ML24103A224

Terrapower, LLC - Audit Plan for TP-LIC-RPT-0005, Radiological Release Consequences Methodology Topical Report, Revision 0 (Cac/Epid No. 000431/L-2023-TOP-0055)

ML24103A224
Person / Time
Site:	99902100
Issue date:	04/24/2024
From:	Brusselmans R NRC/NRR/DANU/UAL1
To:	George Wilson TerraPower
References
CAC 000431, EPID L-2023-TOP-0055
Download: ML24103A224 (1)

Text

1 TERRAPOWER, LLC - AUDIT PLAN FOR TP-LIC-RPT-0005, RADIOLOGICAL RELEASE CONSEQUENCES METHODOLOGY TOPICAL REPORT, REVISION 0 (CAC / EPID NO. 000431 / L-2023-TOP-0055)

Applicant:

TerraPower, LLC Applicant Address:

15800 Northup Way, Bellevue, WA 98008 Plant Name:

Natrium Project No.:

99902100

Background:

By letter dated November 6, 2023, TerraPower, LLC (TerraPower) submitted topical report (TR)

TP-LIC-RPT-0005, Radiological Release Consequences Methodology Topical Report, Revision 0 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML23311A139) to the U.S. Nuclear Regulatory Commission (NRC) staff. The TR provides three evaluation models (EMs) that will be used to determine the consequences of radiological release source terms developed for nuclear power plants using the Natrium sodium fast reactor design according to an interfacing TR, TP-LIC-RPT-0003, Radiological Source Term Methodology Report, Revision 1 (ML24017A116). TP-LIC-RPT-0003 is also under review by the NRC staff. On December 18, 2023, the NRC staff found that the material presented in the TR provides technical information in sufficient detail such that the NRC staff to conduct a detailed technical review (ML23333A070).

TerraPower requested that the NRC staffs review and approval of the EMs presented in this TR for use by applicants using TerraPowers Natrium reactor design as part of future licensing submittals. TerraPowers overall licensing approach for the Natrium reactor design follows the Licensing Modernization Project (LMP) methodology described in Nuclear Energy Institute (NEI) 18-04, Revision 1, Risk-Informed Performance-Based Technology Inclusive Guidance for Non-Light Water Reactor Licensing Basis Development (ML19241A472). Regulatory Guide (RG) 1.233, Guidance for a Technology-Inclusive, Risk-Informed, and Performance-Based Methodology to Inform the Licensing Basis and Content of Applications for Licenses, Certifications, and Approvals for Non-Light Water Reactors, Revision0 (ML20091L698) endorses the LMP methodology described in NEI 18-04.

Purpose:

The purpose of the audit is for the NRC staff to gain a more detailed understanding of TerraPowers EMs presented in the TR. A secondary purpose of the audit is to identify any information that will require docketing to support the NRC staffs safety evaluation.

Regulatory Audit Basis:

The basis for the audit includes the following regulatory requirements:

Title 10 of the Code of Federal Regulations (10 CFR) 50.33(g)(2) with respect to radiological consequence analyses used to determine the size of the plume exposure pathway emergency planning zone for applicants adopting 10 CFR 50.160, Emergency

2 preparedness for small modular reactors, non-light-water reactors, and non-power production or utilization facilities.

10 CFR 50.34(a) with respect to the following minimum information to be included in a preliminary safety analysis report submitted as part of a construction permit application:

o 10 CFR 50.34(a)(1)(ii)(D)(1): An individual located at any point on the boundary of the exclusion area for any 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> period following the onset of the postulated fission product release, would not receive a radiation dose in excess of 25 rem[ ]

total effective dose equivalent (TEDE).

o 10 CFR 50.34(a)(1)(ii)(D)(2): An individual located at any point on the outer boundary of the low population zone, who is exposed to the radioactive cloud resulting from the postulated fission product release (during the entire period of its passage) would not receive a radiation dose in excess of 25 rem [TEDE].

o 10 CFR 50.34(a)(4) requires a preliminary analysis and evaluation of the design and performance of structures, systems, and components of the facility with the objective of assessing the risk to public health and safety resulting from operation of the facility and including determination of the margins of safety during normal operations and transient conditions anticipated during the life of the facility, and the adequacy of structures, systems, and components provided for the prevention of accidents and the mitigation of the consequences of accidents.

Regulatory Audit Methodology:

The regulatory audit will follow the guidance in Office of Nuclear Reactor Regulation Office Instruction LIC-111 Regulatory Audits, Revision 1 (ML19226A274), and focus on information provided by TerraPower in an electronic reading room (ERR).

Information and Other Material Necessary for the Regulatory Audit:

The NRC staff requests TerraPower to make available the information and/or subject matter experts necessary to respond to the audit questions included in the enclosure.

