05000341/FIN-2017004-02
Finding | |
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| Title | Division 2 Residual Heat Removal Service Water System Outlet Flow Control Valve Lower Bonnet (Backseat) Bushing Failure |
| Description | The inspectors evaluated the licensee's handling of selected degraded performance issues involving the following risk-significant structures, systems, and components (SSCs):Residual heat removal service water system.
13 The inspectors assessed performance issues with respect to the reliability, availability, and condition monitoring of the SSCs. Specifically, the inspectors independently verified the licensee's handling of SSC performance or condition problems in terms of:appropriate work practices;identifying and addressing common cause failures;scoping of SSCs in accordance with 10 CFR 50.65(b);characterizing SSC reliability issues;tracking SSC unavailability;trending key parameters (condition monitoring);10 CFR 50.65(a)(1) or (a)(2) classification and reclassification; andappropriateness of performance criteria for SSC functions classified (a)(2) and/or appropriateness and adequacy of goals and corrective actions for SSC functions classified (a)(1).In addition, the inspectors verified problems associated with the effectiveness of plant maintenance for risk-significant SSCs were entered into the licensee's corrective action program with the appropriate characterization and significance. Selected CARDs were reviewed to verify corrective actions were appropriate and implemented as scheduled.This inspection constituted one quarterly maintenance effectiveness inspection samples as defined in IP 71111.12.FindingsDivision 2 Residual Heat Removal Service Water System Outlet Flow Control Valve Lower Bonnet (Backseat) Bushing FailureIntroduction. The inspectors identified an unresolved item (URI) to further evaluate the events and causes of a failure of the Division 2 RHRSW system outlet Flow Control Valve (FSC) lower bonnet (backseat) bushing. Specifically, additional information was needed to determine if one or more performance deficiencies exist.Description. On October 23, 2017, the Division 2 RHRSW system was started to support weekly addition of biocide to the Division 2 RHR reservoir (ultimate heat sink) as a preventative measure to minimize raw water system fouling, which typically entailed running both Division 2 RHRSW pumps for approximately 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. Approximately 20 minutes after system startup, the control room received an overhead annunciator alarm for reactor building south west quad leakage to floor drain sump high along with indication that the reactor building south west quad sump pumps were running. A non-licensed operator was dispatched to the field to investigate the alarms and identified the Division 2 RHRSW outlet Flow Control Valve (FCV) (E1150F068B), located in the Division 2 RHR heat exchanger room in the reactor building, had a significant packing leak calculated to be approximately 16 gallons per minute. The leakage did not impact any other plant equipment in the local area and was captured by the Division 2 RHR heat exchanger room floor drains, which discharge into the reactor building south west quad room sump. Control room operators subsequently shutdown the Division 2 RHRSW pumps to stop the packing leakage and declared the Division 2 RHRSW system inoperable 14 The licensee formed an emergent issues team to further investigate the issue.Following valve disassembly and inspection, the licensee identified the valve lower bonnet (backseat) bushing no longer had sufficient thread engagement to remain in place and that the valve packing had been ejected from the valve stuffing box. A temporary modification was implemented to install a new backseat bushing welded directly to the valve bonnet. The system was subsequently returned to service on October 27, 2017.The Division 2 RHRSW outlet FCV is a safety-related, 24inch Powell globe valve with a motor operator. The primary safety function of the outlet FCV is to fully open to support heat transfer from the Division 2 RHR heat exchanger to the ultimate heat sink. The valve remains fully open during RHRSW pump operation (combined pump flow on the order of 10,000 gallons per minute) and generally is not throttled other than during initial startup of the pumps for a short period of time to help mitigate any potential water hammer events.The licensee completed a root cause analysis documented in CARD 1728611 at the end of the inspection period. The direct cause of the Division 2 RHRSW outlet FCVpacking leakage was determined to be the valve bonnet carbon steel threads corroded to the point of no longer functioning as an adequate mechanical connection. This resulted in the backseat bushing detaching from the valve bonnet allowing the packing to be ejected. The root cause was determined