Second Year 10.0 10.3 NC Fifty Years 313 323 NC

(rem) TF2010 R2

0.570 0.423 8.02

72.2 8.86

2.99E2 2.23 1.90 54.4

Based on 1000 uCi/m2 deposition

Table 7.3 Dose (exposure) Rate DRL Radionuclide Exposure Period RASCAL 4 Turbo FRMAC

2009 FRMAC Manual

2003

Spreadsheet

I-132 First Year 861 862 853 862 Second Year NC NC NC NC Fifty Years 2150 2160 2130 2150 Sr-90 First Year 3.99E-2 2.54E-1 3.04E-2 NC Second Year 4.57E-2 1.02E-1 3.96E-2 NC Fifty Years 2.48E-2 5.34E-2 1.46E-2 NC Sr-90 + Y-90 First Year 7.68E-1 NC NC NC Second Year 4.57E-1 NC NC NC Fifty Years 4.87E-1 NC NC NC Sr-90+ First Year 2.55E-1 2.53E-1 NC NC Second Year 8.42e-2 8.40E-2 NC NC Fifty Years 5.35e-2 5.33E-2 NC NC Am-241 First Year 1.22E-2 1.06E-2 9.25E-3 1.22E-2 Second Year 2.04E-2 1.82E-2 1.68E-2 2.04E-2 Fifty Years 7.22E-3 6.39E-3 4.51E-3 7.02E-3 I-129 First Year 3.52E-1 3.52E-1 3.24E-1 3.52E-1 Second Year 8.70E-2 1.03E-1 8.10E-2 8.70E-2 Fifty Years 3.63E-2 363E-2 1.55E-2 3.65E-2 U-232 First Year 6.37E-5 3.35E-4 NC NC Second Year 7.29E-6 7.00E-4 NC NC Fifty Years 1.69E-6 2.68E-4 NC NC U-232- First Year 3.14E-4 3.35E-4 NC NC Second Year 6.57E-4 7.00E-4 NC NC Fifty Years 2.52E-4 2.68E-4 NC NC

mR/h TF

2010 R2

1.05E-2 2.15E-2 6.38E-3 3.51E-1 1.03E-1 3.60E-2

Table 7.4 Marker Radionuclide DRL Radionuclide Exposure Period RASCAL Turbo FRMAC

2009 FRMAC Manual

2003

Spreadsheet

I-132 First Year 2.50E4 2.50E4 2.94E4 2.50E4 Second Year NC NC NC NC Fifty Years 6.24E4 6.24E4 7.35E4 6.25E4 Sr-90 First Year 9.00E3 2.90E3 8.00E3 NC Second Year 1.03E4 9.65E2 1.04E4 NC Fifty Years 5.59E3 6.12E2 3.85E3 NC Sr-90 + Y-90 First Year 8.78E3 NC NC NC Second Year 1.03E4 NC NC NC Fifty Years 5.57E3 NC NC NC Sr-90+ First Year 2.92E3 2.90E3 NC NC Second Year 9.62E2 9.65E2 NC NC Fifty Years 6.14E2 6.12E2 NC NC Am-241 First Year 28.4 27.8 25.0 28.5 Second Year 47.6 47.7 45.5 47.5 Fifty Years 16.8 16.8 12.2 16.4 I-129 First Year 8.73E2 8.73E2 9.52E2 8.74E2 Second Year 2.16E2 2.56E2 2.38E2 2.16E2 Fifty Years 9.00E1 9.00E1 4.55E1 9.08E1 U-232 First Year 4.03 19.3 NC NC Second Year 4.62E-1 40.4 NC NC Fifty Years 1.07E-1 15.5 NC NC U-232- First Year 19.9 19.3 NC NC Second Year 41.6 40.4 NC NC Fifty Years 16.0 15.5 NC NC

uCi/m2 TF

2010 R2

2.44E4

NC

6.10E4

2.90E3

1.17E3

6.12E2

27.7

56.4

16.7

897E2

2.63E2

91.9

TurboFRMAC 2009, 2010 Pre-Millstone test data into RASCAL4.0: "Field Monitoring to Dose" • Co-58 4.75 E2 pCi/100cm2 • Co-60 5.00 E3 pCi/100cm2 • I-131 9.70 E6 pCi/100cm2 • I-133 5.50 E6 pCi/100cm2 • Cs-134 5.00 E4 pCi/100cm2 • Cs-137 2.01 E4 pCi/100cm2