Team Assignments:

Michelle Hart Senior Reactor Engineer, Audit Lead Stephanie Devlin-Gill Senior Project Manager, Audit Project Manager Roel Brusselmans Project Manager, Audit Project Manager Reed Anzalone Senior Nuclear Engineer, Natrium Technical Lead Keith Compton Senior Reactor Scientist Zachary Gran Reactor Scientist Mike Mazaika Meteorologist Kyle Clavier NRC Contractor Logistics:

Entrance Meeting May 7, 2024, 4:00PM Exit Meeting June 28, 2024, 4:00 PM

3 Audit meetings will take place in a virtual format, using Microsoft Teams or another similar platform. Audit meetings will be scheduled on an as-needed basis after the entrance meeting and once the NRC staff has had the opportunity to review any documents placed in the online reference portal. The audit will begin on May 7, 2024, and continue as necessary, with activities occurring intermittently during the audit period. The audit period may be reduced or extended, depending on the progress made by the NRC staff and TerraPower in addressing audit questions.

Special Requests:

The NRC staff requests that TerraPower ensure that their technical staff are available to answer questions during the audit. The NRC staff also requests that TerraPower provide access to supporting documents via the TerraPower ERR.

Deliverables:

At the completion of the audit, the audit team will issue an audit summary within 90 days after the exit meeting but will strive for a shorter duration. The audit summary will be declared and entered as an official agency record in ADAMS and be made available for public viewing through the publicly available records component of ADAMS.

If you have questions about this audit, please contact me by phone at 301-415-0829 or via email at Roel.Brusselmans@nrc.gov.

Sincerely,

/RA/

Roel Brusselmans, Project Manager Advanced Reactors Licensing Branch 1 Division of Advanced Reactors and Non-Power Production and Utilization Facilities Office of Nuclear Reactor Regulation Project No.: 99902100

Enclosure:

As stated cc: TerraPower Natrium via GovDelivery

Pkg: ML24103A221 Public: ML24103A224 Non-Public: ML24103A223 NRR-106 OFFICE NRR/DANU/UAL1:PM NRR/DANU/UAL1:PM NRR/DANU/UAL1:LA NAME RBrusselmans SDevlin-Gill DGreene DATE 4/3/2024 04/04/2024 4/10/2024 OFFICE NRR/DANU/UTB2:BC NRR/DANU/UAL1:BC NRR/DANU/UAL1:PM NAME CdeMessieres WJessup RBrusselmans DATE 4/3/2024 4/12/2024 4/24/2024

OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - EXPORT CONTROLLED INFORMATION Enclosure OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - EXPORT CONTROLLED INFORMATION Audit Questions Related to TP-LIC-RPT-0005 Radiological Release Consequences Methodology Topical Report, Revision 0 Licensing basis event (LBE) consequence analysis EM The TR states that the LBE consequence analysis EM is used in part to perform select tasks described in NEI 18-04, as endorsed in RG 1.233. NEI 18-04 cites the American Society of Mechanical Engineers (ASME) American Nuclear Society (ANS) probabilistic risk assessment standard, RA-S-1.4, which is endorsed with exceptions in RG 1.247, Acceptability of Probabilistic Risk Assessment Results for Non-Light Water Reactor Risk-Informed Activities (ML21235A008). The following questions were informed, in part, by the ASME/ANS RA-S-1.4-2021 radiological consequence analysis element, described in RG 1.247, Section C.1.3.17, Radiological Consequence Analysis Probabilistic Risk Assessment Element.

Specifically, the NRC staff seeks additional clarification on the application of the MELCOR Accident Consequence Code System (MACCS) code and details on MACCS model execution for the purposes of evaluating radiological release consequences for LBEs that are used in a license application which uses the NEI 18-04 approach.

1. Regarding the radionuclide release characterization described in TR Section 3.5.1, Isotope Sensitivity Method, provide clarification on the following topics:

a. How the isotope sensitivity analysis aggregates across exposure pathways and how it accounts for exposure duration.

b. With respect to the radionuclides which were screened out based on ((

)), what is meant by ((

)) for a radionuclide? Does this suggest that the MACCS dose ((

)) files did not include the values, or that they are not available in general?

c. The TR does not provide a list of radionuclides that were screened out due to

((

)), so it is unclear if any of the radionuclides that would contribute significantly to individual dose were screened out (e.g., novel radionuclides ((

)) that are not included in FGR13GyEquiv_RevA.inp file in MACCS). How was it assessed that those radionuclides which were screened out would not contribute significantly to the dose result?

2. Regarding TR Section 3.5.2, Adaptive Plume Algorithm, clarify whether the adaptive plume algorithm may result in plume segments significantly greater than one hour in duration. The NRC staff notes that the use of plume segments significantly longer than 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> may affect the choice of appropriate plume meander model used in MACCS.

Does the LBE EM take this into consideration to ensure that the releases to environment are appropriately modeled?

