ML21228A184
| ML21228A184 | |
| Person / Time | |
|---|---|
| Issue date: | 08/31/2021 |
| From: | Mallecia Sutton NRC/NRR/DANU/UARL |
| To: | William Kennedy NRC/NRR/DANU/UARL |
| Sutton M | |
| References | |
| Download: ML21228A184 (3) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 August 26, 2021 MEMORANDUM TO: William Kennedy, Acting Chief Advanced Reactor Licensing Branch Division of Advanced Reactors and Non-Power Production and Utilization Facilities Office of Nuclear Reactor Regulation Signed by Sutton, Mall FROM: Mallecia Sutton, Senior Project Manager on 08/26/21 Advanced Reactor Licensing Branch Division of Advanced Reactors and Non-Power Production and Utilization Facilities Office of Nuclear Reactor Regulation
SUBJECT:
TERRAPOWER, LLC -
SUMMARY
OF JULY 22, 2021, PUBLIC MEETING TO DISCUSS THE PROBABILISTIC RISK ASSESSEMENT METHODOLOGY On July 22, 2021, the U.S. Nuclear Regulatory Commission (NRC) staff held an observation public meeting with TerraPower, LLC (TerraPower) to discuss their Probabilistic Risk Assessment (PRA). The staff posted the meeting notice in the NRCs Agencywide Documents Access and Management System (ADAMS) at Accession No. ML21188A068.
The presentation slides can be found at ADAMS Accession No. ML21196A058. The enclosure to this document lists the meeting attendees who participated.
The meeting began with NRC staff providing an introduction and logistical information pertaining to the public meeting. The staff explained that the meeting was an observation meeting and that TerraPower representatives would provide the NRC staff with an overview of the PRA methodology for the Natrium Reactor.
The NRC staff asked several questions during the meeting:
- 1. Is TerraPowers Natrium nuclear power plant (NPP) designed with the physical separation concept in addressing the aircraft impact and loss of large area events?
Answer: TerraPower clarified that its Natrium NPP is designed with enhanced design features and physical separation but did not provide any details.
- 2. Could TerraPower identify the risk significance of direct current, alternating current, and software failure, including the common-cause failures?
CONTACT: Mallecia Sutton, NRR/DANU 301-415-0673
W. Kennedy 2 Answer: TerraPower stated that, due to the inherent and passive safety features, TerraPowers Natrium NPP does not significantly depend on these systems, and thus they are not risk-significant contributors.
Answer: TerraPower stated that the Natrium PRA is built upon General Electric Hitachi (GEH) experience and PRISM PRA. TerraPower concluded that its PRA is in good developmental condition and in conformance with the non light-water reactor PRA standard.
- 4. Are there any challenges when applying the process for incorporation and evaluation of Defense-in-Depth (DID) described in Nuclear Energy Institute 18-04, Figure 5-4?
Answer: TerraPower stated that it applied the explicit Defense Line approach consistent with International Atomic Energy Agency Safety Standard No. SSR-2/1, Safety of Nuclear Power Plants: Design. TerraPower stated that it took this approach to minimize the number of needed design iterations and any surprises when the risk-informed performance-based evaluation of DID adequacy step is performed.
- 5. How does TerraPower set the reliability goals for passive structures, systems, and components (SSCs)?
Answer: TerraPower stated that the performance goals are designed for passive SSCs and it will be applying the reliability and integrity management process.
- 6. Staff inquired about the design margin accommodated by the reactor vessel auxiliary cooling system (RVACS).
Answer: TerraPower/GEH clarified that the RVACS has been designed to accommodate significant system degradation (e.g., duct blockages) while providing adequate residual heat removal.
- 7. Staff inquired about the use the functional reliability assessment of inherent feedback using SAS4a/SASSYS-1. Specifically, staff sought confirmation that this code package uses point kinetics that takes precalculated kinetics parameters (e.g., feedback coefficients) as input.
