ML25069A700

ACRS Presentation for the Terrapower TR on Rad Release Consequences (Public)

ML25069A700
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Site:	99902100
Issue date:	03/19/2025
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NRC Staff Review of TerraPower NAT-9391, Radiological Release Consequences Methodology Topical Report, Revision 0 ACRS Subcommittee Meeting March 19, 2025

Agenda

• Review staff

• Review chronology

• Overview of topical report (TR)

• Relationship to other TerraPower TRs

• Evaluation models (EMs)

• Limitations and Conditions

• Conclusions 2

TerraPower Radiological Release Consequences Methodology TR

Review Staff

• Michelle Hart - Senior Reactor Engineer, Office of Nuclear Reactor Regulation (NRR)/Division of Advanced Reactors and Non-power Production and Utilization Facilities (DANU)/Advanced Reactor Technical Branch 2 (UTB2)

• Zach Gran - Reactor Scientist (Severe Accident), NRR/DANU/UTB2

• Reed Anzalone - Senior Nuclear Engineer, NRR/DANU/UTB2

• Mike Mazaika - Physical Scientist (Meteorologist), NRR/Division of Engineering and External Hazards/External Hazards Branch

• Keith Compton - Senior Reactor Scientist, Office of Nuclear Regulatory Research (RES)/Division of Systems Analysis (DSA)/Accident Analysis Branch (AAB)

• Kyle Clavier - Detailed to RES/DSA/AAB

• Deion Atkinson - Project Manager, NRR/DANU/Advanced Reactor Licensing Branch 1 TerraPower Radiological Release Consequences Methodology TR 3

Review Chronology

• November 2023: TerraPower submitted TP-LIC-RPT-0005 Radiological Release Consequences Methodology Report, Revision 0 (ML23311A139) for NRC review

• December 2023: The NRC staff found that the material presented in the TR provides technical information sufficient for a detailed technical review (ML23333A070)

• May through June 2024: NRC conducted a regulatory audit (ML25024A041)

• July 2024: TerraPower submitted a revision to the TR, which was renumber as NAT-9391, Revision 0 (ML24208A181)

• February 2025: NRC staff issued the draft safety evaluation (ML25057A290)

Related TerraPower submittal:

• March 2024: TerraPower submitted, on behalf of US SFR Owner, LLC, a construction permit application for the Kemmerer Power Station Unit 1 (ML24088A059).

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TR Overview

• This TR is intended for use in Natrium license applications under Part 50 using the Licensing Modernization Project (LMP) approach

• Methodology to determine radiological consequences given a source term

• Event specific source terms are input

• No specific calculations are provided or approved for use

• The TR provides:

• Licensing Basis Events (LBE) EM

• Design Basis Accident (DBA) EM

• Control Room Habitability (CRH) EM

• Appendix to adapt the LBE EM for use in Emergency Planning Zone (EPZ) sizing 5

TerraPower Radiological Release Consequences Methodology TR

Relationship to Other TRs

• NAT-9392 (ML23223A235), Radiological Source Term Methodology Report

• Source terms developed by use of NAT-9392 can be used as input to the Radiological Release Consequences methodology

• NAT-3056 (ML24304B034), Plume Exposure Pathway Emergency (PEP) Planning Zone Sizing Methodology

• Consequence results are used in the PEP EPZ sizing analyses 6

TerraPower Radiological Release Consequences Methodology TR

Licensing Basis Event EM

• Objective of the LBE EM

• Determine through a probabilistic approach, the radiological consequences of an LBE for which a representative source term has been determined

• LBE EM is intended to be used by the applicant in the NEI 18-04 LMP methodology which uses information from a facility-specific probabilistic risk assessment (PRA), including consequences

• TR section 3.4 states that the LBE EM uses the MELCOR Accident Consequence Code System (MACCS) computer code.

• NRC staff reviewed inputs and model parameters, technical rationale, risk metrics, and pertinent details associated with MACCS model execution for the purposes of evaluating radiological release consequences.

