ML24215A227
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Response to SDAA Audit Question Question Number: A-19.2-27 Receipt Date: 09/18/2023 Question:
- 2.
Audit question A-19.2.3-7 requested additional information on the testing and analysis that will be performed to demonstrate that the inside bioshield radiation monitors will survive a post-accident environment. In response to audit question A-19.2.3-7, NuScale stated that the approach to equipment survivability for the US460 design is the same as the approach to equipment survivability for the US600 design, which was approved in the DCA SER.
DCA SER Section 19.2.4.2.8 states that an applicant will confirm or update the severe accident doses for all components identified in DCA FSAR Table 19.2-11 (which is equivalent to SDAA FSAR Table 19.2-8) according to COL Item 19.1-8. SDAA COL Item 19.1-8 is essentially the same as DCA COL Item 19.1-8, and it states that an applicant will confirm the validity of the key assumptions and data used in the PRA and modify, as necessary, for applicability to the as-built, as-operated PRA.
The key assumptions for the PRA are contained in SDA FSAR Table 19.1-21. This table does not provide any key assumptions related to the inside bioshield radiation monitors, nor (( 2(a),(c) Based on the current FSAR content, the staff does not believe that COL Item 19.1-8 requires an applicant to confirm or update the severe accident doses for all components identified in FSAR Table 19.2-8, including the inside bioshield sensor. In response to audit question A-19.2.3-7, NuScale also referenced its response to DCA RAI 9705 question 19.02-1. In its response to DCA RAI 9705, NuScale stated that an evaluation of equipment survivability is considered in the same manner as other updates of the PRA for an as-built, as-operated plant. Since the inside bioshield radiation monitors ((
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2(a),(c) NuScale Nonproprietary NuScale Nonproprietary
Therefore, to support the staffs finding on the survivability of the inside bioshield radiation monitors in a severe accident environment, NuScale is requested to provide FSAR markups to: a. Add equipment survivability of the inside bioshield radiation monitors as a key assumption in Table 19.1-21 that will be addressed by COL Item 19.1-8, or b. Update COL Item 19.1-8 to state that an applicant will confirm or update the severe accident doses for all components identified in FSAR Table 19.2-8 or add a new COL for an applicant to confirm or update the severe accident doses for all components identified in FSAR Table 19.2-8.
Response
NuScale has added a COL item to Section 19.2 of the standard design approval application requiring an applicant to identify equipment whose severe accident dose is greater than its environmental qualification dose. Section 19.2 requires the licensee to address these equipment survivability requirements: For cases in which the severe accident dose is larger, qualitative assessments, testing, or additional analyses are performed to assure survivability. Markups of the affected changes, as described in the response, are provided below: NuScale Nonproprietary NuScale Nonproprietary
NuScale Final Safety Analysis Report Interfaces with Standard Design NuScale US460 SDAA 1.8-15 Draft Revision 2 COL Item 19.1-6: An applicant that references the NuScale Power Plant US460 standard design will specify and describe risk-informed applications during the operational phase (from initial fuel loading through commercial operation). 19.1 COL Item 19.1-7: An applicant that references the NuScale Power Plant US460 standard design will evaluate site-specific external event hazards (e.g., liquefaction, slope failure), screen those for risk-significance, and evaluate the risk associated with external hazards that are not bounded by the standard design. 19.1 COL Item 19.1-8: An applicant that references the NuScale Power Plant US460 standard design will confirm the validity of the key assumptions and data used in the standard design approval application PRA and modify, as necessary, for applicability to the as-built, as-operated PRA. 19.1 COL Item 19.2-1: An applicant that references the NuScale Power Plant US460 standard design will develop severe accident management guidelines and other administrative controls to define the response to beyond-design-basis events. 19.2 COL Item 19.2-2: An applicant that references the NuScale Power Plant US460 standard design will use the site-specific probabilistic risk assessment to evaluate and identify improvements in the reliability of core and containment heat removal systems as specified by 10 CFR 50.34(f)(1)(i). 19.2 Audit Issue A-19.2.6-1 COL Item 19.2-3: Not used. Audit Issue A-19.2-27 COL Item 19.2-4: An applicant that references the NuScale Power Plant US460 standard design will identify from Table 19.2-8 the components and their severe accident doses for cases where the severe accident dose is greater than the environmental qualification dose. 19.2 COL Item 19.3-1: An applicant that references the NuScale Power Plant US460 standard design will identify site-specific Regulatory Treatment of Nonsafety Systems structures, systems, and components and applicable process controls. 19.3 Table 1.8-1: Combined License Information Items (Continued) Item No. Description of COL Information Item Section
NuScale Final Safety Analysis Report Severe Accident Evaluation NuScale US460 SDAA 19.2-22 Draft Revision 2 severe accident functions. As stated in the references, the evaluation is intended to demonstrate that there is reasonable assurance that equipment needed for severe accident mitigation and post-accident monitoring survives in the severe accident environment over the time span for which it is needed. Severe accident environmental conditions may produce extremes in pressure, temperature, radiation, and humidity. Following a severe accident in which core damage occurs, the functions that must be maintained are containment integrity, the capability to control combustible gas, and post-accident monitoring. Post-accident monitoring is not relied upon for mitigating severe accidents, but is intended only to provide information on severe accident conditions as required by 10 CFR 50.34(f)(2)(xix). The time span that survivability is reasonably assured is specific to the equipment and its function. Equipment that is necessary to maintain containment integrity is reasonably assured to survive for at least 48 hours after core damage. Equipment necessary for combustible gas control is reasonably assured to survive for at least 48 hours. Equipment used for post-accident monitoring is reasonably assured to survive for a duration based on the variable monitored and what operators would do with that information, with a maximum duration of 48 hours after core damage. Equipment is qualified to 100-percent humidity. In terms of post-accident dose, the design uses a methodology for assuring equipment survivability based, in part, on environments predicted for severe accidents as modeled in the PRA. This approach provides confidence that the equipment needed for severe accident mitigation and monitoring survives over the time span which it is needed. Equipment survivability in a radiation environment is first evaluated by comparing the severe accident dose to the environmental qualification design-basis dose. The severe accident dose is based on the core damage source term described in Section 15.10. For cases where the environmental qualification dose is larger, survivability is assured. For cases where the severe accident dose is larger, qualitative assessments, testing, or additional analyses are performed to assure survivability. Table 19.2-8 summarizes the evaluation of equipment for survivability; the table identifies each component or variable, its function, and the duration over which it is needed. Post-accident temperature and pressure conditions are discussed with regard to containment integrity, combustible gas control, and post-accident monitoring capabilities as follows. Audit Issue A-19.2-27 COL Item 19.2-4: An applicant that references the NuScale Power Plant US460 standard design will identify from Table 19.2-8 the components and their severe accident doses for cases where the severe accident dose is greater than the environmental qualification dose.}}