05000336/LER-2014-001
| Millstone Power Station Unit 2 | |
| Event date: | 01-31-2014 |
|---|---|
| Report date: | 03-31-2014 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown |
| Initial Reporting | |
| ENS 49779 | 10 CFR 50.72(b)(2)(i), Tech Spec Required Shutdown |
| 3362014001R00 - NRC Website | |
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1. EVENT DESCRIPTION
On January 30, 2014 at 2313, with Millstone Power Station Unit 2 (MPS2) in MODE 1 and at 100% reactor power, the circuit breaker for the group 1 pressurizer proportional heaters tripped. With the 'B' emergency diesel generator (EDG) out of service for its maintenance outage and therefore inoperable, Technical Specification Action Statement (TSAS) 3.4.4 action b was entered. TSAS 3.4.4 action b requires MPS2 be in at least HOT STANDBY (MODE 3) with the reactor trip breakers open within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in HOT SHUTDOWN (MODE 4) within the following 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, unless one group of proportional heaters is restored to operable status. MPS2 completed the shutdown to MODE 3 at 0457 and restored the group 1 proportional heaters to operable status at 0747 on January 31, 2014. The initiation of the shutdown was reported to the NRC (event number 49779) pursuant to 10 CFR 50.72(b)(2)(i) - The initiation of any nuclear plant shutdown required by the plant's technical specifications.
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.
Background Information:
The pressurizer heaters are single unit, direct immersion heaters which protrude vertically into the pressurizer through sleeves welded in the lower head. Each heater is internally restrained from high amplitude vibrations and can be individually removed for maintenance during plant shutdown.
Approximately 20 percent of the heaters are connected to proportional controllers which adjust the heat input as required to account for steady state losses and to maintain the desired steam pressure in the pressurizer. These heaters are separated into two banks (approximately 160 kW each) and are provided with diverse vital power.
The pressurizer TS limiting condition for operation 3.4.4 states:
The pressurizer shall be OPERABLE with:
a. Pressurizer water level b. At least two groups of pressurizer heaters each having a capacity of at least 130 kW.
APPLICABILITY: MODES 1, 2 and 3.
ACTION:
a. With only one group of pressurizer heaters OPERABLE, restore at least two groups to OPERABLE status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or be in at least 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 HOT SHUTDOWN within the following 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.
b. With the pressurizer otherwise inoperable, be in at least HOT STANDBY with the reactor trip breakers open within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in HOT SHUTDOWN within the following 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.
2. CAUSE
The direct cause of the need to shutdown the unit was the failure of the group 1 proportional pressurizer heaters concurrent with the 'B' EDG being out of service for planned maintenance.
3. ASSESSMENT OF SAFETY CONSEQUENCES
Reactor Coolant system (RCS) pressure control is maintained by pressurizer heaters and the pressurizer spray system. Although the 'B' EDG was out service for planned maintenance, MPS2 was in a normal electrical configuration, therefore one bank of proportional pressurizer heaters was functional (i.e., powered from the offsite power system). Additionally, the pressurizer spray system was not affected, therefore RCS pressure control was always functional. There was no indication of any primary to secondary leakage. There was no release of radioactive material. All safety related systems performed as designed.
4. CORRECTIVE ACTION
Troubleshooting activities determined one of the group 1 proportional heaters (P1-B1) had failed.
The P1-B1 heater leads were subsequently lifted to remove the failed heater from service.
Following this maintenance activity, a pressurizer heater capacity test was performed and verified the group 1 proportional heaters had a capacity of at least 130KW as required by TS 3.4.4 b. The group 1 proportional heaters and the pressurizer were declared operable and MPS2 was subsequently returned to service. Additional corrective actions are being taken in accordance with the station's corrective action program.
5. PREVIOUS OCCURRENCES
None 6. Energy Industry Identification System (EIIS) codes
- Electric Resistance Heater — EHTR
- Pressurizer — PZR
- Door — DR