ML24346A143

Relief Request RV-1A - 2nd Extension Request for Thermal Relief Valves (CP-202400460)

ML24346A143
Person / Time
Site:	Comanche Peak
Issue date:	12/11/2024
From:	Barnette J Vistra Operations Company
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
Download: ML24346A143 (1)

Text

WEB-BASED PROPOSED ALTERNATIVE SUBMISSION 10 CFR 50.55a(z)(2)

Submission Date: 12/11/2024 Submitted By: James Barnette Submission Availability: Non-Publicly Available Licensee: Vistra Operations Company LLC Plant Unit(s) and Docket No(s): Comanche Peak 1 ( 05000445 )

Licensee

Contact:

James Barnette (254) 897-5866 james.barnette@luminant.com Project

Title:

RELIEF REQUEST RV-1A - 2nd Extension Request for Thermal Relief Valves (CP-202400460)

Request Type:

10 CFR 50.55a(z)(2)

Inservice Inspection (ISI) or Inservice Testing (IST)

Inservice Testing (IST)

Requested Completion Date:

May 01, 2025 Proposed Alternative Number or Identifier:

RV-1A Brief Description of Proposed Alternative

Since suitable replacement parts or valves to support rework or replacement of two Unit 1 relief valves cannot be procured by 1RF24, Vistra OpCo proposes to replace these two valves no later than 1RF25 (in the Fall of 2026). In the interim, Vistra OpCo proposes to control the service water system in a manner that eliminates the chances of overpressure due to thermal transients by requiring the applicable vent valve to be opened upon isolation of the heat exchanger or cooler and remain open until the heat exchanger or cooler is no longer isolated from the safe shutdown impoundment.

Proposed Duration of Alternative (in terms of ISI/IST Program Interval with Start and End Dates):

This proposed alternative, upon approval, will be applied until 1RF25 in the Fall of 2026. This duration remains entirely within the fourth interval which started on May 22, 2024.

Applicable ASME Code Requirements ASME OM-2017 Mandatory Appendix I, Paragraph I-1390 Test Frequency, Classes 2 and 3 Pressure Relief Devices That Are Used for Thermal Relief Application. Tests shall be performed on all Classes 2 and 3 relief devices used in thermal relief application every 10 yr, unless performance data indicate more frequent testing is necessary. In lieu of tests the Owner may replace the relief devices at a frequency of every 10 yr, unless performance data indicate more frequent replacements are necessary.

ISTA-3170, Inservice Examination and Test Frequency Grace, Subparagraph (a)(2), For periods specified as greater than or equal to 2 yr, the period may be extended by up to 6 months for any given test.

Applicable American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (BPV Code),

or ASME Operation and Maintenanceof Nuclear Power Plants (OM Code), Edition and Addenda American Society of Mechanical Engineers (ASME) Code for Operation and Maintenance of Nuclear Power Plants (OM Code), 2017 Edition.

Current ISI or IST Program Interval Number and Start/End Dates IST Program Fourth Interval Start Date: May 22, 2024 End Date: August 2, 2033

Applicable ASME Code Components and/or System Description Select thermal relief valves in the Station Service Water (SSW) system which provide overpressure protection for the SSW side of the Component Cooling Water Heat Exchangers:

1SW-0442, CCW HX 1-01 SSW RLF VLV 1SW-0443, CCW HX 1-02 SSW RLF VLV

=

Reason for Request===

Pursuant to 10 CFR 50.55a, Codes and standards, paragraph (z), Alternatives to codes and standards requirements, item (2), VISTRA Operations Co. LLC (Vistra OpCo) is providing this proposed alternative to testing or replacing the selected relief valves due to a hardship without a compensating increase in quality and safety.

Full Description of Proposed Alternative Since suitable replacement parts or valves to support rework or replacement cannot be procured by 1RF24, Vistra OpCo proposes to rework/replace the two relief valves no later than 1RF25 (in the Fall of 2026). Until valve rework/replacement, Vistra OpCo proposes to place Shift Manager Caution Tags on the heat exchanger isolation valves and vent valves requiring the heat exchangers to be vented upon isolation and to remain vented until the heat exchanger is no longer isolated from the safe shutdown impoundment.

Description of Basis for Use During preparation of the CPNPP IST Program Interval update, it was discovered that multiple ASME Code Class 3 relief valves that protect systems or portions of systems that are required to perform a specific function in shutting down a reactor to the safe shutdown condition, in maintaining the safe shutdown condition, or in mitigating the consequences of an accident were incorrectly excluded from the IST Program. The extent of condition review determined that the error occurred in 1996 based on a liberal interpretation of the skid-mounted components exclusion (now found in ASME OM Code section ISTC-1200(b)). In total, 54 relief valves were found to have been incorrectly excluded from the IST Program. Many of the valves were tested or replaced within the OM Code required 10-year interval under the Preventative Maintenance Program. In the time since approval of RV-1 (EPID: L-2023-LLR-0019), 18 of the 20 valves which were not in compliance with I-1390 have been tested or replaced to restore code compliance. However, as of December 4, 2024, two valves are not in compliance with the OM Code interval plus the 6-months grace allowed by Code Case OMN-20 and are not expected to be restored to compliance by the expiration of RV-1 at the end of Spring 2025.