7 TerraPower Radiological Release Consequences Methodology TR

LBE EM: PRA Standard Considerations

• Because the LBE EM addresses PRA-related consequence analysis information needs for the LMP methodology, the NRC staff used information in RG 1.247 (ML21235A008) on PRA consequence analysis to aid in the review and evaluate completeness of the methodology.

• The subject areas of the non-light water reactor (NLWR) PRA standard for consequence analysis are as follows:

• Radionuclide release characterization

• Site characterization

• Meteorological data analysis

• Atmospheric transport and diffusion analysis

• Protective action analysis

• Dosimetry

• Health effects analysis

• Economic factors

• Conditional consequence quantification 8

TerraPower Radiological Release Consequences Methodology TR

LBE EM: Radionuclide Release Characterization

• RG 1.247, section C.1.3.17 states the objective of radionuclide release characterization is to identify the attributes of radiological release needed to evaluate radiological consequences

• NRC staff review of the information determined that:

• The isotope sensitivity method is acceptable because it ensures all risk-significant radionuclides are identified by reviewing the treatment of radiological half-life, biological hazard, and relative abundance of the radionuclides in the core.

• The adaptive plume algorithm is acceptable because it would likely result in conservative dose results and results have low sensitivity to the number of plume segments.

9 TerraPower Radiological Release Consequences Methodology TR

LBE EM: Site Characterization

• RG 1.247, section C.1.3.17 states the objective of site characterization is to provide information on the population distribution and patterns of land use and land cover in the vicinity of and region of a site to a distance of 80 km, or 50 miles.

• NRC staff determined that the LBE EM treatment of site characterization is acceptable because:

• The use of uniform population distribution will be shown to be conservative;

• Land use information has a negligible impact on the calculation of dose quantities for LMP; and

• The approach is consistent with previous NRC staff use of the MACCS code in reactor safety studies.

10 TerraPower Radiological Release Consequences Methodology TR

LBE EM: Meteorological Data Analysis

• RG 1.247, section C.1.3.17 states the objective of meteorological data analysis is to evaluate and select the meteorological data used for atmospheric transport and diffusion analysis.

• LBE EM requires input meteorological data including wind speed and direction, stability category, rain rate, and mixing height that is representative of weather conditions at the Natrium power plant over the most limiting year.

• The TR states that in lieu of site-specific meteorological data, the user may opt to use a generic meteorological data file based on the Electric Power Research Institute (EPRI) Advanced Light Water Reactor Utility Requirements Document (URD) if the data is shown to be conservatively representative of the site.

11 TerraPower Radiological Release Consequences Methodology TR

LBE EM: Meteorological Data Analysis

• NRC staff review of TR information determined that:

• The LBE EM adequately identifies the meteorological data needed to characterize atmospheric dispersion for the site;

• The use of generic meteorological data from the EPRI URD is acceptable if shown conservatively representative of the site; and

• The use of the URD generic meteorological data in the LBE EM is similar to the uses described in the URD, with respect to completeness of the data set

• Limitation and Condition 1 is imposed, in part, to ensure that use of the URD generic meteorological data is limited to sites within the contiguous U.S., consistent with the basis for the data.

• Does not constitute approval of the use of generic data instead of site-specific data in future analyses when addressing relevant regulations, including 10 CFR 50.34. Applicants referencing this TR should consider how this methodology may need to incorporate additional information in order to satisfy the regulatory requirements.

