ML24095A307
| ML24095A307 | |
| Person / Time | |
|---|---|
| Site: | 99902076 |
| Issue date: | 04/08/2024 |
| From: | Vechioli L NRC/NRR/DANU/UAL2 |
| To: | Terrestrial Energy USA |
| Lucieann Vechioli, NRR/DANU | |
| Shared Package | |
| ML24095A305 | List: |
| References | |
| EPID L-2021-TOP-0034 | |
| Download: ML24095A307 (1) | |
Text
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION TERRESTRIAL ENERGY USA, INC.
AUDIT PLAN FOR TOPICAL REPORT PRINCIPAL DESIGN CRITERIA FOR IMSR STRUCTURES, SYSTEMS, AND COMPONENTS EPID: L-2021-TOP-0034 Applicant:
Terrestrial Energy USA, Inc.
Applicant Address:
537 Steamboat Road, Suite 200, Greenwich, CT, 06830 Plant Name:
IMSR400 Project No.:
99902076
Background:
By letter dated December 29, 2023, (Agencywide Documents Access and Management System (ADAMS) Accession No. ML24053A171), issued to the U.S. Nuclear Regulatory Commission (NRC) on February 28, 2024, Terrestrial Energy USA (TEUSA), submitted Revision B of the topical report Principal Design Criteria for IMSR Structures, Systems, and Components for the NRC staff review and safety evaluation.
Following a comprehensive review, the NRC staff has determined that conducting a regulatory audit is necessary to facilitate the completion of the evaluation process. Therefore, the NRC staff will undertake the audit in accordance with this audit plan. This regulatory audit encompasses the examination and evaluation of primarily non-docketed information.
Purpose:
The purpose of the audit is for the NRC staff to increase its understanding of the topical report (TR) and identify information that will require docketing to support the NRC staffs regulatory findings. Performing a regulatory audit is necessary to assist the NRC staff in efficiently conducting its review and gaining insights to the applicants design information. The NRC staff plans to conduct the audit virtually at the NRC Headquarters in Rockville, Maryland via TEUSAs established electronic portal. However, should the NRC staff determine that an in-person audit would be a more efficient method to conduct the audit and gather needed information, the NRC staff may use that approach in addition to the virtual audit.
Regulatory Audit Basis:
The audit is conducted with the intent to gain understanding, to verify information, and to identify information that will require docketing to support the basis of a licensing or regulatory decision.
Information that the NRC staff relies upon to make the safety determination must be submitted on the docket. This regulatory audit is conducted in accordance with the following:
Title 10, Code of Federal Regulations (10 CFR) 52.137(a)(3)(i) requires that an application for a standard design approval include the principal design criteria (PDC) for a proposed facility.
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION 10 CFR 50.34(a)(3)(i) requires that an application for a construction permit include the PDC for a proposed facility.
10 CFR Part 50, Appendix A, contains the general design criteria (GDC) that establish the minimum requirements for the PDC for water-cooled nuclear power plants. Appendix A also establishes that the GDC are generally applicable to other types of nuclear power units and are intended to provide guidance in determining the PDC for such other units.
Regulatory Guide (RG) 1.232, Guidance for Developing Principal Design Criteria for Non-Light-Water Reactors, issued April 2018, describes the NRCs guidance on how the general design criteria (GDC) in Appendix A, General Design Criteria for Nuclear Power Plants, of Title 10 CFR Part 50, Domestic Licensing of Production and Utilization Facilities, may be adapted for non-light-water reactor (non-LWR) designs (Ref. 1).
Regulatory Audit Scope and Methodology:
The NRC staff will perform the audit in accordance with Office of Nuclear Reactor Regulation (NRR) Office Instruction LIC-111, Regulatory Audits, Revision 1 (ML19226A274). This audit will focus on supporting documents provided by TEUSA via the online reference portal to determine if additional information will require docketing to develop and support conclusions for the NRC staffs safety evaluation of the topical report. The scope of this audit includes, but is not limited to:
The PDCs that are related to the graphite core.
The PDCs associated with Instrumentation and Control (I&C) related to the Means of Reactor Protection.
The interface between systems.
