ML23248A199
| ML23248A199 | |
| Person / Time | |
|---|---|
| Site: | 99902100 |
| Issue date: | 09/01/2023 |
| From: | Brusselmans R NRC/NRR/DANU/UAL1 |
| To: | George Wilson TerraPower |
| References | |
| EPID L-2023-TOP-0027, CAC 00431 | |
| Download: ML23248A199 (7) | |
Text
TERRAPOWER, LLC - AUDIT PLAN FOR TOPICAL REPORT AN ANALYSIS OF POTENTIAL VOLCANIC HAZARDS AT THE PROPOSED NATRIUM SITE NEAR KEMMERER, WYOMING, REVISION 0A (CAC / EPID NO.00431 / L-2023-TOP-0027)
Applicant:
TerraPower, LLC Applicant Address:
15800 Northup Way, Bellevue, WA 98008 Plant Name:
Natrium Project No.:
99902100
Background:
By letter dated April 25, 2023, TerraPower, LLC (TerraPower) submitted topical report (TR) TP-LIC-LET-0070 Revision 0A, An Analysis of Potential Volcanic Hazards at the Proposed Natrium Site Near Kemmerer, Wyoming (Agencywide Documents Access and Management System (ADAMS) Accession No. ML23115A387) to the U.S. Nuclear Regulatory Commission (NRC) staff. The TR describes TerraPowers volcanic hazard characterization for the design and operation of the proposed Natrium reactor at the Kemmerer Power Station Unit 1 site. On June 28, 2023, the NRC staff found that the material presented in the TR provides technical information in sufficient detail to enable the NRC staff to conduct a detailed technical review (ML23167B211).
TerraPower has requested the NRC staffs review and approval of the volcanic hazard characterization methodology as presented in the subject TR for potential use by future applicants, where applicable. The applicants overall licensing methodology follows the technology-inclusive, risk-informed, and performance-based approach outlined in Revision 0 of 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, Revision 0 (ML17325A611).
Purpose:
The purpose of the audit is for the NRC staff to gain a more detailed understanding of TerraPowers volcanic hazard characterization methodology for the proposed Kemmerer Power Station Unit 1 site near Kemmerer, Wyoming. A secondary purpose of the audit is to identify any information that will require docketing to support the NRC staffs safety evaluation. Therefore, the NRC staff is requesting access to TerraPower documents associated with the volcanic hazards assessment and supporting modeling as discussed in the TR. The NRC staff will summarize its observations in an audit report to be provided to TerraPower, as discussed below.
Regulatory Audit Basis:
The basis for the audit includes:
Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Appendix A, General Design Criteria for Nuclear Power Plants, as it relates to the consideration of the most severe natural phenomena historically reported for the site and surrounding area (General Design Criterion (GDC) 2). The GDC establish minimum requirements for the principal design criteria (PDC) for water-cooled nuclear power plants. However, they are also considered to be generally applicable to other types of nuclear power units and are intended to provide guidance in establishing the PDC for such other units1.
10 CFR 100.23(c), as it relates to the investigation of all geologic and seismic factors, including volcanic activity, that may affect the proposed nuclear power plant.
RG 4.26, Volcanic Hazards Assessment for Proposed Nuclear Power Reactor Sites, Revision 0 (ML20272A168), provides guidance on how to assess volcanic hazards at proposed nuclear power sites.
NUREG-0800, Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR edition, Section 2.5.1 Geological Characterization Information, Revision 5 (ML13316C067), and Section 2.5.3 Surface Deformation, Revision 6 (ML19009A314), which provide information on the content for characterizing the local and regional geology and considering sources of potential surface deformation, respectively.
Regulatory Audit Methodology:
The regulatory audit will follow the guidance in NRR Office Instruction LIC-111 Regulatory Audits, Revision 1 (ML19226A274), and focus on information provided by TerraPower in the electronic reading room.
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 inquiries included in the enclosure. These inquiries fall into the general categories of:
Inputs and assumptions to the PVHA_YM Version 2.0 computer code model, including:
o Any changes or alterations from the original version o Verification of alterations from the original version Inputs and assumptions to the ASHPLUME2 model including:
o Selection of run intervals for mafic and silicic tephra o Verification of alterations from the original version Demonstration of the ASHPLUME2 and PVHA_YM Version 2.0 computer codes Consideration of tephra hazards on proposed site including:
o Notification plans o Mitigating actions 1 The NRC staff is currently reviewing the proposed Natrium PDC, as described in TR NATD-LIC-RPRT-002, Principal Design Criteria for the Natrium Advanced Reactor, (ML23024A281). Natrium PDC 2, as proposed in NATD-LIC-RPRT-002, is similar to GDC 2.
Specific audit information needs and questions include:
Inquiries pertaining to the PVHA_YM Version 2.0 model:
- 1. The TR states that the PVHA_YM Version 2.0 code was used to confirm the probability of a new vent opening as part of the screening analysis. However, the PVHA_YM Version 2.0 documentation indicates that it was developed, validated, and verified exclusively for use at the Yucca Mountain site. What alterations were made to the PVHA_YM Version 2.0 code to run for the Leucite Hills volcanic field (LHVF)? Discuss the verification and validation process for these model modifications.
