05000336/LER-2015-001
| Millstone Power Station Unit 2 | |
| Event date: | 04-17-2015 |
|---|---|
| Report date: | 06-16-2015 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| Initial Reporting | |
| LER closed by | |
| IR 05000245/2016004 (1 February 2017) | |
| 3362015001R00 - NRC Website | |
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1. EVENT DESCRIPTION:
On April 17, 2015, with Millstone Power Station Unit 2 (MPS2) at 100% power and in operating MODE 1, the Nuclear Regulatory Commission questioned the historic operability of Millstone Power Station Unit 2's (MPS2) "C" Reactor Building Closed Cooling Water (RBCCW) pump because several condition reports had reported the need to frequently add oil to the pump's outboard bearing bubbler between November 2014 and early April 2015. Upon further review, Dominion concluded that operability could not be assured since there may not have been sufficient oil to meet mission time requirements at all times with no compensatory measures in place. Plant Technical Specification 3.7.3.1 "Reactor Building Closed Cooling Water System" requires two reactor building closed cooling water loops shall be operable. Since there were periods of time that plant operators were crediting the "C" RBCCW pump for one of the two required reactor building closed cooling water loops, and operability could not be assured at all times, Dominion is reporting this event pursuant to 10 CFR 50.73(a)(2)(i)(B), as a condition that was prohibited by the plant's Technical Specifications.
BACKGROUND:
Technical Specification 3.7.3.1 requires two RBCCW loops to be OPERABLE at all times in MODES 1, 2, 3 and 4. Each loop consists of one RBCCW pump, 'a heat exchanger, and associated piping and valves. The two RBCCW loops are redundant of each other to the degree that each has separate controls and power supplies and the operation of one does not depend on the other. In the event of a design basis accident, one RBCCW loop is required to provide the minimum heat removal capability assumed in the safety analysis for the systems to which it supplies cooling water. To ensure this requirement is met, two RBCCW loops must be OPERABLE, and independent to the extent necessary to ensure that a single failure will not result in the unavailability. If two RBCCW loops cannot 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 />, then the unit must be placed in COLD SHUTDOWN within 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />. In order to meet the necessary safety functions, each of the two RBCCW loops must be available to meet a required 30 day mission time following a design basis accident.
2. CAUSE:
The cause of the event was that administrative procedure OP-AA-102, Operability Determination, Attachment 1 contained guidance that allowed that oil leaks would not require an operability determination under certain conditions even if mission time was challenged.
3. ASSESSMENT OF SAFETY CONSEQUENCES:
The safety consequences of the event were low. An extent of condition review was performed by Engineering, which found that there was an additional period besides the period the NRC questioned in 2014 and 2015, from July 2013 through December 2013 when there was oil leakage which occurred from the "C" RBCCW pump's inboard bearing and challenged mission time. Further investigations by Operations determined that two other RBCCW pumps ("A" and "B" pumps) were available at all times to meet the Technical Specification requirements when oil leaks challenged the "C" RBCCW pump's mission time, except during a 118 hour0.00137 days <br />0.0328 hours <br />1.951058e-4 weeks <br />4.4899e-5 months <br /> period between 0120 on September 22, 2013 and 2339 on September 26, 2013, when only one RBCCW loop was available to perform the required safety functions of the RBCCW system, because the "B" RBCCW pump was removed from service for planned maintenance. Only one RBCCW loop is required to meet the system's safety function, and the "A" RBCCW pump was available in that period of time to meet the safety functions.
4. CORRECTIVE ACTION:
Procedure OP-M-102 has been revised to specify that any time a pump's mission time cannot be met due to oil leakage, the pump should be declared inoperable due to a degraded or non- conforming condition.
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:
- Pump — P