05000254/LER-2015-001
| Quad Cities Nuclear Power Station Unit 1 | |
| Event date: | 01-06-2015 |
|---|---|
| Report date: | 03-06-2015 |
| 2542015001R00 - NRC Website | |
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PLANT AND SYSTEM IDENTIFICATION
General Electric — Boiling Water Reactor, 2957 Megawatts Thermal Rated Core Power Energy Industry Identification System (El(S) codes are identified in the text as [XX].
EVENT IDENTIFICATION
Unit 0 Fuel Oil Transfer Pump Feed Breaker Found Tripped
A. CONDITION PRIOR TO EVENT
Unit: 1 / 2 Event Date: January 6, 2015 Event Time: 1151 Reactor Mode: 1 / 1 Mode Name: Power Operation / Power Operation Power Level: 100% / 100%
B. DESCRIPTION OF EVENT
On January 6, 2015, at 1151, Electrical Maintenance was for preparing planned maintenance activities at Motor Control Center (MCC) 28-1A [SWGR] cubicle A4 [52] and identified that the breaker in cubicle Al [52] was tripped.
This breaker is the Unit 2 power supply to the Unit 0 Fuel Oil Transfer Pump (FOTP) [P]. Operations declared the FOTP motor [MO] were performed with no abnormalities.
On January 7, Electrical Maintenance instrumented the Unit 2 feed breaker to the Unit 0 FOTP in troubleshooting the breaker had trip. During the course of troubleshooting, the Unit 1 feed breaker [52] to the Unit 0 FOTP tripped.
EDG was declared inoperable to Unit 1.
Troubleshooting identified that due to high resistance contacts on the HGA power transfer relay [83], the applied voltage at the main motor contactor [CNTR] would be low enough to cause the contactor to pick up and drop out multiple times (chatter) during operation. This chatter of the contactor causes the motor field to collapse and reform which would result in a mismatch of phases and an instantaneous overcurrent trip of the feed breaker.
A review of Unit 0 EDG operating logs determined the last time the Unit 0 FOTP was powered from Unit 2 was when the Unit 0 EDG was loaded to Unit 2 on December 30, 2014. The tripped supply breaker was not identified at that time because the Unit 0 day tank [TK] level was at the normal standby level which is above the low level alarm setpoint.
If the fuel oil level in the tank had reached the low level alarm, operators would have responded in accordance with approved response procedures to take actions to ensure sufficient fuel was supplied to the day tank. Also, the day tank would have been replenished when the power supply for the Unit 0 FOTP swapped back to the Unit 1 feed breaker when the Unit 0 EDG was unloaded from Unit 2 on December 30, 2014.
The timeline to determine the length of inoperability for the Unit 0 EDG is as follows:
December 29 (0500) Unit 0 EDG declared inoperable for a clearance order to support planned maintenance.
December 29 (1700) Unit 0 EDG declared available upon clearance removal.
December 29 (1940) Unit 0 EDG loaded to Unit 1 for 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> endurance run.
December 30 (1955-2100) Unit 0 EDG loaded to Unit 2 as part of planned surveillances. This is the most likely time the Unit 2 FOTP power supply breaker would have tripped.
December 30 (2132) Unit 0 EDG declared operable after endurance run surveillances.
January 6 (1151) Unit 0 FOTP power supply breaker from Unit 2 found tripped. Unit 0 EDG declared inoperable.
January 8 (0450) Unit 0 EDG declared operable following power transfer relay replacement and testing.
The duration that the Unit 0 EDG was inoperable 2015). This exceeds the allowed outage time inoperable, and the subsequent entry into Condition Technical Specifications. In this instance, there December 30, 2014 and January 6, 2015. A power power is available from the Unit 1 and Unit 2 power checked daily on operator rounds. However, identify when a deficient condition existed that available for this condition to have been identified
C. CAUSE OF EVENT
The cause of the Unit 2 power supply breaker the HGA power transfer relay. The high resistance reduced voltage at the contactor coil and subsequent to back electromotive force (EMF) from the motor closed on the chatter.
D. SAFETY ANALYSIS
System Design was 10 days (0500, December 29, 2014, through 0450, January 8, of Technical Specifications 3.8.1 Condition B, one required EDG - F, to be in MODE 3. This resulted in a condition prohibited by were missed opportunities to identify the tripped breaker between available light is located in the Unit 0 EDG room to indicate if supply breakers for the Unit 0 EDG auxiliaries. These lights are the operator rounds did not provide enough detail for the operator to would require further investigation. There was sufficient indication and corrected in a timeframe allowed by Technical Specifications.
to the Unit 0 FOTP tripping was due to high resistance contacts of contacts resulted in main motor contactor chatter because of power supply breaker trip on instantaneous overcurrent due field collapsing and reforming as the contactor opened and source of clean fuel oil to the engine at proper pressure and also from storage in the event of sustained operation. Each fuel oil fuel oil storage tank, an electric fuel priming pump, an engine-driven and associated piping and instrumentation.
by design the Unit 0 EDG auxiliaries (cooling water pump, ventilation from either Unit 1 or Unit 2. Normally, the Unit 0 FOTP receives tank level drops to the point where the FOTP needs to run to Unit 1 power feed under normal conditions. The FOTP will run until power supply from Unit 2 if: 1) the Unit 1 power feed is lost, Unit 2 is closed, or 3) Unit 2 receives a safety injection signal. This from a HGA relay. There are interlock contacts in line with the motor of the Unit 0 FOTP motor does not occur from the Unit 1 and The EDG fuel oil system provides an immediate provides a means of transferring oil to the diesel system consists of a day tank, an underground fuel pump, a fuel oil transfer pump, filters, strainers, Since the Unit 0 EDG is common to both units, fan, etc.) have the capability to receive power power from Unit 1. If the Unit 0 EDG fuel oil day restore level, the FOTP is energized from the the day tank level is restored.
