05000482/LER-2013-010
| Wolf Creek Generating Station | |
| Event date: | 10-18-2013 |
|---|---|
| Report date: | 12-17-2013 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown |
| 4822013000R00 - NRC Website | |
There were no structures, components or systems (SSC) that were inoperable at the start of the event and contributed to the event.
DESCRIPTION OF THE EVENT
On October 18, 2013 at 1050 Central Daylight Time (CDT), the control room was notified that the 'A' train Class 1 E electrical equipment air conditioning (A/C) unit [EllS: VI, ACU] (SGKO5A) had stopped running and the alarm light for lube oil failure' was illuminated. SGKO5A was declared nonfunctional per Technical Requirement (TR) 3.7.23, "Class 1 E Electrical Equipment Air-Conditioning (NC).
Because of the essential support function provided by the Class 1 E electrical equipment A/C trains, the correct application of the Technical Specification (TS), upon discovery of a nonfunctional Class 1 E electrical equipment A/C train, is to immediately enter the applicable Conditions and Required Actions under TS 3.8.4, TS 3.8.7, TS 3.8.9, as well as Limiting Condition for Operation (LCO) 3.0.3.
After entry into LCO 3.0.3, the Oil Pressure Sensing System was reset inside of the SGK05A control cabinet. The unit was observed operating properly with all parameters within their normal band. At 1100 CDT, the control room exited TR 3.7.23, TS 3.8.4, TS 3.8.7, TS 3.8.9, and LCO 3.0.3. The control room stationed an operator at SGKO5A to continuously monitor operation of the unit and to report any abnormal conditions. At 1141 CDT, SGKO5A again tripped on low oil pressure. The control room re-entered the applicable Conditions and Required Actions under TR 3.7.23, TS 3.8.4, TS 3.8.7, TS 3.8.9, and LCO 3.0.3.
A plant shutdown was commenced on October 18, 2013 at 1211 CDT. Wolf Creek Generating Station (WCGS) entered Mode 3 on October 18, 2013 at 1735 CDT.
The cause of the low oil pressure trip of the SGKO5A unit was a clogged screen on the pressure switch, which activates the low-pressure trip. The clogging of the screen was due to the existence of black debris, which prevented the pressure switch from sensing system pressure.
In May 2013, a filter-drier [EllS: VI, FLT] failure on the SGKO5A unit introduced contaminates into the system including the SGKO5A compressor. The compressor was removed from the system and replaced with another compressor. The removed compressor was set aside and cleaned, but not cleaned to an adequate level. This compressor was then reinstalled in September 2013. The compressor in the SGKO5A unit, at the time of the October 18, 2013 failure, was the same compressor that was removed from the SGKO5A unit in May 2013, following the filter-drier failure.
Further review found that procedure AP 12-002, "Internal/External System Cleanliness," was applicable to the refrigerant side of the Class 1 E electrical equipment air conditioning (A/C) system but was not used. Use of this procedure would have removed the contaminants from the Class 1 E electrical equipment air conditioning (A/C) system and compressor.
Work on the 'A' train Class 1 E electrical equipment NC unit was completed and the unit returned to a functional status on October 21, 2013 at 1915 CDT. WCGS returned to Mode 1 on October 27, 2013 at 2007 CDT.
BASIS FOR REPORTABILITY
10 CFR 50.73(a)(2)(i)(A) requires reporting "the completion of any nuclear plant shutdown required by the plant's Technical Specifications." A shutdown of the plant was completed per LCO 3.0.3.
Additionally, a 4-hour notification was made per 10 CFR 50.72(b)(2)(i) when the plant shutdown was initiated.
CAUSE OF THE EVENT
The direct cause of this condition is the loss of lube oil pressure sensing to the pressure switch of the SGKO5A compressor. A filter-drier failure in May 2013 on the SGKO5A unit introduced contaminates into the system causing the loss of lube oil pressure sensing to the pressure switch.
The root cause of this condition is attributed to the lack of station awareness in relation to how procedure AP 12-002, "Internal/External System Cleanliness," applied to the refrigerant side of the Class 1E electrical equipment air conditioning (NC) system. In May 2013, an inadequate chemical flush and evacuation performed after a filter-drier failure allowed filter element material to enter the refrigerant stream. Failure of the filter-drier was reported in LER 2013-006-01.
CORRECTIVE ACTIONS
The compressor was removed from the system and a gravity flush of the crankcase was performed.
Core work instructions will be generated to provide specific guidance for the maintenance technicians performing flushing and restoration evolutions on air conditioning systems.
Procedure MPE GK-004, "GK Unit Preparation for Work," will be revised to include critical steps that are important for ensuring an effective flush and evacuation of the Class 1 E electrical equipment NC system.
SAFETY SIGNIFICANCE
The Class 1 E electrical equipment NC system operates in a continuous recirculation mode to maintain the engineered safety features (ESF) switchgear rooms [EMS: EB, SWGR], battery rooms [EMS: EJ, BTRY] and the DC switchgear rooms [EllS: EJ, SWGR] at or below the design temperature of 90 degrees F during all modes of plant operation, including loss of preferred offsite power and post- accident operation. The safety significance of this event is low since only one train of Class 1 E electrical equipment was potentially affected. The 'B' train Class 1 E electrical equipment NC unit, SGKO5B, was not affected and remained functional, and its associated train of Class 1 E electrical equipment was operable. Additionally, the 'A' train Class lE electrical equipment room temperatures, cooled by SGKO5A, remained below 90 degrees F.
a calculation that concluded one train of air conditioning was not capable of supporting both trains of Class 1E equipment. Technical Requirement (TR) 3.7.23 allowed a train to be nonfunctional if compensatory measures were established for the affected unit. During the operability determination and functionality assessment process, it was determined that the operability of the associated train Class 1 E electrical equipment could not be maintained without additional compensatory measures and for a limited period of time.
nonfunctional and one train of control room air conditioning had been inoperable during the previous cycle. This was discovered during refueling outage 19 when the SGKO5A compressor terminal box mounting screws were found over torqued. This resulted in a condition prohibited by Technical Specification and a condition that could have prevented the fulfillment of a safety function.
nonfunctional due to a partial blockage of the thermostatic expansion valve [EllS: VI, TCV] feeding the SGKO5A evaporator coils. Failure of a filter-drier in the system created the contamination that led to the blockage. This resulted in a plant shutdown required by Technical Specifications.
nonfunctional due to an analysis of an oil sample that showed elevated levels of aluminum. The NRC granted enforcement discretion that allowed the plant to remain at power while the train was restored to functional status.
to an inadequate flush of contaminates created by a filter-drier failure. This resulted in a plant shutdown required by Technical Specifications.