ML20262H077
| ML20262H077 | |
| Person / Time | |
|---|---|
| Site: | 05200049 |
| Issue date: | 09/15/2020 |
| From: | Mazza J NRC/NRR/DANU/UARL |
| To: | Cochran C, Renner A Oklo Inc |
| Mazza J, NRR/DANU/UARL, 301-415-0498 | |
| Shared Package | |
| ML20262H043 | List: |
| References | |
| Download: ML20262H077 (2) | |
Text
DRAFT Request for Additional Information Issue Date:
Application
Title:
Oklo Aurora COL - Docket 52-049 Operating Company: Oklo Power LLC Docket No.52-049 Review Section: Aurora Step 1 - MCA Application Section: FSAR Section 2.2 Aurora Step 1 - MCA - Draft Question 1 - Heat Transfer in the Reactor System Regulatory Basis 10 CFR Part 52.79(a)(5) requires in part that an applicant provide an analysis and evaluation of the design and performance of structures, systems, and components with the objective of assessing the risk to public health and safety resulting from operation of the facility and including determination of the margins of safety during normal operations and transient conditions anticipated during the life of the facility, and the adequacy of structures, systems, and components provided for the prevention of accidents and the mitigation of the consequences of accidents.
Issue NRC staff conducted a regulatory audit to clarify their understanding of the heat transfer analyses presented in FSAR Section 2.2, "Reactor system," and FSAR Section 5.6, "Safety analysis," (ML20225A227). During this audit, NRC staff observed design information that is important to the safety case of the Aurora design. Specifically, Oklo presented information to clarify NRC staff's understanding of the thermal bonds between the reactor cell can and heat pipe, and between the heat pipe and heat exchanger. This information on thermal bonds affects the margin to the fuel safety limits during (1) normal operations and transient conditions anticipated during the life of the facility, and (2) the heat redistribution phase of the maximum credible accident. Specifically, these thermal bonds affect the fundamental safety function of heat removal because they are significant points of thermal resistance along the heat transfer pathway between the fuel and passive heat structures. Accordingly, NRC staff is requesting that Oklo incorporate this information in its licensing documentation on the docket to support the NRC staff's safety review.
Request NRC staff requests that the FSAR be updated to describe the thermal bonds between (1) the reactor cell can and heat pipe, and (2) the heat pipe and heat exchanger. Specifically, NRC staff requests updates to the following sections of the FSAR:
- FSAR Section 2.1,3,1, "Key dimensions," to clarify the reactor conditions that correspond to the dimensions provided in FSAR Table 2-1 (i.e., hot or cold).
- FSAR Section 2.2.2, "Reactor core system," to describe the thermal bond between the reactor cell can and heat pipe and to provide, as necessary, design commitments and programmatic controls associated with the thermal bond design in order to support 1
DB.RXS.04, "The reactor core system provides a pathway to conduct heat from the fuel to the surrounding systems and ultimately to reject it to the environment."
- FSAR Section 2.6, "Heat exchanger system," to describe the thermal bond between the heat pipe and heat exchanger and to provide, as necessary, design commitments and programmatic controls associated with the thermal bond design in order to support DB.HXS.01, "The heat exchanger system provides a pathway to conduct heat from the heat pipes of the reactor core system to the surrounding systems and ultimately to reject it to the environment."
- FSAR Table 5-7, "Summary of assumptions in safety analysis and reason for conservatism," to include the assumptions imposed on the thermal bonds between (1) the reactor cell cans and heat pipes, and (2) the heat pipes and heat exchanger.
Aurora Step 1 - MCA - Draft Question 2 - Heat Transfer in the Reactor System Regulatory Basis 10 CFR 52.79(a)(24) and 10 CFR 50.43(e) require that for an application for a nuclear power reactor design that uses innovative means to accomplish their safety function, that (1) the performance of each safety feature of the design be demonstrated through either analysis, appropriate test programs, experience, or a combination thereof, and (2) that sufficient data exist on the safety features of the design to assess the analytical tools used for safety analyses.
Issue NRC staff conducted a regulatory audit to clarify their understanding of the heat transfer analyses presented in FSAR Section 2.2, "Reactor system," and FSAR Section 5.6, "Safety analysis," (ML20225A227). During this audit, NRC staff observed design information that is important to the safety case of the Aurora design. Specifically, Oklo presented additional information to clarify NRC staff's understanding of the current FSAR description of the thermal bonds between the reactor cell can and heat pipe, and between the heat pipe and heat exchanger. These thermal bonds affect the margin to the fuel safety limits during (1) normal operations and transient conditions anticipated during the life of the facility, and (2) the heat redistribution phase of the maximum credible accident. Specifically, these thermal bonds affect the fundamental safety function of heat removal because they are significant points of thermal resistance along the heat transfer pathway between the fuel and passive heat structures. The methods to thermally bond these heat transfer surfaces appear to be an innovative means that support the safety function of heat removal. Accordingly, NRC staff is seeking evidence to demonstrate the adequacy of the thermal bond design and to support the modeling used in the safety analyses.
Request NRC staff requests that Oklo incorporate into the FSAR, either directly or by reference, information to (1) provide evidence of analysis, appropriate test programs, experience, or combination thereof to support the efficacy of the design features used to thermally bond the heat pipes in the Aurora to the reactor cell cans and heat exchanger, and (2) explain how this evidence supports the modeling parameters used in the safety analyses.
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