Part 21 Report - 1996-150

ACCESSION #: 9601050092 Public Service Electric and Gas Company E. C. Simpson Public Service Electric and Gas Company P.O. Box 236, Hancocks Bridge, NJ 08038 Senior Vice President - 609-339-1700 Nuclear Engineering DEC 28 1995 LR-N95244 United States Nuclear Regulatory Commission Document Control Desk Washington, DC 20555 Gentlemen: 10CFR21 INTERIM REPORT - SCRAM DISCHARGE VOLUME DRAIN VALVE FAILURE HOPE CREEK GENERATING STATION FACILITY OPERATING LICENSE NO. NPF-57 DOCKET NO. 50-354 Pursuant to the notification requirements of 10CFR21.21(a)(2), Public Service Electric & Gas Company (PSE&G) hereby provides the attached interim report regarding failure of Scram Discharge Volume (SDV) drain valve 1BFHV-F011. This failure is considered potentially reportable in accordance with 10CFR21. However, further evaluation is required to determine the root cause of this failure, and if this failure mechanism constitutes a Deviation as defined in 10CFR21.3(e). Therefore, a determination whether the condition is reportable under 10CFR21 can not be made at this time. The attached provides a summary of the results of the investigation completed to date, and actions planned to evaluate this deficiency and determine reportability in accordance with 10CFR21. The final determination of reportability will be completed prior to restart of Hope Creek from the current refueling outage presently scheduled for February 6, 1996. Please contact us should you have any questions regarding this submittal. Sincerely, Attachment DEC 28 1995 Document Control Desk 2 LR-N95244 c Mr. T. T. Martin, Administrator - Region I U. S. Nuclear Regulatory Commission 475 Allendale Road King of Prussia, PA 19406 Mr. D. Jaffe, Licensing Project Manager - Hope Creek U. S. Nuclear Regulatory Commission One White Flint North 11555 Rockville Pike Mail Stop 14E21 Rockville, MD 20852 Mr. R. Summers (X24) Senior Resident Inspector Mr. K. Tosch, Manager, IV Bureau of Nuclear Engineering 33 Arctic Parkway CN 415 Trenton, NJ 08625 LR-N95244 ATTACHMENT 10CFR21 INTERIM REPORT - SCRAM DISCHARGE VOLUME DRAIN VALVE FAILURE HOPE CREEK GENERATING STATION FACILITY OPERATING LICENSE NO. NPF-57 DOCKET NO. 50-354 I. BACKGROUND Scram Discharge Volume (SDV) Drain Valves (1BFHV-F011 & F181) are redundant air operated valves installed in series that are normally open to keep the SDV drained, and are automatically closed following a reactor scram. The SDV drain valves are 2 inch 2500 lb. globe valves that were manufactured by Hammel Dahl which is now owned and serviced by Neles Jamesbury. These valves are designed such that in the event of a single failure, isolation of the SDV drain line is ensured to prevent the loss of reactor coolant inventory. Should failure of both SDV drain valves occur, this could result in a flow path from the reactor pressure vessel through the SDV. While performing the monthly surveillance test in accordance with Technical Specification 4.1.3.1.1 for SDV drain valve 1BFHV-F011 on September 9, 1995, the monitoring instrumentation did not actuate to indicate that the valve was fully closed. Further investigation determined the measured valve travel was 7/8 inch instead of the expected 1-1/8 inch travel. When the valve was stroked a second time, it was observed that the spring tension on the actuator was completely relaxed when the valve was in the closed position. This prevented the valve from going to the fully closed position. It was concluded at that time that the cause of the incomplete closure was due to the spring adjuster on the valve stem backing off the spring, possibly due to vibration. The spring adjuster was tightened to provide positive valve closure. The valve was then retested and declared operable within the required Technical Specification allowed outage time of 24 hours. II. EVALUATION An evaluation of possible causes of the failure has been performed. The evaluation included (1) a review of plant documentation including incident reports/problem reports, work orders and drawings, (2) a review of vendor documentation including drawings and engineering data, and (3) discussions with site personnel and valve engineering personnel. It was initially identified that the cause of the failure of SDV drain valve 1BFHV-F011 was the result of the spring adjuster Page 1 of 5 LR-N95244 ATTACHMENT backing off the spring. Further evaluation identified three (3) possible failure mechanisms including changes in the spring adjuster setting during normal operation which could result in loss of spring compression. Loss of spring compression could result in the valve sticking open due to hydraulic forces present when the valve is required to close following a reactor scram. The following is a discussion of the three (3) possible failure mechanisms: Spring Mis-adjustment - Following actuator disassembly (such as for diaphragm replacement), reset of the spring adjuster is required. Following completion of some maintenance activities such as replacement of valve packing, resetting of the spring adjuster may be performed. If the adjustment is not performed in accordance with the vendor's instruction, the adjustment may result in the spring being nearly or completely unloaded with the valve in the closed position. Change in spring Adjuster Setting Due to Normal Operation - The existing