05000313/LER-2012-001
| Arkansas Nuclear One - Unit 1 | |
| Event date: | 02-15-2012 |
|---|---|
| Report date: | 04-12-2012 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3132012001R00 - NRC Website | |
A. Plant Status During the time of the subject conditions prohibited by Technical Specifications (TS) in December 2011, ANO-1 was at approximately 100% power.
B. Event Description
On February 15, 2012, ANO-1 received the NRC 4th quarter Integrated Inspection Report identifying a noncited violation of ANO-1 TS 3.8.4, "DC Sources-Operating," TS 3.8.7, "Inverters- Operating," and TS 3.8.9, "Distribution Systems-Operating," due to the licensee's failure to complete the associated required actions prior to the specified completion times while the associated emergency switchgear room chillers were out of service for planned maintenance.
Specifically, on December 7, 2011, VCH-4A [KM][CHU] Switchgear Room Chiller was removed from service to perform maintenance for 27.3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />, and on December 19, 2011, VCH-4B [KM][CHU] Switchgear Room Chiller was removed from service to perform maintenance for 15.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />. During both maintenance periods, ANO-1 did not enter the subject specifications above, but entered the following: (1) TS 3.7.7 Condition A for one loop of Service Water System (SWS) [BI] being inoperable with an associated completion time of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, (2) TS 3.8.1 Condition B for one emergency diesel generator inoperable with a 7 day completion time, and (3) TS 3.0.6, to support the emergency switchgear room chiller being out of service for planned maintenance.
The SWS specification was applied as allowed by the ANO-1 TS Bases, considering that the switchgear room chillers were supplied by the SWS, which is the ultimate cooling medium for the rooms which contain the electrical equipment.
Basis for changing the ANO-1 TS Bases to utilize the SWS specification In May of 2011, using the Process Applicability / 50.59 Process, Revision 41 was issued for the ANO-1 TS Bases which incorporated the allowance to enter the SWS 72-hour specification and invoke TS 3.0.6 when removing the ANO-1 switchgear room chillers from service. This was based in part on the fact that the SWS is the ultimate cooling medium for the electrical equipment (i.e., if SWS is inoperable, the associated chiller would also be inoperable) and because the SWS TS clearly defines actions to be taken, it was deemed appropriate to follow the requirements of the SWS TS 3.7.7 and the requirements LCO 3.0.6, which states:
"When a supported system LCO is not met solely due to a support system LCO not being met, the Conditions and Required Actions associated with this supported system are not required to be entered.
Only the support system LCO ACTIONS are required to be entered. This is an exception to LCO 3.0.2 for the supported system. In this event, an evaluation shall be performed in accordance with specification 5.5.15, "Safety Function Determination Program (SFDP)." If a loss of safety function is determined to exist by this program, the appropriate Conditions and Required Actions of the LCO in which the loss of safety function exists are required to be entered. When a support system's Required Action directs a supported system to be declared inoperable or directs entry into Conditions and Required Actions for a supported system, the applicable Conditions and Required Actions shall be entered in accordance with LCO 3.0.2.
TS Required Actions associated with electrical sources and equipment (with the exception of the Emergency Diesel Generator) are not entered when a SWS loop is inoperable as directed by LCO 3.0.6. The SWS provides a cooling medium, in conjunction with ventilation systems, to ensure electrical equipment room temperatures remain below acceptable limits following a design basis accident (DBA). GOTHIC software models indicated that the temperature rise in these rooms, given only the compensatory measures of opening specified doors, would not immediately challenge post-accident temperature limits. Because the electrical equipment is not immediately affected by a loss of the SWS loop, challenges to equipment operability will not occur until sometime after the onset of an event, and, because the 72-hour TS 3.7.7 Completion Time considers the redundant capabilities afforded by the operable SWS loop and the low probability of a DBA occurring during this period, ANO-1 concluded that compliance with the SWS TS was appropriate with regard to the effects on associated electrical equipment.
C. Event Cause The ANO-1 TS Bases allowed the use of the 72-hour Service Water specification and TS 3.0.6 as acceptable specifications to apply when removing the non-TS switchgear room chillers from service. The NRC determined that not entering all applicable TSs for the switchgear located in the rooms supported by the switchgear room chillers was a violation of the TS requirements.
D. Corrective Actions
In light of the aforementioned non-cited violation, ANO-1 currently enters all applicable switchgear TSs, with the most limiting being 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />, when removing the switchgear chillers from service.
E. Safety Significance Evaluation A probabilistic risk analysis has shown that the increase in risk of ANO-1 operation with one emergency switchgear room chiller out of service beyond the most limiting TS 8-hour completion time and within the window of any maintenance or failures of Emergency Switchgear Chillers is insignificant and considered acceptable. Additionally, considering the fact that compensatory measures were implemented during the time that the subject TS action statements were exceeded, the significance of this event is considered to be minimal.
G. Additional Information
10CFR 50.73(b)(5) states that this report shall contain reference to "any previous similar events at the same plant that are known to the licensee." NUREG-1022 reporting guidance states that term "previous occurrences" should include previous events or conditions that involved the same underlying concern or reason as this event, such as the same root cause, failure, or sequence of events.
A review of the ANO corrective action program and Licensee Event Reports for the previous three years revealed one event where the underlying cause could be considered similar to this subject event. In April 2011, Licensee Event Report 50-313/2011-001-00 for ANO-1 was submitted to report a Condition Prohibited by TS pursuant to 10 CFR 50.73(a)(2)(i)(B).
Specifically, the cause of the event was a misapplication of industry guidance that resulted in the use of non-safety related room coolers and additional compensatory measures as an acceptable alternative to satisfy TS requirements during switchgear room chiller maintenance or failure.
Energy Industry Identification System (EllS) codes and component codes are identified in the text of this report as p0q.