ENS 46060
ENS Event | |
|---|---|
04:00 Jul 1, 2009 | |
| Title | |
| Event Description | The information below is a summary of a report received via facsimile from GE Hitachi; Report MFN 10-192 dated July 1, 2010.
Background: A diaphragm used in a 1" HPCI turbine stop valve / mechanical trip hold valve operator failed at a domestic BWR 4 in July 2009. The failure resulted in a HPCI turbine lube oil leak, which was the indication that the diaphragm had failed. The BWR 4 plant completed an Apparent Cause Evaluation and concluded that a material defect in the diaphragm allowed the diaphragm to tear after being installed for 2 years 8 months. The diaphragm that failed was a Robertshaw (RS) part number 25471-A2, and was installed in a Robertshaw model VC-210 diaphragm control valve operator. The diaphragm was made from Buna-n rubber and was designed to have two layers of Dacron reinforcement fabric over all pressure bearing surface areas of the diaphragm. The diaphragms are manufactured by Chicago-Allis using a 2-plate compression mold process. The diaphragms are purchased as commercial grade and are dedicated by GEH and supplied as safety related under GE part number Q25471-A2. The failed diaphragm was manufactured in 2006. Discussion: Reinforcement fabric is considered a critical design requirement that is essential to ensure durability, reliability, and prevents tearing of the diaphragm material when these diaphragms are used in the HPCI turbine lube oil system as turbine trip and reset valves. An inspection was performed on six diaphragms, three manufactured in 2006 and three manufactured in 2008. All six of these diaphragms were found to have areas without fabric reinforcement. Inspection of the three samples from 2006 found non-uniform reinforcement. Inspection of the three samples from 2008 found all diaphragms were void of reinforcement in the sidewalls and inspection indicates that the reinforcement fabric was torn away from the inner sidewall during the manufacturing process. The inspections identified no diaphragms that were in full compliance with the design requirements for two layers of reinforcing fabric over all pressure bearing surfaces of the diaphragm. Safety Analysis: The failure of the HPCI turbine over-speed reset control valve's diaphragm would result in a loss of HPCI turbine lube and control oil through the failed diaphragm. Depending on the amount of oil lost and the system demands, this loss could ultimately result in a failure of the HPCI System. Failure is not imminent, but cannot be precluded. Other safety related equipment is sufficient to mitigate design basis events in the event of a loss of HPCI. Conclusion: Because of the similarity of the defects in all diaphragms inspected, it is credible to believe that this type of deviation from technical requirement also exists in other diaphragms manufactured by Chicago Allis and sold by GE as part number Q25471-A2 and 25471-A2Q, and as part of Control Valve Assembly DD233A3600P001. The identified defective diaphragms were present in two lots; one manufactured in 2006 and one in 2008. Based on the observations it is reasonable to believe that other diaphragms manufactured in 2006 and 2008 have similar deviations. GEH has been unable to determine if the identified manufacturing deviation exists in diaphragms manufactured prior to 2006. Since GEH is not able to rule out defects in diaphragms manufactured prior to 2006, it is credible to believe that similar deviations existed in diaphragms manufactured prior to 2006. In order to determine the possible extent of condition, all diaphragms in service or in stock at plants as spare parts inventory are suspect. Since the diaphragms have a designated service life of 5 years, and a shelf life of 10 years, the extent of condition is bounded by replacement of all diaphragms purchased by plants since 1995. GEH has evaluated the consequences of the failure of this diaphragm and concluded that this type of failure could result in the HPCI system not performing its safety function. The HPCI system is considered an essential safety related system. Failure of the HPCI system is considered a major degradation of essential safety related equipment. Therefore this condition is determined to be a Substantial Safety Hazard and is a Reportable condition per 10CFR Part 21. Recommended Action: GEH has evaluated the consequences of the failure of this diaphragm and concluded that this type of failure could result in the HPCI system not performing its safety function. The HPCI system is considered an essential safety related system. Failure of the HPCI system is considered a major degradation of essential safety related equipment. Therefore this condition is determined to be a Substantial Safety Hazard and is a Reportable condition per 10CFR Part 21. US Plants With Affected Diaphragms: Fermi 2 Limerick Peach Bottom Duane Arnold Cooper Susquehanna Brunswick Hatch Browns Ferry |
| Where | |
|---|---|
| Ge Hitachi Nuclear Energy Wilmington, North Carolina (NRC Region 1) | |
| Organization: | Ge Hitachi Nuclear Energy |
| Reporting | |
| 10 CFR 21.21 | |
| Time - Person (Reporting Time:+8765.45 h365.227 days <br />52.175 weeks <br />12.007 months <br />) | |
| Opened: | Dale Porter 09:27 Jul 1, 2010 |
| NRC Officer: | Bill Huffman |
| Last Updated: | Jul 1, 2010 |
| 46060 - NRC Website | |
Ge Hitachi Nuclear Energy with 10 CFR 21.21 | |
WEEKMONTHYEARENS 464292010-11-18T05:00:00018 November 2010 05:00:00
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