05000306/LER-2003-001
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 3062003001R00 - NRC Website | |
EVENT DESCRIPTION
On January 25, 2003 (0100hrs) both Prairie Island Units were operating at 100% power. Plant Operators, while adjusting the travel stop on a Component Cooling Water Heat Exchanger Cooling Water Outlet Flow Control Valvel, noticed a drip coming from the % inch pipe stub2 that feeds the heat exchanger3 relief valve'. Closer inspection showed that the drip was caused by a pinhole leak in the pipe stub. A request was submitted to repair the leak. At 0405hrs, the Shift Supervisor issued a Corrective Action document describing the condition.
The Shift Manager, evaluating the document and the leak condition, determined the system was "Operable".
On January 27 a work order was issued to repair the pinhole leak. Later that day, the Systems Engineering Manager recognized the need for an engineering evaluation of operability and an Operability Recommendation (OPR) was assigned to Engineering.
On January 28 the OPR was completed which did not conclude any system or component to be inoperable. The engineer performed a "wall thinning" analysis and no new testing was performed on the flaw. The recommendation was based on an Ultrasonic Testing Report dated February 17, 2002. Later a copy of Generic Letter 90-05 was retrieved and actions were taken to revise the OPR. An action was issued to have Engineering inspect the pinhole leak daily until it was repaired. The Shift Manager reviewed and approved the OPR and concluded the system "operable and capable of performing its function".
On February 20, the heat exchanger was removed from service to repair the pinhole leak. The attempt to isolate and drain the heat exchanger to facilitate repair was unsuccessful and the system was returned to service without repair of the pinhole leak. The repair was rescheduled for the next Refueling Outage.
On March 14, the NRC Senior Resident Inspector (SRI), following a routine review of operability determinations, contacted Engineering to discuss the operability status of the pinhole leak as related to Generic Letter 90-05 guidance. Following the discussions it was determined that actions taken did not completely follow the guidance of the Generic Letter, and that the cooling water header should be considered inoperable until further actions were completed. At 1628 hrs, the Shift Supervisor declared "A" Train Cooling Water Header and all supported systems inoperable and entered all appropriate LCO Action Statements. Later that day, the heat exchanger was successfully isolated from the "A" Train Cooling Water Header 1 EIIS System Identifier:BI; Component Indentifier: FCV 2 EIIS System Identifier:BI; Component Indentifier: PSP 3 EIIS System Identifier:BI; Component Indentifier: HX 4 EIIS System Identifier:BI; Component Indentifier: RV and supported systems (except for the component cooling heat exchangers and its supported systems) were returned to operable status.
On March 15, a code weld repair and post maintenance testing for the leak was completed.
The heat exchanger was returned to service, and all the associated LCO Action Statements were exited.
CAUSE OF THE EVENT
The investigation and analysis of the event identified two root causes; 1) Methods utilized by the Shift Manager to make prompt operability calls are not clearly defined.
2) The site organization does not recognize that the Operability Recommendations (OPRs)) are a "High Risk Activity". At NMC a "High Risk Activity" is defined as; "An activity with high probability of error, event or re-work, and/or significant consequences of re-work, error, or event.
ANALYSIS OF THE EVENT AND RISK SIGNIFICANCE
Discussion of Reportability Prairie Island Technical Specification 3.7.8.B "One CL supply header inoperable" has a Completion Time of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. When the leak was first discovered on January 25, 2003 the operability determination concluded that system was "Operable but Degraded" and that immediate corrective action was not needed. Subsequently, on March 14 following discussions with the NRC that the operability determination did not meet Generic Letter 90-05 guidance, the Shift Supervisor declared "A" Train Cooling Water Header "Inoperable". Thus this condition exceeded the completion time specified in the Technical Specifications and is being reported per 10 CFR 50.73(a)(2)(i)(B).
However, NMC staff is still reviewing with NRC staff whether the guidance of generic Letter 90- 05 actually required the "A" Train Cooling Water Header to be declared "Inoperable". If this review concludes the "A" Train Cooling Water Header was "Operable", a supplement to this LER will be issued.
5 EMS System Identifier:CC Risk Significance The pinhole leak occurred on the 3/4" line to Relief Valve (RV) on the cooling water side of the heat exchanger. An assessment was completed by Engineering concerning the potential impacts of the leak, which concluded the following.
1) RV Function Capability- The RV provides overpressure protection for the tube side of the HX. The small leak on the inlet to the RV would not have affected this function.
2) Flow/Heat Removal Capability- It was determined that the maximum flow through an assumed failed RV inlet line would be 109 gallons per minute (gpm). The assessment concluded this flow loss would not jeopardize the needed heat removal capability of the Component Cooling Heat Exchanger for analyzed accident conditions.
3) Flooding Impact- With the max flow at 109 gpm it would take 25 hours2.893519e-4 days <br />0.00694 hours <br />4.133598e-5 weeks <br />9.5125e-6 months <br /> for water to reach the Residual Heat Removal6 room barriers allowing sufficient time for Operator action before flooding of equipment would occur.
4) Water Spray Impact- a walk down/review of the area was done to determine if a "water spray" could affect safety-related equipment. No problems were identified.
IMPACT ON SAFETY SYSTEM FUNCTIONAL FAILURE PERFORMANCE INDICATORS
Since the cooling water system was available, this event did not involve either a partial or complete loss of a safety system function and is not reportable per 10 CFR 50.73(a)(2)(v).
CORRECTIVE ACTIONS TO PREVENT RECURRENCE
1) To address the concerns associated with the methods used by the Shift Managers to make prompt operability calls, site administrative procedures will be revised to include a symptom based guide, flow chart or checklist for the Shift Manager to use. In addition, all Shift Managers will receive training on the use of this process following its revision.
2) To correct the concerns that OPRs are not considered "High Risk Activity", site administrative procedures will be revised to require that OPRs be evaluated under the "high risk" process.
6 EIIS System Identifier:BP 3) Persons performing, reviewing and approving OPRs will receive training on the use of the revised operability determination process, NRC Inspection Manual Part 9900 and GL 90-05.
PREVIOUS SIMILAR EVENTS
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