05000293/LER-2016-010

LER-2016-000, MSIV Inoperability Led to a Condition Prohibited by the Plant s Technical Specifications

Pilgrim Nuclear Power Station (Pnps)
Event date:	12-15-2016
Report date:	02-13-2017
Reporting criterion:	10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
2932016000R00 - NRC Website

LER 16-010-01 for Pilgrim Nuclear Power Station re MSIV Inoperability

ML17174A674
Person / Time
Site:	Pilgrim
Issue date:	06/14/2017
From:	Perkins E P Entergy Nuclear Operations
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
2.17.045 LER 16-010-01
Download: ML17174A674 (7)

The function of the Main Steam Isolation Valves (MSIVs) is to prevent reactor coolant inventory loss in the event of a steam line break outside primary containment. Also, MSIVs provide a primary containment boundary after a loss of coolant accident inside primary containment. The MSIVs are 20-inch air/spring operated, balanced "Y"-type globe valves. There are four main steam lines. Each steam line has two MSIVs; one inside primary containment and one outside of primary containment. The MSIV outboard valves are located inside the steam tunnel in secondary containment.

The MSIVs are part of the primary containment isolation system (PCIS) which provides timely protection against the gross release of radioactive materials from the fuel, nuclear system process barrier, and from the primary containment. The PCIS automatically initiates whenever monitored variables exceed preselected operational limits. Immediate shutdown of the reactor is appropriate in such a situation. The scram initiated by the MSIV closure anticipates a reactor vessel low water level scram. The main steam line isolation scram setting is selected to give the earliest positive indication of isolation valve closure.

EVENT DESCRIPTION

On December 15, 2016, at 1500 [EST], with the reactor at approximately 22 percent power, while performing a steam tunnel walkdown the MSIVs 2C (AO-203-2C) and 2D (AO-203-2D) were discovered to have steam leaks.

MSIV 2D, which had a body to bonnet steam leak, was declared inoperable and Technical Specifications (TS) Limiting Condition for Operation Action Statement (LCOAS) 3.7.A.2.b was entered at 1530 on December 15, 2016. Outboard MSIV 2D and inboard MSIV 1D were both closed and deactivated to isolate Main Steam Line D at 1753 [EST] on December 15, 2016, in accordance with TS requirements. Input to Operability for the outboard MSIV 2C packing leak was requested. On December 16, 2016, it was concluded there was not reasonable assurance of Operability and MSIV 2C was declared inoperable,. Accordingly, on December 16, 2016 at 1524 [EST] TS LCOAS 3.7.A.2.b was entered for the outboard MSIV 2C. Actions were also taken to close and deactivate the inboard MSIV 1C, which included a controlled plant shutdown to reduce reactor pressure below the MSIV closure scram bypass setpoint.

Based on the evidence found, it was reasonable to conclude that the MSIV 2D valve body to bonnet steam leak and the MSIV 2C packing leak had likely started sometime prior to the event date and both were leaking for a period of time greater than that allowed by TS. Therefore, PNPS is making this submittal in accordance with 10 CFR 50.73(a)(2)(i)(B), any operation or condition prohibited by the plant's TS. In addition, PNPS closed the inboard MSIV 1C in accordance with TS LCOAS 3.7.A.2.b prior to going to Cold Shutdown. However, PNPS is also conservatively making this submittal in accordance with 10 CFR 50.73(a)(2)(i)(A), the completion of any nuclear plant shutdown required by the plant's TS, because PNPS chose to shutdown the plant while completing the action required by TS 3.7.A.2.b to close and deactivate the inboard MSIV 10 with Main Steam Line D previously isolated.

The plant was placed in Cold Shutdown on December 17, 2016, to repair both of the leaking outboard MSIVs, 2C and 2D. MSIV 2D was seal welded, Post Work Tested (PWT) and returned to service. The outboard MSIV 2C packing was repaired stopping the packing leakage. MSIV 2C PWT was performed and the valve returned to service.

Although the discovery date of the two outboard MSIV steam leaks was December 15, 2016, the last time both of these MSIVs were tested and confirmed to be operable was during Refueling Outage 20, which ended on May 23, 2015. MSIV 2D outboard valve body to bonnet leak and MSIV 2C outboard valve packing leak both likely occurred sometime during the operating cycle following restart from the refueling outage. However, there is no way to pinpoint the specific dates.

CAUSE OF THE EVENT

The causal factor for MSIV 2D leakage was that the gasket that was used in the valve body to bonnet interface was out of specification. The extent of condition review identified that the only other valve with the possible incorrect gasket material was MSIV 2A which will be dispositioned during the upcoming refueling outage.

The causal factor for MSIV 2C leakage was scoring on the valve stem. The valve stem was polished to remove obtrusions for a smoother finish.

CORRECTIVE ACTIONS

The immediate corrective action to prevent recurrence was to shut down the reactor and repair both of the , leaking outboard MSIVs 2C and 2D. MSIV 2D was seal welded, PWT was performed, and the valve returned to service. MSIV 2C repair involved polishing the scoring on the valve stem to remove obtrusions and repacking the valve which stopped the packing leakage. MSIV 2C PWT was performed and the valve was returned to service.

The outboard MSIV 2C will be disassembled, inspected, and additional repairs will be made if needed, during the upcoming Refueling Outage 21. If additional repairs are needed for the outboard MSIV 2C, it will be handled within the Corrective Action Program.

SAFETY CONSEQUENCES

There were no consequences to the safety of the public, nuclear safety, industrial safety or radiological safety due to this event because there was no loss of safety function. Main Steam Line D was isolated on December 15, 2016, in accordance with TS requirements. Main Steam Line C was isolated on December 17, 2016, also in accordance with TS requirements. In addition, on December 15, 2016 the plant was shutdown and the two outboard MSIVs were repaired and returned to service.

Based on the defense in depth of redundant inboard and outboard MSIVs, risk is considered to be Low.

No actions to reduce the frequency or consequence are necessary.

REPORTABILITY

This report is submitted in accordance with 10 CFR 50.73(a)(2)(i)(B), any operation or condition which was prohibited by the plant's Technical Specifications and 10 CFR 50.73(a)(2)(i)(A),the completion of any nuclear plant shutdown required by the plant's Technical Specifications.

PREVIOUS EVENTS

A review of Pilgrim Nuclear Power Station Licensee Event Reports for the past three years did not identify any similar occurrences of declaring two MSIVs inoperable due to steam leakage.

REFERENCES:

CR-PNP-2016-10039 CR-PNP-2016-10040