ML24127A055
| ML24127A055 | |
| Person / Time | |
|---|---|
| Site: | 99902100 |
| Issue date: | 05/16/2024 |
| From: | Stephanie Devlin-Gill Office of Nuclear Reactor Regulation |
| To: | TerraPower |
| References | |
| L-2023-TOP-0046 | |
| Download: ML24127A055 (1) | |
Text
TERRAPOWER, LLC - AUDIT PLAN FOR TOPICAL REPORT RADIOLOGICAL SOURCE TERM METHODOLOGY REPORT, REVISION 1 (EPID NO. L-2023-TOP-0046)
Applicant:
TerraPower, LLC Applicant Address:
15800 Northup Way, Bellevue, WA 98008 Plant Name:
Natrium Project No.:
99902100
Background:
By letter dated August 11, 2023, TerraPower, LLC (TerraPower) submitted topical report (TR) number TP-LIC-RPT-0003, Radiological Source Term Methodology Report, Revision 0 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML23223A234), which documents the radiological source term evaluation model (EM) development process for the Natrium reactor. On November 15, 2023, the U.S. Nuclear Regulatory Commission (NRC) staff determined that that additional information was needed for the staff to begin its detailed review and that TerraPower could supplement the submittal with the additional information (ML23292A269). On January 16, 2024, TerraPower supplied the supplemental information that the NRC staff requested by submitting Revision 1 (ML24017A115) of the TR as a replacement to the information contained Revision 0.
TerraPower requested that the NRC staff review and approve the EM presented in the 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) 50.34(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:
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).
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].
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:
Zachary Gran Reactor Scientist Michelle Hart Senior Reactor Engineer Stephanie Devlin-Gill Senior Project Manager, Audit Project Manager Roel Brusselmans Project Manager, Audit Project Manager Reed Anzalone Senior Nuclear Engineer, Natrium Technical Lead Logistics:
Entrance Meeting May 28, 2024, 1:00 PM Exit Meeting July 17, 2024, 4:00 PM 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 28, 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 at 301-415-5301 or via email at Stephanie.Devlin-Gill@nrc.gov.
Sincerely,
/RA/
Stephanie Devlin-Gill, Senior 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
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-0003 Radiological Source Term Methodology Report, Revision 1 The topical report (TR) cites Nuclear Energy Institute (NEI) 18-04, Revision 1, Risk-Informed Performance-Based Technology Inclusive Guidance for Non-Light Water Reactor Licensing Basis Development (ML19241A472). NEI 18-04 references 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 Regulatory Guide (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 guidance on the elements of a mechanistic source term contained in RG 1.247 and ASME/ANS RA-S-1.4-2021.
- 1. How will the risk-significant radionuclides be determined by the methodology for use in the consequence analysis? Confirm if this is a process that will be addressed by the evaluation model (EM). If not addressed by the EM, describe how risk-significant radionuclides will be determined.
- 2. Will this methodology be used to characterize release locations? If so, describe how release locations will be characterized?
- 3. How does this methodology determine the physical and chemical form of released radioisotopes? From review of information contained in TR Figure 4-1, Source Term Evaluation Model, the NRC staff understands that ((
)). Confirm what codes are used in this EM to determine the physical and chemical form of released radioisotopes. In addition, make available the
((
)) user manuals so that the NRC staff can better understand the computer code methods.
- 4. How are time dependent isotopic release rates to the atmosphere handled (e.g.
determination of timesteps, documentation of assumed timesteps, modeling a release over timesteps, number of timesteps for use in consequence assessment)? Will this aspect be addressed by the source term methodology EM or a different EM? TR Section 4.2, Evaluation Model Structure, contains some discussion related to the various codes and their timestep abilities. Confirm what methods will be used in this EM to characterize time dependent releases to the atmosphere.
- 5. How is the heat content (or energy) of the carrier fluid determined? TR Section 4.2 contains discussion related to the ability of ((
)) to model heat transfer of the carrier fluid. The NRC staff is confirming what codes the applicant will use in this EM to model the heat content of the carrier fluid.
- 6. Is plume buoyancy determined by this EM (e.g. release rate, release height, plume heat content)? Describe plans for determining plume buoyancy to support the calculation of radiological consequences for license applications.
- 7. How are radionuclide releases grouped into smaller representative source term groups or release categories? Are the representative events stated in TR Section 2.4, Identification and Ranking of Phenomena and Processes (i.e., fuel handling accident, sodium purification system leak, and unprotected loss of flow with degraded pump coastdown) the release categories used to address Section 4.3.16, Mechanistic Source Term Analysis (MS) of ASME/ANS RA-S-1.4-2021?
- 8. With regard to TR Section 4.2.5, Normal Operation Methodology, is there a difference in source term development for different plant conditions (e.g., accident vs. normal operations)? Also, provide information related to the computer code ((
)) to
OFFICIAL USE ONLY PROPRIETARY INFORMATION OFFICIAL USE ONLY - EXPORT CONTROLLED INFORMATION 2
OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - EXPORT CONTROLLED INFORMATION enable the NRC staffs understanding of the EM inputs. Specifically, provide the output of this computer code and what information is used to determine ((
)). The NRC staff is looking to gain an understanding of how inputs into the ((
)) computer code differ between normal and accident releases.
- 9. What will be the stated outputs of this radiological source term methodology TR?
Describe how these outputs are to be used by the radiological release consequences methodology TR, TP-LIC-RPT-0005 (ML23311A138) and confirm that they provide sufficient information for the follow-on analyses. What does the source term documentation look like and are there any example results available for audit?
- 10. In TR Section 2.2, Figures of Merit, what is the difference between the following:
- a. inhalation dose potential and inhalation dose,
- b. submersion dose potential and submersion dose.
- 11. Provide an overview discussion of functional containment as it relates to source term scenario development (e.g., what aspects of the design are credited for functional containment for each source term). Clarify the aspects of functional containment considered in the source term for each type of event being assessed, as well as the difference between modeling of functional containment versus other potential radionuclide transport barriers.
- 12. Provide additional discussion on the conservative approach ((
)) in TR Table 3-2, Phenomena/Processes with High and Medium Importance Ranking - Conservative Approaches. Also provide additional discussion of the conservative approaches described in TR Table 3-2.
- 13. Provide and discuss an example calculation to illustrate the Design Basis Accident source term modeling methodology.
- 14. In TR Table 4-7 Conservative Potential Approach Related to Phenomena/Processes,
((
))
- 15. Provide the NRC staff access to the following TR references in the electronic reading room: 21, 22, 23, and 24.