05000423/LER-2008-006
| Millstone Power Station - | |
| Event date: | 11-24-2008 |
|---|---|
| Report date: | 01-28-2009 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4232008006R00 - NRC Website | |
1. Event Description:
(MPS3) control room operators identified the turbine-driven auxiliary feedwater (TDAFW) pump [BA-P] steam trap [TRP] isolation valves [ISV] (3DTM-AOV63A, B, & D and 3DTM-AOV64A, B, & D) were closed. Upon discovery of this condition, the shift manager declared the TDAFW pump inoperable for the steam traps being isolated and entered Technical Specification Action Statement (TSAS) 3.7.1.2.c. The valves were promptly re opened, the steam traps blown down, and the TDAFW pump restored to operable status at 0346 hours0.004 days <br />0.0961 hours <br />5.720899e-4 weeks <br />1.31653e-4 months <br /> on November 24, 2008.
During the 34 hour3.935185e-4 days <br />0.00944 hours <br />5.621693e-5 weeks <br />1.2937e-5 months <br /> period the TDAFW pump was inoperable, the unit went through two mode changes (i.e., from Mode 3 to Mode 1).
Motive steam for the TDAFW pump is provided by main steam from Steam Generators (SGs) [AB] A, B, and D.
The supply line from each of the steam generators ties into a common steam supply header to the TDAFW pump. Each of the three steam supply lines is provided with a steam trap to remove any condensate in the line upstream of the normally closed, air-operated valve which isolates the auxiliary feedwater turbine from the main steam during normal operation. Closure of the steam trap isolation valves prevents the steam traps from removing condensate in the steam supply piping for the TDAFW pump.
Technical Specification (TS) 3.7.1.2 Action c. requires, if the TDAFW pump is inoperable in MODES 1, 2, or 3 for reasons other than those identified in Actions a. or b., the pump must be restored 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 />. Because evidence exists to show the TDAFW pump was inoperable for 34 hours3.935185e-4 days <br />0.00944 hours <br />5.621693e-5 weeks <br />1.2937e-5 months <br /> before being restored to operable status, the requirements of this TSAS were met.
TS 3.0.4 states entry into an OPERATIONAL MODE or other specified condition shall not be made when the conditions for the Limiting Condition for Operation are not met and the associated ACTION requires a shutdown if they are not met within a specified time interval. Because two mode changes occurred during the time period the TDAFW pump was rendered inoperable and because TS 3.7.1.2 Action c. requires a shutdown if not restored within the specified time interval, the provisions of TS 3.0.4 were not met.
Although the pump would have been able to perform its safety function following operator reset from an overspeed trip due to water entrainment in the steam supply, MPS3 was in a configuration prohibited by TS 3.0.4. Hence, this condition is reportable in accordance with 10CFR50.73(a)(2)(i)(B) as any "Operation or Condition Prohibited by Technical Specifications.
2. Cause:
Investigation determined the TDAFW pump steam trap isolation valves had been closed since 1746 hours0.0202 days <br />0.485 hours <br />0.00289 weeks <br />6.64353e-4 months <br /> on November 22, 2008, when the operating procedure for turbine shell and chest warming directed operators to close the steam trap isolation valves. Failure to restore proper alignment of the TDAFW pump steam trap isolation valves was due to an inadequate procedure change to the subject operating procedure. Specifically, an attachment had been added to the turbine shell and chest warming procedure which closed numerous drain valves, however, the procedure did not contain an explicit step(s) to ensure the steam trap isolation valves were subsequently reopened.
Millstone Power Station — Unit 3 05000423 YEAR SEQUENTIAL I REVISION NUMBER� NUMBER OF� 3 3. Assessment of Safety Consequences:
This condition is judged to be of low safety significance. Although it is possible the TDAFW pump would have tripped on turbine overspeed when called upon to start, procedures and training provide guidance to operators to manually start the pump in the event of a pump trip. During the time the valves were closed, both motor-driven AFW pumps [BA-13] were operable. When the plant is operating at low power levels (post refuel), there is low decay heat and increased SG water inventory. Hence, if auto-initiation of the TDAFW pump had resulted in a pump trip, the low decay heat and increased SG water inventory would have provided sufficient time to restart the pump if operation was required. Therefore, the potential impact of a loss of normal feedwater flow at low power levels is minimized because of available response time.
4. Corrective Actions:
Upon discovery of this condition, MPS3 entered TSAS 3.7.1.2.c. The steam trap isolation valves were promptly re-opened, the steam traps blown down, and the TDAFW pump restored to operable status.
The operating procedure for main turbine shell and chest warming has been revised to specify the TDAFW pump steam trap isolation valves will remain open during future shell and chest warming evolutions.
Additional corrective actions to address this event will be evaluated in accordance with the station's Corrective Action Program.
5. Previous Occurrences:
None Energy Industry Identification System (EIIS) codes are identified in the text as [XX].