ML20294A337

Letter and Final Safety Evaluation for Kairos Power, LLC Topical Report-KP Fhr Risk-Informed Performance-Based Licensing Basis Development Methodology (Revision 1) (EPID No. L-2019-TOP-0009/CAC No. 000431)

ML20294A337
Person / Time
Site:	99902069
Issue date:	11/10/2020
From:	Beasey D NRC/NRR/DANU/UARL
To:	Hastings P Kairos Power
Magruder S
References
CAC 000431, EPID L-2019-TOP-0009
Download: ML20294A337 (12)

Text

November 10, 2020 Mr. Peter Hastings Vice President, Regulatory Affairs and Quality Kairos Power LLC 707 W Tower Ave Alameda, CA 94501

SUBJECT:

FINAL SAFETY EVALUATION FOR KAIROS POWER LLC TOPICAL REPORT KP-FHR RISK-INFORMED PERFORMANCE-BASED LICENSING BASIS DEVELOPMENT METHODOLOGY (REVISION 1) (EPID NO. L-2019-TOP-0009/CAC NO. 000431)

Dear Mr. Hastings:

By letter dated August 6, 2019 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML19217A420), Kairos Power LLC (Kairos Power, the applicant) submitted for U.S. Nuclear Regulatory Commission (NRC) staff review, Topical Report (TR)

KP-FHR Risk-Informed Performance-Based Licensing Basis Development Methodology. The NRC staff provided initial feedback and questions to Kairos Power on January 8, 2020 (ADAMS Accession No. ML20009E754), and on March 19, 2020 (ADAMS Accession No. ML20104A031). In response to these questions and following a teleconference between the NRC staff and Kairos Power, the applicant submitted an updated TR (Revision 1) by letter dated April 10, 2020 (ADAMS Accession No. ML20101P623), on which this final safety evaluation (SE) is based.

A draft SE was issued on September 9, 2020 (ADAMS Accession No. ML20191A357). This draft SE was discussed with the Advisory Committee on Reactor Safeguards (ACRS) Kairos Power Subcommittee on September 24, 2020. The ACRS discussed the SE at a full committee meeting on October 9, 2020 and decided not to write a letter report on the TR. The NRC staffs final SE for TR KP-FHR Risk-Informed Performance-Based Licensing Basis Development Methodology (Revision 1) is enclosed.

If you have any questions, please contact Stewart Magruder at 301-348-5766 or by e-mail at Stewart.Magruder@nrc.gov.

Sincerely,

/RA/

Benjamin G. Beasley, Chief Advanced Reactor Licensing Branch Division of Advanced Reactors and Non-Power Production and Utilization Facilities Office of Nuclear Reactor Regulation Project No. 99902069

Enclosure:

Final SE

ML20294A337 *via e-mail OFFICE NRR/DANU/UARL/PM*

NRR/DANU/UARL/LA*

NRR/DANU/UART/BC*

NAME SMagruder SLent MHayes DATE 10/14/2020 10/22/2020 10/22/2020 OFFICE OGC*

NRR/DANU/UARL/BC*

NAME MASpencer BBeasley DATE 11/04/2020 11/10/2020 Enclosure UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 FINAL SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO TOPICAL REPORT KP-FHR RISK-INFORMED PERFORMANCE-BASED LICENSING BASIS DEVELOPMENT METHODOLOGY (REVISION 1)

KAIROS POWER, LLC PROJECT NO. 99902069

1.0 INTRODUCTION

By letter dated August 6, 2019 (Reference 5), Kairos Power LLC (Kairos Power, the applicant) submitted for U.S. Nuclear Regulatory Commission (NRC) staff review, Topical Report (TR)

KP-FHR Risk-Informed Performance-Based Licensing Basis Development Methodology. On October 3, 2019 (Reference 2), the NRC staff found that the material presented in the TR provides technical information in sufficient detail to enable the staff to conduct a detailed technical review.