• The use of random weather sampling to assess consequence uncertainty due to weather conditions is acceptable because it is consistent with guidance on radiological consequence analysis for NLWR PRAs in RG 1.247 12 TerraPower Radiological Release Consequences Methodology TR

LBE EM: Atmospheric Transport and Diffusion Analysis

• RG 1.247, section C.1.3.17 states the objective of atmospheric transport and diffusion analysis is to perform an evaluation that provides time dependent air and ground concentrations resulting from a release of radioisotopes

• NRC staff review of TR information determined that:

• The LBE EM atmospheric dispersion modeling, including the specifics on use of the MACCS for atmospheric dispersion modeling, are acceptable because it is consistent with implementation in NRC-developed atmospheric dispersion codes used in reactor licensing analyses, as well as technical guidance for MACCS in NUREG/CR-7270 (ML22294A091)

Characteristics of the area and distance ranges under consideration Nearfield effects, such as elevated releases of radioactive material Building wake effects Plume meander Plume rise Plume deposition based on wet and dry deposition 13 TerraPower Radiological Release Consequences Methodology TR

LBE EM: Atmospheric Transport and Diffusion Analysis

• NRC staff review of TR information determined that:

• The use of the Gaussian plume segment model in MACCS is acceptable because it is based on the guidance contained in RG 1.145 (ML003740205) and RG 1.249 (ML22024A241); and

• The LBE EM use of the MACCS CHRONC module to model long term exposure to radionuclides deposited on the ground is appropriate because it models the effects of weathering on the ground contamination concentration, as well as resuspension of the radionuclides to the atmosphere and is consistent with the risk analyses using the MACCS code as described in NUREG/CR-7270.

• Limitation and Condition 1 is imposed, in part, to ensure that use of the TR is limited to sites within the contiguous U.S., because the atmospheric dispersion models described in the accident-related guidance referenced are based on weather conditions that are expected in the contiguous U.S.

14 TerraPower Radiological Release Consequences Methodology TR

LBE EM: Protective Action Analysis

• RG 1.247, section C.1.3.17 states the objective of protective action analysis is to characterize the impact of mitigation measures such as evacuation, sheltering, relocation, and interdiction of land, food, or water on doses resulting from releases of radioisotopes.

• The LBE EM conservatively models no protective actions (e.g.,

evacuation or sheltering) to calculate dose at the EAB and for the individual risk of early fatality.

• NRC staff determined that the LBE EM modeling for short-term exposure without credit for protective actions is acceptable because it results in conservative dose results 15 TerraPower Radiological Release Consequences Methodology TR

LBE EM: Protective Action Analysis

• The LBE EM models the intermediate-and long-term phase protective actions such as land decontamination and condemnation based on reaching specified dose levels based on the Environmental Protection Agency (EPA) protective action guides (PAGs) to evaluate the individual risk of latent cancer from long-term exposure to radionuclides deposited on the ground.

• NRC staff determined that the LBE EM modeling of protective actions for long-term exposure is acceptable because it is consistent with the recommendations contained within NUREG/CR-7270 and EPA PAGs.

• The NRC staff will evaluate the modeling of dose reduction factors associated with occupancy of structures or vehicles, which are not described in the LBE EM, in its review of the analysis supporting a license application referencing the TR.

16 TerraPower Radiological Release Consequences Methodology TR

LBE EM: Dosimetry

• RG 1.247, section C.1.3.17 states the objective of dosimetry is to identify the analyses needed to estimate the dose to offsite populations, arising from airborne and deposited radioisotopes.

• NRC staff review of TR information determined that

• The information on organs of risk is acceptable because it is consistent with reactor risk analyses using the MACCS code described in NUREG/CR-7270, as well as the guidance in RG 1.183 (ML23082A305) on use of Dose Conversion Factors (DCFs) from Federal Guidance Report (FGR) 11 and FGR 12 to calculate TEDE;

• The information on the calculation of the risk of early fatality and risk of latent cancer fatality, including the parameter values listed in the TR tables, is acceptable because it is consistent with the reactor risk analysis using the MACCS code as described in NUREG/CR-7270;

• The method for calculating dose is acceptable because all relevant short-term and long-term exposure pathways are identified and calculated considering inhalation dose, cloudshine, and groundshine consistent with guidance in RG 1.183 for estimating TEDE;

• The calculation for the risk metrics is acceptable because the dosimetry is based on FGR 13, which is a recognized information source developed by the EPA as a resource for the federal government and reflects an age-and gender-averaged adult population; and

• The modeling of the exposure periods is acceptable because it is consistent with the description in NEI 18-04 of the dose quantity to be compared to the LMP frequency-consequence target, the Quantitative Health Objective (QHO) figures of merit for early fatality risk and latent cancer fatality risk and is reasonable for the evaluation of the cumulative probability per plant-year of exceeding the 100 mrem TEDE at the site boundary as required described in the LMP.