- 2. The PVHA_YM Version 2.0 results in the following figures are difficult to read (low resolution pictures). The NRC staff requests access to higher resolution copies of the following figures:
Figure 15, Smoothing factors (i.e., bandwidths) for (A) Gaussian and (B)
Epanechnikov kernels, Figure 16, Evaluation of changes in smoothing bandwidth for a Gaussian kernel, using PVHA_YM Version 2.0, and Figure 17, Evaluation of changes in smoothing bandwidth for an Epanechnikov kernel, using PVHA_YM Version 2.0.
- 3. Provide a demonstration of the PVHA_YM Version 2.0 code as modified and used for the analysis. Additionally, provide the input file used in the analysis.
Inquiries pertaining to the ASHPLUME2 Model:
- 4. Section 6.2, Modifications to ASHPLUME Version 1.0, of the TR describes the modifications TerraPower made to create the ASHPLUME2 model and states that the changes were verified to produce the correct distribution. How were these modifications verified?
- 5. Provide a demonstration of the ASHPLUME2 code as modified and used for the analysis. Additionally, provide the input file used in the analysis.
- 6. Section 6.4, Mafic Tephra-Fall Hazards at the Proposed Natrium' Site, of the TR describes numerical modeling of tephra hazards. TerraPower describes that the ASHPLUME2 runs were performed along a specified axis of the source volcanic field.
The LHVF is divided into 2-kilometer-long segments, the Upper Wind River Basin realizations were conducted every 1-kilometer (km) along its axis, the Blackfoot Reservoir volcanic field (BRVF) realizations were conducted every 5 km, and the Eastern Snake River Plain realizations were conducted every 4 km. What is the basis for the distance realizations performed along each axis, which varies for the different sources for both mafic and silicic tephra hazards?
- 7. In addition to the observations made in Question 6, above, there was also a difference in realization intervals for silicic tephra hazards and between mafic and silicic hazards for the same source. For example, the Eastern Snake River Plain uses different intervals for silicic (2 km) and mafic (4 km) and for the BRVF, a 5 km interval was used for mafic and 2 km interval for silicic. Across the silicic tephra sources, intervals range from 1 km for the Curlew Valley up to 4 km for Yellowstone. What was the reasoning behind choosing
different realization intervals for the individual silicic tephra sources? Would choosing the same realization intervals for both mafic and silicic tephra events alter the results in a meaningful way?
- 8. In Section C, Leucite Hills, of Figure 23, Results of hazard calculations for LHVF eruption sources, the Leucite Hills mafic tephra hazard shows a gap in the results between about 30-50 km per hour (km/hr) wind speed. Similar gaps exist in Section C, BRVF, of Figure 27, Results of hazard calculations for BRVF eruption sources, around 50 km/hr wind speed and in Section C, BRVF, of Figure 33, Results of silicic tephra-fall hazard calculations for BRVF eruption sources, around 50 km/hr. Explain the gaps in the results in these figures.
Inquiries related to hazard assessment:
- 9. Section 7, Analysis of Silicic Tephra-Fall Hazards, mentions that there is a lack of preservation of smaller volume (<1 km3) eruptions in the site region. Does the lack of preservation of smaller volume (<1 km3) eruptions affect any of the assumptions made for the volume of silicic eruptions?
Inquiries related to mitigation actions:
- 10. Section 10.3, Operational Activities, discusses several operational activities that may be implemented to mitigate tephra hazards at the proposed site. However, it is unclear whether these are actual planned actions or a list of potential actions to be considered and finalized in a future license application. How are these actions going to be addressed in a future license application (e.g., operating license application) that TerraPower plans to submit and what would be considered the initiating event?
- 11. Section 10.3 also discusses the role of the U.S. Geological Survey (USGS) Yellowstone Volcano Observatory in monitoring the volcanic source, performing any modeling of potential hazards, and issuing notifications of impending events. The underlying implication appears to be that the USGS will be performing that modeling using the Ash3d computer code, should it be necessary. What would be the time difference between start of the event and completion of model to determine if tephra reaches the site? Would this calculation time be considered adequate to implement the planned mitigating actions, or will the initiation of mitigating actions occur before the completion of the hazard modeling?
- 12. If relying on the USGS for notification of an impending event to begin the implementation of mitigating activities, how does the applicant expect to receive that notification?
- 13. The applicant will need to clarify what the initiating event would be to implement the proposed operational activities to mitigating an impending volcanic hazard reaching the site. Would initiation of these mitigating measures be contingent on a combination of notification of an impending event and a determination that the event likely to deposit tephra at the site? Conversely, would mitigating actions begin immediately upon notification of an event, regardless of whether the Ash3d modeling is complete?
Team Assignments Jenise Thompson Geologist, Audit Lead
Jason White Meteorologist Scott Stovall Seismologist Stephanie Devlin-Gill Senior Project Manager Roel Brusselmans Project Manager Logistics Entrance Meeting September 11, 2023, 9:00 a.m.
Exit Meeting October 13, 2023, 4:00 p.m.
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 September 11, 2023, 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 online reference portal.
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 301-415-0829 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
ML23248A199 NRR-106 OFFICE NRR/DANU/UAL1:PM NRR/DANU/UAL1:LA NRR/DEX/EXHB NAME SDevlin-Gill DGreene JThompson DATE 8/31/2023 8/31/2023 8/31/2023 OFFICE NRR/DEX/EXHB:BC NRR/DANU/UAL1:BC NRR/DANU/UAL1:PM NAME BHayes WJessup RBrusselmans DATE 8/31/2023 9/1/2023 9/1/2023