05000482/LER-2002-002
| Wolf Creek Generating Station | |
| Event date: | 04-25-2002 |
|---|---|
| Report date: | 6-17-2002 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4822002002R00 - NRC Website | |
Plant Conditions Prior to the Event:
MODE — 4 Power -- 0 percent Temperature and Pressure — 350 degrees; 390 psig
Event Description:
On April 24, 2002, at 2023 hours0.0234 days <br />0.562 hours <br />0.00334 weeks <br />7.697515e-4 months <br />, while in Mode 4, Wolf Creek Nuclear Operating Corporation (WCNOC) personnel completed surveillance procedure STS BB-004, "Reactor Water Inventory Balance." The licensed operator performing the calculation rounded the pressurizer level initial and final readings to whole numbers.
The calculation resulted in a value less than the required Technical Specification (TS) 3.4.13, "RCS Operational LEAKAGE," limit of 1.0 gpm for Reactor Coolant System (RCS) (EIIS system code AB) unidentified leakage.
On April 25, 2002, at 0712 hours0.00824 days <br />0.198 hours <br />0.00118 weeks <br />2.70916e-4 months <br />, Wolf Creek Generating Station (WCGS) entered Mode 3 from Mode 4.
Subsequently on April 25, 2002, the Surveillance Coordinator reviewed the STS BB-004 procedure performed on April 24, 2002, and identified a calculation error. A recalculation determined that the TS limit of 1.0 gpm RCS unidentified leakage had been exceeded. The unidentified leakage was actually 1.091 gpm, or .091 gpm above the TS limit.
On April 25, 2002, at 2300 hours0.0266 days <br />0.639 hours <br />0.0038 weeks <br />8.7515e-4 months <br />, the Control Room Shift Manager entered TS 3.4.13, Condition A, Required Action A.1, to reduce RCS leakage to within limits within four (4) hours.
On April 25, 2002, at 2326 hours0.0269 days <br />0.646 hours <br />0.00385 weeks <br />8.85043e-4 months <br />, WCNOC personnel identified leakage past the "A" Seal Injection Filter to the vent and drain piping sections. Chemical Volume and Control (BG system) (EIIS system code CB) valves BGV0346, 0273, 0271, and 0272 were closed an additional 3/4 turn each.
On April 26, 2002, at 0300 hours0.00347 days <br />0.0833 hours <br />4.960317e-4 weeks <br />1.1415e-4 months <br />, Control Room personnel entered TS 3.4.13, Condition B, due to an inability to verify RCS leakage within the four (4) hours specified by Required Action A.1. Condition B was entered because steady state plant conditions could not be achieved for performing surveillance test STS BB-004.
The RCS water inventory balance calculation is performed at steady state conditions to provide an accurate indication of RCS leakage. Required Action B.2 requires the plant to be in Mode 5 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />.
Procedure STS BB-004 was performed satisfactorily after achieving steady state plant conditions. On April 26, 2002, at 1010 hours0.0117 days <br />0.281 hours <br />0.00167 weeks <br />3.84305e-4 months <br />, Control Room personnel exited Condition B of TS 3.4.13 since LCO 3.4.13 was met.
Basis for Reportability:
TS LCO 3.0.4 states: "When an LCO is not met, entry into a MODE or other specified condition in the Applicability shall not be made except when the associated ACTIONS to be entered permit continued operation in the MODE or other specified condition in the Applicability for an unlimited period of time. This Specification shall not prevent changes in MODES or other specified conditions in the Applicability that are required to comply with ACTIONS or that are part of a shutdown of the unit.
Entry into Mode 3 with RCS leakage greater than 1.0 gallons per minute constituted a violation of TS LCO 3.0.4. Violation of LCO 3.0.4 is reportable per 10 CFR 50.73(a)(2)(i)(B), "Any operation or condition which was prohibited by the plant's Technical Specifications." NUREG 1022, "Event Reporting Guidelines, 10 CFR 50.72 and 50.73," Revision 2, further explains: LCO statements that include action statements (required actions and associated completion time in TS) provide constraints on the length of time that components or systems may remain inoperable or out of service before the plant must be shut down or other compensatory measures must be taken. In this event, the required LCO was not met, so compensatory measures were taken to correct the violated TS.
Root Cause:
The root cause of this event has been determined to be inadequate procedural guidance to ensure consistent results of RCS leakage calculations. Relevant procedures contained no guidance on significant digits and rounding, nor is that guidance included in any of the Licensed Operator classes.
Corrective Actions:
As an immediate action, Control Room personnel entered appropriate Conditions/Required Actions of TS 3.4.13, "RCS Operational LEAKAGE." This returned the plant to compliance with TS. WCNOC personnel identified leakage on the "A" Seal Injection Filter to the vent and drain piping sections. Valves BGV0346, 0273, 0271, and 0272 were closed an additional 3/4 turn each. The surveillance procedure was performed again and the RCS unidentified leakage was less than the TS limit of 1.0 gpm for unidentified leakage.
Additional corrective actions to address the root cause of this event are being addressed in the WCNOC corrective action program. The first corrective action is to revise surveillance procedure STS BB-004 to provide additional calculational guidance to determine unidentified RCS leakage. The second corrective action is that the Licensed Operator training lesson plans will be evaluated for enhancement.
Safety Significance:
The safety significance of this event is low. At the time of this event, all mitigating systems were functional.
Systems that would have provided indications of excessive leakage were operable. Various indicators of different levels of the water inventory remained functional throughout the event and would have detected increased inventory loss. Pursuant to TS, RCS leakage is calculated at least every 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
The actual RCS leak rate was minor. The allowed unidentified leakage is 1.0 gpm; the actual amount was 1.091 gpm, which existed for approximately 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br /> from the time of the first test completion to the leakage identification.
Previous Events No previous events of inadequate procedural were identified.
guidance causing a calculational error leading to a TS violation