3. Regarding the LBE EM site characterization as described throughout TR Section 3.6, MACCS Model Parameters, provide information to address the following topics:

a. Clarify the effect of uniform population distribution on population-weighted outputs. For example, a population concentrated close to the site would, all else equal, result in a higher population-weighted 10-mile risk than a uniform population over the 10-mile radius.

OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - EXPORT CONTROLLED INFORMATION 2

OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - EXPORT CONTROLLED INFORMATION

b. The analysis area (e.g., 10-mile zone, 50-mile zone) does not appear to be specified in the MACCS model; provide the analysis area used for each of the consequence metrics under consideration.

4. Regarding the LBE EM meteorological data described in TR Section 3.6.1, Data File Specifications, provide information to address the following topics:

a. Clarify whether the TR would apply only before site selection or whether it could be used after site selection, and whether this would affect the source of meteorological data.

b. Clarify how the generic meteorological data from Electric Power Research Institute report 3002003129, Advanced Nuclear Technology: Advanced Light Water Reactor Utility Requirements Document (URD), would be shown to be appropriate for a specific site.

c. Describe whether the URD generic meteorological data provides sufficient meteorological information to successfully complete a MACCS code calculation with respect to the atmospheric dispersion model (e.g., at least one full annual cycle of hourly meteorological data that are representative of long-term meteorological conditions of the site). Clarify how the quality and completeness of meteorological data is assessed for the URD data. The NRC staff notes that RG 1.23, Meteorological Monitoring Programs for Nuclear Power Plants, Revision 1 (ML070350028), provides one acceptable approach.

5. Regarding the LBE EM atmospheric transport and diffusion, as described in TR Sections 3.6.2, Atmospheric Dispersion, and 3.6.3, Plume Deposition, provide information to address the following topics:

a. Clarify how uncertainty in dispersion coefficients can be assessed if a lookup table is used.

b. Clarify whether a user of this methodology is directed to use their own plume buoyancy or the given default constant value for a low sensible heat release rate.

c. Clarify the technical basis (e.g., primary reference) for the resuspension parameters.

6. Regarding the LBE EM modeling of protective actions, as described in TR Section 3.6.5, Protective Actions, provide information to address the following topics:

a. Clarify how the individual latent cancer risk will be computed without consideration of long-term protective actions.

b. Clarify how dose reduction factors associated with occupancy of structures or vehicles are developed and applied.

7. Regarding the LBE EM dosimetry modeling and use of MACCS, provide information to address the following topics:

a. Clarify how the MACCS parameter L-ICRP60ED relates to the TEDE. TR Section 3.6.1 states that DCFs from the FGR13GyEquiv_RevA.inp file supplied with MACCS are used which reflects total effective dose (TED) based on Federal Guidance Report No. 13: Cancer Risk Coefficients for Environmental Exposure

OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - EXPORT CONTROLLED INFORMATION 3

OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - EXPORT CONTROLLED INFORMATION to Radionuclides, (FGR-13). The NRC staff notes that the MACCS DCF file has recently been updated so both TED and TEDE, as well as FGR-13 dose coefficients, can be used from the same DCF file.

b. Clarify how MACCS will be configured to estimate a 30-day dose (e.g., Will MACCS parameter ENDEMP be set to 30 days? Will additional time be added to ENDEMP to allow for transit of radionuclides?)

c. Clarify the exposure duration for MACCS parameter PWILCF (related to individual latent cancer risk) and how that relates to typical practice for comparison to the quantitative health objectives.

8. The NRC staff notes that TR Section 3.6.6, Dosimetry, states dose is computed with the [linear no threshold (LNT)] model. Though dose is an input to the LNT model, the LNT model applies to health effects and not dose. Clarify whether the statement dose is computed with the LNT model in the TR could be phrased as, cancer fatality risk is computed with the LNT model.

9. Regarding the LBE EM treatment of uncertainty and conditional consequence quantification, provide information to address the following topics:

a. Clarify the source of parameter distributions to be used in sensitivity and uncertainty analyses.

b. Clarify how model uncertainty will be addressed.

c. Clarify how presentation of meteorological variability (used to estimate the mean, 5th, and 95th percentiles) will be combined with the estimation of weather uncertainty.

Design basis accident EM

10. The NRC staff requests the documentation related to the RRCAT computer code be made available for audit (e.g., user manual and other documents that provide insight into the calculations that are done by this computer code). This information will assist the NRC staff in better understanding how the RRCAT computer code follows the applicable consequence analysis models contained in RG 1.183, Alternative Radiological Source Terms for Evaluating Design Basis Accidents at Nuclear Power Reactors, Revision 1 (ML23082A305), and the RADTRAD consequence analysis code.

Control room habitability EM

11. The NRC staff requests that example calculations, or other resources, be made available for audit to assist the NRC staff in understanding how the shine dose conversion factor (SDCF) calculation is being implemented in this EM. The supporting

((

)) code input and output files and supporting technical report information would assist the NRC staff understand how the proposed SDCF is being implemented.