The applicant requested the NRC staffs review and approval to use the methodology presented in the TR to select the licensing basis events (LBEs) for, and classify the structures, systems, and components (SSCs) and assess the defense-in-depth (DID) adequacy of, a Fluoride-Salt-Cooled, High-Temperature Reactor (KP-FHR). The methodology would be used as part of safety analysis reports required by Title 10 of the Code of Federal Regulations (10 CFR) Part 50 Domestic Licensing of Production and Utilization Facilities, and 10 CFR Part 52, Licenses, Certifications, and Approvals for Nuclear Power Plants.

As part of the NRC staff review, initial feedback and questions were provided to the applicant on January 8, 2020 (Reference 6), and March 19, 2020 (Reference 7). In response to these questions and a teleconference with the NRC staff, the applicant submitted Revision 1 of the TR on April 20, 2020 (Reference 12). This safety evaluation (SE) is based on Revision 1 of the TR.

2.0 REGULATORY EVALUATION

The regulations in 10 CFR 50.34, 10 CFR 52.47, 10 CFR 52.79, 10 CFR 52.137, and 10 CFR 52.157 contain the technical requirements for applications for a construction permit, operating license, standard design certification, combined license, standard design approval, and manufacturing license, respectively. The applicable portions of the regulations above require a safety analysis and an evaluation of the safety features and barriers to a radioactive release to be included in a preliminary or final safety analysis report (FSAR).

The safety features and barriers to a radioactive release are required by 10 CFR 50.34(a)(1)(ii)(D) to be evaluated to ensure that:

(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 [Roentgen equivalent man] total effective dose equivalent (TEDE).

(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 total TEDE.

This requirement is echoed for the FSAR in 10 CFR 50.34(b)(11) and for Part 52 licensing paths in 10 CFR 52.47(a)(2)(iv), 10 CFR 52.79(a)(1)(vi), 10 CFR 52.137(a)(2)(iv), 10 CFR 52.157(d).

In addition to addressing these regulations, the TR also addresses the quantitative health objectives (QHOs) in the NRC Safety Goal Policy Statement, 51 FR 30028, Safety Goals for the Operations of Nuclear Power Plants, which are as follows:

The risk to an average individual in the vicinity of a nuclear power plant of prompt fatalities that might result from reactor accidents should not exceed one-tenth of one percent (0.1%) of the sum of prompt fatality risks resulting from other accidents to which members of the U.S. population are generally exposed.

The risk to the population in the area of nuclear power plant of cancer fatalities that might result from nuclear power plant operation should not exceed one-tenth of one percent (0.1%) of the sum of cancer fatality risks resulting from all other causes.

Regulations in 10 CFR 50.2 define safety-related SSCs as those SSCs that are relied upon to remain functional during and following design basis events to assure:

(1) The integrity of the reactor coolant pressure boundary (2) The capability to shut down the reactor and maintain it in a safe shutdown condition; or (3) The capability to prevent or mitigate the consequences of accidents which could result in potential offsite exposures comparable to the applicable guideline exposures set forth in § 50.34(a)(1) or § 100.11 of this chapter, as applicable.

Kairos Power intends to request an exemption from the first safety-related criterion above as discussed in another TR, Principal Design Criteria for the Kairos Power Fluoride Salt-Cooled High Temperature Reactor, KP-TR-003, December 2018 (Reference 11). The TR under review in this SE does not provide a justification for a requested exemption, and the staff is not taking a position in this SE on whether such an exemption would be granted. The guidance in Nuclear Energy Institute (NEI) 18-04 provides a methodology to identify the SSCs that would fall under only the third criterion above. This TR explicitly adds the second criterion (SSCs that assure the capability to shut down the reactor and maintain it in a safe shutdown condition) to the definition of safety-related SSCs to ensure that the portions of the 10 CFR 50.2 definition for which Kairos does not intend to request an exemption are addressed.

