ML24346A327
| ML24346A327 | |
| 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: ML24346A327 (1) | |
Text
Response to SDAA Audit Question Question Number: A-19.1-66 Receipt Date: 05/13/2024 Question:
Per the request documented in ML24269A008, dated October 24, 2024, only the relevant portions of the question and response are included.
The non-ATWS Level 1 notebook includes results from thermal-hydraulic (T-H) calculations for scenarios LCU-07T, LCU-05T, and LCU-03T representing unisolated CVCS line break outside containment scenarios. These scenarios demonstrate ECCS actuation on the low RPV level setpoint. According to Table 7.1-4 of the SDAA FSAR, the low RPV level setpoint spans a range from 552 inches to 540 inches. Section 2.2.6 of ER-116289, Confirmation of Passive System Reliability (in Chapter 19 eRR) indicates that 540 inches is used. However, Section 2.1.3 of EC-157962 (in the Chapter 15 eRR) appears to indicate otherwise. Further, the response to A-19.1-47 states that the low RPV level signal for the NRELAP5 PRA analysis uses a nominal value from the acceptable range. Therefore, the value in the range that was used for the (T-H) calculations for above-mentioned scenarios and the basis for the selected value are unclear to the staff. NRC staffs calculations have identified that the results of the T-H calculations for unisolated CVCS line breaks outside containment are highly sensitive to the low RPV level setpoint value used in the simulations. The response to A-19.1-47 also acknowledges such an outcome. Therefore, if the value used is not 540 inches, the impact of using 540 inches on the results of LCU-07T and LCU-05T, and consequently, the PRA, is unclear to the staff. In addition, an unisolated break in the high point vent (HPV) line is not included in the non-ATWS Level 1 notebook. NuScale is requested to:
1.
Clarify the value used for the low RPV level setpoint in the non-ATWS Level 1 notebook, especially scenarios LCU-07T and LCU-05T.
2.
If the value used is different from 540 inches:
b.
Provide results and their discussion for LCU-07T and LCU-05T using 540 inches as the low RPV level setpoint.
3.
Describe how the selected value for the low RPV setpoint for the non-ATWS T-H NuScale Nonproprietary NuScale Nonproprietary
simulations, especially, for LCU-50T and LCU-07T, is modeled and implemented in the NRELAP5 PRA model.
Response
Background:
The reactor pressure vessel (RPV) riser level sensor is ((2(a),(c) The low RPV riser level has a setpoint range of 540 inches to 552 inches. However, the nominal setpoint (i.e., the elevation of the switch responsible for signaling low RPV riser level) ((
}}2(a),(c)
Response
- 1. The low RPV riser level setpoint modeled for the simulations documented in the non-anticipated transient without scram (non-ATWS) Level 1 notebook, including cases LCU-07T and LCU-05T, is ((
}}2(a),(c) 2b. Simulations for LCU-07T and LCU-05T were repeated with the low RPV riser level setpoint
((
}}2(a),(c) As shown in Table 1, (( }}2(a),(c)
NuScale Nonproprietary NuScale Nonproprietary
Table 1: Low Reactor Pressure Vessel Riser Level Setpoint Sensitivity Parameters Case Minimum Collapsed RPV Level above Top of Active Fuel Peak Cladding Temperature (( }}2(a),(c)
- 3. For LCU-05T and LCU-07T base cases, which model ((
}}2(a),(c) Table 2: Relevant Elevations for Low Reactor Pressure Vessel Riser Level Setpoint Modeling Volume Bottom Elevation Top Elevation Upper plenum, 140-01 ((
}}2(a),(c)
Top of upper riser, 130-13 ((
}}2(a),(c)
(( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary
(( }}2(a),(c) No changes to the SDAA are necessary. NuScale Nonproprietary NuScale Nonproprietary}}