05000336/LER-2012-002
| Millstone Power Station - | |
| Event date: | 08-12-2012 |
|---|---|
| Report date: | 10-02-2012 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown |
| LER closed by | |
| IR 05000245/2012005 (16 January 2013) | |
| 3362012002R00 - NRC Website | |
1.� Event Description At 13:46 on August 12, 2012, Millstone Power Station Unit 2 (MPS2) completed a controlled plant shutdown from Mode 1 to Mode 3 (Hot Standby) as required by plant Technical Specification (TS) 3.7.11 Ultimate Heat Sink. TS 3.7.11 stipulates the ultimate heat sink (UHS) shall be operable with a water temperature of less than or equal to 75 degrees F. TS 3.7.11 Action a. allows continued plant operation when UHS temperature is between 75 degrees F and 77 degrees F, provided UHS temperature averaged over the previous 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> is verified to be less than 75 degrees F once per hour. Otherwise, be in Hot Standby within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in Cold Shutdown within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.
The UHS [BS] for MPS2 is Long Island Sound. The UHS temperature had initially gone above the temperature limit at 16:30 on August 11, 2012, but had cooled below the limit based on environmental factors. At 00:44 on August 12, 2012 the UHS temperature again rose above the TS limit and operators initiated a plant shutdown as required by plant TS 3.7.11. At 02:55 the Shift Manager directed that power be stabilized at 65% power since UHS temperatures had cooled below the TS limit. Plant power was held at approximately 65% power until 08:35 on August 12, 2012 when temperature again rose above the UHS limit. The Shift Manager directed completion of the plant shutdown from Mode 1 to Mode 3, completed at 13:46 on August 12, 2012. The UHS temperature continued to cycle above and below the TS limit. The plant entered Mode 5 Cold Shutdown at 22:31 on August 13, 2012.
The last time the UHS 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> average temperature went above 75 degrees F was August 14, 2012 at 14:35.
This condition is being reported pursuant to 10 CFR 50.73(a)(2)(i)(A) "the completion of any nuclear plant shutdown required by the plant's technical specifications".
2. Cause Prolonged hot weather in the Long Island Sound, in conjunction with high humidity during the day and minimal cooling at night resulted in sustained elevated cooling water temperature (UHS) supplied to the plant. Ambient air temperatures in July were the hottest on record in the contiguous United States since record keeping began in 1895 according to the National Oceanic and Atmospheric Administration, and temperatures continued to remain high in August.
3. Assessment of Safety Consequences The limitations on the ultimate heat sink temperature ensure that sufficient cooling capacity is available to either, 1) provide normal cooldown of the facility, or 2) to mitigate the effects of accident conditions within acceptable limits.
The limitations on maximum temperature are based on a 30-day cooling water supply to safety related equipment without exceeding their design basis temperature. The UHS temperature fluctuations were relatively short in duration.
The UHS temperature never exceeded the upper limit of 77 degrees F.
4, Corrective Action Since the shutdown was required by environmental factors beyond licensee control, no corrective actions were required.
5, Previous Occurrences There are no previous occurrences identified.
Energy Industry Identification System (ElIS) codes are identified in the text as [XX].