05000336/LER-2013-001
| Millstone Power Station - Unit 2 | |
| Event date: | 01-17-2013 |
|---|---|
| Report date: | 03-12-2013 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| LER closed by | |
| IR 05000245/2013002 (11 April 2013) | |
| 3362013001R00 - NRC Website | |
1. EVENT DESCRIPTION
At 0938 on January 15, 2013, with Millstone Power Station Unit 2 (MPS2) in Mode 1, operating at 100 percent power, while performing a monthly required channel check on the safety valve's position indication, technicians discovered that the channel B primary safety valve [AB] [RV] acoustic valve monitor system (AVMS) position indicator [MON] failed to meet acceptance criteria contained in Surveillance Procedure SP2410A. A CHANNEL CHECK is defined in the TS as the qualitative assessment of channel behavior during operation by observation. Its purpose is to verify Operability of the channel of AVMS. In this instance, the technicians had expected to observe a frequency peak at or near 74.25 Hz on the AVMS' output, which is induced by an operating reactor coolant pump. After reviewing a printout obtained from the instrumentation loop, it was determined that the frequency peak expected at or near 74.25 Hz was not detected. Therefore, the AVMS channel was declared inoperable and Operators entered Technical Specification (TS) 3.3.3.8, Accident Monitoring Instrumentation, Action 3, for Item 6, Safety Valve Position Indicator, which specifies that alternate indications shall be checked once each shift.
On January 17, 2013, upon reviewing the results from the previous month's completed channel check surveillance performed on the AVMS on December 18, 2012, it was discovered that the AVMS had also failed to meet the acceptance criteria for a channel check in SP2410A at that time. It was not, however, recognized in December 2012 that the surveillance results did not meet acceptance criteria, so the instrument was not declared inoperable at the time. The technicians and condition based maintenance personnel had observed a frequency peak at approximately 72.5 Hz and incorrectly interpreted the observed frequency to be sufficiently near 74.25 Hz and therefore acceptable. On November 15, 2012, the channel check on AVMS was verified to have been successfully completed.
Troubleshooting was performed on accessible portions of the AVMS on January 25, 2013, which revealed problems with the AVMS equipment located inside reactor containment. Work has been scheduled in the station's work management process for investigation and troubleshooting of AVMS during the next MPS2 refueling outage.
This condition is being reported pursuant to 10 CFR 73(a)(2)(i)(B) as any operation or condition which was prohibited by the plant's TS.
2. CAUSE
The cause was determined to be inadequate procedure guidance in SP2410A which led to confusion when interpreting surveillance results.
3. ASSESSMENT OF SAFETY CONSEQUENCES
The AVMS provides indications and alarms that are a diagnostic aid for operators to determine the position of the primary (Reactor Coolant System) code safety valves. Although the AVMS provides an alarm to alert operators whenever the safety valve is open, AVMS provides no automatic equipment or protective actions. Alternative means are and always were available in the MPS2 control room which provide indication of the safety valve's position and most of these indications can be trended. Therefore, there were no adverse safety consequences.
4. CORRECTIVE ACTION
Surveillance Procedure SP2410A has been revised to include clearer acceptance criteria for a channel check, specific working group interface and peer review of data evaluation. Other actions are being taken in accordance with the station's corrective action program.
5. PREVIOUS OCCURRENCES
No previous similar events/conditions were identified.
Energy Industry Identification System (EllS) codes are identified in the text as [XX].