ML25014A273
| ML25014A273 | |
| Person / Time | |
|---|---|
| Site: | 05200050 |
| Issue date: | 01/13/2025 |
| From: | NuScale |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML25013A204 | List: |
| References | |
| LO-178078, LO-177590 | |
| Download: ML25014A273 (1) | |
Text
Response to NuScale Topical Report Audit Question Question Number: A-NonLOCA.LTR-56 Receipt Date: 06/28/2024 Question:
TR Sections 7.2.2.3 and 7.2.3.3 state Sensitivity studies are performed as needed to identify the limiting response(s) for the acceptance criteria parameter(s) challenged by the event (i.e.,
system pressures for overheating events, MCHFR for overcooling events). Consequently, sensitivity studies are performed to identify cases with the lowest CHFR response for this overcooling event.
TR Section 7.2.4.3 states Sensitivity studies are performed as needed to identify the limiting response(s) for the acceptance criteria parameter(s) challenged by the event. Consequently, sensitivity studies are performed to identify cases with the lowest CHFR response and challenging mass releases for this overcooling event.
TR Sections 7.2.6.3, 7.2.8.3, 7.2.9.3, and 7.2.12.3, state Sensitivity studies are performed as needed to identify the limiting response(s) for the acceptance criteria parameter(s) challenged by the event (i.e., system pressures for overheating events, MCHFR for overcooling events).
Consequently, sensitivity studies are performed to identify cases with the highest pressure responses for this overheating event.
TR Section 7.2.10.3 states Sensitivity studies are performed as needed to identify the limiting response(s) for the acceptance criteria parameter(s) challenged by the event. Consequently, sensitivity studies are performed to identify cases with the highest primary and secondary pressures, varying the magnitude of the feedwater flow rate decrease (other parameters are biased as indicated in Table 7-48).
TR Section 7.2.11.3 states Sensitivity studies are performed as needed to identify the limiting response(s) for the acceptance criteria parameter(s) challenged by the event. Consequently, sensitivity studies are performed to identify cases with the highest pressure responses for this event.
NuScale Nonproprietary NuScale Nonproprietary
TR Section 7.2.13.3 states Sensitivity studies are performed as needed to identify the limiting response(s) for the acceptance criteria parameter(s) challenged by the event. Consequently, a sensitivity study is generally performed to identify cases for lowest MCHFR and highest fuel centerline temperature for this reactivity event.
TR Sections 7.2.14.3 and 7.2.15.3, state: Sensitivity studies are performed as needed to identify the limiting response(s) for the acceptance criteria parameter(s) challenged by the event. Consequently, a sensitivity study is generally performed to identify cases for lowest MCHFR for this reactivity event.
(( 2(a),(c) TR Section 7.2.17.3 states Sensitivity studies are performed as needed to identify the limiting response(s) for the acceptance criteria parameter(s) challenged by the event, including cases with the highest pressure responses for this inventory increase event. TR Sections 7.2.18.3 and 7.2.19.3 state Sensitivity studies are performed as needed to identify the limiting response(s) for the acceptance criteria parameter(s) challenged by the event. However, the TR does not provide instructions for how and when to perform the sensitivity studies. Please provide proposed markups to the TR to include this information.
Response
The audit question identifies sections in TR-0516-49416-P, Revision 4, Non-Loss-of-Coolant Accident Analysis Methodology, that contain the phrase Sensitivity studies are performed as needed... Note that Sections 7.2.1.3 and 7.2.5.3 of TR-0516-49416-P, Revision 4, also contain the phrase, but were not identified in the audit question. The following response is applicable to these two additional sections although they were not included in the audit question. Each use of the phrase identified in the audit question is directly preceded by a table that identifies the biases or conservatism to be applied to specific parameter. These tables include one or more biases or conservatisms that state varied. The use of varied in the tables for a specific parameter indicates that different values of that parameter should be used in the implementing analysis. ((
}}2(a),(c)
NuScale Nonproprietary NuScale Nonproprietary
((
}}2(a),(c) In other words, use of varied in the tables means that a sensitivity study is performed on that parameter. Therefore, the sensitivity studies to be performed as needed are those that are indicated as needed by the tables. Based on this discussion, TR-0516-49416-P, Revision 4, already identifies when to perform the sensitivity studies.
The how of performing the sensitivity studies is consistent with generic safety analysis practice: if a specific parameter has a range of initial values, the high and low ends of the range are considered. Multiple examples of how to perform such sensitivity studies given a range of initial values are provided in TR-0516-49416-P, Revision 4, Section 7.1.6.1. ((
}}2(a),(c) Therefore, there is also sufficient information existing in TR-0516-49416-P, Revision 4, to identify how to perform the sensitivity studies.