The TR references Draft Regulatory Guide DG-1353 (Reference 1), which provided draft NRC staff guidance on using a technology-inclusive, risk-informed, and performance-based methodology to inform the licensing basis and content of applications for non-light water reactors (non-LWRs). The DG-1353 endorsed, with clarifications, NEI 18-04, Draft Report Revision N (Reference 3), as one acceptable method for non-LWR designers to use when carrying out these activities and preparing their applications. In December 2019, the NRC staff submitted to the Commission SECY-19-0117, 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. (Reference 8) The SECY paper requested that the Commission find that the staff's use of the technology-inclusive, risk-informed, and performance-based methodology described in the paper (referring to DG-1353 and NEI 18-04, Revision 1 (Reference 4)), is a reasonable approach to establish key parts of the licensing basis and content of applications for licenses, certifications, and approvals for non-LWRs. The Commission issued a Staff Requirements Memorandum (SRM) to SECY 0117 (Reference 9), which approves the use of the technology-inclusive, risk-informed, and performance-based methodology described in SECY-19-0117 as a reasonable approach for establishing key parts of the licensing basis and content of applications for licenses, certifications, and approvals for non-LWRs. Subsequently, DG-1353 was finalized and issued as Regulatory Guide (RG) 1.233, Revision 0 (Reference 10), which endorses with clarifications, NEI 18-04, Revision 1 as one acceptable method for non-LWR designers to use when carrying out these activities and preparing their applications.

This TR provides the applicants methodology for LBE identification, SSC classification, and DID adequacy using the guidance in DG-1353 and NEI 18-04, Revision 1. As part of this review, the staff confirmed there is no significant change from DG-1353 to RG 1.233 or in the primary referenced document NEI 18-04, Revision N to NEI 18-04, Revision 1. The staff confirmed that the guidance and clarifications in DG-1353 and RG 1.233 are the same.

The methodology does not exempt licensing applicants of the KP-FHR design from applicable regulations, nor does it address all regulations applicable to nuclear power plants. Rather, the TR describes the methodology to inform the safety analysis report for the KP-FHR design, which demonstrates compliance with the regulations.

3.1 INTRODUCTION

This TR provides a KP-FHR-specific methodology for the selection of LBEs, classification and special treatment of SSCs, and assessment of DID adequacy, which are considered fundamental to the safe design of a nuclear reactor, including a non-LWR. The staff finds that this TR:

Is based on NEI 18-04, Revision 1, (Reference 4) and DG-1353 (Reference 1) which has been finalized and issued as RG 1.233, Revision 0 (Reference 10). NEI 18-04, Revision 1, has been endorsed by the NRC staff via RG 1.233, Revision 0, with clarifications. The applicable clarifications have been incorporated into the TR; Is a customized version of the technology-inclusive NEI 18-04 methodology for the KP-FHR technology; and Deviates from NEI 18-04 with a limited number of minor differences that do not alter the principles and methodology of DG-1353 and NEI 18-04.

As a result, the NRC staff narrowed its review scope to assessing the differences between this TR and NEI 18-04 and confirming that this TR incorporates the applicable clarifications identified in RG 1.233. The NRC staff reviewed all the differences but primarily focused its review on those considered to be of some significance.

Since the TR is based on NEI 18-04 and guidance included in RG 1.233, statements from RG 1.233 regarding exemptions from NRC regulations apply. For example, the applicants methodology defines and uses some terms in a manner that differs from NRC regulations.

Thus, consistent with RG 1.233, an applicant referencing this TR is expected to identify exceptions to and exemptions needed from NRC regulations, as needed. Also, as stated in RG 1.233, system designs and safety evaluations may also demonstrate compliance with or justify exemptions from specific NRC regulations. The TR does not request approval of any exemptions and the staff is not approving any exemptions in this SE. Thus, the NRC staff is adding Item 1 in Section 4.0 of this SE, Limitations and Conditions, to clarify that this SE is not approving any exemptions and that an applicant using this TR will need to address compliance with pertinent regulations and request exemptions as needed.

