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Automating the Level 2 - Level 3 Interface: Lessons Learned from Soarca and the NRC Site Level 3 PRA Project
	ML23093A162
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Issue date:	04/14/2023
From:	Hathaway A; NRC/RES/DSA
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Automating the Level 2-Level 3 Interface:

Lessons Learned from SOARCA and the NRC Site Level 3 PRA Project Trey Hathaway, PhD U.S. Nuclear Regulatory Commission Office of Nuclear Regulatory Research Accident Analysis Branch Alfred.Hathaway@nrc.gov 14th European MELCOR User Group Meeting Ljubljana, Slovenia 12-14 April, 2023

MACCS Overview 2

Early (Emergency) Phase Intermediate Phase Long-Term Phase Primary Offsite Accident Response Objective(s)

Protect public from exposures to passing plume and deposited materials

Protect public from exposures to deposited materials

Plan for long-term cleanup and recovery activities

Protect public from exposures to deposited materials

Conduct long-term cleanup and recovery activities Typical Duration and Time Frame

~1 week, starting at the time of the accident initiation Weeks to months, starting at the end of the early phase Months to years, starting at the end of the intermediate phase Exposure Pathways

Inhalation

Skin Deposition

Cloudshine

Groundshine

Groundshine

Inhalation of resuspended materials

Groundshine

Inhalation of resuspended materials

Food and water ingestion Protective Actions

Sheltering

KI ingestion

Evacuation

Relocation

Relocation

Decontamination

Interdiction

Condemnation

MACCS Overview MACCS is a fully integrated, engineering-level severe accident consequence computer code developed to analyze the offsite consequences of a hypothetical release of radioactive material to the environment 3

SOARCA - UA Process 4

Level 3 PRA

Numerous Release Categories (16) with representative source terms and release category frequencies

Representative accident sequences have specific Emergency Action Level (EAL) timings

Five possible Emergency Plans depending on source term characteristics 16.1 km [0-10 mile] EPZ evacuation (e.g. ~7 cohorts) 16.1 km [0-10 mile] EPZ evacuation with 16.1-24.1 km [10-15 mile] expanded evacuation with/without a schools cohort (e.g. ~12/13 cohorts) 16.1 km [0-10 mile] EPZ evacuation with 16.1-32.2 km [10-20 mile] expanded evacuation with/without a schools cohort (e.g. ~17/18 cohorts) 5

SOARCA vs Level 3 PRA Source Terms 6

SOARCA Sequoyah Level 3 PRA - IEIF

Level 3 PRA Want to rely on WinMACCS to create and execute MACCS calculations

- Challenge

16 source terms

Perform a base set of calculations along with potential sensitivities

MACCS models have a lot of release category dependent input which could be error prone if building multiple models Goal: Minimize potential input error by creating a base model which defines global input and change only emergency plan and source term input

- Ideally a user could define an emergency plan and add it to a MelMACCS source term and execute the calculation as a cyclic file set

Challenge: Users must define the number of cohorts at the beginning of the problem, which must be acknowledged by the user

- Want to create a text file which defines source term and emergency plan

Import model changes and execute the calculation with WinMACCS 7

WinMACCS Methodology

Create a calculation pipeline to minimize user interaction during calculations

- Excel macro created to execute pipeline

Three phases to calculation methodology employed:

- MelMACCS processing of MELCOR Source Terms

- MACCS Non-Evacuating Calculations

Used to select Emergency Plan

- MACCS Consequence Calculations

Including additional sensitivities 8

WinMACCS Methodology 9

Automatic generation of inputs minimizes time needed for input file development, improves traceability, and minimizes chances for user error by reducing manual data entry

MelMACCS

Rely on batch processing of MELCOR source terms

Create a *.mel file which defines flowpath and plume segment information

- Defined for all flowpaths in a MELCOR problem

Execute MelMACCS from Windows Command Prompt

- Create batch files to perform calculations 10 Demo.mel from MelMACCS distribution