Information and Other Material Necessary for the Regulatory Audit:
Specific analyses that provide design basis information used to support PDC should be available, such as:
- 1. Design information pertaining to the graphite core, for example:
- a. assessments pertaining to blockages/flow area alteration in channels and graphite displacement.
- 2. Design information pertaining to I&C relevant to the Means of Reactor Protection, for example:
- a. the I&C architecture (to include an I&C architecture drawing), along with a list of the safety functions that the I&C systems performs;
- b. any exemptions to regulatory requirements, such as IEEE Std. 603-1991, that may be required for this design; and, c.
the reactor design characteristics and expected performance during design basis events.
- 3. Design information regarding the interface between irradiated fuel system, off-gas system, containment atmosphere, cover gas, vapor in the upper head of the reactor vessel.
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION Topics for Discussion:
- 1. RG 1.232, Revision 0, Guidance for Developing Principal Design Criteria for Non-Light-Water Reactors, states that applicants may use RG 1.232 to develop all or part of the PDC and are free to choose among the Advanced Reactor Design Criteria (ARDC),
Sodium-Cooled Fast Reactor design criteria FR-DC, or Modular High-Temperature Gas-Cooled Reactors design criteria (MHTGR-DC) to develop each PDC after considering the underlying safety basis for the criterion and evaluating the rationale for the adaptation described in the RG. In each case, it is the responsibility of the designer or applicant to provide not only the PDC for the design but also how the PDC demonstrate adequate assurance of safety. Also, the selected PDCs will serve as the fundamental criteria for the NRC staff when reviewing the SSCs that make up a facility particularly when assessing the performance of their intended safety functions in design basis events postulated to occur during normal operations, anticipated operational occurrences (AOOs), and postulated accidents.
What is the necessary design, fabrication, construction, testing, and performance requirements for structures, systems, and components important to safety?
Provide supporting information that justifies how the PDCs ensure adequate safety.
- 2. TEUSA 20 through 25, in TR Rev B the applicant revises (( protection system to means of protection and this revision is being justified by relying on the inherent reactor design feature of strong negative reactivity coefficient of temperature. The TR explains that a reactor protected by an inherent design feature is better than protection provided by an engineering design feature such as a protection system, considering the fact that an inherent design feature is more reliable and has a faster response when compared to a physical protection system. However, the TEUSA PDCs are worded as though they refer to a physical system rather than an inherent attribute of the reactor. Examples are as follows:
TEUSA 20 refers to the means of reactor protection as being able to initiate automatically, sense accident conditions, and initiate the operation of systems and components.
TEUSA-21 refers to the reliability and in-service testability of the means of reactor protection.
TEUSA-22 refers to component design and principles of operation of the means of reactor protection.))
Further information is needed about whether TEUSA intends to rely on any physical systems to assure conformance with PDCs that include the term means of reactor protection, and the bases for that determination.
- 3. TEUSA states that [T]here are no systems that are designated as protection systems for the IMSR400. Due to the inherent and passive features of the IMSR400, there are currently no automatic reactor trips or system actuations that would be needed to mitigate AOOs or accident conditions. It also states that (( [T]he IMSR design relies on the safety aspects of its inherent negative temperature reactivity coefficient to support the magnitude and promptness of the reactivity response to off-normal events. ))
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION Further information is needed to understand the bases for these claims, including how the IMSR design temperature reactivity coefficient changes over the life of the reactor core and how the IMSR design temperature reactivity coefficient protects against AOOs and postulated accidents where the bulk temperature of the fuel salt is reduced.
- 4. It is unclear to NRC staff whether the I&C architecture is being implemented solely for supporting control functions, or whether it also supports safety functions. For example, the TR states [emphasis added]:...the IMSR does not contain I&C systems that are designated as protection systems in the same manner as protection systems are used in LWRs. The IMSR does employ instrumentation that performs safety functions of monitoring the condition of the IMSR core unit and operation of other key safety systems (such as the Internal Reactor Vessel Auxiliary Cooling System (IRVACS).
Clarifying information is needed, which may include an I&C architecture drawing, along with a list of the safety functions that the I&C systems perform.
- 5. The TR states, [p]resently there are no trip parameters identified for automatic initiation of the SDM rod drop, however the system is designed such that trip parameters can be added if identified by safety analysis.
