05000298/LER-2017-005

LER-2017-005, Traversing In-core Probe In-shield Limit Switch Mounting Failure Results in Common Cause Inoperability of Independent Trains or Channels and Condition Prohibited by Technical Specifications

Cooper Nuclear Station
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability
2982017005R00 - NRC Website

LER 17-005-00 for Cooper Nuclear Station Regarding Traversing In-core Probe In-shield Limit Switch Mounting Failure Results in Common Cause lnoperability of Independent Trains or Channels and Condition Prohibited by Technical Specifications

ML17236A166
Person / Time
Site:	Cooper
Issue date:	08/17/2017
From:	Dent J Nebraska Public Power District (NPPD)
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NLS2017077 LER 17-005-00
Download: ML17236A166 (4)

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Cooper Nuclear Station 05000- 298 NUMBER NO.

PLANT STATUS

Cooper Nuclear Station (CNS) was in Mode 1, Power Operations, 100 percent power, at the time of discovery; i.e., June 22, 2017.

BACKGROUND

The Traversing In-Core Probe (TIP) subsystem is a part of the Neutron Monitoring System [EIIS:IG]. The TIP subsystem allows calibration of Local Power Range Monitor (LPRM) [EllS:MON] signals by correlating TIP signals to LPRM signals as the TIP is positioned in various locations in the core. A TIP drive mechanism [EIIS:DRIV] uses an ionization chamber attached to a flexible drive cable, which is driven from outside Primary Containment [El IS:NFI] and is contained by guide tubes that continue into the reactor core.

A valve system is provided with a valve on each TIP guide tube entering the primary containment. A ball valve [EIIS:V] and a cable shearing valve [EIIS:V] are mounted in the TIP guide tubing just outside of the primary containment. The ball valve opens when the TIP is being inserted and closes automatically upon receipt of the proper signal and after the TIP cable and ionization chamber have been retracted. An in- shield limit switch [El IS:33] actuates to stop withdrawal of the TIP detector and also provides a permissive for closing the ball valve. The shear valve is used in the event the ball valve should fail to close or the chamber drive cable should fail to retract during the time that primary containment isolation is required.

CNS Technical Specifications (TS) Limiting Condition for Operation (LCO) 3.6.1.3 requires each Primary Containment Isolation Valve (PCIV) to be operable. The TIP ball valves are PCIVs.

EVENT DESCRIPTION

On June 21, 2017, TIP C failed to stop at the designated in-shield position when being withdrawn from the core. The TIP machine was manually stopped approximately seven inches beyond the in-shield position, and was then manually moved to the correct position by Operations. The TIP C ball valve was declared inoperable as a PCIV due to the failure of the in-shield limit switch. TS LCO 3.6.1.3, Primary Containment Isolation Valves, Condition A, was entered at 0524 and the Required Actions taken.

On June 22, 2017, TIP D failed to stop at the designated in-shield position when being withdrawn from the core. The TIP machine was manually stopped at approximately six inches past the in-shield position, and was then manually returned to in-shield location by Operations. The TIP D ball valve was declared inoperable as a PCIV due to failure of the in-shield limit switch. TS LCO 3.6.1.3, Primary Containment Isolation Valves, Condition A, was entered at 0445 and the Required Actions taken.

In each case, the condition would have prevented the ball valve from automatically closing on initiation of a Group 2 containment isolation signal.

control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

Cooper Nuclear Station - 005 -00 2017 The valves were declared operable on July 13, 2017, at 1133, and TS LCO 3.6.1.3, Condition A, was exited.

BASIS FOR REPORT

CNS is reporting these events under 10 CFR 50.73(a)(2)(vii) as common cause inoperability of independent trains or channels, as the primary containment isolation ball valves on TIPs C and D were inoperable at the same time. It is also being reported as a condition prohibited by Technical Specifications as defined in 10 CFR 50.73(a)(2)(i)(B).

SAFETY SIGNIFICANCE

There were no safety consequences associated with this condition. The potential safety significance of this event was low. The TIP ball valves are able to be closed by taking manual action to remove power in the case of a primary containment isolation signal. In addition, the TIP shear valves remained operable during the period of time the TIP ball valves were inoperable. The safety function of the primary containment isolation system was maintained. This condition did not cause an impact to the safety of the general public, nuclear safety, industrial safety, or radiological safety.

CAUSE

Inadequate mounting and securing of the in-shield limit switch to the chamber shield caused the limit switch to fail to actuate as designed.

CORRECTIVE ACTIONS

A Work Order was implemented to repair the mounting of the in-shield limit switches for all TIP channels.

In addition, the procedure for TIP chamber shield maintenance was revised to provide guidance for properly mounting the TIP in-shield limit switches.

PREVIOUS EVENTS

CR-CNS-2016-02424 — On May 3, 2016, TIP B detector failed to stop at its in-shield position when being retracted back into its chamber shield. This failure was attributed to inadequate maintenance associated with mounting the limit switch to the chamber shield.

CR-CNS-2016-08539 — On November 29, 2016, TIP C detector failed to stop at its in-shield position when being retracted back into its chamber shield. This failure was attributed to inadequate maintenance associated with mounting the limit switch to the chamber shield.