05000366/LER-2015-001
| Docket Number Sequential Rev Year Day Year Year Day Number No. Month | |
| Event date: | 02-09-2015 |
|---|---|
| Report date: | 04-02-2015 |
| 3662015001R00 - NRC Website | |
PLANT AND SYSTEM
General Electric - Boiling Water Reactor Energy Industry Identification System codes appear in the text as (EllS Code XXX)
OF EVENT
On 02/09/2015, at approximately 0504 EDT, with Unit 2 operating at approximately zero percent rated thermal power in hot shutdown (Mode 3) as part of a scheduled refueling outage, the "A" and "C" outboard main steam isolation valves (MSIV) (EllS Code ISV) failed to close within the required isolation time of 3 to 5 seconds. The "A" outboard MSIV closed in 6.8 seconds, while the "C" outboard MSIV closed in 10.3 seconds. The surveillance tests for the remaining Unit 2 MSIVs were successfully completed with each valve meeting the surveillance acceptance criteria by closing within the required isolation time of 3 to 5 seconds.
There are two isolation valves, one on each side of the primary containment barrier, on each main steam line.
The "outboard" MSIVs are located just outside of the primary containment barrier, while the "inboard" MSIVs are located inside the primary containment boundary. The MSIVs are relied upon to assure the integrity of the reactor coolant pressure boundary by closing off the main steam lines within a time frame of 3 to 5 seconds established by design basis accident (DBA) analysis to limit the release of reactor coolant or radioactive material. Due to the excessive stroke times, the fast closure tests for the "A" and "C" outboard MSIV were declared unsatisfactory and the affected main steam lines were maintained in an isolated configuration as all the MSIVs remained closed.
CAUSE OF EVENT
The 2, 3, & 4-way valves on the pneumatic assemblies of the Unit 2 MSIV actuators are supplied to Ralph A.
Hiller from Norgren. As part of the troubleshooting process, Engineering learned that during internal validation testing of the pneumatic valves by Ralph A. Hiller in 2012, shuttering was witnessed in the Norgren 2-way and 3-way valves. This resulted in a delay in the valves' stroke times. The corresponding valves were disassembled and excess super a-lube, along with minor foreign material (FM), was observed throughout the valve internals. The valves were then cleaned, and lubricated appropriately with a thin layer of super a-lube and reassembled. After this action was completed, the actuator functioned appropriately with no degradation in performance. Engineering learned that excess lubrication applied to valve internals can plasticize and become tacky over time. The tacky substance can hinder the smooth operation of the valve internals, causing it to stick or delay in shuttling.
Subsequent disassembly and inspection of the 2-way and 4-way valves on both the Unit 2 "A" and "C" outboard MSIVs revealed excess lubrication on the pistons and springs that had become tacky. The resulting causal analysis for the unsatisfactory fast stroke times on the "A" and "C" outboard MSIVs concluded that the most probable cause was attributed to a delay in the opening of the air supply and exhaust paths for the air operator cylinder due to sticking in the 2-way and 4-way valves of the pneumatic manifold assembly of the MSIV actuator. This cause was confirmed by a bench test of the "C" outboard MSIV pneumatic assembly in which the valves would not shuttle appropriately when energized.
As a result of the observed "as-found" condition of the Norgren valves, on 11/01/2012 Ralph A. Hiller implemented procedures for inspection, cleaning, and lubrication for all incoming Norgren 2-way, 3-way, and 4- way valves. Per Ralph A. Hiller, because only one occurrence of the over-lubrication issue was identified during their internal testing process, it was treated statistically as an isolated occurrence.
The pneumatic manifold assemblies installed on the Unit 1 MSIVs are designed and manufactured by Automatic Valve Corporation (AVCO) and do not contain Norgren valves. Additionally, AVCO was contacted to confirm that their nuclear products have had no history of failures or functionality issues caused by excess lubrication. This event is therefore isolated to Unit 2 only.
REPORTABILITY AND ASSESSMENT
The event is reportable per 10 CFR 50.73{a)(2)(i)(B) due to an event occurring in which a Limiting Condition for Operation (LCO) existed for a time longer than permitted by the Technical Specifications (TS). Normally a discrepancy found during surveillance testing should be assumed to have occurred at the time of its discovery, unless there is firm evidence to indicate that the discrepancy existed previously. The excessive lubrication of the pneumatic manifold valves that led to excessive fast stroke times for the MSIVs existed while the MSIVs were in service. Therefore, since there is firm evidence that the discrepancy existed previously, this condition is reportable as it existed for a time frame that was greater than the TS Required Action Statement Completion Time.
The "as found" stroke times for the Unit 2 "A" and "C" inboard MSIVs met the required TS surveillance acceptance criteria which demonstrated their continuing operability. Therefore, primary containment isolation capability of the main steam lines remained operable which ensured the required isolation safety function was maintained. Based on this information this condition was determined to have a very low safety significance.
CORRECTIVE ACTIONS
The pneumatic valves for the "A" and "C" outboard MSIVs were inspected, cleaned, and re-lubricated per Ralph A. Hiller's improved procedures. The MSIVs were then reassembled and functionality tested to ensure they were capable of meeting their stroke time of 3 to 5 seconds. The surveillance tests were satisfactorily completed and no other corrective actions were necessary.
A broadness review was conducted to determine the manufacture and receipt date of pneumatic manifold assemblies supplied by Ralph A. Hiller to ensure all the corresponding 2-way, 3-way, and 4-way valves for the remaining Unit 2 MSIVs had been correctly lubricated under the vendor's improved procedural requirements that were implemented in November 2012. As a result of this review, the following additional Unit 2 MSIVs were determined to be susceptible to excess lubrication: Unit 2 "A", "B", "C", & "D" inboard MSIVs and the Unit 2 "D" outboard MSIV. The 2-way, 3-way, and 4-way valves that were determined to be susceptible to excess lubrication were replaced or inspected, cleaned, re-lubricated and reassembled in accordance with Ralph A.
Hiller's procedures. The surveillance testing for the associated MSIVs was successfully performed and demonstrated operability such that the stroke time for these MSIVs satisfied the TS surveillance testing acceptance criteria.
As part of the broadness review, an item in the warehouse was also identified to be susceptible to excess lubrication. As a preventative measure a hold was placed on the item and a work order was generated to ensure the item is inspected, cleaned, re-lubricated, and returned to stock.