05000333/LER-2008-004
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No. N/A 05000 | |
| Event date: | 09-23-2008 |
|---|---|
| Report date: | 12-05-2008 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(i) |
| 3332008004R00 - NRC Website | |
BACKGROUND
The Emergency Onsite Power System [EllS=EK] Loss of Power (LOP) instrumentation monitors 4.16KV Emergency Buses [EIIS=BU] 10500 and 10600 to ensure timely transfer from offsite power sources and to onsite emergency power sources in the event of a loss of voltage or a degraded voltage condition. The 4.16 KV Emergency Bus Degraded Voltage Time Delay Relays prevent momentary fluctuations in line voltage from resulting in actuation of the Emergency Diesel Generators, however, the delay is short enough to ensure that equipment necessary for safe shutdown is not operated at degraded voltages. The 4.16 KV Emergency Bus Degraded Voltage Time Delay Relays are "on-delay" type Agastat [EllS=A109] relays [Model E7012 (004)], meaning that upon energization, the relays delay the transfer of loads from one set of contacts to another for a preset period of time.
4.16 KV Emergency Bus Degraded Voltage Time Delay Relay, 71-27T3-1HOEB03 [EIIS=2], is the degraded voltage time delay relay for Emergency Bus 10600 for non-LOCA conditions. The TS allowable value (AV) range is from greater than or equal to (>) 41.0 seconds to less than or equal to ( TS Surveillance Requirements(SR) 3.3.8.1.1 and 3.3.8.1.2 test the degraded voltage time delay relay set points "as-found" values every twenty-four (24) months during the LOP instrument channel calibration and channel functional tests. In order to assess the effects of calibration intervals on instrument drift, the relays are also subject to drift analysis per AP-19.10, Drift Monitoring Program (DMP).
In October, 2004, non-LOCA relay, 71-27T3-1HOEB03, was replaced, as were the other degraded bus voltage time delay relays associated with the "A" and "B" trains of emergency power. During "as-found" calibration testing in October, 2006, non-LOCA relay, 71-27T3-1HOEB03, exceeded the allowable TS value. The other Non-LOCA relay, 71-27T3-1H0EA03, and LOCA relays, 71-27T2-1H0EA03 and 71-27T2-1HOEB03, were verified within their allowable TS ranges at that time. Since there was no history of failure to meet the acceptance criteria and the time of failure was assumed to be time of discovery as allowed by the guidance in NUREG 1022. The relay was calibrated and the "as left" value was within the AV range.
EVENT DESCRIPTION
On 9/23/08, with the plant shutdown and in the refueling mode (Mode 5), 4.16 KV Emergency Bus Degraded Voltage non-LOCA Time Delay Relay, 71-27T3-1 HOEB03, "as-found" delay time failed to meet TS AV limit of 46.6 seconds.
The relay was found to actuate at 46.99 seconds. The immediate corrective action was to re-calibrate the relay to within TS AV limits and place the unit back into service On 10/06/2008, following completion of the DMP analysis, non-LOCA Time Delay Relay, 71-27T3-1HOEB03, was declared inoperable and the appropriate TS REQUIRED ACTIONS were` entered. On 10/08/2008, the relay was replaced.
The apparent cause evaluation conducted by plant staff determined that the selection of this type of relay (Agastat electro-pneumatic Model E7012) was a marginal choice for this application. This type of relay is not designed or tested to be resistant to set point drift. While other relays manufactured and installed at times have performed better in terms of set point drift, they have all experienced the set point drift to some extent.
Since non-LOCA Time Delay Relay, 71-27T3-1HOEB03, was found to be outside the TS AV on successive surveillance tests it was determined that "time of discovery" could not be taken as "time of failure". Therefore, the associated channel of the Emergency Onsite Power System LOP Instrumentation may have been inoperable for a , period longer than that allowed by TS 3.3.8.1 during the previous plant cycle.
This event is reportable pursuant to 10 CFR 50.73(a)(2)(i)(B), "Any operation or condition which was prohibited by the plant's Technical Specifications".
EVENT ANALYSIS
The 4.16 KV Emergency Bus Degraded Voltage Time Delay Relays prevent momentary fluctuations in line voltage from resulting in actuation of the Emergency Diesel Generators, however, the delay is short enough to ensure that equipment necessary for safe shutdown is not operated at degraded voltages.
An instrument channel calibration of the LOP degraded voltage time delay relays is performed every 24 months in accordance with plant procedure, ISP-91-1, 4KV Emergency Bus (Buses 10500 and 10600) Degraded Voltage Timer Instrument Calibration. During the procedure, the relay trip and the reset functions are verified to be within the "as-found" zone (AFZ) and re-adjusted, if necessary, to within the "as-left" tolerance (ALT), respectively.
In October, 2004, all four (4) Agastat Model E7012 (004) degraded voltage time delay relays were replaced with new relays of the same model. This replacement is based on vendor recommendations to replace the relays every ten (10) years. Prior to their replacement, the relays had a reliable performance history with only one (1) relay exceeding the TS limit during "as-found" testing within the previous six (6) years. In October, 2006, "as-found" calibration testing revealed that one (1) relay (71-27T3-1HOEB03) exceeded the TS AV. In September, 2008, during "as-found" calibration testing three (3) relays exceeded their TS AV. Non-LOCA Time Delay Relay, 71-27T3-1HOEB03, was
- one of the three. Since relays 71-27T2-1H0EA03 and 71-27T2-1HOEB03 have no history of failing to meet surveillance testing criteria they are not assumed to have failed during the cycle. However based on the previous failure of non-LOCA Time Delay Relay, 71-27T3-1HOEB03, time of failure is assumed to be at some point during the cycle, which may resulted in exceeding the TS allowed out of service time. Based on its earlier failure non-LOCA Time Delay Relay, 71-27T3-1HOEB03, was replaced with a new relay of the same type and model and the other relays that experienced their first failure to meet the TS AV were calibrated and left within the "as left" tolerance.