Answer: TerraPower/GEH confirmed staffs understanding and further clarified that core design tools like DIF3D are used to develop input for SAS4a/SASSYS-1.
- 8. Staff inquired about the strong inherent negative reactivity feedback for core reactivity control. Specifically, staff inquired about the potential for the Natrium core design to have a positive void coefficient and whether TerraPower/GEH plans to address this potential deterministically and/or through PRA.
Answer: TerraPower/GEH clarified that, based on the current design, a net positive void coefficient is likely, but that plans to address this potential are ongoing. During the public comment portion of the meeting, the Union of Concerned Scientists inquired about the need for an exemption if a reactor has a positive void coefficient. The NRC staff stated that the Commissions regulations (specifically General Design Criterion (GDC) 11 and similarly Advanced Reactor Design Criterion 11) require that the reactor design have a negative overall
W. Kennedy 3 power coefficient, and that departures from the Commissions regulations require exemptions.
Staff further stated that such exemptions, if required, would consider risk insights from the PRA.
- 9. Staff inquired about the applicability of previously conducted failure modes and effects analyses (FMEAs), such as those completed to support the GE PRISM design, to the Natrium.
Answer: TerraPower/GEH clarified that some system specific FMEAs have already been completed (e.g., the Natrium RVACS) but that the PRA for a construction permit is expected to rely on some generic studies. All system specific FMEAs are expected to be completed in support of an operating license application.
During the comment portion of the meeting, staff also responded to several public comments, including:
- 10. Does the NRC staff have an option if an exemption is needed for GDC 11?
Answer: The NRC staff has no position at this time for this question. The NRC staff will evaluate this when the application is accepted, docketed, and the applicant requests such an exemption.
- 11. Would the NRC staff be able to meet the submittal schedules in the regulatory engagement plan?
Answer: The NRC staff stated that it is planning to have the necessary resources available to support the schedule in the regulatory engagement plan.
- 12. Is the NRC expecting to issue a license condition for PRA?
Answer: The NRC staff could not provide an answer to this question because the staff does not have an application in front of them at this time.
The meeting concluded with an open discussion between the NRC staff and members of the public. The NRC staff requested feedback about how these meetings can be more engaging and how to increase participation by prospective applicants.
Enclosure:
List of Attendees
ML21228A184 OFFICE NRR/DANU/UARL/PM NRR/DANU/UARL/LA NRR/DANU/UARL/BC(A) NRR/DANU/UARL/PM NAME MSutton SLent WKennedy MSutton DATE 8/16/2021 8/16/2021 8/25/2021 8/26/2021 PUBLIC MEETING U.S. NUCLEAR REGULATORY COMMISSION Thursday, July 22, 2021 1:00 p.m. - 3:00 p.m.
List of Attendees Name Organization Brian Smith U.S. Nuclear Regulatory Commission (NRC)
Mallecia Sutton NRC William Kennedy NRC Hanh Phan NRC Timothy Drzewiecki NRC Alexandra Siwy NRC Michael Orenak NRC Michael Spencer NRC Eric Williams TerraPower, LLC (TerraPower)
Benoit Dionne TerraPower Brian Johnson TerraPower Tara Neider TerraPower Ryan Sprengel TerraPower Lisa Schichlein General Electric Hitachi (GEH)
Shelby Small GEH Dennis Henneke GEH Micelle Cats GEH Nikki Harless GEH Jonathan Li GEH George Wadkins GEH Steven Kline Bechtel Tim Beville Department of Energy (DOE)
Steven Kline Public Citizen Dave Grabaskas Public Citizen Adam Stein Public Citizen Christopher P. Chwasz Public Citizen Kalene Walker Public Citizen Edwin Lyman Union of Concerned Scientist Lisa Matis Public Citizen Justin Vazquez Public Citizen Ben Chen Public Citizen Steven Pope Public Citizen
2 Lawrence Svetlana Public Citizen Neil Sheehan Public Citizen Eric Williams Public Citizen Chris Sterreagan Public Citizen