ML24215A218
| ML24215A218 | |
| Person / Time | |
|---|---|
| Site: | 05200050 |
| Issue date: | 08/02/2024 |
| From: | NuScale |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML24215A000 | List: |
| References | |
| LO-169995 | |
| Download: ML24215A218 (1) | |
Text
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Question:
In the NuScale DCA, drop of a module being moved for refueling ((2(a),(c) DCA Part 2, Tier 2, Table 19.1-71, Key Assumptions for the Low Power and Shutdown Probabilistic Risk Assessment, documents that movement of the RBC is modeled as being operator controlled in the PRA. In the SDA, Based on Table 19.1-60: Summary of Results, module drop contributes over 34% of the total NuScale SDA CDF results. In contrast to the DCA, as reported in ((
}}2(a),(c) In FSAR Section 9.1.5.2.3, there is one reference to the reactor building crane (RBC) control system. In Table 19.1-21 regarding the Key Assumptions for the PRA, there is no information regarding the reactor building crane control system or the risk impact of operator error. The staff notes that the non-safety related, non-risk significant Module Control System (MCS) is treated in a global sense in Chapter 7 of the FSAR. Common cause failure analysis of the MCS is provided in FSAR Section 7.1.6. In contrast, there are a few sentences in the FSAR about the Reactor Building Crane Control System that is non-safety related, but risk significant. Based on the NuScale meeting on October 10, 2023, the staff has the following questions about the NuScale reactor building control system design, testing, and PLC reliability data, to ensure that risk insights regarding the reactor building crane have been appropriately incorporated into the FSAR Chapter 19 consistent with the Commission Severe Accident Policy Statement.
- 1. Regarding the Appendix B of the Reactor Building Crane PRA, in the NuScale ERR, the Control System Functional Diagrams, as shown in Figure B-1, Figure B-2, and Figure B-3 depict the ((
}}2(a),(c)
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- 4. The staff needs to make a reasonable assurance finding that the RBC will not be operated following high winds, external floods, and extended losses of offsite power which is explicitly stated in the DCA for POS 3 and POS 5. For example, SDA FSAR Table, 19.1-74 for external flooding states, In the event of loss of AC power, the RBC brakes will set and stop motion. The RBC is designed with redundant holding brakes so that if one set fails to engage, the other brake automatically holds the load. Because both brake systems are designed and rated to maintain a hoisted load at the maximum allowable crane load, a loss of power will halt operations but not result in a load drop. The module can be maintained in position suspended by the RBC until power is restored and the lift can resume; therefore, external flooding effects
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