05000305/LER-2006-006
| Docket Number | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3052006006R00 - NRC Website | |
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) Kewaunee Power Station 05000305 YEAR
Event Description:
On July 13, 2006, with the plant at 100 percent power, non-conservative values were identified for the safety injection accumulator [ACC] levels. The non-conservatism was caused by incorrect volume to level correlations and resulted in incorrect level alarm [LA] setpoints. Questions had been raised on how to determine the proper indicated safety injection accumulator level to ensure compliance with the Technical Specification requirement of 1225 to 1275 cubic feet volume for each accumulator. Accumulator level is indicated from instrumentation in percent level. Two operator aids provide a correlation graph of cubic feet versus percent level. The operator aids identified the low level limit in accumulator A as 25% and the high level limit as 50%. The low level limit in accumulator B was identified as 22% and the high level limit as 50%.
Additionally, there were low and high accumulator level alarms at 26% and 50% respectively. Acceptance criteria per the surveillance procedure for meeting the Technical Specification was between 26% and 50%. If either alarm was reached, level was established between 38% and 40%.
Recent calculations show the minimum required level to meet the Technical Specification is 39% for accumulator A and 42% for accumulator B. The maximum required level to meet the Technical Specification is 60% for accumulator A and 62% for accumulator B. A new normal operating range has been established between 46% and 48% accumulator level.
Operator aids for accumulator level were not correct based on 1978 set point determination. They were also not updated when the accumulator level calibration was reevaluated in 1991 for not being properly pressure compensated or when a volumetric test was performed in 1992.
With the new calculated safety injection accumulator levels, there would have been numerous times in the past where accumulator level would have been below the required Technical Specification volume limit of 1225 cubic feet when the accumulators were required to be operable. In the surveillance procedure for "Shift Instrument Channel Checks-Operating," the acceptance criteria for accumulator low level were "no alarm annunciated" and "level greater than or equal to 26%." Additionally, the operator aids showed 1225 cubic feet corresponding to an indicated level of 25% for accumulator A and 22% for accumulator B. This would have been below the newly calculated minimum required levels.
Event Analysis:
This is being reported in accordance with 10 CFR 50.73(a)(2)(i)(B), "Any operation or condition which was prohibited by the plant's Technical Specifications.
The SI accumulators actuate during the following transients and accidents: LOCA, main steamline break with offsite power available, main steamline break without offsite power, and feedwater malfunction at hot zero power. At a minimum level corresponding to the existing low level alarm, the volumetric shortfall below Technical Specification requirements would have been 27.2 cu. ft (2.2% of 1225 cu. ft.). Evaluation of the Kewaunee safety analyses has concluded that the accumulators would continue to satisfy the safety analysis acceptance criteria at this minimum level. Therefore, there was no safety significance associated with this event.
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) There is no safety system functional failure associated with this event since the condition would not have prevented fulfillment of the safety function of the system.
Cause:
The causes of this event were:
1. A 1978 set point methodology not taking into account test equipment and instrument loop accuracy tolerances.
2. Failure to update the operator aids and level alarm setpoints after a similar issue was identified in 1991 (calibration of the accumulator level instruments inaccurate due to not being properly pressure compensated - LER 91-009).
Corrective Actions:
1. An analysis was performed to determine conservative limits (in percent) to maintain the level between the Technical Specification required volumes. Proper accumulator levels were established.
2. Interim actions were established to monitor accumulator levels hourly until the level alarm setpoints are revised.
3. The station setpoint program was verified to require addressing all potential setpoint error contributors.
4. Technical Specifications will be reviewed to identify any setpoints with potential translation errors between the requirement and the indication. The calculations for these set points will be re-verified.
5. Controls for the use of operator aids are being enhanced. Existing operator aids will be reviewed and dispositioned into the correct process (operator aid, procedure, or drawing).
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