Since these relief valves have been in service for the licensed life of the plant without record of testing or maintenance, replacement valves are anticipated to be needed to support installation of valves that meet set pressure and/or seat leakage performance requirements. At minimum, it is expected that the valves will require

rework to restore set pressure within specification and seat tightness to an acceptable condition. Some critical parts are extremely likely to require replacement due to the potential for corrosion or buildup of mineral deposits from exposure to the lake water chemistry circulating in the SSW system. Corrosion or mineral deposits could impair our ability to disassemble the valves without damage to the critical components for which there are no available replacements. The potential for these issues was confirmed during recent replacement of sister relief valves in the same service conditions (2SW-0423 discharge was packed with contaminants and would not lift - CR-2024-007049).

Since Vistra OpCo does not have sufficient parts to support anticipated rework, and suitable replacements have a 60-week lead time (which began on November 16, 2024), implementing the OM Code requirement to test the valves has the potential to cause an extended outage of the service water system and result in a hardship without a compensating level of quality and safety.

Between approval of RV-1 in April of 2023 and approval of the purchase order for replacement valves in November of 2024, suitable alternate on-hand spare valves were identified for installation in the SSW/CCW heat exchanger relief valve locations. Since the on-hand valves were available without a long lead time, the design change was generated to incorporate the on-hand valves into the proper location with a change out of the internals to obtain the needed flow capacity. However, the valves were stored in the Radiologically Controlled Area (RCA) and when it came time to remove the valves from the RCA for the shop work scope only one of the four (two per Unit) valves were successfully removed from the RCA due to fixed contamination. Therefore, based on this discovery, different model relief valves were pursued to avoid Unit/Train differences. Once appropriate model relief valves were identified, only two were in stock. The design change was then modified for the selected model relief valves and the two in stock were successfully installed (2SW-0422 and 2SW-0423) during the Unit 2 outage thus restoring code compliance for all of the Unit 2 valves for which relief was previously granted. Purchase Order 2621278 was issued on November 16, 2024 for the other two relief valves needed for Unit 1 with a lead time of 60 weeks (30 weeks was reported in the original RV-1) which did not support the next Unit 1 refueling outage in Spring of 2025. In summary, by the time fixed contamination was discovered on the spare valves, it was too late to acquire new valves in support of replacement activities in the Spring of 2025. The expected delivery date for the Unit 1 relief valves is January 2026.

None of the subject station service water relief valves have an open safety function because the SSW system is an open system which cannot be over-pressurized unless the system is isolated. System isolation is only required when the system is out of service for maintenance and not credited to perform a nuclear safety function. When the SSW system is in service and required to be operable, the only safety function of the relief valves is to be closed to maintain the system pressure boundary. The overpressure design function of the relief valves is only required when the heat exchangers or coolers are isolated for maintenance or in response to a condition requiring the heat exchanger/cooler to be taken out of service (i.e. Alarm Procedure ALM-011A/B requires isolation of the CCW/SSW Heat Exchanger in the event of an alarm indicating a potential tube leak). Operation of the SSW relief valves is not required to support the function of the CCW system. There are no indications that the valves leak or that the lack of testing has adversely affected their close function. The SSW system does not have a history of pressure transients that cause the valves to open during pump start transients or system valve manipulations. In the history of licensed plant operation, there has not been a single instance of relief valve leakage at these locations. In the unlikely event of a transient that resulted in a stuck open relief valve, the full open relief rate of a valve over the full mission time of the SSW system would be insignificant compared to the available margin in Safe Shutdown Impoundment (SSI) inventory and less than half the capacity of the Auxiliary Building or Safeguards building sump pumps.

Since the relief valves only have an open function when the heat exchanger is isolated, Vistra OpCo proposes to place Shift Manager Clearances (in the form of Caution Tags) on the affected heat exchanger/cooler isolation valves and vent valves. The Caution Tags will provide directions to open the respective vent valve upon isolation of the heat exchanger from the safe shutdown impoundment. The open vent valve will eliminate the chances of overpressure due to thermal expansion. A caution tag is preferred over a danger tag because a danger tag would unnecessarily delay operators from responding appropriately to alarms and/or system leakage. The position of components that are danger tagged cannot be changed without a time-consuming process to remove the tags. Caution tags can be written to provide appropriate guidance whether the heat exchanger is in service or isolated, and caution tags are superior to operating procedures or specific maintenance clearances because these caution tags would be

referenced in all scenarios prior to isolation of the heat exchanger/cooler.

Include Any Additional Information None Precedents L-2023-LLR-0019 Comanche Peak Thermal Relief Valve Extension Alternative RV-1 L-2020-LLR-0062 Comanche Peak Relief Valve Test Interval Extension Verbal Authorization 2020-04-09 L-2020-LLR-0096 Comanche Peak Unit 1 COVID IST Interval Extension Verbal Authorization 2020-08-11 References None Attachments