ML18101B392
| ML18101B392 | |
| Person / Time | |
|---|---|
| Site: | NuScale |
| Issue date: | 04/11/2018 |
| From: | NRC |
| To: | NRC/NRO/DNRL/LB1 |
| References | |
| Download: ML18101B392 (4) | |
Text
NuScaleDCRaisPEm Resource From: Chowdhury, Prosanta Sent: Wednesday, April 11, 2018 3:45 PM To: Request for Additional Information Cc: Lee, Samuel; Cranston, Gregory; Franovich, Rani; Karas, Rebecca; Burja, Alexandra; NuScaleDCRaisPEm Resource
Subject:
Request for Additional Information No. 415 eRAI No. 9472 (15.02.01 - 15.02.05)
Attachments: Request for Additional Information No. 415 (eRAI No. 9472).pdf Attached please find NRC staffs request for additional information (RAI) concerning review of the NuScale Design Certification Application.
The NRC Staff recognizes that NuScale has preliminarily identified that the response to one or more questions in this RAI is likely to require greater than 60 days. NuScale is expected to provide a schedule for the RAI response by email within 14 days.
If you have any questions, please contact me.
Thank you.
Prosanta Chowdhury, Project Manager Licensing Branch 1 (NuScale)
Division of New Reactor Licensing Office of New Reactors U.S. Nuclear Regulatory Commission 301-415-1647 1
Hearing Identifier: NuScale_SMR_DC_RAI_Public Email Number: 446 Mail Envelope Properties (BN7PR09MB26098EBE2D2A9C6624B31D069EBD0)
Subject:
Request for Additional Information No. 415 eRAI No. 9472 (15.02.01 - 15.02.05)
Sent Date: 4/11/2018 3:44:45 PM Received Date: 4/11/2018 3:44:49 PM From: Chowdhury, Prosanta Created By: Prosanta.Chowdhury@nrc.gov Recipients:
"Lee, Samuel" <Samuel.Lee@nrc.gov>
Tracking Status: None "Cranston, Gregory" <Gregory.Cranston@nrc.gov>
Tracking Status: None "Franovich, Rani" <Rani.Franovich@nrc.gov>
Tracking Status: None "Karas, Rebecca" <Rebecca.Karas@nrc.gov>
Tracking Status: None "Burja, Alexandra" <Alexandra.Burja@nrc.gov>
Tracking Status: None "NuScaleDCRaisPEm Resource" <NuScaleDCRaisPEm.Resource@nrc.gov>
Tracking Status: None "Request for Additional Information" <RAI@nuscalepower.com>
Tracking Status: None Post Office: BN7PR09MB2609.namprd09.prod.outlook.com Files Size Date & Time MESSAGE 675 4/11/2018 3:44:49 PM Request for Additional Information No. 415 (eRAI No. 9472).pdf 17166 Options Priority: Standard Return Notification: No Reply Requested: No Sensitivity: Normal Expiration Date:
Recipients Received:
Request for Additional Information No. 415 (eRAI No. 9472)
Issue Date: 04/11/2018 Application
Title:
NuScale Standard Design Certification 048 Operating Company: NuScale Power, LLC Docket No.52-048 Review Section: 15.02.01-15.02.05 - Loss of External Load; Turbine Trip; Loss of Condenser Vacuum; Closure of Main Steam Isolation Valve (BWR); and Steam Pressure Regulator Failure (Closed)
Application Section:
QUESTIONS 15.02.01-13 General Design Criterion (GDC) 15 in 10 CFR Part 50, Appendix A, requires that the reactor coolant system (RCS) and associated auxiliary, control, and protection systems shall be designed with sufficient margin to assure that the design conditions of the reactor coolant pressure boundary (RCPB) are not exceeded during any condition of normal operation, including anticipated operational occurrences (AOOs).
Design-Specific Review Standard (DSRS) for NuScale Small Modular Reactor Section 15.2.1-15.2.5, "Loss of External Load; Turbine Trip; Loss of Condenser Vacuum; Closure of Main Steam Isolation Valve; and Steam Pressure Regulator Failure (Closed)," provides the staff guidance on reviewing the listed undercooling events to determine compliance with GDC 10 and 15, among other regulations. DSRS Section 15.2.1-15.2.5 guides the reviewer to review the timing of the initiation of protection, engineered safety, and other systems needed to limit the consequences of the transient.
Based on the sequence of events tables (FSAR Tables 15.2-4 through 15.2-6) for the FSAR Section 15.2.1-15.2.3 events (Loss of External Load, Turbine Trip, and Loss of Condenser Vacuum), these events assume it takes 7 seconds for the feedwater isolation valves (FWIVs) and main steam isolation valves (MSIVs) to close after the decay heat removal system (DHRS) actuation signal. However, the FSAR Section 15.2.4 MSIV closure event assumes it takes 5 seconds for the FWIVs to close, according to the corresponding sequence of events table (Tables 15.2-11 through 15.2-13). The reason for the inconsistency is not clear.
Furthermore, FSAR Tier 2, Section 6.2.4.4.1, states that the containment isolation valves are verified to close within (emphasis added) the time specified in Table 6.2-4, which shows a closure time of 5 seconds and an isolation signal of 2 seconds for the FWIVs and MSIVs. From this statement, it appears possible for the valves to close more quickly than the listed times. For reduction in heat removal events, the staff expects the earliest possible FWIV and MSIV closure to be limiting for RCS pressure due to the earlier loss of cooling, though the earliest possible MSIV closure and latest possible FWIV closure would be limiting for steam generator pressure. The most limiting valve characteristics for the particular analysis should be applied to ensure a conservative calculation of transient response. Therefore:
- 1. Justify the difference in assumed FWIV closure times between FSAR Sections 15.2.1-15.2.3 and FSAR Section 15.2.4.
- 2. Confirm whether the MSIVs and FWIVs can close faster than what is listed in FSAR Tier 2, Table 6.2-4.
- 3. Justify the conservatism of the assumed FWIV and MSIV closure times for each of the above-mentioned events and for all FSAR Chapter 15 events, including the differences in limiting closure times for the different acceptance criteria being examined (e.g., RCS pressure, SG pressure, MCHFR). Alternatively, update the analyses to incorporate the most conservative closure times.
- 4. Update the FSAR as necessary.
15.02.01-14 GDC 10 requires that the reactor core and associated coolant, control, and protection systems shall be designed with appropriate margin to assure that specified acceptable fuel design limits are not exceeded during any condition of normal operation, including the effects of AOOs. GDC 15 requires that the RCS and associated auxiliary, control, and protection systems shall be designed with sufficient margin to assure that the design conditions of the RCPB are not exceeded during any condition of normal operation, including AOOs. DSRS Section 15.2.1-15.2.5 provides guidance for meeting the requirements of GDC 10 and 15 and guides the reviewer to evaluate the values of system parameters and initial core and system conditions as input to the model.
The high-biased initial feedwater temperature assumed for the events in FSAR Sections 15.2.1-15.2.4 is inconsistent with the event-specific methodologies described in TR-0516-49416-P, "Non-Loss-of-Coolant Accident Analysis Methodology," which is referenced in FSAR Chapter