05000445/LER-2002-004
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability |
| 4452002004R00 - NRC Website | |
I. DESCRIPTION OF THE REPORTABLE EVENT
A. REPORTABLE EVENT CLASSIFICATION
Any event where a single cause or condition caused at least one independent train or channel to become inoperable in multiple safety related systems or two independent trains or channels to become inoperable in a single safety related system designed to mitigate the consequences of an accident.
B. PLANT OPERATING CONDITIONS PRIOR TO THE EVENT
On October 30, 2002, Comanche Peak Steam Electric Station (CPSES) Unit 1 was in Mode 5, making preparations for plant startup after refueling. The Reactor Coolant System (RCS)(EIIS:(AB)) was at a temperature of approximately 85 degrees Fahrenheit and atmospheric pressure.
C. STATUS OF STRUCTURES, SYSTEMS, OR COMPONENTS
THAT WERE INOPERABLE AT THE START OF THE EVENT AND THAT
CONTRIBUTED TO THE EVENT
There were no inoperable structures, systems, or components that contributed directly to the event.
D. NARRATIVE SUMMARY OF THE EVENT, INCLUDING DATES AND
APPROXIMATE TIMES
On October 5, 2002, the Pressurizer Safety Valves (PSVs) were removed from the system and were sent off-site to NWS Technologies for surveillance testing in support of the ninth refueling outage on Comanche Peak Unit 1. Testing was performed using a procedure designed to comply with ASME/ANSI OM-1987 Part 1 and Westinghouse Owner's Group guidance, using saturated steam as the test medium.
On October 6, 2002, the as-found lift of PSV 1-8010A was 2436 psig, which is 2.0% below the Technical Specification 3.4.10.1 setpoint of 2485 psig, which specifies a plus or minus 1% range. On October 7, 2002, the as-found lift of PSV 1-8010B was 2446 psig, which is 1.6% below the Technical Specification setpoint. PSV 1-8010C was found with an acceptable setpoint. Both of the unsatisfactory PSVs were reworked by the vendor and the as-left lift pressures were verified to be within Technical Specification limits. The PSVs were subsequently returned to CPSES by the vendor and reinstalled in the system.
On October 23, 2002, the PSVs were declared operable by the Shift Manager, based upon a review of the completed surveillance test packages. This review also identified the two as- found surveillance test failures, and the failures were then entered into the Corrective Action Program.
On October 30, 2002, the as-found surveillance testing failures were determined to have been caused by a single condition which caused two independent trains or channels to become inoperable in a single safety related system designed to mitigate the consequences of an accident, a reportable condition under 10CFR50.73(a)(2)(vii).
E. THE METHOD OF DISCOVERY OF EACH COMPONENT OR SYSTEM FAILURE,
OR PROCEDURAL OR PERSONNEL ERROR
The PSVs were being tested to satisfy the requirements of the CPSES Inservice Testing Plan and to satisfy Technical Specification (TS) surveillance requirements. The unsatisfactory as- found lift setpoints were discovered as the result of this test.
II. COMPONENT OR SYSTEM FAILURES
A. FAILURE MODE, MECHANISM, AND EFFECT OF EACH
FAILED COMPONENT
Not applicable - there were no component failures associated with this event.
B. CAUSE OF EACH COMPONENT OR SYSTEM FAILURE
Not applicable - there were no component failures associated with this event.
C. SYSTEMS OR SECONDARY FUNCTIONS THAT WERE
AF'F'ECTED BY FAILURE OF COMPONENTS WITH MULTIPLE FUNCTIONS Not applicable - there were no failed components with multiple functions that affected this event.
D. FAILED COMPONENT INFORMATION
Not applicable - there were no component failures associated with this event.
III. ANALYSIS OF THE EVENT
A. SAFETY SYSTEM RESPONSES THAT OCCURRED
Not applicable - no safety system responses occurred as a result of this event.
B. DURATION OF SAFETY SYSTEM TRAIN INOPERABILITY
The PSVs were initially set to within Technical Specification limits on April 17, 2001, and were considered operable until they were determined to have been inoperable on October 23, 2002. Although the PSV lift set pressures were out of the Technical Specification range, the PSVs were still capable of fulfilling their safety function.
C. SAFETY CONSEQUENCES AND IMPLICATIONS OF THE
EVENT
The PSVs operate to prevent the RCS from being pressurized above its Safety Limit of 2735 psig. Each PSV is designed to relieve 420,000 pounds per hour of saturated steam at the valve set pressure.
The adequacy of the PSVs to perform the overpressure protection function is demonstrated in the accident analyses by assuming that the valves do not fully open until the pressure has increased to 3% over the nominal set pressure. The potential adverse effects associated with premature PSV opening at pressures as low as 5% below the nominal set pressure, potentially resulting in interaction with the Pressurizer PORVs, have also been considered. The CPSES Unit 1 as-found PSV set pressures were within the analyzed range of +3/-5% about the nominal set pressure, therefore, the assumptions of the accident analyses remain valid. In addition, the actual relief capacities of the PSVs were not affected, and the PSVs would have fulfilled their overpressure protection function with the PSVs opening slightly lower than the set pressure.
In conclusion, although these Unit 1 PSVs did not meet the setpoint criteria required by the CPSES Technical Specifications by a narrow margin, the functional capacity of these PSVs was not affected. During the time period these PSVs were in service with the potential for set pressure drift, there were no plant events which challenged the PSVs. Based on the foregoing, it is concluded that the health and safety of the public was unaffected.
IV. CAUSE OF THE EVENT
Based on a failure analysis evaluation, performed by CPSES Engineering Programs personnel based on experience with these valves, the root cause was determined to be setpoint drift. A specific cause of the setpoint drift could not be determined. The test results were within the 3% acceptance range of ASME/ANSI OM-1987 Part 1. Per past discussions with the valve vendor, deviations within this range are within the design requirements of the valve and do not indicate a material problem with the valves. This conclusion is further supported by the fact that the valves demonstrated satisfactory test results after adjustment.
V. CORRECTIVE ACTIONS
Maintenance was performed by the vendor on both PSVs before retesting in order to restore them to the required lift setpoints. On October 23, 2002, the required surveillances were completed satisfactorily, with all three PSVs being tested satisfactorily to state-of-the-art requirements identified through the Westinghouse Owners Group program.
VI. PREVIOUS SIMILAR EVENTS
Three previous similar events have been reported for CPSES pursuant to 10CFR50.73(a)(2)(vii), LER 445/91-026 on Unit 1, LER 446/94-018 on Unit 2, and LER 445/96-08 on Unit 1.
The initial event, LER 445/91-026, resulted from use of an inadequate test method, while the two subsequent events were a result of setpoint drift of a magnitude within the design requirements of the valves, similar to the current event.