CP-202200481, Response to Request for Additional Information - Relief Request Application P-1, Inservice Testing (IST)

Response to Request for Additional Information - Relief Request Application P-1, Inservice Testing (IST)

ML22342B279
Person / Time
Site:	Comanche Peak
Issue date:	12/07/2022
From:	Hicks J Luminant
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
CP-202200481, TXX-22094, EPID L 2022-LLR-0058
Download: ML22342B279 (1)

Text

Jack C. Hicks Comanche Peak Manager, Regulatory Affairs Nuclear Power Plant (Vistra Operations Company LLC)

P.O. Box 1002 6322 North FM 56 Glen Rose, TX 76043 T 254.897.6725 CP-202200481 TXX-22094 December 7, 2022 U. S. Nuclear Regulatory Commission Ref 10 CFR 50.55a ATTN: Document Control Desk 10 CFR 50.4 Washington, DC 20555-0001

Subject:

Comanche Peak Nuclear Power Plant Docket Nos. 50-445 and 50-446 Response to Request for Additional Information - Relief Request Application P-1, Inservice Testing (IST)

References:

1. NRC email from Dennis Galvin to Jack Hicks, Comanche Peak - Request for Additional Information - Proposed Alternative P-1 Regarding Inservice Testing of Safeguards Building Sump Pumps (EPID: L 2022-LLR-0058), dated November 21, 2022

2. Letter TXX-22064 from Jack Hicks to the NRC, Relief Request Application P-1, Inservice Testing (IST), dated July 20, 2022 [ML22201A555]

Dear Sir or Madam:

Vistra Operations Company LLC (Vistra OpCo) hereby submits a response to the NRC request for additional information (RAI) (Reference 1) regarding the Inservice Testing (IST) relief request application P-1 submitted with Reference 2. The attachment to this letter provides Vistra OpCos response to the NRC information request.

This communication contains no new commitments regarding Comanche Peak Units 1 and 2.

Should you have any questions, please contact Jim Barnette at (254) 897-5866 or James.Barnette@luminant.com.

Sincerely, Jack C. Hicks

Attachment:

Response to Request for Additional Information - IST Relief Request P-1 c(email) - Scott Morris, Region IV [Scott.Morris@nrc.gov]

Dennis Galvin, NRR [Dennis.Galvin@nrc.gov]

John Ellegood, Senior Resident Inspector, CPNPP [John.Ellegood@nrc.gov]

Neil Day, Resident Inspector, CPNPP [Neil.Day@nrc.gov]

Attachment to TXX-22094 Comanche Peak Nuclear Power Plant Response to NRC Request for Additional Information - Proposed Alternative P-1 Regarding IST of Safeguards Building Sump Pumps

[ML22201A555]

(EPID: L 2022-LRO-0065)

(5 pages including this cover page)

Attachment to TXX-22094 Page 2 of 5 The NRC Staffs requests for additional information (RAI) are provided below in bold text and are followed by the Vistra OpCo responses.

EMIB-RAI-1:

Comanche Peak Alternative Request P-1, Section Description of Basis for Use, second paragraph, states:

In addition, Regulatory Guide (RG) 1.175 Revision 1, "An Approach for Plant-Specific, Risk-Informed Decision- making: Inservice Testing," (ML21140A055) states that for LSSCs [low safety significant components], like the SBSPs, the testing may be less rigorous. This philosophy of demonstrating that the SBSPs have adequate design margin (greater than 50 gpm) is consistent with RG 1.175 testing strategy for LSSCs.

The Comanche Peak IST plan for pumps and valves for the third 10-Year IST program interval, Revision 4, Table 0, Inservice Pump Testing Plan, on pages 5 and 6 specifies that the SBSPs are LSSC (ML21082A299). Please confirm that the SBSPs remain LSSC for the 4th 10-Year IST program interval.

Response

The risk rank of each component in the IST Program is re-assessed every three years. In the latest risk assessment performed in 2021, the expert panel confirmed that the SBSPs remain LSSC.

Attachment to TXX-22094 Page 3 of 5 EMB-RAI-2:

Comanche Peak Alternative Request P-1, Section Description of Basis for Use, fourth paragraph, states:

The SBSPs are of low safety significance and are not explicitly modeled in the Probabilistic Risk Assessment (PRA) for internal events analysis. As stated previously, the SBSPs are installed to prevent flooding from a LOCA [loss-of-coolant accident]. Alarms associated with these pumps alert the operator of potential leakage in the Safeguards Building and mitigate the consequences of the leakage. The proposed alternative test will provide reasonable assurance that the sump pumps will perform their intended functions and not impact the assumptions in the PRA

[probabilistic risk assessment] assessment.

The licensee states that the SBSPs are of low safety significance and are not explicitly modeled in the PRA for internal events analysis at CNPP Units 1 and 2. Please explain the applicable PRA assumptions and how the proposed alternative test will provide reasonable assurance without impacting the assumptions in the PRA assessment.

