05000461/LER-2016-012
| Clinton Power Station, Unit 1 | |
| Event date: | 12-05-2016 |
|---|---|
| Report date: | 02-01-2017 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4612016002R00 - NRC Website | |
comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
3. LER NUMBER
2016 - 00 012
PLANT AND SYSTEM IDENTIFICATION
General Electric—Boiling Water Reactor, 3473 Megawatts Thermal Rated Core Power Energy Industry Identification System (EIIS) codes are identified in the text as [XX]
EVENT IDENTIFICATION
Residual Heat Removal (RHR) "C" Pump Failure During Surveillance Testing as a Result of Breaker Latch Check Switch Adjustment Results in a Condition Prohibited by Technical Specifications A. Plant Operating Conditions before the Event Unit: 1 Mode: 1 Event Date: 12/05/16 Mode Name: Power Operation Event Time:
Reactor Power:
2011 99 percent
B. DESCRIPTION OF EVENT
On December 5, 2016 at 2011 hours0.0233 days <br />0.559 hours <br />0.00333 weeks <br />7.651855e-4 months <br />, Westinghouse DHP Breaker 1APO9EF for the Residual Heat Removal (RHR) "C" pump failed to close during the operability surveillance. During the test, the pump control switch was held in the start position for approximately 3 seconds with no indication of a pump start. When the control switch was released to the auto position, the pump trip indication illuminated. The RHR "C" pump was declared INOPERABLE and Technical Specification (TS) Limiting Condition of Operation (LCO) 3.5.1, "Emergency Core Cooling System-Operating", Required Action A.1 was entered to restore RHR "C" to OPERABLE status within seven days.
During the event investigation, the breaker charging springs were found to be charged and the latch check switch contacts open with the breaker installed in the cubicle. The function of the latch check switch is to indicate when the circuit breaker is "ready to close," providing a permissive for the breaker closure. In restoring the RHR "C" pump to OPERABLE status, the latch check switch was measured to be zero inches overtravel. The setting was adjusted to an overtravel value of 3/16 inch past the point that the contacts are closed as specified in plant procedures. Technicians that adjusted the latch check switch during the post event investigation indicated that the contact resistance was acceptable and the switch operated mechanically as expected. The mounting screws were subsequently verified to be tight following the failure. The breaker was placed back in service and post maintenance testing of RHR pump "C" was concluded satisfactorily. The RHR "C" pump was declared OPERABLE on December 6, 2016 at 0822 hours0.00951 days <br />0.228 hours <br />0.00136 weeks <br />3.12771e-4 months <br />.
comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
3. LER NUMBER
2016 - 00 012 Breaker performance records indicate that the breaker was prepared for installation in the RHR "C" pump cubicle on January 19, 2016. The latch check switch setting was measured and recorded at 3/16 inch overtravel at that time. The breaker was installed in the RHR "C" pump cubical on March 11, 2016. On this date, the latch check switch setting before the installation was verified to be within specification but the value was not recorded. The most likely time that the switch would have become out of adjustment would have been during transport to the RHR "C" pump breaker cubicle on March 11, 2016. The latch check switch verification was not sufficient to identify an out of adjustment condition.
Following installation on March 11, 2016, the breaker operated satisfactorily on March 11, 2016, June 9, 2016, and September 6, 2016 prior to the failure. Since it is unlikely that the switch adjustment would change without breaker operation, it's assumed that switch contacts failed to close following the last successful surveillance test on September 6, 2016. Consequently, since the RHR "C" pump breaker would likely not closed since its last satisfactory surveillance on September 6, 2016 until the failed RHR pump operability surveillance on December 5, 2016, this constitutes a condition prohibited by Technical Specifications.
C. CAUSE OF EVENT
The cause of this event is that an inadequate latch check switch verification was performed prior to installation of the breaker into the cubicle. The required switch adjustment value of 1/8 to 3/16 inch past the point that the contacts are closed was verified but not recorded. As a result, a supervisory review of the switch adjustment value could not be performed and the out adjustment condition went undetected.
D. SAFETY ANALYSIS
There were no safety consequences associated with the event described in this report. The event is reportable under 10CFR50.73(a)(2)(i)(B) as an "operation or condition which was prohibited by the plant's Technical Specifications." Failure of the RHR pump "C" to start during the surveillance test was a condition prohibited by the TS; however, this surveillance failure did not adversely affect the ability the plant to safely shutdown in the event of an accident. When the pump was declared INOPERABLE, TS 3.5.1, Required Action A.1 was entered to restore it to OPERABLE status. RHR "C" was restored in approximately 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. The RHR system safety function to transfer fission product decay heat and other residual heat from the reactor core at a rate such that specified acceptable fuel design limits and the design conditions of the reactor coolant pressure boundary was not jeopardized. Since RHR "A", "B" and low pressure core spray pumps remained OPERABLE during this event, a redundancy of plant components and features remained available to assure that operation the RHR system safety function could be accomplished.
comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
3. LER NUMBER
2016 - 00 012
E. CORRECTIVE ACTIONS
Actions have been initiated to revise plant procedures to ensure the tightness of the mounting screws of the latch check switch prior to measuring the adjustment value and record the latch check switch setting prior to breaker installation. A sample of completed latch check switch settings will be reviewed for similar inadequacies.
F. PREVIOUS SIMILAR OCCURENCES
No previous Event Reports were identified which detail an occurrence similar to the event described in this report.
G. COMPONENT FAILURE DATA
Manufacturer: Westinghouse Component Type: DHP 6900, 4160 Volt Power Circuit Breaker