ML24346A277
| ML24346A277 | |
| Person / Time | |
|---|---|
| Site: | 05200050 |
| Issue date: | 12/11/2024 |
| From: | NuScale |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML24346A130 | List:
|
| References | |
| LO-175762 | |
| Download: ML24346A277 (1) | |
Text
Response to SDAA Audit Question Question Number: A-15.2.4-1 Receipt Date: 06/17/2024 Question:
The paragraph describing the limiting case presented in FSAR Figure 15.2-18 appears incorrect. The paragraph states, Figure 15.2-18 shows the MCHFR for the most limiting event, concurrent closure of both MSIVs with a loss of AC power. However, other statements in FSAR Section 15.2.4 note that the limiting event for MCHFR retains AC power. Further, EC-117459, Rev. 2 and EC-117482, Rev. 0, also indicate the limiting MCHFR event retains AC power. Please propose markups to the FSAR.
Response
The limiting case for minimum critical heat flux ratio (MCHFR) assumes alternating current (AC) power is available. The discussion of Final Safety Analysis Report (FSAR) Figure 15.2-18 is revised for consistency with the other descriptions in FSAR Section 15.2.4 and supporting calculations.
Markups of the affected changes, as described in the response, are provided below:
NuScale Nonproprietary NuScale Nonproprietary
NuScale Final Safety Analysis Report Decrease in Heat Removal by the Secondary System NuScale US460 SDAA 15.2-12 Draft Revision 2 Audit Question A-15.2.4-1 The subchannel analysis indicates that the MCHFR is above the limit and is acceptable. Figure 15.2-18 shows the MCHFR for the most limiting MCHFR case.event, concurrent closure of both MSIVs with a loss of AC power.
15.2.4.4 Radiological Consequences The radiological consequences of a MSIV closure event are bounded by the design-basis accident analyses presented in Section 15.0.3.
15.2.4.5 Conclusions The DSRS acceptance criteria are met for the MSIV closure event.
- 1) Pressure in the reactor coolant and main steam systems should be maintained below 110 percent of the design values.
The limiting RCS pressure for this event, listed in Table 15.2-12, is below 110 percent of the design value for the RCS.
The limiting SG pressure, listed in Table 15.2-12, is below 110 percent of the design value for the MSS up to the MSIVs.
- 2) Fuel cladding integrity should be maintained by ensuring the minimum DNBR remains above the 95/95 DNBR limit.
The MCHFR for this event, listed in Table 15.2-12, is above the CHF analysis limit.
- 3) An incident of moderate frequency should not generate a more serious plant condition without other faults occurring independently.
The analyses presented for this event shows that stable DHRS cooling is reached, and the acceptance criteria are met.
- 4) The guidance provided in RG 1.105, Instrument Spans and Setpoints, can be used to analyze the impact of the instrument spans and setpoints on the plant response in order to meet the requirements of GDCs 10 and 15.
Allowances for instrument inaccuracy are accounted for in the analytical limits of mitigating systems in accordance with the guidance provided in RG 1.105.
- 5) The most limiting plant systems single failure shall be identified as assumed in the analysis and shall satisfy the positions of RG 1.53.
No single failure for an MSIV closure event results in greater challenges to the RCS pressure acceptance criteria. Failure of a FWIV results in the peak SG pressure and limiting MCHFR but margin to the acceptance criteria is shown in Table 15.2-12.