17 TerraPower Radiological Release Consequences Methodology TR

LBE EM: Health Effects Analysis

• RG 1.247, section C.1.3.17 states the objective of health effects analysis is to assess the risk of early or latent health effects, either fatal or nonfatal, or both, arising from acute and chronic exposure to released radioisotopes.

• NRC staff review of TR information determined that the evaluation of health effects is appropriate because the list of cancer fatality sites in the human body is consistent with FGR 13, and the list of early fatality health effects is consistent with those identified in NRC reactor risk studies with consequence analyses as found in NUREG-1150 (ML120960691) as well as NUREG/CR-7270.

18 TerraPower Radiological Release Consequences Methodology TR

LBE EM: Economic Factors

• RG 1.247, section C.1.3.17 states the objective of economic factors PRA analysis is to assess the economic impact of releases of radioisotopes, including the economic impact of protective actions taken to limit exposure to released materials.

• The LMP methodology, as endorsed in RG 1.233 (ML20091L698), does not use economic factors or cost-benefit analysis to determine events, classify SSCs, or evaluate the adequacy of defense-in-depth, consistent with the requirements in 10 CFR 50.34 which it addresses.

19 TerraPower Radiological Release Consequences Methodology TR

LBE EM: Conditional Consequence Quantification

• RG 1.247, section C.1.3.17 states the objective of conditional consequence quantification is to integrate the models and data developed in the preceding technical elements to quantify results of interest

• NRC staff review of TR information determined that:

• The use of MACCS in the LBE EM is consistent with the purposes for which MACCS was developed and is well within the limits of the codes applicability;

• The MACCS model inputs and accompanying data files and specifications are acceptable for use in the LBE EM because they are consistent with sample problems supplied with MACCS and NUREG/CR-7270;

• Uncertain parameters that contribute significantly to radiological consequences were analyzed and conservatively bounding values were prescribed in the LBE EM. and

• The LBE EM weather sampling approach is acceptable because it addresses the uncertainty in the weather in combination with the variability in meteorological conditions, consistent with the NRCs approach in probabilistic consequence analyses.

20 TerraPower Radiological Release Consequences Methodology TR

LBE EM Conclusions

• The TR methodology provides estimates of LBE radiological consequences for use in the LMP methodology consistent with the non-light water reactor radiological consequence analysis PRA elements detailed in section C.1.3.17 of RG 1.247.

• The LBE EM consequence analysis results when used in the LMP are sufficient to address the analysis requirements in 10 CFR 50.34(a)(4).

• The identification of MACCS to evaluate PRA consequences is appropriate because it is an NRC-developed, widely used PRA analytical tool specific to consequence analysis.

21 TerraPower Radiological Release Consequences Methodology TR

Design Basis Accident EM

• The objective of the DBA EM is to describe the methodology that would be used by a future applicant to calculate the highest TEDE received over any 2-hour period by a receptor on the EAB and the 30-day TEDE received by a receptor at the outer LPZ boundary, considering contributions due to inhalation and submersion dose

• The dose criteria are in 10 CFR 50.34(a)(1)(ii)(D)(1) and 10 CFR 50.34(a)(1)(ii)(D)(2) which specify a limiting dose of 25 rem TEDE for each DBA

• The NRC staff review determined that the DBA EM performs calculations consistent with the guidance contained in RG 1.183 for radiological consequence analysis assumptions and inputs 22 TerraPower Radiological Release Consequences Methodology TR

Control Room Habitability EM

• The objective of the CRH EM is to determine the dose consequences required to demonstrate habitability in the CR in conformance with Natrium PDC 19, which states in part that [a]dequate radiation protection shall be provided to permit access and occupancy of the control room under accident conditions without personnel receiving radiation exposures in excess of 5 rem total effective dose equivalent, as defined in § 50.2 for the duration of the accident