Appendix B of the TR includes a sample application of the KP-FHR methodology, which is outside the scope of the NRC staffs review.

3.2 STAFF EVALUATION OF THE METHODOLOGY Licensing Basis Development Process (TR Section 2)

For this section, this TR makes minor deviations from and does not alter the principles and methodology in NEI 18-04. One of the deviations of note is that the terminology Safety Function is used in the TR instead of Probabilistic Risk Assessment (PRA) Safety Function.

This TR replaces the following in NEI 18-04:

The LBEs are defined in terms of successes and failures of SSCs that perform safety functions modeled in the PRA, hereafter referred to as PRA Safety Functions (PSFs). PSFs are defined as those functions responsible for the prevention and mitigation of an unplanned radiological release from any source within the plant.

With:

The LBEs are defined in terms of successes and failures of SSCs that perform Safety Functions (SFs). The SFs are defined as those functions responsible for the prevention and mitigation of an unplanned radiological release from any source within the plant.

The NRC staff finds this deviation to be minor because the definitions of Safety Function in this TR and PRA Safety Function in NEI 18-04 are essentially the same and the deviation does not change the principles and methodology of NEI 18-04.

The NRC staff reviewed TR Section 2 and found it acceptable because it is essentially the same as NEI 18-04.

Selection of Licensing Basis Events (TR Section 3)

In describing Task 7a (Evaluate LBEs Against F-C Target) of Figure 3.2, this TR replaces the following text in NEI 18-04 The upper bound consequences for each DBA, defined as the 95th percentile of the uncertainty distribution, shall meet the 10 CFR 50.34 dose limit at the EAB [exclusion area boundary].

With:

The upper bound consequences for each DBA shall meet the 10 CFR 50.34 dose limit at the EAB. Justification that the DBA evaluation models are sufficiently bounding may be based on qualitative arguments rather than direct calculation of 95th percentile figures of merit. This justification will be provided in future licensing submittals.

The applicant deviates from NEI 18-04 in that it allows for the use of qualitative arguments instead of quantitative calculation of uncertainty for determining the bounding consequences of each design basis accident (DBA). The applicant proposes to justify that the DBA evaluation models are sufficiently bounding using future licensing submittals. The NRC staff finds it reasonable from a methodology perspective, as this TR is intended, because the staff will have a future opportunity to assess the acceptability of any qualitative arguments. The staff is not now making a finding on the acceptability of potential future qualitative arguments from a technical perspective.

In the TR, Section 3.3.6, Contributors to Risk and Risk Importance Measures, uses the risk reduction importance measure, among the various importance measures listed in NEI 18-04 to assess risk significance of PRA basic events. The risk reduction measure is compared to 1 percent of each of the cumulative risk metrics as in TR Table 3-1. Regarding the use of risk reduction importance measure, the staff finds it reasonable because it is an element of the integrated risk informed performance based (RIPB) approach in the TR, which is expected to determine a reasonable set of risk-or safety-significant SSCs and associated special treatments.

The staff notes, however, that the Joint Committee on Nuclear Risk Management (JCNRM) of the American Nuclear Society/American Society of Mechanical Engineers (ANS/ASME) is developing a PRA standard for non-LWRs. The NRC staff is expected to review this standard after publication to determine whether to endorse the standard via a Regulatory Guide. The standard may define risk significance of SSCs differently from this TR. Licensing applicants referencing this TR should address, or justify alternatives to, the acceptance criteria in a possible future Regulatory Guide and endorsed standard related to the determination of risk significance of SSCs. Accordingly, the NRC staff included Item 2 in Section 4.0 of this SE, Limitations and Conditions, to clarify that licensing applicants referencing this TR should address, or justify alternatives to, the acceptance criteria in such an RG and endorsed standard related to the determination of risk significance of SSCs if the RG is issued at least 6 months before submission of the license application.

