05000454/LER-2015-001
| Byron Station, Unit 1 | |
| Event date: | 01-11-2015 |
|---|---|
| Report date: | 03-11-2015 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4542015001R00 - NRC Website | |
Reported lessons Warned are incorporated Into the licensing process and fed back to Industry.
Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (--5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by Internet e-mail to Infocollects Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget Washington, DC 20503. If a means used to Impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
2. DOCKET
A. Plant Condition Prior to Event Event Date/Time: January 11, 2015 / 2055 hours0.0238 days <br />0.571 hours <br />0.0034 weeks <br />7.819275e-4 months <br /> CST Unit 1 - Mode 1 — Mode 1 Power 100 percent Unit 2 - Mode 1 — Mode 1 Power 100 percent Reactor Coolant System [AB]: Normal operating temperature and pressure. There was no inoperable equipment that contributed to this event.
B. Description of Event
On January 11, 2015, at 2055 hours0.0238 days <br />0.571 hours <br />0.0034 weeks <br />7.819275e-4 months <br />, the Byron Station Unit 2, Train 'A' (2A), Main Steam Isolation Valve (MSIV) was declared inoperable due to the inoperability of one of the associated redundant actuator trains. Byron Station Operations immediately entered Technical Specification (TS) 3.7.2, "Main Steam Isolation Valves (MSIVs)," Condition A, which requires that with one MSIV inoperable in Mode 1, restore the MSIV to Operable status within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />. If the inoperable MSIV is not restored to Operable status, Condition B must be entered.
Condition B requires that the unit be placed in Mode 2 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. Byron Station successfully restored the inoperable MSIV to Operable status prior to the expiration of the TS 3.7.2, Condition A, 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> Completion Time.
On January 13, 2015 a Byron Station system engineer initiated Issue Report (IR) 2436822 to document that declaring a MSIV inoperable due to a condition that affects only one accumulator/hydraulic train may not have been performed in the recent past. The IR referenced a specific prior occurrence on June 30, 2014 associated with the 2A MSIV Accumulator (reference IR 1676838). This IR prompted a Byron Station action to review for extent of condition for a period of three years back from January 11, 2015.
The extent of condition review identified two occurrences at Byron Station in the prior three years where an accumulator/hydraulic train for an MSIV was inoperable and the inoperable train was not restored within the 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> Completion Time required by TS 3.7.2, Condition A. These occurrences are noted as follows:
1. June 30, 2014: Byron Station Unit 2, "Nitrogen leakage from 2A MSIV Standby Accumulator" (reference IR 1676838). During System trending, an engineer observed a minor and longer term decrease in 2A MSIV standby pressure when compared with the Active Train accumulator pressure. Follow-up determined a nitrogen leak of unknown quantity, but the accumulator nitrogen pre-charge was low and, therefore, the accumulator was inoperable. The accumulator was restored to Operable status on July 3, 2015. This restoration time exceeded the 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> completion time of TS 3.7.2, Condition A.
2. September 25, 2013: Byron Station Unit 1, " 1B MSIV Has No Oil Level in Sight Glass" " (reference IR 1563273). Operations identified that the 1B MSIV had no oil level visible in the oil sight glass. The 1B MSIV active side accumulator had a nitrogen pre-charge check performed under Work Order 01083671 on September 27, 2013. The pre-charge check found the active side accumulator pre-charge was lower than allowed. Proper pre-charge was established and the accumulator restored on September 30, 2015.
This restoration time exceeded the 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> completion time of TS 3.7.2, Condition A This event is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B) for any operation or condition which is prohibited by the plant's Technical Specifications due to TS 3.7.2 Condition A Required Action not being completed within the Completion Time.
The January 11, 2015 entry into Byron TS 3.7.2, Condition A was predicated on industry experience and an NRC staff interpretation that Surveillance Requirement 3.7.2.2 requires both actuator trains for a single valve to be tested. (Reference NRC Memorandum, "Operability Determination for the Callaway Plant Technical Specifications Requirements When One Main Steam Isolation Valve Actuator Train is Removed from Service," dated October 19, 2006 (ADAMS Accession Number ML061730396).
On the event date, Byron TS 3.7.2 did not specifically address or reflect the two independent actuator trains for one MSIV. Inoperability of one of the two actuator trains associated with an MSIV does not by itself make the valve incapable of closing since the remaining Operable actuator train can alone effect valve closure on demand.
The NRC staff interpretation results in declaring an MSIV inoperable for those plants with dual MSIV actuator trains when one actuator train is inoperable. The existing Completion time for an inoperable MSIV does not typically provide a reasonable amount of time to effect repairs to one inoperable actuator train. Declaring an MSIV inoperable and having to enter the Condition(s) and Required Action(s) for an MSIV inoperable due only to one inoperable actuator train is unnecessarily restrictive. To address this condition, Byron Station had previously submitted a License Amendment Request (LAR) on August 21, 2013 (ADAMS Accession Number ML13235A095) to incorporate requirements specifically for the MSIV actuator trains within TS 3.7.2 such that the specification would include Conditions and Required Actions to address inoperable MSIV actuator trains. This LAR was approved by the NRC for Byron Station on January 30, 2015.
C. Cause of Event
The cause of the event was a departure from Byron Station's previous practice to one that was based on the October 19, 2006 NRC position in regard to entering TS 3.7.2, Condition A, under similar conditions. The previous practice was based on the following factors:
1. The original TS did not explicitly address the MSIV actuator trains.
2. The redundancy in the MSIV actuator design permits an MSIV to close on demand, with one actuator train unavailable.
D. Safety Significance
This event is not considered an event or condition that could have prevented fulfillment of a safety function.
The Byron events of June 30, 2014 and September 25, 2013 document a single actuator train as inoperable for three days and five days respectively. The probabilistic risk analysis (PRA) used to validate the acceptability of the 7 day allowed Completion Time for the NRC approved Byron LAR bounds these events
E. Corrective Actions
Byron Operations communicated the MSIV operability position to operating crews on January 12, 2015.
Byron Station had previously submitted a LAR on August 21, 2013 to incorporate Conditions and Required Actions to address inoperable MSIV actuator trains within TS 3.7.2. This LAR was approved by the NRC for Byron Station on January 30, 2015. Byron implemented the new TS on February 2, 2015. Operating procedures for the TS change have been approved and implemented.
F. Previous Occurrences
No previous similar events are known.