In addition, the downstream application of the methodology always has the option to perform additional sensitivity studies beyond the minimum required. It is important to note that each of use of the phrase Sensitivity studies are performed as needed... in TR-0516-49416-P, Revision 4, also existed in the TR-0516-49416-P-A, Revision 3 that was previously reviewed and approved by the NRC. Therefore, the uses of this phrase are not changes or departures from what was previously reviewed and approved by the NRC. For this reason, further information is not required to be added to TR-0516-49416-P, Revision 4, to describe how and when to perform sensitivity studies. ((
}}2(a),(c) Note that TR-0516-49416-P-A, Revision 3, Section 7.2.16.3, identified that the sensitivity studies of interest were for initial power and dilution flow rate. TR-0516-94916-P, Revision 4, Section 7.2.16.1, does identify that different initial power levels and dilution flow rates are considered, although this is not identified in Table 7-74 or the Section 7.2.16.3 discussion. The topical report is revised as indicated in the attached markup to resolve this minor inconsistency.
NuScale Nonproprietary NuScale Nonproprietary
Markups of the affected changes, as described in the response, are provided below. NuScale Nonproprietary NuScale Nonproprietary
Non-Loss-of-Coolant Accident Analysis Methodology TR-0516-49416-NP Draft Revision 5 © Copyright 2024 by NuScale Power, LLC 622 7.2.16.3 Biases, Conservatisms, and Sensitivity Studies The biases and conservatisms presented in Table 7-74 are considered in order to identify the bounding conditions for loss of shutdown margin. Audit Question A-NonLOCA.LTR-56 Table 7-73 Acceptance criteria - inadvertent decrease in boron concentration Acceptance Criteria Discussion Primary pressure This criterion is not evaluated because an NPM does not introduce more challenging conditions for primary pressure compared to other AOOs. Secondary pressure This criterion is not evaluated because an NPM does not introduce more challenging conditions for secondary pressure compared to other AOOs. Critical heat flux ratio This criterion is evaluated by downstream subchannel analysis; or by demonstrating that a loss of shutdown margin does not occur. Maximum fuel centerline temperature This criterion is not evaluated because the reactivity insertion rates are insufficient to challenge the temperature limit. Containment integrity Containment integrity is evaluated by a separate analysis methodology. Escalation of an AOO to an accident This criterion is satisfied by demonstrating stable RCS flow rates and constant or downward trending RCS and DHRS (if actuated) pressures and temperatures exist at the end of the transient, all acceptance criteria evaluated in the transient analysis are met, and shutdown margin is maintained at the end of the transient. RCS conditions during extended DHRS cooling are addressed in a separate analysis. Table 7-74 Initial conditions, biases, and conservatisms - inadvertent decrease in boron concentration Parameter Bias / Conservatism Basis Initial reactor power ExcludedVaried. (( }}2(a),(c) Initial RCS average temperature Biased to the high condition. (( }}2(a),(c) Initial RCS flow rate Biased to the low condition. (( }}2(a),(c) Initial PZR pressure Nominal. (( }}2(a),(c)
Non-Loss-of-Coolant Accident Analysis Methodology TR-0516-49416-NP Draft Revision 5 © Copyright 2024 by NuScale Power, LLC 623 Initial PZR level Excluded. Not part of mixing model. Initial feedwater temperature Excluded. Not part of mixing model. Initial fuel temperature Excluded. Not part of mixing model. MTC Excluded. Not part of mixing model. Kinetics Biased to BOC conditions. (( }}2(a),(c) Decay heat Excluded. Not part of mixing model. Initial SG pressure Excluded. Not part of mixing model. SG heat transfer Excluded. Not part of mixing model. RSV lift setpoint Excluded. Not part of mixing model. SG tube plugging Excluded. Does not alter active RCS volume. Shutdown margin Biased to the low condition. (( }}2(a),(c) Initial boron concentration Biased to the high condition (( }}2(a),(c) Boron worth Biased to the high condition. (( }}2(a),(c) Active RCS volume Biased to the low condition. (( }}2(a),(c) Makeup flow rate Biased to the high conditionVaried. (( }}2(a),(c) Makeup temperature Biased to the low condition. (( }}2(a),(c) RCS Temperature Control Automatic rod control Excluded. Not part of mixing model. Boron concentration Not credited. (( }}2(a),(c) PZR Pressure Control PZR spray (normal) Excluded. Not part of mixing model. (bypass) Excluded. Not part of mixing model. PZR heaters (non-prop.) Excluded. Not part of mixing model. (prop.) Excluded. Not part of mixing model. Table 7-74 Initial conditions, biases, and conservatisms - inadvertent decrease in boron concentration (Continued) Parameter Bias / Conservatism Basis}}