Safety Classification and Performance Criteria for SSCs (TR Section 4)

This TR proposes the definition of the safetyrelated SSCs to be as follows:

SSCs relied on to perform the required safety function (RSF)s to mitigate the consequences of design basis event (DBE)s to within the LBE F-C Target, and to mitigate DBAs that only rely on the safety-related SSCs to meet the dose limits of 10 CFR 50.34 using conservative assumptions.

SSCs relied on to perform RSFs to prevent the frequency of beyond design basis event (BDBE) with consequences greater than the 10 CFR 50.34 dose limits from increasing into the DBE region and beyond the F-C Target.

SSCs relied on to shut down the reactor and maintain it in a safe shutdown condition.

The first two criteria are the same as those in NEI 18-04; however, this TR adds a third criterion that is the same as the second criterion in the definition of safety-related in 10 CFR 50.2. The addition is to ensure that the definition in 10 CFR 50.2, Definitions, is addressed, with the exception of the portion of this definition for which Kairos plans to request an exemption. The applicants definition adds a traditionally used criterion for a set of SSCs performing reactor shutdown function in addition to the criteria in NEI 18-04. The NRC staff finds that the applicants proposal to add the third criterion is acceptable since the prescriptive criterion is consistent with the regulations and has the potential to increase the number of safety-related SSCs beyond those identified by the two other criteria.

Evaluation of Defense-In-Depth Adequacy (TR Section 5)

Under TR Section 5.7, Evaluation of LBEs against Layers of Defense, Kairos Power included the following:

NEI 18-04 contains some general guidance in Section 5.7 for defense in depth layers and source term that do not translate to specific actions or documentation for this process. Detail on the mechanistic source term approach for the KP-FHR will be provided as part of future licensing submittals.

The applicant proposes to justify the mechanistic source term approach for the KP-FHR using future licensing submittals. The NRC staff finds this reasonable from a methodology perspective because the staff will have a future opportunity to assess the acceptability of the mechanistic source term approach. The staff is not now making a finding on the acceptability of the mechanistic source term approach from a technical perspective.

Under TR Section 5.8.1, Guidelines for Programmatic DID Adequacy, Kairos Power deviates from the objectives of the programmatic DID adequacy in NEI 18-04. Specifically, the TR replaces the following in NEI 18-04:

Assuring that appropriate targets for SSC reliability and performance capability are reflected in design and operational programs for each LBE Providing adequate assurance that the risk, reliability, and performance targets will be met and maintained throughout the life of the plant with adequate consideration of sources of significant uncertainties With:

Providing adequate assurance that the risk, reliability, and performance margins are maintained throughout the life of the plant in design and operational programs with adequate consideration of sources of significant uncertainties The TR states:

These objectives differ slightly from the objectives stated in NEI 18-04. The Kairos Power approach to establishing programmatic DID adequacy focuses activities on assuring that frequency targets are maintained at the event sequence level. At the more detailed SSC level, the focus shifts to performance-based measures such as surveillance frequency and test success rates.

The NRC staff finds the deviation acceptable because the programmatic DID adequacy can be effectively addressed with targets for reliability at the event sequence level while detailed performance-based measures are used at the individual SSC level.

4.0 LIMITATIONS AND CONDITIONS The staff imposes the following limitations and conditions with regard to the TR:

1. (Section 3.1) This SE does not approve any exemptions from NRC regulations, and an applicant using this TR will need to address compliance with pertinent regulations and request exemptions as needed.

2. (Section 3.3.6) The JCNRM of the ANS/ASME is developing a PRA standard for non-LWRs. If the NRC staff concludes that the ANS/ASME PRA standard is acceptable, the staff expects to endorse the standard via a Regulatory Guide. If the Regulatory Guide is issued 6 months before submission of the licensing application, the applicant should address, or justify alternatives to, the acceptance criteria in the Regulatory Guide and endorsed PRA standard related to the determination of risk significance of SSCs as a part of implementing the methodology in this TR.