• Found DRL results (1st year, 2nd year, 50 year - mR/h - using mix): • • RASCAL 4.0 (11.1, 0.0986, 11.2) • TurboFRMAC 2009 (11.2, 0.0986, 11.2) • TurboFRMAC 2010 (11.1, 10.8, 11.2)

• TF 2010 – in order to plot, calculates 2nd yr DRL at beginning of 1st yr

RASCAL / NARAC

• NRC exports a source term to NARAC (IMAAC) • NARAC uses that source term as input to its

3D model and then posts results back for NRC to use and quality control (QC).

• Comparisons have been done at several exercises.

• During Japan incident, good NRC-DOE alliance, and due to complexities, DOE NIT QCed.

Sample NARAC Result

Results from Millstone Exercise Distance To Which Dose Was Exceeded

RASCAL NARAC

TEDE > 1 rem 1.8 km 7.7 km

> 5 rem 0.7 km 3.1 km

Thyroid > 5 rem 13 km 11.9 km

> 25 rem 2.2 km 4.5 km

RASCAL lower, 4x for TEDE, 1-2x for thyroid. Expected with the new transport and diffusion models.

Ongoing and Future Efforts

Automated Meteorological Data Retrieval

• Prototype being developed by PNNL • Will access National Weather Service data via

the internet • Observations reported hourly but retained for

only 1 hour • Forecast updated every 3 hours; gridded • NARAC supported NRC with Met for Daiichi

Issues to be Addressed

• How to keep the data available to RASCAL current? – Regular, scheduled retrieval; full U.S. or just sites? – Run on demand

• How to get site tower data in? – Manual entry – Interface with ERDS

• Support for events that happened in the past • Support for “canned” meteorology

New source term work

• SOARCA – Have a LTSBO scenario from Sandia – Need others to be developed – Will greatly change the timing for source terms

• New reactor designs • Standardization of source term files

– Would XML be a useful format? – Improve ease of export and import

0.00E+00

2.00E-01

4.00E-01

6.00E-01

8.00E-01

1.00E+00

1.20E+00

0 5 10 15 20 25

Core

frac

tiona

l rel

ease

to co

ntai

nmen

t

Time (hrs) since reactor shutdown

PWR Melcor source term - noble gas

PWR Nureg-1465 source term - noble gas

PWR Melcor source term - halogen

PWR Nureg-1465 source term - halogen

PWR Melcor source term - alkali metals

PWR Nureg-1465 source term - alkali metalsGap release

Early in-vessel

Ex-vessel

Late in-vessel

SOARCA – NUREG-1465 vs Melcor

Distribution Issues

• Have been able to freely distribute RASCAL in the U.S. and fairly easily worldwide

• May be restrictions coming • Requirements

– Non-Disclosure Agreement – More stringent registration of users – Protected distribution

Work with other Groups

• Unified RASCAL Interface (URI)- continue to support the Entergy / Exelon effort

• InterRAS – provide support for the IAEA international version of RASCAL

• Improve ways to stay in touch with RASCAL users

User Forum Ideas

• Online forum for sharing questions and answers between users

• Online resource for solving problems with the software

• Gathering place for new ideas, requests for changes and new capabilities

• Send your thoughts and ideas to George Athey and Lou Brandon

ISSUES – Still Being Resolved

• Large variation in results from past models • Can’t easily calculate new dispersion

parameters from 1st principles. • Which model is better for protective action

decisions? • How would one go about upgrading old

models? In RASCAL 4, the activity released remains about the same while the distribution

curve flattens.

Questions?

Lou Brandon 301-415-8013

lou.brandon@nrc.gov