05000400/LER-2011-002
| Harris Nuclear Plant - Unit 1 | |
| Event date: | 04-02-2011 |
|---|---|
| Report date: | 02-20-2012 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 4002011002R00 - NRC Website | |
Energy Industry Identification System (EIIS) codes are identified in the text within brackets [J.
EVENT DESCRIPTION
On 0840 on 12/20/11, with the Harris Nuclear Plant at 100% power in Mode 1, the 1B-SB Emergency Diesel Generator (EDG) [ DG ] was declared inoperable due to drift of the mechanical speed setting on the EDG governor [ 65 J. Trending of the drift has identified that continued drift of the mechanical governor speed setting over the duration of the seven-day (168 hour0.00194 days <br />0.0467 hours <br />2.777778e-4 weeks <br />6.3924e-5 months <br />) mission time could result in the mechanical governor interfering with the ability of the electric governor to perform its design basis function for controlling the 1B-SB EDG frequency (speed) within the Technical Specifications limits during an emergency. The trend of the speed setting drift identified that the EDG speed setting would have remained in acceptable limits and able to perform its safety function for the first 64 hours7.407407e-4 days <br />0.0178 hours <br />1.058201e-4 weeks <br />2.4352e-5 months <br /> of engine operation before drifting outside the acceptable range.
The drifting of the speed setting was first identified on April 2, 2011 (time of discovery) during a weekly performance test but the resultant impact of this condition relative to the 7-day mission time was not immediately recognized. Since there is firm evidence that indicates that the mechanical governor speed drift condition existed for longer than the allowed LCO time of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, it is concluded that the speed drift condition represents a condition prohibited by Technical Specifications and is reportable under 10 CFR 50.73(a)(2)(i)(B).
Since the 1A-SA EDG was made inoperable several times for maintenance and surveillance testing during the time period that the 1B-SB EDG was inoperable (April 2, 2011 to December 21, 2011), this event is also reportable as a condition that could have prevented fulfillment of a safety function to mitigate the consequences of an accident and is reportable under 10 CFR 50.73(a)(2)(v)(D). The longest inoperable duration for the 1A-SA EDG during the period of interest was less than 64 hours7.407407e-4 days <br />0.0178 hours <br />1.058201e-4 weeks <br />2.4352e-5 months <br />.
CAUSE OF EVENT
The root cause was determined to be that technical guidance does not exist for adjustment of the speed adjusting motor to prevent shaft movement.
The primary contributing cause was a failure to initially recognize that the 'B' EDG speed setting drift could adversely impact the 7-day mission time.
SAFETY SIGNIFICANCE
There were no actual safety significant consequences as a result of this event. No events occured that required the Emergency Diesel Generators to assume safety related loads. As stated previously, the 1B-SB EDG would have been fully capable of performing its safety function for approximately 64 hours7.407407e-4 days <br />0.0178 hours <br />1.058201e-4 weeks <br />2.4352e-5 months <br /> before the mechanical governor speed setting drifted low enough to interfere with the electric governor control. The longest inoperable duration for the 1A-SA EDG during the period of interest was less than 64 hours7.407407e-4 days <br />0.0178 hours <br />1.058201e-4 weeks <br />2.4352e-5 months <br />. Thus it is concluded that at least one EDG was available and functional at all times.
112
IMMEDIATE CORRECTIVE ACTIONS
Corrective actions were taken to revise the existing engine monitoring instructions to add a periodic check and adjustment of the speed setting during engine operation. This action is complete.
Instructions were issued for Operators.
CORRECTIVE ACTIONS
Planned corrective actions are to:
1. Complete Work Order 2021129 to eliminate speed setting drift during engine operation.
2. Revise MPT-M0113, Emergency Diesel Generator Governor Replacement Maintenance procedure to include adjustment of the inactive Bodine motor to prevent output shaft movement.
PREVIOUS SIMILAR EVENTS
A review of License Event Reports for the previous five years did not reveal any similar events at the Harris Plant.