5.0 CONCLUSION

Based on the above evaluation, the NRC staff concludes that the applicant has provided an acceptable KP-FHR design-specific risk-informed, performance-based methodology for LBE selection, classification and special treatments of SSCs, and assessment of DID adequacy to inform the licensing basis and content of licensing applications under 10 CFR Parts 50 and 52 for the KP-FHR design, subject to the limitations and conditions above. In summary, this conclusion is based on (1) the methodology being essentially the same as NRC staff-approved NEI 18-04, Revision 1, and incorporating the applicable clarifications and points of emphasis from RG 1.233, Revision 0 and (2) the differences between this TR and NEI 18-04 have been evaluated to be reasonable as described in Section 3.0.

6.0 REFERENCES

1.

U.S. Nuclear Regulatory Commission, 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, Draft Regulatory Guide DG-1353, dated April 2019 (ADAMS Accession No. ML18312A242)

2.

U.S. Nuclear Regulatory Commission, Kairos Power LLC - Acceptance Of KP-FHR Risk-Informed Performance-Based Licensing Basis Development Methodology Topical Report (CAC NO. 000431), dated October 23, 2019 (ADAMS Accession No. ML19284D767)

3.

Nuclear Energy Institute, Risk-Informed Performance-Based Technology Inclusive Guidance for Non-Light Water Reactor Licensing Basis Development, NEI 18-04, Draft Report Revision N, dated September 28, 2018 (ADAMS Accession No. ML18271A172)

4.

Nuclear Energy Institute, Risk-Informed Performance-Based Technology Inclusive Guidance for Non-Light Water Reactor Licensing Basis Development, NEI 18-04, Revision 1, dated August 2019 (ADAMS Accession No. ML19241A472)

5.

Kairos Power LLC, KP-FHR Risk-Informed Performance-Based Licensing Basis Development Methodology Topical Report., KP-TR-009, Revision 0, dated August 6, 2019 (ADAMS Accession No. ML19217A420)

6.

Email, Nuclear Regulatory Commission Stewart Magruder to Darrell Gardner, Discussion Items on Kairos Risk-Informed Performance-Based Licensing Basis Development Methodology Topical Report (KP-TR-009), dated January 8, 2020 (ADAMS Accession No. ML20009E836)

7.

Email, Nuclear Regulatory Commission Stewart Magruder to Drew Peebles and Darrell Gardner, Discussion Items on Kairos LMP topical, dated March 19, 2020 (ADAMS Accession No. ML20104A041)

8.

U.S. Nuclear Regulatory Commission, SECY-19-0117, 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 dated December 2, 2019 (ADAMS Accession No. ML18312A253)

9.

U.S. Nuclear Regulatory Commission, SRM to SECY-19-0117, Staff Requirements -

SECY-19-0117 - 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 dated May 26, 2020 (ADAMS Accession No. ML20147A504)

10.

Regulatory Guide 1.233, Revision 0, 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, dated June 2020 (ADAMS Accession No. ML20091L698)

11.

Kairos Power LLC, letter KP-NRC-1907-006, P. Hastings, Vice President, Regulatory Affairs and Quality, to USNRC document control desk, re: Principal Design Criteria for the Kairos Power Fluoride Salt-Cooled, High Temperature Reactor (Revision 1), dated July 31, 2019 (ADAMS Accession No. ML19212A756)

12.

Kairos Power LLC, KP-FHR Risk-Informed Performance-Based Licensing Basis Development Methodology Topical Report., KP-TR-009, Revision 1, dated April 10, 2020 (ADAMS Accession No. ML20101P623)

Principal Contributors: Ian Jung, NRR Antonio Barrett, NRR Date: November 10, 2020