05000373/LER-2004-001
| Lasalle County Station, Unit 1 | |
| Event date: | 08-02-2004 |
|---|---|
| Report date: | 09-30-2004 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3732004001R00 - NRC Website | |
PLANT AND SYSTEM IDENTIFICATION
General Electric - Boiling Water Reactor, 3489 Megawatts Thermal Rated Core Power
A. CONDITION PRIOR TO EVENT
� Unit(s): 1/1 Event Date: 08/02/04� Event Time: 1423 � Reactor Mode(s): 1/1 Power Level(s): 100/100 Mode(s) Name: Run/Run
B. DESCRIPTION OF EVENT
On 08/02/04, during the development of operator Local Leak Rate Test (LLRT) training, simulated LLRTs were performed in the lab to determine the viability of the training procedures and of the mock-up test rig to be used during training activities. A review of the data obtained during a test run resulted in the LLRT Program Owner questioning the method used for determining static head pressure correction factors.
LLRT of containment isolation valves is required to be performed at a differential pressure equal to or greater than the postulated containment Design Basis Accident (DBA) Peak Accident Pressure (P,), and less than or equal to 1.1 Pa . When a volume of water is on the other side of the valve being tested (e.g., the suppression pool), the static head pressure of the volume of water must be determined and added to insure the required differential pressure is obtained ' during testing.
The typical method for determining the static head pressure is to obtain the water level and convert it into a pressure (psig). However, in LTS-100-38, "RCIC Vacuum Pump Discharge Isolation Valves Local Leak Rate Test 1E51-F069 and 1E51- F028," the "bubbler" method was used. A leak rate monitor is connected to an existing test connection between the two isolation valves. The inboard isolation valve is then opened and air pressure applied. When the air supply is removed and a stable pressure is achieved, that pressure equals the head pressure on the pipe opening in the suppression pool.
This method has an inherent problem in that, should the boundary isolation valve leak, the piping pressure would decrease, resulting in an inaccurate approximation of the static head pressure.
The E51-F069 and E51-F028 valves were last tested on 01/24/04 for Unit 1 and 02/02/03 for Unit 2. The LLRT results for the 1E51-F069 valves are considered valid, because a higher than expected static head pressure would force the globe valve disc away from its seat and tend to increase leakage. However, because a higher than expected pressure would provide increased sealing for check valves 1E51-F028, the LLRT results were considered invalid.
The Reactor Core Isolation Cooling (RCIC)[BN] Barometric Condenser Vacuum Pump Discharge Containment Isolation Valve 1E51-F028 were declared inoperable at 1423 on 08/02/04. Technical Specification 3.6.1.3 Action Requirement A.1 was entered, and the affected penetration flow paths were isolated by closing and deactivating the E51-F069 valve.
LTS-100-38 was changed to use actual suppression pool level to determine the static head correction factor, and on 09/09/04, valve 1E51-F028 was re-tested using the revised procedure. The valve failed the LLRT. On 09/17/04, the valve was disassembled, the valve internals were cleaned, and the disc and spring were replaced. The valve passed its post-maintenance LLRT and was declared operable.
This event is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B) as an operation or condition prohibited by the plant's Technical Specifications.
The Unit 2 valve (2E51-F028) successfully passed its LLRT on 09/10/04.
C. CAUSE OF EVENT
The root cause of this event was an inadequate procedure, in that LTS-100-38 used an inaccurate method for determining static head pressure correction factors.
This method has been in use since 1986.
SAFETY ANALYSIS D.C The safety significance of this issue was minimal. The correction factor for the static head pressure was minor, since the column of water is only about 1.5 feet.
Also, although the error was non-conservative for the 1(2)E51-F028 valves, it was conservative for the 1(2)E51-F069 valves, and the total leakage for the affected penetration was acceptable.
CORRECTIVE ACTIONS E.
1.LTS-100-38 was revised to use actual suppression pool level to determine the static head correction factor (Complete).
2.All LLRT procedures that use a static head pressure correction factor will be revised to include a sign off for the person calculating the correction factor with an additional sign off for the person verifying that calculation (AT# 241004-13).
PREVIOUS OCCURRENCES F.U A review of Licensee Event Reports for the past 10 years identified no previous occurrences of a failed or invalidated LLRTs due to procedural inadequacy.
COMPONENT FAILURE DATA G.
No components failed during this event.