The logic in the FOTP circuit provides for an alternate 2) the output breaker from the Unit 0 EDG to transfer of power is accomplished via contacts contactors to ensure that simultaneous energization Unit 2 power supplies.
Safety Impact During the time the Unit 0 EDG was inoperable, the redundant Unit 1 and Unit 2 EDGs were operable except for a short period of time on January 2, 2015. On January 2, 2015 the Unit 2 EDG was declared inoperable from 0940- 1330 for planned maintenance activities on the Unit 2 EDG fire protection system. This configuration exceeded the allowed two hours Allowed Outage Time (AOT) for TS 3.8.1 Condition E, two required diesels inoperable, but did not exceed the subsequent Mode 3 transition time of 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> required by TS 3.8.1 Condition F. Therefore, this EDG was inoperable solely due to an impaired fire protection system. The Unit 2 EDG was available and would —have-respanded-as-expectecFforalFdesign-basisevents-requiring-emergency-AC—power:—AlFsupported-redundant--- equipment (Core Spray, Standby Gas Treatment, etc.) was operable during the time the Unit 0 EDG was inoperable. Therefore, the emergency AC function was met while the Unit 0 EDG was inoperable from December 29, 2014 to January 8, 2015.
An engineering analysis was performed that demonstrated this event did not constitute a Safety System Functional Failure. (Reference NEI 99-02, Revision 7, Regulatory Assessment Performance Indicator Guideline, Section 2.2, Mitigating Systems Cornerstone, Safety System Functional Failures, Clarifying Notes, Engineering analyses.) As such, this event will not be reported in the NRC Performance Indicator (PI) for safety system functional failures since an engineering analysis was performed which determined that the system was capable of performing its safety function with the identified degraded condition.
Risk Insights The Unit 0 EDG was available from 1700 December 29, 2014 to January 8, 2015. The Unit 0 EDG Fuel Oil Day Tank low level alarm is annunciated in the control room. Proceduralized operator response actions can be credited in the Probabilistic Risk Assessment (PRA) to maintain availability of equipment. Therefore, using the plant PRA, risk is unaffected since the Unit 0 EDG was maintained available and there was no unavailable equipment. As a result, there is no change in Core Damage Frequency (CDF) due to the degraded relay in the transfer logic of the Unit 0 FOTP.
E. CORRECTIVE ACTIONS
Immediate:
- The HGA power transfer relay was replaced.
Follow-up:
- Establish preventive maintenance tasks for periodic maintenance on the power transfer relay.
- Provide enhancements to daily operator rounds.
F. PREVIOUS OCCURRENCES
The station events database, LERs, and INPO Consolidated Event System (ICES) were reviewed for similar events at Quad Cities Nuclear Power Station. This event was caused by high resistance relay contacts. Based on causes of this event, the events listed below are similar events that could have contributed to preventing this event.
In an attempt to make the actions from previous events be focused and specific, the organization missed opportunities to address the issues involved in a more comprehensive manner that may have prevented future issues from occurring in a similar fashion. Actions to address these types of missed opportunities have been developed as part of the causal analysis performed for this failure.
- Station Issue Report (IR) 1445181: 13A-K29 Relay Did Not Energize, November 28, 2012 - During a logic functional test, the Reactor Core Isolation Cooling (RCIC) Auto Isolation Circuit relay did not energize as expected. The apparent cause was high resistance contacts on the relay. This investigation concluded that functional testing on a two year interval was sufficient to detect a degraded component prior to loss of function. The extent of condition from this event was focused on relays in RCIC and in the Primary Containment Isolation System (PCIS) protective relays. The extent of condition from this event could have assessed similar relays in other safety related applications.
- Station Issue Report (IR) 1611255: Unit 2 EDG Start Failure Relay Failure During Surveillance, January 23, 2014 - During the performance of, "U2 Emergency Diesel Generator Start Failure Logic Test," it was suspected that-the-TD=2-relay did-nottirne-ouras-expectect-After pressing-the EDG-8-tan pushbutton, the sfop pushbutton was depressed when it was apparent the start cycle was continuing. The relay contacts were mechanically closed but did not have any continuity. This event was a relay failure in the EDG start logic circuitry due to high resistance contacts and no preventative maintenance task for periodic replacement. The corrective actions from this investigation could have identified the HGA relay in the Unit 0 EDG FOTP power transfer logic as having no preventative maintenance.
- LERs — A review of LERs at Quad Cities Nuclear Power Station did not identify any events that were associated with this type of event.
G. COMPONENT FAILURE DATA
Failed Equipment: Relay Component Manufacturer: General Electric Component Model Number: 12HGA1 1 H70 Component Part Number: N/A This event has been reported to ICES as Failure Report No. 315121.