ML24346A260
| ML24346A260 | |
| Person / Time | |
|---|---|
| Site: | 05200050 |
| Issue date: | 12/11/2024 |
| From: | NuScale |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML24346A130 | List:
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| References | |
| LO-175762 | |
| Download: ML24346A260 (1) | |
Text
Response to SDAA Audit Question Question Number: A-15.0.5-3 Receipt Date: 05/06/2024 Question:
SDAA FSAR Figure 15.1-45 shows that the RCCW break flowrate is assumed to be 90 lbm/s for 600 seconds which is equal to a mass of 54,000 lb inside of the containment from the RCCW flooding. FSAR figure 15.1-47, RCCW water is assumed to flood containment up to a level of 18 ft.
The Reactor Component Cooling Water Line Break Case described in FSAR section 15.0.5.3.1 states that the mass of reactor component cooling water added in the analysis is 6840 kg (approx. 15,000 lb) which is equivalent to a containment level of approximately 8 ft.
Please explain the difference between these assumptions. What is the maximum amount of RCCW inventory available? What are the isolation signals for RCCW?
Response
The containment flooding analysis in final safety analysis report (FSAR) Section 15.1.6 and the boron transport analysis in FSAR Section 15.0.5.3.1 intentionally use different assumptions for the amount of reactor component cooling water (RCCW) available to be added to the containment vessel (CNV) through a break in a RCCW line.
((2(a),(c) NuScale Nonproprietary NuScale Nonproprietary
(( }}2(a),(c) Table 1: Calculated Reactor Component Cooling Water Masses in the Boron Transport Analysis (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary
As described in FSAR Section 15.0.5.3.1, the boron transport analysis uses an available RCCW mass of 6840 kg (( }}2(a),(c) The audit item asks for the isolation signals for RCCW. Isolation of the RCCW system is described in FSAR Section 9.2.2, Section 6.2.4, and Section 7.1.1.2.1. Markups of the affected changes, as described in the response, are provided below: NuScale Nonproprietary NuScale Nonproprietary
NuScale Final Safety Analysis Report Increase in Heat Removal by the Secondary System NuScale US460 SDAA 15.1-24 Draft Revision 2 15.1.6.2 Sequence of Events and Systems Operation The event sequence table for the limiting containment flooding case is provided in Table 15.1-18. Unless specified below, the analysis of the containment flooding event assumes the plant control systems and ESFs perform as designed, with allowances for instrument inaccuracy. No operator action is credited to mitigate the effects of a containment flooding event. Audit Question A-15.0.5-3, Audit Question A-15.1.6-2 The containment flooding is initiated by a break in a CRDS line that transports reactor component cooling water inside containment. A conservative total RCCWS volume is assumedmass of approximately 24,300 kg is assumed as a bounding volume of the entire RCCWS inventory. The containment flooding cases assume one or more RCCWS pumps continue operating after the break. The number of operating RCCWS pumps assumed in the analysis is varied to determine the most limiting case. The containment evacuation pumps could malfunction to cause a loss of containment vacuum scenario, but are assumed to operate at nominal capacity for the limiting containment flooding scenario in order to delay reaching the high containment pressure MPS setpoint. Operator action is not credited for regulating control rod movement or increasing boron concentration, which ensures the maximum reactivity insertion is reached as the control system attempts to maintain RCS temperature by pulling the regulating control rods from the core. The MPS high containment pressure signal is credited to provide protection against loss of containment vacuum and containment flooding events. In cases that result in a reactor trip, the same high containment pressure signal actuates SSI and DHRS to maintain reactor cooling. There are no single failures that could make a containment flooding event more severe with respect to the acceptance criteria. Normal AC power is assumed to be available for this event. A loss of AC power, either at event initiation or at reactor trip, is not a conservative condition for a containment flooding event. The loss of AC power results in a reactor trip, DHRS actuation, and containment isolation on other MPS signals earlier than the high containment pressure signal. 15.1.6.3 Thermal Hydraulic and Subchannel Analyses 15.1.6.3.1 Evaluation Model The thermal hydraulic analysis of the plant response to containment flooding is performed using NRELAP5. A description of the NRELAP5 model is}}