05000482/LER-2010-004
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No. 05000 | |
| Event date: | 02-11-2010 |
|---|---|
| Report date: | 04-08-2010 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| Initial Reporting | |
| 4822010004R00 - NRC Website | |
On 2/11/2010 the NRC issued violation 2009005-009, "Positive Reactivity Addition Prohibited by technical specifications while in Mode 2." The inspectors identified a noncited violation of Technical Specification 3.3.1, Condition I, for making positive reactivity addition prohibited by technical specifications in Mode 2 because one Source Range Neutron Flux channel [EllS Code: IG] was inoperable.
A loss of off-site power event on 8/19/2009 caused a reactor trip and turbine trip and the plant entered Mode 3.
As a result, power to the Containment Cavity Cooling fans was lost. During this period, Source Range Neutron Flux channel, SEN0031, was reading somewhat lower than Source Range Neutron Flux channel SEN0032, then increased and stabilized significantly higher than SEN0032.
On 08/20/2009, a Containment Cavity Cooling fan [EllS Code: VA-FAN] was started and SEN0031 indication rapidly returned to near the same relative indication of SEN0032, as existed initially. Later on 08/20/2009, procedure STS IC-231, "Channel Operational Test Nuclear Instrumentation System Source Range N-31 Protection Set 1," was completed satisfactorily. This surveillance injects a test signal and verifies the Source Range Neutron Flux Trip bistable functions when the trip setpoint is exceeded. Channel checks in accordance with surveillance requirement (SR) 3.3.1.1 between SEN0031 and SEN0032 indicated satisfactory agreement.
Outside of the short period of time when the cavity cooling fans were unavailable, SEN0031 performed as expected without deviation. It passed all surveillances and no anomalies were noted during its operation.
SEN0031 was energized, as expected, shortly after the Loss of Offsite Power and the instrument functioned continuously until de-energized during startup on 8/23/2009. The abnormally high indication was confined solely to the period shortly after cavity cooling was lost, and indication recovered and acted as expected approximately one hour after cavity cooling was restored.
On 08/22/2009, Wolf Creek entered the mode of applicability when the reactor trip breakers were closed. Wolf Creek entered Mode 2 and the reactor became critical on 8/23/2009. During the reactor startup and power ascension to point of de-energizing the source range instruments above P-6, which exited the mode of applicability, both source range instruments indicated normally and passed all normal channel checks.
During the startup, both channels of Source Range Neutron Flux indication were used to generate a 1/M plot per procedure GEN 00-003, "Hot Standby to Minimum Load," and both were found to be acceptable. This further demonstrated that SEN0031 was functioning normally, as there was good agreement between the 1/M plots.
At the beginning of Refuel Outage 17, Electrical Characterization and Diagnostic (ECAD) Tests were performed 10/10/09 through 10/13/09 that assessed the condition of the detector circuits. The Source Range Neutron Flux channels have been operating normally over the last few years and the ECAD data indicated that the circuit condition had remained essentially constant over the same period.
This condition is being reported based on NRC issuance of noncited violation 2009005-009, "Positive Reactivity Addition Prohibited by technical specifications while in Mode 2." Additionally, during a review of this event, it was identified that the transitioning from Mode 3 to Mode 2, and closing the reactor trip breakers, with one Source Range Neutron Flux channel inoperable is a failure to meet Limiting Condition for Operation (LCO) 3.0.4a.
This condition is being reported per 10 CFR 50.73(a)(2)(i)(B) as an operation or condition prohibited by Technical Specifications.
CAUSE
The most probable cause of the behavior for SEN0031 following loss of cavity cooling was increased temperature of the detector and associated cabling resulting in increased count rate indication. The violation occurred, because after cavity cooling was restored and SEN0031 indication returned to normal, Wolf Creek did not consider SEN0031 to be inoperable prior to entering the mode of applicability.
CORRECTIVE ACTIONS
Source range detector SEN0031 was replaced during Refueling Outage 17 in November 2009.
SAFETY SIGNIFICANCE
The safety significance of this condition is low. Outside of the short period of time when the Containment Cavity Cooling fans were unavailable, SEN0031 performed as expected without deviation. It passed required surveillances and no anomalies were noted during its operation. During the subsequent reactor startup and power ascension to point of de-energizing the Source Range Neutron Flux channels above P-6, which exited the mode of applicability, both Source Range Neutron Flux channels indicated normally and required channel checks were satisfactory. SEN0032 was able to perform its Source Range High Flux Trip function during the modes of applicability, and there is no indication that SEN0031 would not have been able to perform its Source Range High Flux trip function.
OPERATING EXPERIENCE/PREVIOUS EVENTS
None