Drift analysis, including a review of performance history, determined that the trend in set point drift was non-conservative (positive) rather than random. The manufacturer was contacted to determine if there had been any changes in the manufacturing of the relays. The manufacturer stated that there were no changes in materials or manufacturing processes. The manufacturer also noted that if there were changes in materials or processes they would not be able to correlate such changes to changes in drift characteristics since they do not monitor or test for set point drift. The vendor applies a configuration code suffix (e.g. 004) to the relay model number to provide a means of identifying significant product changes. The current Configuration Code (004) to Model E7012 was issued in December, 1991 and has been in effect since that time.
Though the as-found value for non-LOCA degraded time delay relay, 71-27T3-1HOEB03, exceeded the TS AV (46.6 seconds), and was inoperable, it remained capable of performing its safety function. The plant design bases accident analyses assumes a delay 58.5 seconds and the "as found" actual value was 46.99 seconds. Therefore, plant barriers providing safety to the public were not compromised and the safety significance of this event is considered low.
JAF will continue to use agastat E7012 relays in this application. However, based on the drift analysis which indicates that relays may exceed their TS AV as early as 14 months following calibration, the calibration frequency is being changed from once every twenty-four (24) months to once every nine (9) months. The revised calibration frequency will remain in place until the relays are replaced with a more reliable model (e.g. digital in lieu of electro-pneumatic).
CAUSE OF EVENT
The selection of this type of relay (Agastat electro-pneumatic Model E7012) was a marginal choice for this application. This type of relay is not designed or tested to be resistant to set point drift. While other relays manufactured and installed at times have performed better in terms of set point drift, they have all experienced the set point drift to some extent.
EXTENT OF CONDITION
Set point drift failures can occur on any Agastat timing relay. A review of the corrective action database indicated that he condition has not been observed in other locations that could exceed TS acceptance criteria for qualified Agastat Model E7012 (004) relays not currently subject to the drift analysis program.
FAILED COMPONENT IDENTIFICATION
Manufacturer: New Amerace Corporation (Agastat) (Tyco) Model No: Model E7012 (004) NPRDS Manufacturer Code: A109 NPRDS Component Code: Time Delay Starting (Closing) Relay FitzPatrick Component ID: 71-27T2-1H0EA03, 71-27T2-1HOEB03 71-27T3-1H0EA03, 71-27T3-1HOEB03
CORRECTIVE ACTIONS
Immediate Corrective Actions
1.Calibrated 71-27T3-1HOEB03 and returned to service.
2. Calibrated 71-27T2-1H0EA03 and 71-27T2-1HOEB03 and returned to service.
3. Entered relay calibration failures into the corrective action program.
Completed Corrective Actions
1.Performed drift analysis in accordance with DMP.
2. Replaced relay 71-27T3-1HOEB03 with another Model E7012 (004) relay.
3.Performed Apparent Cause Evaluation
Planned Corrective Actions
1.Place ISP-91-1 on an increased frequency of 9-month intervals until the relay(s) can be replaced.
2. Perform engineering modification (EC) to replace relays 71-27T2-1H0EA03, 71-27T2-1 HOEB03, 71-27T3-1H0EA03 and 71-27T3-1HOEB03 with electronic timer relays.
3.Return the removed relay for 71-27T3-1HOEB03 to the vendor for further analysis.
4. Update the Apparent Cause Evaluation with results from the vendor analysis of removed relay 71-27T3-1HOEB03.
5. Upon completion of the Apparent Cause evaluation, share this event with the industry through the INPO Operating Experience Program.
ASSESSMENT OF SAFETY CONSEQUENCES
Plant barriers providing safety to the public were not compromised as a result of this event and the safety significance of this event is considered low. Though the as-found values for the degraded time delay relays exceeded the TS AVs, and were inoperable, the relays remained capable of performing their safety functions. The plant design bases accident analyses credit calculated allowable values for the LOCA and non-LOCA degraded voltage time delay relays of 9.94 seconds and 58.5 seconds, respectively (Ref. 5). The "as-found" values measured in September, 2008 for the LOCA and non-LOCA time delay relays were within these bounding limits.
SIMILAR EVENTS
There have been no similar events at the plant within the previous ten (10) years involving Agastat Model E7012(004) relays.
REFERENCES
1. JAF Condition Report CR-JAF-2008-03286, "During the performance of ISP -91-1 for the 10600 Bus, 71-27T2-1HOEB03 and 71-27T3-1HOEB03 were found outside (HI) their NO ADJUST range.
2. JAF Condition Report CR-JAF-2008-03546, "During performance of WO 51193792; ISP-91-1 timer was high out of tolerance. This is a level 1 criteria.
3. JAF Condition Report CR-JAF-2008-03796, "CR-JAF-2008-03286 failed to identify that the effected components ' failed LEVEL 1 acceptance criteria and the CR was screened incorrectly.
4. JAF Condition Report CR-JAF-2008-04044, "The Extent of Condition (EOC) for CR-JAF-2008-03796 and ' CR-JAF-2008-03546 found that several additional model Agastat E7012 relays are susceptible to the apparent cause and need operability reviews.
5. JAF Engineering Calculation JAF-CALC-ELEC-01488, Revision 5, 4KV Emergency Bus Loss of Voltage, Degraded Voltage and Time Delay Relay Uncertainty and Set-Point Calculation 6. JAFNPP Modification F1-88-001, Second Level of Under-voltage Protection-Addition of 45 Second Time Delay and associated Safety Evaluation JAF-SE-88-067.