to be previous operating experience resolution for galvanic corrosion for valves in the safety-related service water systems was less than adequate resulting in a failure to recognize the vulnerability of galvanic corrosion on passive valve components. Contributing causes consisted of (1) RHRSW system operation produces significant valve vibration levels and periodic wetting and then drying conditions promoting a corrosive environment and (2) high levels of ionic impurities, as measured by chloride concentration, in RHRSW accelerate galvanic corrosion.The inspectors reviewed the root cause analysis report and several previous issues associated with the Division 2 RHRSW outlet FCV. Those events included, but were not limited to:On May 22, 2017, while placing Division 2 RHRSW in service for biocide treatment of the Division 2 RHR reservoir, the Division 2 RHRSW outlet FCVfailed to fully open. Troubleshooting discovered the direct cause was failure of the anti-rotation bushing stem key due to broken tack welds caused by high vibration during system operation. Previous troubleshooting on what was believed to be an indication issue on May 5, 2017 for the Division 2 RHRSW outlet FCV was inadequate and did not identify the failure of the anti-rotation key. As a result, the RHRSW FCV was returned to service on May 7, 2017, and subsequently failed on the next on-demand stroke on May 22, 2017. The licensee submitted Licensee Event Report 05000341/201700300 to report this event in accordance with 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by Technical Specification 3.7.1 and 10 CFR 50.73(a)(2)(v)(B) as a condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to remove residual heat. The system was returned to service on May 24, 2017. On September 28, 2017, while Division 2 RHRSW was out of service for planned valve performance monitoring, a partial stem-to-disc separation was detected.This additional monitoring was put in place based on previous industry operating experience of potential stem-to-disc separation following anti-rotation key failures. Upon further investigation and valve-disassembly, the stem-to-disc jam nut tack welds were found broken and the stem had unthreaded approximately 0.225 inches from the disc. Repairs were performed to replace the broken tack welds on the disc jam nut. The disc guide pin was also identified to be damaged and the licensee performed an engineering evaluation to permanently remove the disc guide pin. A broken tack weld was also noted on the backseat bushing which was repaired. The system was returned to service on October 3, 2017.The inspectors questioned the potential relationships between the aforementioned events given the potential for each event to have influenced the eventual failure of the backseat bushing. The inspectors needed additional information to determine whether or not the valve, including the backseat bushing, was subject to an over thrust condition as a result of one or a combination of irregular limit switch settings, anti-rotation key failure, broken and subsequent removal of the disc guide pin, stem-to-disc unthreading, and various broken tack welds. Other additional information was needed in order to determine:if the Division 2 RHRSW outlet FCV was of appropriate design for the known conditions of high vibrations, periods of cavitation on startup and shutdown, and a highly susceptible corrosive environment due to periods of wet and dry conditions with known dissimilar metals highly susceptible to galvanic corrosion;the technical basis behind not including globe valves in the corrosion monitoring program following previously noted and evaluated concerns of RHRSW system susceptibility from years past; andthe technical basis and management of chemistry controls on the RHR reservoirs.Because the licensee completed their root cause evaluation at the end of the inspection period and additional information was required to determine if one or more performance deficiencies exists associated with the various Division 2 RHRSW outlet FCV problems, this issue is being treated as an unresolved item pending receipt of additional information and subsequent inspector review. (URI 05000341/201700402, Division 2 Residual Heat Removal Service Water System Outlet Flow Control Valve Lower Bonnet (Backseat) Bushing Failure) |
| Site: | Fermi  |
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| Report | IR 05000341/2017004 Section 1R12 |
| Date counted | Dec 31, 2017 (2017Q4) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.12 |
| Inspectors (proximate) | T Briley P Smagacz B Bergeon G Hansen V Myers R Walton B Dickson |
| INPO aspect | |
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Finding - Fermi - IR 05000341/2017004 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Fermi) @ 2017Q4
Self-Identified List (Fermi)
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