ML21336A825
| ML21336A825 | |
| Person / Time | |
|---|---|
| Site: | 99902069 |
| Issue date: | 11/30/2021 |
| From: | Hart M Office of Nuclear Reactor Regulation |
| To: | |
| Cuadrado de Jesus S | |
| References | |
| Download: ML21336A825 (10) | |
Text
NRC Staff Evaluation of the KP-FHR Mechanistic Source Term Methodology, Revision 1 Michelle Hart Senior Reactor Engineer Office of Nuclear Reactor Regulation Presentation to the ACRS November 30, 2021
Introduction
- KP-FHR Mechanistic Source Term Methodology topical report, KP-TR-012, Revision 1 (August 2021)
- Applicable to Kairos Power fluoride salt cooled, high temperature reactor (KP-FHR) designs
- Including a nuclear test reactor and commercial power reactors
- Methodology to develop event-specific radiological source terms and short-term atmospheric dispersion values for EAB and LPZ at distances less than 1,200 meters
- DBAs for siting and safety analysis
- AOOs and DBEs for use in NEI 18-04 methodology to categorize events, classify SSCs, and evaluate defense-in-depth
- Does not address source terms and atmospheric dispersion for normal operation and effluents, BDBEs, or control room habitability November 30, 2021 2
Staff Review Focus
- Staff review focused on the bases for models in the methodology
- Radionuclide transport and retention in the fuel, Flibe, gas space and buildings
- Tritium production, transport and retention
- Aerosol formation and deposition
- Near-field atmospheric dispersion and use of ARCON96 November 30, 2021 3
Mechanistic Source Term Approach Methodology develops MSTs by evaluating sources of radioactive materials at risk of release (MAR) and release fractions for each barrier that contains the MAR DBA MSTs are developed crediting only the TRISO particle and Flibe coolant radionuclide retention as the KP-FHR functional containment MSTs for AOOs and DBEs are developed using a more realistic accounting of radionuclide barriers Staff finds the MST approach acceptable because it is consistent with
- Safety analysis regulatory requirements
- Discussion of MSTs in SECY-93-092 and RG 1.233
- Description of functional containment in SECY-18-0096 November 30, 2021 4
Vaporization of Radionuclide from Flibe
- The NRC staff finds the methodology acceptable because of conservative assumptions and KP-FHR design features November 30, 2021 5
Conditions and Limitations
- Kairos Power proposed 8 limitations on use of the TR, which were acceptable to the Staff
- Includes relationships to other Kairos Power TRs under review
- KP-FHR fuel performance methodology TR and use of KP-Bison computer code
- KP-FHR fuel qualification methodology November 30, 2021 6
Conditions and Limitations
- The Staff imposed two additional conditions and limitations
- #9: Use of the methodology is limited to the KP-FHR design. The combination of TRISO and Flibe allows for assumptions that may not be valid for liquid-fueled MSRs.
- #10: Applicant to provide information to justify that the calculation of tritium absorption onto graphite is not sensitive to the assumptions on tritium diffusivity and solubility in Flibe.
November 30, 2021 7
Changes to SE
- Changes made to the SE since issuance of Draft SE do not impact the NRC staff conclusions November 30, 2021 8
Staff Conclusions
- KP-TR-012, KP-FHR Mechanistic Source Term Methodology, Revision 1, provides an acceptable methodology for development of event-specific mechanistic source terms for use by KP-FHR designs in offsite radiological consequence analyses for AOOs, DBEs, and DBAs
- Staff approvals are subject to the Limitations and Conditions of the SE November 30, 2021 9
Acronyms and Definitions AOO anticipated operational occurrence ARCON96 Atmospheric Relative Concentrations in Building Wakes computer code BDBE beyond design basis event DBA design basis accident DBE design basis event EAB Exclusion Area Boundary Flibe salt mixture of lithium fluoride (LiF) and beryllium fluoride (BeF2)
KP-FHR Kairos Power Fluoride-Salt Cooled High Temperature Reactor LPZ Low Population Zone MAR materials at risk for release MSR molten salt reactor MST mechanistic source term NEI Nuclear Energy Institute RG regulatory guide SE safety evaluation SECY Commission paper SRM staff requirements memorandum SSCs structures, systems, and components TR topical report TRISO Tristructural isotopic November 30, 2021 10