• The specific dose consequences calculated in the CRH EM are the 30-day TEDE dose received by a CR receptor considering inhalation and submersion dose, as well as gamma radiation shine from airborne radionuclides external to the CR, built up on filtration equipment and held in a compartment before release to environment 23 TerraPower Radiological Release Consequences Methodology TR

Control Room Habitability EM

• The NRC staff review determined that:

• The methods to calculate the inhalation and submersion doses are consistent with the discussions contained in the DBA EM. The CRH EM performs calculations consistent with RG 1.183 guidance for calculating inhalation and submersion doses and is therefore acceptable.

• The CRH EM describes a proprietary method for calculating shine dose received by control room operators

• The CRH EM is acceptable because the method produces integrated CR dose results that include inhalation, submersion, and shine pathways

• NRC staff will evaluate the acceptability of the specific methods used to calculate release-specific radiological source terms, CR atmospheric dispersion factors, and modeling of the CR used as input to the CRH consequence analysis during the review of an application that references this TR and implements the CRH EM 24 TerraPower Radiological Release Consequences Methodology TR

Appendix: Adapting the LBE EM for EPZ Sizing

• TR section 8, Appendix - Adaptation of Licensing Basis Event Evaluation Model to Emergency Planning Zone Sizing, describes minor changes to the LBE EM for use in the TerraPower PEP EPZ sizing methodology provided in TR NAT-3056, which is undergoing separate NRC review.

• The NRC staff determined that the adapted LBE EM described in the Appendix is acceptable because it provides dose results in the form of TEDE to an individual from a 96-hour exposure at various distances to address the PEP EPZ requirement in 10 CFR 50.33(g)(2).

• The LBE EM as adjusted by the TR Appendix provides information needed for the TerraPower PEP EPZ sizing methodology with respect to dose aggregation and evaluation of early deterministic health effects.

TerraPower Radiological Release Consequences Methodology TR 25

Limitations and Conditions

1. Application of the methodology in this TR with respect to the described deterministic and probability-based atmospheric dispersion modeling analyses and use of generic meteorological data is limited to sites within the contiguous United States unless technical justification for their applicability is provided.

2. The conclusions reached in this SE are not valid if a process other than that described in NEI 18-04 is used to perform the Natrium safety analysis.

TerraPower Radiological Release Consequences Methodology TR 26

Overall Conclusions

• NRC staff determined that the TR, subject to the limitations and conditions in the SE, provides an acceptable approach to develop analyses to aid in the determination of site-specific radiological release consequences for the proposed Natrium reactor designs.

• The NRC staff found that the discussion of the radiological consequence analysis PRA element in RG 1.247 was useful to ensure the completeness of the review of the LMP-related analysis methodology (LBE EM) 27 TerraPower Radiological Release Consequences Methodology TR

Acronyms CR - Control Room CRH - Control Room Habitability DBA - Design Basis Accident DCF - Dose Conversion Factor EAB - Exclusion Area Boundary EM - Evaluation Model EPA - Environmental Protection Agency EPRI - Electric Power Research Institute EPZ - Emergency Planning Zone FGR - Federal Guidance Report LBE - Licensing Basis Events LMP - Licensing Modernization Project MACCS - MELCOR Accident Consequence Code System NEI - Nuclear Energy Institute NLWR - Non-light water reactor NRC - Nuclear Regulatory Commission PAG - Protective Action Guides PRA - Probabilistic Risk Assessment PEP - Plume Exposure Pathway PDC - Principal Design Criteria QHO - Quantitative Health Objective RG - Regulatory Guide SE - Safety Evaluation SFR - Sodium Fast Reactor TEDE - Total Effective Dose Equivalent TR - Topical Report URD - Utility Requirements Document U.S. - United States TerraPower Radiological Release Consequences Methodology TR 28