ML25013A206
| ML25013A206 | |
| Person / Time | |
|---|---|
| Site: | 05200050 |
| Issue date: | 01/13/2025 |
| From: | NuScale |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML25013A204 | List: |
| References | |
| LO-177590, LO-178078 | |
| Download: ML25013A206 (1) | |
Text
Question Number: DWO-SC-22 Receipt Date: 09/27/2024 Question:
(( 2(a)(c)
Response
((
}}2(a),(c),ECI
((
}}2(a),(c),ECI The NuScale standard design approval application final safety analysis report (FSAR) includes requirements for operating procedures to be developed (COL Item 13.5-3). These procedures will include direction for operators to monitor for system level instabilities including, but not limited to, coherent DWO and take actions to mitigate them.
Followup from October 23, 2024 Audit Meeting In the October 23, 2024 audit meeting, the NRC requested that NuScale strengthen the connection between DWO conditions and the operational procedures. Based on this NuScale Nonproprietary NuScale Nonproprietary
discussion, NuScale has revised the FSAR Section 5.4.1.3 to include a reference to the operating procedures required by FSAR Section 13.5.2, where COL Item 13.5-3 is located. Markups of the affected changes, as described in the response, are provided below: NuScale Nonproprietary NuScale Nonproprietary
NuScale Final Safety Analysis Report Reactor Coolant System Component and Subsystem Design NuScale US460 SDAA 5.4-9 Draft Revision 2 main steam superheat; this time is accrued against the Section 3.9.1 cyclic limits for ASME design transients. Operation in Region 2 occurs when RCS average temperature is greater than or equal to 520 degrees F with main steam superheat and indicates that there is no DWO in the SG tubes; therefore, time is not accrued against the Section 3.9.1 cyclic limits. The boundary between Region 1 and Region 2 in Figure 5.4-16 does not indicate that there is DWO in the SG tubes; there is margin from the boundary between Region 1 and Region 2 to DWO onset in the SG tubes. The SG and inlet flow restrictor design assures that DWO transient conditions are acceptable to meet applicable ASME BPVC criteria. Audit Question DWO-SC-22 Procedures that address actions to perform during possible DWO conditions are identified in Section 13.5.2, Operating and Maintenance Procedures. Comprehensive Vibration Assessment Program Performance The results of the Comprehensive Vibration Assessment Program screening and performance analysis for the SG is in technical report TR-121353, "NuScale Comprehensive Vibration Assessment Program Analysis Technical Report," (Reference 5.4-10). Section 17.4, Reliability Assurance Program, describes the reliability assurance plan used for SG reliability evaluation; the guidance in Chapter 19, Probabilistic Risk Assessment and Severe Accident Evaluation, describes the determination of SG risk significance. 5.4.1.3.1 Allowable Tube Wall Thinning under Accident Conditions The SG tubes have a nominal wall thickness of 0.050 in. The design adds a lifetime degradation allowance of 0.010 in. to the calculated ASME BPVC minimum SG tube wall thickness per NB-3121 (Reference 5.4-3). This degradation allowance provides margin for potential in-service tube degradation mechanisms (e.g., general corrosion, erosion, wear). This degradation allowance also includes margin for SG tube wall thickness manufacturing tolerances, including wall thinning due to tube bending. The SG tubes construction meets the rules of ASME BPVC, Section III, Subsection NB. 5.4.1.4 Tests and Inspections The SGs testing and inspection ensures conformance with the design requirements described in Section 5.2.4, RCPB ISI and Testing. Equipment requiring inspection or repair is in an accessible position to minimize time and radiation exposure during refueling and maintenance outages. The SG tube inspections and testing meet requirements of the SG program. Performance of a preservice volumetric examination on the entire length of the SG tubing meets specifications in Table IWB-2500-1 (B-Q). A preservice eddy}}