05000499/LER-2021-001, Condition Prohibited by Technical Specifications Due to Inoperable Containment Isolation Valve

Condition Prohibited by Technical Specifications Due to Inoperable Containment Isolation Valve

ML21252A756
Person / Time
Site:	South Texas
Issue date:	09/09/2021
From:	Harshaw K South Texas
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NOC-AE-21003833, STI: 35208185 LER 2021-001-00
Download: ML21252A756 (6)

LER-2021-001, Condition Prohibited by Technical Specifications Due to Inoperable Containment Isolation Valve

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
4992021001R00 - NRC Website

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Nuclear Operating Company

South Texas Project Electric Generating Station P.O. Box 289 Wadsworth, Texas 77483

September 9, 2021 NOC-AE-21003833 10 CFR 50.73 STI:35208185

ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001

South Texas Project Unit 2 Docket No. STN 50-499 Licensee Event Report 2021-001-00 Condition Prohibited by Technical Specifications Due to InoperabteC^^^ Valve

Pursuant to 10 CFR 50.73(a)(2)(i)(B), STP Nuclear Operating Company submits South Texas Project (STP) Unit 2 Licensee Event Report 2021-001-00 for a condition prohibited by Technical Specifications due to an inoperable containment isolation valve. This event is reportable pursuant to 10 CFR 50.73(a)(2)(i)(B) because the Technical Specification 3.6.3 required action statement for an inoperable containment isolation valve was not met.

The event did not have an adverse effect on the health and safety of the public.

There are no commitments in this letter.

If you should have any questions on this submittal, please contact All Albaaj at (361) 972-8949 or me at (361) 972-4778. k^UW^-"

Kimberly A. Harshaw Executive Vice President and Acting Chief Nuclear Officer

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Attachment: STP Unit 2 LER 2021-001-00, Condition Prohibited by Technical Specifications Due to Inoperable Containment Isolation Valve

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Regional Administrator, Region IV U.S. Nuclear Regulatory Commission 1600 E. Lamar Boulevard Arlington, TX 76011-4511 NOC-AE-21003833 Attachment

Attachment

STP Unit 2 LER 2021-001-00, Condition Prohibited by Technical Specifications Due to Inoperable Containment Isolation Valve

Abstract

On July 1, 2021, at 2344 hours0.0271 days <br />0.651 hours <br />0.00388 weeks <br />8.91892e-4 months <br />, the STP Nuclear Operating Company discovered that Steam Generator 2D outside reactor containment isolation valve R/-4150 was indicating valve closure but only reduced the flow rate by about 8.33%. On July 2, 2021, at 0350 hours0.00405 days <br />0.0972 hours <br />5.787037e-4 weeks <br />1.33175e-4 months <br />, the valve was declared inoperable due to inadequate isolation. Site engineering determined on July 12, 2021, that FV-4150 was inoperable since March 29, 2021, due to preventative maintenance performed on that date. On July 3, 2021, FV-4150 was determined to be operable following a valve stem adjustment and a satisfactory performance of the surveillance test.

The causes of the event were associated with inadequate written guidance. This event is reportable because the Technical Specification 3.6.3 required action statement for an inoperable containment isolation valve was not met. Specifically, the containment isolation valve was inoperable from March 29, 2021, to July 3, 2021, for a total of 96 days. The allowed outage time is 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> or apply the requirements of the configuration risk management program. Planned corrective actions include revising the work instructions and the post-maintenance testing guidance.

I. Description of Reportable Event

A. Reportable event classification

This event is reportable pursuant to 10 CFR 50.73(a)(2)(i)(B) because the Technical Specification 3.6.3 required action statement for an inoperable containment isolation valve was not met.

B. Plant operating conditions prior to event

Prior to the event, Unit 2 was at 100% power in Mode 1.

C. Status of structures, systems, and components that were INOPERABLE at the start of the event and that contributed to the event

No other structures, systems, or components were inoperable at the start of this event that contributed to this event.

D. Background information

The steam generator blowdown system provides the means to continuously blowdown the steam generator to maintain the prescribed water chemistry in the steam generators. The system also removes dissolved solids and corrosion products from the blowdown stream to make it suitable for reuse in the condenser hotwell.

The steam generator blowdown system is a closed system. Steam Generator 2D outside reactor containment isolation valve R/-4150 meets the requirements in General Design Criteria 57 for Closed Systems Isolation Valves. There was no open pathway between the reactor containment building and the outside.

E. Narrative summary of the event

Note: all times are Central Daylight Time

On July 1,2021, at 2344 hours0.0271 days <br />0.651 hours <br />0.00388 weeks <br />8.91892e-4 months <br />, a condition report was written documenting that during the performance of the steam generator blowdown system valve operability test, Steam Generator 2D outside reactor containment isolation valve R/-41 50 local valve indication showed closed. However, the flow across the valve only reduced from about 36 klb/hrto about 33 klb/hr. On July 2, 2021, at 0350 hours0.00405 days <br />0.0972 hours <br />5.787037e-4 weeks <br />1.33175e-4 months <br />, R/-41 50 was declared inoperable due to inadequate isolation.