>melmaccs.exe ProjectFile.mel -i SourceTerm.ptf -o MACCSSourceTerm.inp -r

Non-Evacuating Calculations Used to select base-case emergency response models Simplified analysis with single non-evacuating cohort Used subset of weather trials based on SOARCA methodology Estimates the size of population subject to normal and hotspot early-phase relocation (i.e. exceeding the early phase PAG levels of 10-50 mSv [1-5 rem] in 4 days) as a function of distance from the site Estimate distance range encompassing 90%

of affected population to select emergency plan Estimate the size of the affected population to determine the intermediate-and long-term phase durations Data from Fukushima suggests most recovery actions would be focused on the area adjacent to residences, farmland, and public spaces 11 Example: Fraction of population affected by emergency phase protective actions curve EP Model 2 selected

WinMACCS Level 3 PRA Base Consequence Model

Create a Base Consequence Model containing all possible cohorts (18 cohorts)

8760 weather trials

Tabulated results include:

12 Measure MACCS Output Type Spatial Interval Units Collective total effective dose 5

0-50 and 0-100 mi person-rem Total latent fatality cases 1

0-50 and 0-100 mi persons Population-weighted individual latent fatality risk 8

0-10 mi individual risk (unitless)

Total early fatality cases 1

0-50 mi persons Population-weighted individual early fatality risk 8

0-1.8 mi individual risk (unitless)

Area exceeding 555 kBq/m2 Cs-137 D

0-50 and 0-100 mi mi2 Population relocated during intermediate phase 14 0-50 and 0-100 mi persons Total economic costs 10 0-50 and 0-100 mi 2015$

WinMACCS Emergency Plan Consequence Models

SUMPOP file

- Provides spatially dependent population distributions for individual cohorts

- Create a SUMPOP file for each Emergency Plan (EP)

5 files

- If a cohort is not present in an emergency plan, its population distribution is set to 0 for all grid sectors

Population of neglected cohorts is shifted into remaining non-evacuating cohort

Base model was copied and a EP specific SUMPOP files provided to define EP specific consequence model 13

Emergency Plan Definition OALARM - reference point from which protected actions are initiated Set to 0 seconds for this analysis Delay-to-Shelter (DLTSHL) - time from OALARM to until cohort begins to shelter Time from accident initiation until cohort begins to shelter since OALARM is set to 0 seconds Covers time for a protective action recommendation to the offsite response organization, notification of the public to evacuate by the offsite response organization, and the time needed to begin sheltering Delay-to-Evacuation (DLTEVA) - length of the sheltering period from the time a cohort enters the shelter until the cohort begins to evacuate Cohorts are assumed to travel a fixed average distance during evacuation phase DURBEG - Beginning phase of the evacuation Typically a few minutes as evacuees begin to enter the evacuation network Has accompanying travel speed: ESPEED1 DURMID - remaining time required to safely exit the evacuation zone Travel speed assumed to decrease due to congestion on evacuation network Has accompanying travel speed: ESPEED2 ESPEED3 Cohort speed from the end of the evacuation zone to the end of evacuation network DLTEVA, DURBEG, DURMID, ESPEED1, ESPEED2, and ESPEED3 assumed to be independent of release category 14

Emergency Plan Definition Mobilized Time until cohort is ready to begin evacuation Exited Time cohort has fully exited the evacuation zone Cohort 1 30% of the EPZ population (0-30%)

Cohort 2 30% of the EPZ population (30-60%)

Cohort 3 30% of the EPZ population (60%-90%)

Tail 10% of the EPZ population (90%-100%)

15 Evacuation Time Estimate (ETE)

+

Emergency Plan Definition

Relocation time (Hotspot and Normal)

- Non-evacuating individuals relocated based on dose projections

- Amount of time affected non-evacuating individuals are exposed prior to relocating

