ML22024A485

OEDO-21-00545 -Safety Evaluation of the Kairos Power LLC Topical Report KP-TR-012-P, Revision 1, KP-FHR Mechanistic Source Term Methodology

ML22024A485
Person / Time
Site:	99902069
Issue date:	02/08/2022
From:	Andrea Veil Office of Nuclear Reactor Regulation
To:	Rempe J Advisory Committee on Reactor Safeguards
Cuadrado de Jesus S; 301-415-2946
Shared Package
ML21356A028	List: ML22024A485
References
OEDO-21-00545
Download: ML22024A485 (4)

Text

February 08, 2022 Joy Rempe, Chairman Advisory Committee on Reactor Safeguards U.S. Nuclear Regulatory Commission Washington, DC 20555

SUBJECT:

SAFETY EVALUATION OF THE KAIROS POWER LLC TOPICAL REPORT KP-TR-012-P, REVISION 1, KP-FHR MECHANISTIC SOURCE TERM METHODOLOGY

Dear Chairman Rempe:

By letter dated December 20, 2021 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML21342A179), the Advisory Committee on Reactor Safeguards (ACRS) reported on its review of the U.S. Nuclear Regulatory Commission (NRC) staffs safety evaluation (SE) of the Kairos Power LLC (Kairos Power) Topical Report KP-TR-012-P, Revision 1, KP-FHR Mechanistic Source Term Methodology. The NRC staff appreciates the ACRS review, and its conclusions and recommendations listed below:

1.

The topical report presents the methodology used by Kairos to calculate the mechanistic source term of fission products, activation products, and corrosion products produced in the Kairos Power fluoride salt-cooled high temperature reactor (KP-FHR) core. The approach is consistent with existing high-level regulatory guidance on source terms for advanced reactors.

2.

Staff review of an application that employs this methodology will need to ensure that the assumptions on the number of failed pebbles as well as the experimental limitations related to tritium behavior in the molten salt coolant for the KP-FHR (Flibe0 F1) and diffusion and trapping effects in graphitic components are adequately considered in conservative safety analyses and relevant sensitivity studies.

3.

The staff SE does not require experimental validation of vaporization of fission products from Flibe. This has an important effect on the overall source term, and experimental validation data are needed to confirm the approach used by the applicant. The SE should be changed to address this concern.

1 Flibe is a mixture of lithium fluoride (LiF) and beryllium fluoride (BeF2), with a nominal chemical composition of 2LiF:BeF2.

Regarding Recommendation 1, the NRC staff appreciates that the ACRS agrees with the NRC staffs position that the methodology used by Kairos for the mechanistic source term is consistent with existing regulatory guidance for advanced reactors.

Regarding Recommendation 2, the NRC staff notes that the ACRS discussion of tritium behavior points out specific topics that the NRC staff should ensure are covered in the subsequent review of an application for a KP-FHR. For example, the ACRS points out several considerations, including the different heat treatment of the various carbon-based materials, which can affect the amount of tritium retained in those materials through traps. The NRC staff agrees that modeling the concentration of fission products in the matrix relative to the trap concentration is an important consideration in the determination of tritium retention and the subsequent effect on radionuclide release; therefore, validation of these diffusion and trapping models by the applicant using the methodology, is necessary. The ACRS also notes that experience with pebble bed reactor operation shows that pebbles are broken during operation, and that applicants using the report will need to justify the assumption on the number of pebbles being damaged. The NRC staff agrees that the number of damaged pebbles is an important consideration in the implementation of the methodology. In any application which uses an approved topical report methodology, the NRC staff will assess the applicability of the topical report to the application, including assumptions in the approved methodology.

The staffs SE also includes limitations and conditions on the use of the topical report that concern issues addressed in ACRS Recommendation 2. Specifically, SE limitations and conditions 6 and 10, ensure that the applicant is to provide information related to modeling of tritium behavior in the Flibe and graphite. The NRC staff appreciates the technical issues pointed out in the ACRS letter, which will aid the NRC staff in future reviews of an application which implements the topical report methodology.

The NRC staff considered ACRS Recommendation 3 and agrees that vaporization of fission products from Flibe is important to the overall source term and that experimental data are needed to confirm modeling of radionuclide vaporization. The NRC staff are engaging with the applicant (ADAMS Accession No. ML22033A483) to ensure that the approach used by the applicant is confirmed with experimental data. The NRC staff will also address this in its final safety evaluation of the topical report.

The NRC staff appreciates the ACRS review. The NRC staff plans to issue the SE report in early spring 2022 and looks forward to future interactions with the ACRS regarding Kairos licensing topical reports or applications.

Sincerely, Robert M.

Taylor Digitally signed by Robert M. Taylor Date: 2022.02.08 08:19:27 -05'00' Andrea D. Veil, Director Office of Nuclear Reactor Regulation Project No. 99902069 cc: Chairman Hanson Commissioner Baran Commissioner Wright SECY

SUBJECT:

SAFETY EVALUATION OF THE KAIROS POWER LLC TOPICAL REPORT KP-TR-012-P, REVISION 1, KP-FHR MECHANISTIC SOURCE TERM METHODOLOGY DATED: FEBRUARY 08, 2022 DISTRIBUTION: OEDO-21-00545 PUBLIC UARL R/F MHart, NRR AChereskin, NRR SCuadrado, NRR BBeasley, NRR CdeMessieres, NRR RidsNrrOd RidsNrrDanu RidsNrrDanuUARL RidsNrrDnrl RidsOpaMail RidsOcaMailCenter RidsOgcMailCenter RidsNrrMailCenter RidsAcrsAcnwMailCtr RidsNrrLACSmith ADAMS Accession Number: ML22024A485 NRR-106 OFFICE NRR/DANU/UARL:PM NRR/DANU/UARL:LA NRR/DANU/UTB2:BC NAME SCuadrado CSmith CdeMessieres DATE 01/26/2022 01/27/2022 02/01/2022 OFFICE NRR/DANU/UARL:BC NRR/DANU:D NRR:D NAME WKennedy JBowen for MShams RTaylor for AVeil DATE 02/02/2022 02/03/2022 02/08/2022 OFFICIAL RECORD COPY