ML24348A070
| ML24348A070 | |
| Person / Time | |
|---|---|
| Site: | 05200050 |
| Issue date: | 12/13/2024 |
| From: | NuScale |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML24348A006 | List:
|
| References | |
| LO-176318 | |
| Download: ML24348A070 (1) | |
Text
Response to NuScale Topical Report Audit Question Question Number: A-NonLOCA.LTR-49 Receipt Date: 06/24/2024 Question:
The NRC staff notes that several parameters identified in TR Section 7.1.6.1, Initial Conditions, of the TR are not truly independent initial conditions but must be determined through initial steady-state calculations. For example, initial RCS flow rate for a natural circulation NPM is related to the power input by the reactor, the heat removal by SGs, and the hydraulic characteristics of the circuit. The TR also states: The initial RCS flow rate is biased to either end of the range expected for normal operation. As an example, consider a normal operational range of 535 kg/s to 690 kg/s for RCS flow rate at 100 percent RTP. For this situation, the initial RCS flow rate is set to either 535 kg/s or 690 kg/s.
Please provide a method that can be used to determine how to count for the interdependence of the initial flow rate and when to set the flow to 535 kg/s or 690 kg/s.
Please provide proposed markup to the TR.
Response
The NRC is correct that the reactor coolant system (RCS) flow for a natural circulation NuScale Power Module (NPM) is related to the power input by the reactor, the heat removal by the steam generators (SGs), and the hydraulic characteristics of the circuit. Given that reactor power and SG conditions are also set as input for the initial conditions, the RCS flow initial condition is set by adjusting the form loss coefficients in the RCS loop. If low RCS flow is desired as the initial condition, high loss values are selected. If high RCS flow is desired as the initial condition, low loss values are selected. ((2(a),(c) NuScale Nonproprietary NuScale Nonproprietary
Note that the values of 535 kg/s and 690 kg/s discussed in Section 7.1.6.1 of TR-0516-49416, Revision 4, Non-Loss-of-Coolant Accident Analysis Methodology are identified as examples only. The specific range of RCS flow applicable to an NPM is found in the Final Safety Analysis Report (FSAR) associated with the NPM design. For the Standard Design Approval Application (SDAA) for the US460 design, the RCS flow rate range is identified in FSAR Table 15.0-6. The basis provided with the values provides information consistent with this response regarding the relationship between RCS flow, power, and hydraulic resistance, as well as information regarding biasing the resistance to achieve the desired flow. Section 7.1.6.1 of TR-0516-49416, Revision 4, does not specify a generic direction of flow biasing to apply. The direction of flow biasing to apply (e.g., low, nominal, high) is addressed in the bias tables associated with each specific event in Section 7.2 of TR-0516-49416, Revision
- 4. Markups to TR-0516-49416, Revision 4, Section 7.1.6.1 are not required because the process described here is consistent with the process used in the previously approved version of the topical report, TR-0516-49416-A, Revision 3. In the NRCs prior approval of TR-0516-49416-A, Revision 3, no additional explanation was required to be included in Section 7.1.6.1.
No changes to the SDAA are necessary. NuScale Nonproprietary NuScale Nonproprietary}}