05000261/LER-2013-001
| H. B. Robinson Steam Electric Plant, Unit No. 2 | |
| Event date: | |
|---|---|
| Report date: | |
| 2612013001R01 - NRC Website | |
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H. B. Robinson Steam Electric Plant, Unit No. 2 05000 261
PLANT IDENTIFICATION
Westinghouse - Pressurized Water Reactor
BACKGROUND
On 10/6/2013, with the plant de-fueled and no involvement of out-of-service structures, systems or components, it was discovered that a non-environmentally-qualified butt-splice was installed on a wire connected to the 'closed' limit switch for a containment isolation valve, which rendered the Post-Accident Monitoring (PAM) [IP] Instrumentation function - Containment Isolation Valve Position Indication - inoperable. This condition has been present for an extended period of time, and it is presumed that on multiple occasions this function was inoperable for a period of time greater than allowed by Technical Specifications (TS) 3.3.3, PAM Instrumentation Limiting Conditions for Operation (LCO). Condition Report 640902 was generated to address this violation.
EVENT DESCRIPTION
On 10/6/2013, with the plant de-fueled, personnel performing work to replace the limit switches of the Chemical Volume and Control System (CVCS) [CB] Letdown Line isolation Valve, CVC-204B [ISV] discovered a non-environmentally-qualified (non-EQ) butt- splice installed in a wire connected to this valve's 'closed' limit switch, CVC-204B-LS-C [33]. Per TMM-036, "Environmentally Qualified (EQ) Electrical Equipment Program," the limit switches associated with CVC-204B are required to be EQ to assure compliance with H. B. Robinson Steam Electric Plant, Unit No. 2 (HBRSEP2) commitments regarding Regulatory Guide 1.97, Rev. 3, May 1983, "Instrumentation for Light Water-Cooled Nuclear Power Plants to Assess Plant and Environs Conditions During and Following an Accident." The subject splice was found to be installed without the proper heat shrink insulators as required by procedure.
CVC-204A&B are air-operated globe valves [ISV] that isolate the CVCS Letdown Line, are normally open, and will close on Phase 'A' containment isolation signal or loss of supply air. These valves are arranged in series to ensure letdown can be isolated, even if one valve fails. The potential impact of the use and subsequent failure of a non-EQ splice in the 'closed' limit switch wiring would be loss of 'closed' indication for CVC-204B at the main control board [MCBD]. However, this loss of indication would not prevent the valve from functioning as designed.
The improper splice in the wiring to limit switch CVC-204B-LS-C did not meet EQ requirements, which rendered the PAM Instrumentation function - Containment Isolation Valve Position Indication - inoperable. This condition has been present for an extended period of time, and HBRSEP2 presumes that on multiple occasions this function was inoperable for a period of time greater than allowed by Technical Specifications (TS) 3.3.3, PAM Instrumentation LCO.
CAUSAL FACTORS
The investigation into the cause of this event indicates this was an isolated human performance event in which the non-licensed air- operated valve (AOV) technician failed to use the proper (Raychem) heat shrink insulators identified for the task per the work order instructions and the procedure (CM-309) directing the task.
A review of work orders (WO) for CVC-204B was performed to identify a date for installation of the non-EQ butt-splice. In May 1992, under WO 90AMPA2-CM, limit switch CVC-204B-LS-C was disconnected and reconnected with no documentation of the proper heat shrink insulators being installed for the six butt-splices performed: one of which is presumed to be the origin of the non- EQ butt-splice. There is no evidence that would suggest any time or situational pressures present during performance of WO 90AMPA2-CM.
CAUSAL FACTORS (continued) The same technician, which performed the improper butt-splice, performed similar splices properly less than two weeks later under a different WO, 92AES11. The completed work documentation for this WO clearly documents the splices were performed per CM-309 using non-insulated butt-splices insulated with the proper heat shrink insulators as required per EQ guidelines. The technician's accurate performance of the butt-splices in the latter WO, and the WO under which the improper splice was performed, illustrates an established understanding of the EQ requirements for this component, the capability of the technician to satisfactorily perform CM-309, and the isolated nature of this event.
CORRECTIVE ACTIONS
Completed:
Removal of the non-EQ splice and subsequent installation of an EQ splice under WO 2066875-01, which returned the component to operable condition.
SAFETY ANALYSIS
There are three plausible events in which CVC-204B-LS-C failure would be important to safety. First, the spurious closure of the isolation valve CVC-204B could lead to loss of CVCS given failure of Volume Control Tank (VCT) [TK] makeup from the Refueling Water Storage Tank (RWST) [TK]. The spurious closure of CVC-204B has a low probability of occurrence and the resulting loss of closure indication would not prevent the VCT level indications from providing sufficient information to operations to take action in mitigating the event. Second, failure to isolate CVC-204B would only be important if the other isolation valve were to fail. Third, a break in the letdown line in pipe alley would be mitigated by the automatic closure of containment isolation valves LCV-460A&B [ISV], which are upstream of CVC-204B.
The mitigation of these events would not be impacted by the loss of closure indication for CVC-204B, and would not prevent valve CVC-204B from functioning as intended; therefore, the risk significance is low.
ADDITIONAL INFORMATION
An Operating Experience (OE) search for related events at HBRSEP2 and across the industry was conducted. None of the internal OE reviewed revealed a workmanship issue similar to that evaluated in this event. The review of the related external OE indicates that, across the industry, there have been similar occurrences to the event at RNP. The OE did not provide additional insights regarding effective corrective actions for the current event.
Energy Industry Identification System (EllS) codes for systems and components relevant to this event are identified in the EQUIPMENT IDENTIFICATION section and in the text of this document within brackets [ ].