05000354/LER-2008-003
| Docket Number | |
| Event date: | 10-05-2008 |
|---|---|
| Report date: | 12-04-2008 |
| Initial Reporting | |
| 3542008003R00 - NRC Website | |
PLANT AND SYSTEM IDENTIFICATION
General Electric — Boiling Water Reactor (BWR/4) High Pressure Coolant Injection System { BJ } *Energy Industry Identification System {EIIS} codes and component function identifier codes appear as {SS/CCC} IDENTIFICATION OF OCCURRENCE .
Event Date/Time: October 5, 2008 / 0431 Discovery Date/Time: October 5, 2008 / 0431
CONDITIONS PRIOR TO OCCURRENCE
Hope Creek was in Operational Condition 1 with reactor power at 100%. No structures, systems, or components were inoperable that contributed to the event.
DESCRIPTION OF OCCURRENCE
On October 5, 2008 at 0431, during a channel calibration associated with the HPCI Div 3 Steam Leak Detection Temperature Monitor display, the NUMAC drawer failed. During troubleshooting activities the drawer was down powered and re-powered resulting in a HPCI isolation signal and HPCI turbine trip signal.
The HPCI isolation valve had been de-energized to prevent an inadvertent isolation, however the troubleshooting activities also resulted in a HPCI turbine trip signal and a subsequent turbine trip. This resulted in unavailability and inoperability of the HPCI System. The condition existed for twenty-nine minutes during maintenance activities.
The event was reported to the NRC in accordance with 10CFR50.72 (b) (3) (v) (D) — [EVENT OR CONDITION THAT COULD HAVE PREVENTED FULFILLMENT OF A SAFETY FUNCTION - ACCIDENT MITIGATION] (Event Notification System report number 44541). This LER reports the event under 50.73(a)(2)(v)(D) [EVENT OR CONDITION THAT COULD HAVE PREVENTED FULFILLMENT OF A SAFETY FUNCTION- ACCIDENT MITIGATION] because the event resulted in HPCI inoperability, and 50.73(a)(2)(iv)(A) [SYSTEM ACTUATION] because although the actuation was invalid, none of the exceptions listed were satisfied.
The purpose of the Leak Detection System NUMAC is to provide indication and alarm signals and isolation inputs to the Nuclear Steam Supply Shutoff System (NSSSS) logic to isolate the monitored system in the event of a steam line break outside of the containment. Inputs into the NUMAC drawer include local area temperatures. A HPCI isolation and turbine trip is initiated if high ambient temperatures or ventilation differential temperatures reach set points indicative of a steam line rupture.
A channel calibration of the HPCI Div 3 Steam Leak Detection Temperature.Monitor channel was being performed using the appropriate Instrumentation and Control procedure, when the NUMAC drawer display became brightly lit and the touch keys were inoperable. The procedure was stopped and the problem was documented in the Corrective Action Process.
A troubleshooting log was prepared and approved. The troubleshooting log did not list a precaution to prevent a HPCI turbine trip in the Troubleshooting Limits or-Boundaries section, which would have prevented � the unexpected trip. The approach used in the troubleshooter was to down power the drawer, replace the display card, inspect the drawer, and if no further indication of damage was present, re-power the drawer and restore the isolation instrument to normal. After card replacement a visual inspection did not note any other damage. The next step was to return the drawer to service. When the drawer was re-powered the display and keypad functioned properly, however a HPCI Turbine Trip occurred.
When the drawer was re-powered the NORMAL/BYPASS switch was in NORMAL, which allowed the isolation and turbine trip signals to be passed from the NUMAC drawer. The breaker for the isolation valve (F002) had been opened, so the valve did not change position. No actions had been taken to prevent the HPCI Turbine Trip from occurring.
SAFETY CONSEQUENCES
The safety consequences of this event were minimal. This event resulted in no nuclear, radiological, or industrial safety consequences. HPCI was inoperable for a short period of time well within the14-day allowable Technical Specification Limiting Condition of Operation (LCO) time.
A review of this event determined that a Safety System Functional Failure (SSFF) occurred as defined in Nuclear Energy Institute (NEI) 99-02.
CAUSE OF OCCURRENCE
The apparent cause of the event was a human error in that a mindset resulted in the failure to consider the potential that the troubleshooting could also cause a turbine trip. The technicians and supervisor involved were experienced in performing this procedure and were knowledgeable of all protective functions provided by this drawer. The technicians and supervisor preparing the troubleshooting log believed they had adequate protection in place to prevent the isolation. Their mind set was that with the breaker open, replacing the display card would not result in an isolation. They did not discuss or consider that the troubleshooting actions would cause a turbine trip. They were focused on the isolation and not the turbine trip, therefore they did not address the additional function the drawer provided.
A contributing cause was the planning of the troubleshooting. A troubleshooting log was prepared and approved. One step of the troubleshooting log "Limits or Boundaries" only listed: "Isolation valve actuation from the NUMAC drawer will be prevented by opening the breaker for the inboard isolation valve, HV-F002.
It did not list a step (place the NORMAL/BYPASS switch in BYPASS) to prevent a turbine trip actuation.
Contributing to the lack of a step to prevent HPCI turbine trip actuation was that the troubleshooting log used the test and calibration procedure Operations Information Sheet from the surveillance as the reference of possible alarms and functions for this evolution. The Operations Information Sheet does not list a HPCI Turbine Trip actuation as one of the functions. Since only the valve (F002) actuation was listed, it was the only actuation considered.
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PREVIOUS OCCURRENCES
A review of failure history associated with NUMAC equipment back to 1991 did not identify any events caused by improper troubleshooting.
CORRECTIVE ACTIONS
1. Roll-out communications are being provided to all supervisors regarding adequate rigor and questioning attitude in preparing simple troubleshooting:
2. The HPCI Turbine Trip is being added to the test and calibration procedure Operations Information Sheet and the other leak detection channel test and calibration procedures.
3. A sampling of Instrumentation and Control procedures' Operations Information Sheets are being reviewed to assess the need to add information to the sheet regarding protective functions.
4. A needs analysis is being presented to the Licensed Operator Requalification Curriculum Review Committee for knowledge of protective functions of GE type switches.
COMMITMENTS
This LER contains no commitments.
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