05000305/LER-2012-006
| Kewaunee Power Station | |
| Event date: | 07-18-2012 |
|---|---|
| Report date: | 09-14-2012 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3052012006R00 - NRC Website | |
Event Description
At 1555 CDT on July 18, 2012, while in Mode 1, Technical Specification (TS) Limiting Condition for Operation (LCO) 3.7.12, Auxiliary Building Special Ventilation (ASV) System [VF], was discovered not met for Train A. This was due to the ASV Train A charcoal [ABS] sample failing its 18-month filter efficiency test.
The ASV Train A charcoal filter [FLT] bed had last been replaced December 16, 2010. The charcoal failure was considered premature.
The acceptance criteria specified by TS 5.5.9, Ventilation Filter Testing Program, is 2.5% penetration 97.5% efficiency). Test data showed that actual penetration of the charcoal sample was 2.87% (97.13% efficiency), which is less than the minimum efficiency required by TS 5.5.9. With the Train A charcoal filter media efficiency below the test criteria, the associated train of ASV did not meet its TS Surveillance Requirement (SR). Per SR 3.0.1, failure to meet a Surveillance shall be failure to meet the TS Limiting Condition for Operation (LCO). Therefore, LCO 3.7.12, ASV System, was not met for Train A.
The SR was considered to have not been met from the time that the charcoal sample was removed for testing (July 11, 2012) until the charcoal filter was replaced (July 21, 2012). With the charcoal filter not meeting its SR for this period, LCO 3.7.12 was also not met for ASV Train A for a longer period than allowed by Technical Specifications. Thus, this event is being reported pursuant to 10 CFR 50.73(a)(2)(i)(B) for any operation or condition prohibited by the plant's Technical Specifications.
From the time of discovery on July 18, 2012, the filter was replaced within the required TS Completion Time of seven days as required by LCO 3.0.2 (filter testing was performed at the laboratory on July 17, 2012, and the data provided to KPS staff the following day).
Technical Specification (TS) Limiting Condition for Operation (LCO) 3.7.12 states (in part):
Two ASV trains shall be OPERABLE.
TS LCO 3.7.12, Required Action A.1 states the following for one ASV train inoperable:
Restore ASV train to OPERABLE status.
The Completion Time for Required Action A.1 is 7 days.
SR 3.7.12.2 directs performance of required ASV System filter testing in accordance with the Ventilation Filter Testing Program (VFTP).
TS SR 3.0.1 states (in part):
Failure to meet a Surveillance, ... shall be failure to meet the LCO.
With the ASV charcoal filter not meeting its acceptance criteria, SR 3.7.12.2 was not met. As a result, TS LCO 3.7.12 was not met. Although the filter was replaced and thereby Required Action A.1 was performed within its Completion Time (from time of discovery), LCO 3.7.12 was not met prior to discovery of this condition, such that the total time that LCO 3.7.12 was not met exceeded the time allowed by TS. Therefore, this event is being reported pursuant to 10 CFR 50.73(a)(2)(i)(B) for any operation or condition prohibited by the plant's Technical Specifications.
Although LCO 3.7.12 was not met for ASV Train A during this period, this train nevertheless remained Operable (prior to removing the charcoal for replacement) because the definition of Operability, as stated in TS 1.1, Definitions, was met as discussed in the Event and Safety Consequence Analysis section below.
Earlier on July 18, 2012, ASV Train B had been removed from service for routine maintenance and was inoperable for about six hours. However, since ASV Train A remained Operable during this period, this inoperability of B Train ASV was within the allowance of TS.
Event and Safety Consequence Analysis Although LCO 3.7.12 was not met for ASV Train A for a longer period than allowed by TS (from July 11 to July 21, 2012), the filter remained Operable (except during the period when it was removed from service to replace the charcoal media).
TS 1.1, Definitions, defines "Operable — Operability", in part as follows.
A system, subsystem, train, component, or device shall be OPERABLE or have OPERABILITY when it is capable of performing its specified safety function TS 5.5.9, Ventilation Filter Testing Program (VFTP), requires that the penetration (degradation of efficiency) of ASV system charcoal filters be limited to 2.5% when tested in accordance with ASTM D3803-1989.
This method includes a safety factor of 2. This safety factor ensures that the efficiency credited in the accident analysis is still valid at the end of the surveillance interval. The accident analysis is based on a charcoal filter efficiency of 95% (i.e., penetration of 5%). Therefore, the safety function of the filter was met, since its efficiency remained above 95%. As such, the filter remained Operable.
Since the filter remained Operable, the safety significance of this event was minimal.
The guidance in NUREG-1022, Section 3.2.2 states that "technical specifications contain LCO statements that include action statements... to provide constraints on the length of time components or systems may remain inoperable or out of service before the plant must shut down or other compensatory measures must be taken." This guidance then states "An LER is required if a condition existed for a time longer than permitted by the technical specifications [i.e., greater than the allowed outage time (or completion time in ISTS)] even if the condition was not discovered until after the allowable time had elapsed and the condition was rectified immediately upon discovery.
Therefore, this condition is being conservatively reported in accordance with this guidance as a condition prohibited by TS.
Cause
LCO 3.7.12 was not met for ASV Train A for a longer period than allowed by TS (from July 11 to July 21, 2012), because the filter test results were not obtained until the allowed outage time (for one train being inoperable) had elapsed.
The time to ship the charcoal sample to the testing laboratory, the time to analyze the sample, and the time transmit the results, is typically expected to take longer than one week (up to 30 days). These combined process times resulted in the test results not being obtained until the allowed outage time had elapsed.
Additionally, incorporating a safety factor of 2 into the acceptance criteria in TS 5.5.9.c can result in a condition where LCO 3.7.12 is not met even when the ASV charcoal filter meets its safety analysis assumptions, and is therefore Operable.
No direct cause for the premature degradation of the charcoal was able to be identified.
Corrective Actions
1. As immediate corrective action, the ASV Train A charcoal media was replaced and the ASV system was restored to service.
2. A second (backup) sample from the filter that failed was subsequently sent to the lab for testing.
The test showed satisfactory results of 98.09% efficiency. Three additional filter samples (obtained to further evaluate this condition) also showed satisfactory results. This indicates that only one section of the filter was adversely (prematurely) degraded, whereas the filter bank as a whole likely continued to meet the efficiency criteria.
3. In response to the disparity in tested efficiency of the various charcoal samples, actions were initiated to revise the process for testing charcoal filters to increase the number of samples that are obtained for initial testing.
Similar Events A review of Licensee Event Reports covering the last three years identified the following similar event.
Specification Condition