Corrective maintenance was performed on the valve on July 2, 2021. The as-found condition was described as "craft identified valve was not making contact with the valve seat." The valve stem was screwed out three turns from the marriage block, adjusting the valve stroke to bring the valve plug to the seat. This indicated the valve stroke was slightly short, not allowing the plug to contact the valve seat. R/-4150 is quick-opening, thus only a slight distance between the seat and the plug is necessary for the valve to allow a large percentage of flow through while closed.

On July 3, 2021, at 0501 hours0.0058 days <br />0.139 hours <br />8.28373e-4 weeks <br />1.906305e-4 months <br />, R/-4150 passed the steam generator blowdown system valve operability test and was declared operable. Site engineering determined on July 12, 2021, that the valve stroke length inaccuracy was the result of an actuator overhaul preventative maintenance activity that was completed on March 29, 2021, duhng the most recent refueling outage (2RE21). The scope of the preventative maintenance was to disassemble the actuator, replace soft parts and worn or damaged parts, measure the free length of the actuator spring, replace air filter, and reassemble. Under this preventative maintenance, the actuator stem is removed, and the stroke of the actuator is adjusted.

F. Method of discovery

This event was self-revealed when R/-4150 did not pass the quarterly sun/eillance test due to inadequate isolation.

A. Failure Mode, mechanism, and effects of failed component

The failed component of this event was the steam generator 2D blowdown valve FV-4150. The valve plug was not contacting the valve seat creating a slightly short valve stroke. There were no effects on safety systems and functions due to the failed component because the steam generator blowdown system is a closed system. The steam generator blowdown valve is an outside containment isolation valve and meets the requirements of General Design Criteria 57 for Closed Systems Isolation Valves. There were no other components affected by the failed component.

B. Cause of component or system failure or personnel error

The direct cause of this event was the valve stem was seated in the marriage block short, shortening the valve stroke and not allowing the plug to contact the valve seat.

C. Systems or secondary functions that were affected by failure of components with multiple functions

There are no secondary systems or functions for this component.

D. Failed component information

Steam generator blowdown system outside reactor containment isolation valve;

4-inch ASME Section III, Class 2, quick-opening type globe valve

III. Analysis of the event

A. Safety system responses that occurred

No safety system responses occurred due to this event.

B. Duration of safety system inoperability

Steam Generator 2D blowdown outside reactor containment isolation valve R/-41 50 was inoperable from March 29, 2021, to July 3, 2021, for a total of 96 days.

C. Safety consequences and implications

Valve FV-4150 is connected to the secondary side of Steam Generator 2D and not directly connected to containment atmosphere. Secondary water exiting through the blowdown line will enter the condenser hotwell and return to Steam Generator 2D as main feedwater. The steam generator blowdown system is a closed system. The steam generator blowdown valve is an outside containment isolation valve and meets the requirements of General Design Criteria 57 for Closed Systems Isolation Valves. There is no open pathway in the physical integrity of reactor containment due to an inoperable blowdown valve. This event did not result in any offsite release of radioactivity or increase of offsite dose rates, and there were no personnel injuries or damage to any safety-related equipment associated with this event. Therefore, there was no adverse effect on the health and safety of the public.

IV. Cause of the event

The causes for this event were determined to be:

1. Vendor Technical Document work instructions do not work as written when leaving the actuator installed during actuator disassembly.

2. Post-Maintenance Testing did not include guidance to ensure valve plug was fully seated.

3. The valve remote position indicator verification test procedure assumes the local valve position indication reflects the actual (internal) valve position.

V. Corrective actions

Planned corrective actions are as follows:

1. Revise Vendor Technical Document for containment isolation valve FV-4150 to ensure the work instructions for "Reassembling the Actuator" work as written if the actuator is disassembled while on the valve in accordance with the work instructions for "Disassembling the Actuator."

2. Revise Maintenance Work Instructions to include the following post-maintenance testing guidance:

Perform Valve Diagnostic Testing to ensure full open and close stroke of valve.

Verify the valve plug is fully seated in the closed position.

Verify correct local and remote indication of valve position in the open and closed position.

No corrective actions were determined to be necessary for Cause 3. The remote position indication and the local valve position indicator are verified accurate during post-maintenance testing under maintenance guidance via valve diagnostic testing (Cause 2). This will establish reasonable assurance of the validity of the subsequent performances of the valve remote position indicator verification test and the steam generator blowdown system valve operability test.

VI. Previous similar events

No previous similar events were identified.