Based on the longest evacuating cohort

Assumes 4 hours4.62963e-5 days 0.00111 hours 6.613757e-6 weeks 1.522e-6 months to identify areas subject to evacuation following plume arrival

Hotspot relocation

- 4 hours4.62963e-5 days 0.00111 hours 6.613757e-6 weeks 1.522e-6 months plus 90% ETE

Normal relocation

- 4 hours4.62963e-5 days 0.00111 hours 6.613757e-6 weeks 1.522e-6 months plus 100% ETE 16

Consequence Calculations

Excel macro:

- Creates a directory for the release category consequence model

- Copies emergency plan specific base consequence model into the release category directory

Selection based on simplified non-evacuating calculation

- Determines if school cohort is necessary based on timing of the accident progression

- Creates text file defining source term and release category emergency plan

User individually imports source term and emergency plan file then executes MACCS models 17

Output Post-Processing A script may be used to post-process the model1.out files and convert them into a database format Post-processed files for each source term are concatenated into one file

- Enables quick parsing of the data Scripts were written to automatically create plots based on user input

- User supplies the Cohort, Output Type, Output Subtype, and Range/Level to define a specific figure

- A graphical user interface was constructed to enable the exploration of data 18 Output Type Output Subtype Range/Level Mean Example output from WinMACCS model using SOARCA Sequoyah Realization 554 source term

Output Post-Processing

WinMACCS 3.11 can output results to tab delimited text file

- Change DEBUG_BIN_RESULTS flag in WinMACCS.ini file to TRUE

Binary file contents saved as text file in RESULTS_DB folder

tbl_outStat.txt and tbl_outCCDF.txt 19 Model1.out tbl_outStat.txt

One data block-must break into subcomponents Example output from WinMACCS model using SOARCA Sequoyah Realization 554 source term

Conclusion

Creating a calculation pipeline for consequence calculations requires upfront effort but assists in future analysis efforts

- Increases efficiency for future analyses

e.g. sensitivities, alternative initiating events, potential reruns due to calculation errors

- Increases quality assurance of results by minimizing user interaction 20

References U.S. Nuclear Regulatory Commission. U.S. NRC Level 3 Probabilistic Risk Assessment (PRA) Project, Volume 3d: Reactor, At-Power, Level 3 PRA for Internal Events and Floods (Draft). Washington, DC.

April 2022. ADAMS Accession Number: ML22067A215.

U.S. Nuclear Regulatory Commission. Level 3 PRA Project Volume 3 (Draft). Washington, DC. April 2022. ADAMS Accession Number: ML22067A194 U.S. Nuclear Regulatory Commission. NUREG/CR-7270. Technical Bases for Consequence Analyses Using MACCS (MELCOR Accident Consequence Code System). Washington, DC.

October 2022. ADAMS Accession Number: ML22294A091.

U.S. Nuclear Regulatory Commission. NUREG-2254. Summary of the Uncertainty Analyses for the State-of-the-Art Reactor Consequence Project. Washington, DC. October 2022. ADAMS Accession Number: ML22193A244.

U.S. Nuclear Regulatory Commission. NUREG/CR-7155. State-of-the-Art Reactor Consequence Analyses Project: Uncertainty Analysis of the Unmitigated Long-Term Station Blackout of the Peach Bottom Atomic Power Station. Washington, DC. May 2016. ADAMS Accession Number:

ML16133A461.

U.S. Nuclear Regulatory Commission. NUREG/CR-7245. State-of-the-Art Reactor Consequence Analyses (SOARCA) Project: Sequoyah Integrated Deterministic and Uncertainty Analyses.

Washington, DC. October 2019. ADAMS Accession Number: ML19296B786.

U.S. Nuclear Regulatory Commission. NUREG/CR-7262. State-of-the-Art Reactor Consequence Analyses Project: Uncertainty Analysis of the Unmitigated Short-Term Station Blackout of the Surry Power Station. Washington, DC. December 2022. ADAMS Accession Number: ML22194A066.

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