Further information is needed to clarify whether the addition of trip parameters would contradict the description of the means of reactor protection, referring to inherent reactor attributes, which is referenced in other PDCs.
- 6. The staff requests a clarification providing a brief description, including a simplified diagram, of how the irradiated fuel system, off-gas system, containment atmosphere, cover gas, vapor in the upper head of the reactor vessel, and molten salt interface because these systems functions or how they interface is unclear.
- 7. It is unclear to staff whether any of the PDCs are intended to ensure graphite component integrity.
Further information is needed to clarify whether the graphite core is safety-related and, if so, which, if any, PDCs are intended to ensure that graphite components can perform their safety functions.
If the NRC staff determines that additional documentation needs to be made available on the portal after reviewing the requested information, it will generate new Open Items to request such information.
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION Team Assignments:
The audit team will consist of the following NRC staff from NRR.
NAME DIVISION BRANCH Role Lucieann Vechioli Feliciano Division of Advanced Reactors and Non-power Production and Utilization Facilities (DANU)
Advanced Reactor Licensing Branch 2 (UAL2)
Project Manager Mathew Gordon DANU Advanced Reactor Technical Branch 1 (UTB1)
Audit Leader, Lead Technical Reviewer Christopher Adams DANU Advanced Reactor Technical Branch 1 (UTB1)
Technical Reviewer Joseph Ashcraft Division of Engineering and External Hazards (DEX)
Instrumentation and Controls Branch (EICB)
Technical Reviewer Hanh Phan DANU Advanced Reactor Technical Branch 2 (UTB2)
Peer Reviewer Logistics:
The audit will take place in a virtual format, using Microsoft Teams, or via 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 read any documents placed in the online reference portal. The audit will begin March 20, 2024, and continue as necessary, with activities occurring intermittently during the audit period.
To improve the efficiency of the audit, TEUSA and the NRC staff discussed the use of the online reference portal (i.e., Watchdog), established by TEUSA, that would allow the NRC staff limited read-only access to the material and other technical information placed in the portal by TEUSA.
Use of the online reference portal is acceptable provided that TEUSA establishes measures to limit access to specific NRC staff (e.g., based on NRC e-mail addresses or the use of passwords which will only be assigned to the NRC staff directly involved in the audit on a need-to-know basis), and to make the documents view-only (i.e., prevent NRC staff from saving, copying, downloading, or printing any documents). The conditions associated with the online reference portal must be maintained throughout the audit process. The NRC staff who should initially be granted access to the portal are those listed in the Audit Team section above. As needed, the NRC Project Manager may provide TEUSA with the names of additional NRC staff who are added to the audit team and should subsequently be granted access.
When the NRC staff determines that any information on the portal is relevant to the safety determination, the NRC staff will request that TEUSA to place that information on the docket via the request for additional information (RAI) process. Additionally, the NRC staff will use the RAI or confirmation of information processes in lieu of using an exit meeting for that purpose. The NRCs licensing project manager will inform TEUSA via routine communications when the NRC staff no longer needs access to the portal.
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION Deliverables:
The NRC staff will develop any RAIs or confirmations of information, as needed, which will be provided to TEUSA via separate docketed correspondence. 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.
Reference:
1.
U.S. Nuclear Regulatory Commission, Regulatory Guide 1.232, Guidance for Developing Principal Design Criteria for Non-Light-Water Reactors, April 2018. ADAMS Accession No. ML17325A611).
If you have questions regarding this audit, please contact me via email at Lucieann.VechioliFeliciano@nrc.gov.
Sincerely,
/RA/
Lucieann Vechioli, Project Manager Advanced Reactors Licensing Branch 2 Division of Advanced Reactors and Non-Power Production and Utilization Facilities Office of Nuclear Reactor Regulation Date: April 8, 2024 Project No.: 99902076 cc: dcarleton@terrestrialusa.com
Package: ML24095A305 Audit Plan Proprietary: ML24066A060 Audit Plan Non-Proprietary: ML24095A307 NRR-106 OFFICE NRR/DANU/UAL2:PM NRR/DANU.UTB1: BC NRR/DANU/UAL2: BC NAME LVechioli GOberson MWentzel DATE 04/08/2024 04/08/2024 04/08/2024 OFFICE NRR/DANU/UAL2:PM NAME LVechioli DATE 04/08/2024