05000348/LER-2014-002
| Joseph M. Farley Nuclear Plant, Unit 1 | |
| Event date: | 02-28-2014 |
|---|---|
| Report date: | 10-09-2014 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 3482014002R02 - NRC Website | |
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I. FACILITY NAME
I 2. DOCKET 6. LER NUMBER 3. PAGE Westinghouse - Pressurized Water Reactor Energy Industry Identification Codes are identified in the text as [XX].
Requirement for Report This report is required per 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by Technical Specification due to the B-Train Residual Heat Removal (RHR) system being inoperable for a period longer than the Required Action Completion Time of Technical Specification 3.5.2 (Emergency Core Cooling Systems — Operating) and due to Unit 1 having entered an operational mode applicable to Technical Specification 3.5.2 with an inoperable train of RHR in violation of Technical Specification Limiting Condition for Operation 3.0.4. Due to concurrent periods of A-Train RHR inoperability this is also reportable as an event or condition that could have prevented fulfillment of a safety function to remove residual heat (10 CFR 50.73(a)(2)(v)(B)) and to mitigate the consequences of an accident (10CFR 50.73(a)(2)(v)(D)).
Unit Status at Time of Event At the time of discovery of this issue on February 28, 2014 Unit 1 was operating in Mode 1 at 100 percent reactor power. During the replacement of the actuator linkage on the B-Train RHR Heat Exchanger Discharge Valve, Unit 1 was in Mode 6 conducting a refueling outage.
Description of Event
On October 13, 2013, with Unit 1 in Mode 6, the actuator linkage [CON] for the 1B RHR Heat Exchanger discharge Valve [HCV], Q1E11HCV603B, was replaced. An incorrect actuator linkage length was established during the linkage replacement. Post-maintenance testing for the linkage replacement did not identify the altered linkage length.
On December 5, 2013, with Unit 1 at full reactor power in Mode 1, while performing procedure FNP-1- STP-11.2, "16 RHR Pump Comprehensive Inservice Test", a lower than normal flow rate was noted while in the system test configuration. While investigating the low flow rate, the altered length of the heat exchanger discharge valve linkage was identified. An engineering analysis of the flow rate determined that the existing flow rate was sufficient to meet system operability requirements.
On February 28, 2014, during a subsequent performance of procedure FNP-1-STP-11.2, the system flow rate was noted to be lower than during the December 5, 2013 performance and was insufficient to justify operability of the B-Train RHR system. Investigation of test results determined the difference in flow rates was attributed to the heat exchanger bypass valve not being fully closed during the December 5, 2013 surveillance, invalidating the December 5, 2013 test results, and due to slight rotational slip between the discharge valve stem and the attached disc. Adjustments were made to the actuator linkage to establish adequate system flow rate and account for the rotational slip. The B-Train RHR system was returned to operable status at 2235 on March 1, 2014. Based on the February 28, 2014 surveillance test results, the B-Train RHR system is considered to have been inoperable from October 13, 2013 until March 1, 2014 due to not meeting the minimum required Technical Specification injection flow requirement.
From October 13, 2013 until March 1, 2014, while the B-Train RHR system was in a condition of reduced flow, the A-Train RHR system was placed in an inoperable status for brief periods on four occasions for various maintenance and testing activities. No other structures, components, or systems contributed to this event.
Cause of Event
The direct cause of the event is attributed to the incorrect actuator linkage length that was established during the linkage replacement. The apparent cause was non-conservative decision making and improper understanding of risk acceptance associated with the post maintenance testing requirements. A contributing cause was inadequate procedural guidance for correct valve position verification.
Safety Assessment During the period from October 13, 2013 until March 1, 2014 the B-Train RHR system would have exhibited less than the Technical Specification minimum required flow rate in the post-accident injection mode of operation during a large-break Loss of Coolant Accident (LOCA). An engineering analysis was performed for the B-Train RHR. The conclusions were that the B-Train RHR would have continued to perform its specified safety function with the reduced flow if a large break loss of coolant accident (LBLOCA) would have occurred, assuming A-Train was unavailable. The evaluation determined that the Small Break loss of coolant accident (SMLOCA) was not impacted by the reduced flow. This analysis is preliminary. If the final analysis changes any conclusions, then a supplement to this report will be issued.
Corrective Action To correct the insufficient flow rate observed during B-Train RHR surveillance testing, the 1B RHR Heat Exchanger Discharge Valve actuator linkage dimensions were adjusted to provide sufficient flow to meet system operability requirements. A full performance of the surveillance procedure for adjusting the 1B RHR Heat Exchanger Discharge Valve will be performed no later than the end of the next refueling outage. Completed corrective actions included the establishment and communication — using training, briefings, and performance monitoring plans — of goals and expectations to improve issue resolution and prioritization, risk management, and response to operational challenges. Procedures that verify the mechanical stop positions for the RHR Heat Exchanger Discharge Valves were revised to clearly identify all valve adjustment verifications.
Additional Information
Farley Unit 1 and Unit 2 Licensee Event Reports for the previous five years have been reviewed with no reports being identified that were similar to this event or related to RHR system flow. A review of internal operating experience for the previous five year period identified no similar previous issues at Farley.