Response

The PRA model does not explicitly model any of the plants sump pumps. The internal flood (IF) PRA model propagation path development methodology does consider backflow through the drains connecting local sumps and allows flood water to accumulate based on plant configuration.

All the information necessary to build the CPNPP IF PRA model is identified on a scenario-by-scenario basis. Such information includes equipment scenario frequency, error factors, involved sources, affected equipment, and associated basic events and the mapping to existing initiators.

This development does not credit sump pumps to limit or mitigate the flood height/depth calculations.

With respect to Operator Actions, specifically actions to isolate/mitigate a pipe break, sump pumps were not explicitly credited. The time allotted for the flow out of a ruptured pipe that is capable of being isolated was assumed to be three (3) hours. Due to a flood event, it is expected that the flood/pipe break would be identified at a minimum of 2.4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> after the onset of the event (assuming that no other signals are present, such as high sump or sump pumps running signals that would potentially shorten the time before the identification of the problem). The plant is walked down at least 10 times a day by procedure which averages out to at least 2.4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> between each walkdown. From the discovery of the rupture, it is assumed to take operators at most 30 minutes to isolate. The three-hour timeframe that is used in the flooding analysis is commonly used for operation actions by the industry and the NRC.

As the PRA does not directly credit the sump pump or their alarms, the alternate test, from a PRA perspective, ensures their ability to perform their design functions and thereby provides additional non-quantifiable benefit to plant risk.

Attachment to TXX-22094 Page 4 of 5 EMB-RAI-3:

The Comanche Peak IST plan for pumps and valves for the third 10-Year IST program interval, Revision 4, Table 0 on pages 5 and 6 specifies the test schedule for the SBSPs as 6 years for the Group A test and 6 years for the Comprehensive Pump Test (CPT).

The NRC safety evaluation dated June 26, 2013, authorizing Alternative Request P-1 for the Third 10-Year IST Program interval (ML13148A437) at Comanche Peak states that the licensee established a 6-year staggered test frequency which resulted in one pump per unit tested every 18 months. The Comanche Peak Alternative Request P-1 for the Fourth 10-Year IST Program specifies that the Alternative Request P-1 for the Third 10-Year IST Program interval is a precedent for the Alternative Request P-1 for the Fourth 10-Year IST Program interval.

However, Alternative Request P-1 for the Fourth 10-Year IST Program interval does not provide information regarding this frequency of the SBSP testing.

Please describe the staggered test frequency approach for the SBSPs during the Fourth 10-Year IST Program interval at CPNPP Units 1 and 2. Also, please specify any differences between Alternative Request P-1 for the Fourth 10-Year IST Program interval and Alternative Request P-1 that the NRC authorized for the Third 10-Year IST Program interval.

Response

During the Fourth 10-Year IST Program interval at CPNPP Units 1 and 2, the SBSPs will be on a 6-year staggered test frequency which results in one pump per unit tested every 18 months. In short, the test frequency during the 4th interval is requested to be the same as it is in the 3rd interval.

Differences between Alternative Request P-1 for the Fourth 10-Year IST Program interval and Alternative Request P-1 that the NRC authorized for the Third 10-Year IST Program interval:

1. The applicable Code Edition and Addenda has changed from ASME OM Code 2004 Edition/2006 Addenda to ASME OM Code 2017 Edition. Please note that CPNPP is currently evaluating whether to implement the recently approved 2020 Edition of the ASME OM Code for the Fourth 10-Year IST Program interval.

2. The applicable Code requirements (ISTB-3540(b), ISTB-5200(a), ISTB-5221, and ISTB-5223) have been updated consistent with the updated language in the 2017 Edition of the ASME OM Code. ISTB-3540(b) and ISTB-5200(a) were not updated between the 2004Edition/2006 Addenda and ASME OM Code 2017 Edition. OM Code changes were made to ISTB-5221, Group A Test Procedure and ISTB-5223, Comprehensive Test Procedure, to allow the pump to be operated as close as practical to a specified reference point within the variances from the reference point as described in this paragraph.

The changes to the OM Code offer flexibility in establishing the reference values for pumps.

However, even with the additional flexibility, the physical limitations of plant design resulting in the short test duration remain the same as they were in the 3rd interval and continue to impact the ability to meet the applicable OM Code requirements. The small capacity of the sump, lack of a test loop, and lack of plant installed pressure or differential pressure instruments on the suction and discharge of the SBSPs remain the same and continue to impact the ability to establish pump test conditions at a reference differential pressure (or flow rate) while measuring the flow rate (or differential pressure, respectively) in accordance with ISTB-5221 and ISTB-5223.

Attachment to TXX-22094 Page 5 of 5 The intent of the alternative request is to continue to test the SBSPs in the same manner as has been performed in the Third IST Program Interval because the OM Code requirements cannot be met without significant plant modifications and the alternative test continues to provide an adequate test to demonstrate that the pumps can achieve their intended safety functions.

Any other differences between the 3rd interval P-1 Alternative Request and the 4th Interval P-1 Alternative Request are editorial in nature in order to simplify the request and/or meet the submittal format required by the NRC.