valve design does not include a locking device to maintain the spring adjuster in its set position. Vibration or normal cycling of the valve may result in the spring adjuster backing out from its original set position. This failure mechanism could also be a result of spring mis-adjustment as discussed above if the spring is nearly or completely unloaded with the valve in the closed position. The design relies on frictional loads between the threads in the actuator stem and spring adjuster to prevent movement of the spring adjuster. Spring Relaxation - The stresses of the actuator spring are greatest in the normally open position. If the stresses at this position exceed the yield point due to mis-adjustment, a defective spring or a design deficiency, compression set may occur which would reduce the compression in the closed position. If the compression set changes over time, the spring compression may reduce sufficiently to keep the valve from fully closing. III. DISCUSSION Evaluation has determined that the three possible failure mechanisms discussed above could affect the SDV drain valves 1BFHV-F011 and 1BFHV- F181, and SDV vent valves 1BFHV-F010 and 1BFHV-F180. Page 2 of 5 LR-N95244 ATTACHMENT A review of operating experience for the SDV drain valves was performed to determine if evidence exists to directly support the failure mechanisms proposed above. A review of monthly and quarterly surveillance test results was performed. In general, the SDV drain valves have tested satisfactorily, and no failures were identified related to incomplete valve closure. The five second time delay between the closure of the inboard and outboard drain valves sometimes requires readjustment. Readjustment typically consists of slightly changing the regulated air pressure so that the time needed to bleed down the air is changed. Some maintenance has been performed on valve 1BFHV-F011 that would require reset of the spring adjuster from initial receipt from the manufacturer. In 1989, the diaphragm was replaced which required spring removal. In 1991, the actuator was rebuilt which required spring readjustment. As of the date of the failure, no work activities on the valve were identified since 1991 that would have reset the spring adjuster. In addition, no preventive maintenance requirements were identified by the vendor for the valves to ensure proper spring adjustment is maintained. A failure of 2500-lb Hammel Dahl SDV vent and drain valves was reported to the NRC (see NRC Information Notice 86-82, Revision 1). These failures were attributed to the manual handwheel not being positioned in the neutral position which resulted in the deformation and disengagement of the coupling between the actuator stem and valve stem when the valve was operated. This failure does not appear to be a possible cause for loss of spring compression. This model actuator and other similar models are not provided with locking devices. The design relies on frictional loads between the threads in the actuator stem and spring adjuster to prevent movement of the spring adjuster. The valve is normally open which is when the spring is under its maximum compression. The frictional loads resisting loosening are also maintained during this period. Neles-Jamesbury does not use a locking device on any spring adjuster for the actuator model in question, or the new actuator model that has replaced it. Neles-Jamesbury has indicated that valve/actuator combinations of this configuration have never been reported to have lost spring compression either by the adjuster becoming loose or spring relaxation. Seismic qualification testing on a similar 2 inch valve with a frame yoke actuator has been performed. The results showed that the valve was operating acceptably after the vibration test. Although not specifically identified for Page 3 of 5 LR-N95244 ATTACHMENT inspection, no indication was given that the stem adjuster loosened during the test. Industry operating experience indicates that helical springs in compression over an extended period of time can develop some relaxation or compression set (See NRC Information Notice 89-43). Based on the vendor information for this model valve, a compression set of 0.3 inches (with a nominal free spring length of 9 inches) is sufficient to unload the spring in the closed position. IV. SUMMARY AND CORRECTIVE ACTIONS Both SDV drain valves 1BFHV-F011 and 1BFHV-F181 and the SDV vent valves 1BFHV-F010 and 1BFHV-F180 are susceptible to each of the three possible failure mechanisms. The identified failure could have resulted from a deficiency in the design of the valve and actuator including the spring, or due to lack of proper valve maintenance requirements. However, insufficient information is presently available to determine the specific root cause of the failure, and if this failure mechanism constitutes a Deviation as defined in 10CFR21.3(e). Therefore, a determination whether the condition is reportable under 10CFR21 can not be made at this time. Further investigation is ongoing to identify the root cause and necessary corrective actions, and determine reportability. This investigation will consist of the following: (1) measuring valve stroke versus air pressure for each of the four affected SDV drain and vent valves both with and without stem packing loads applied, (2) removing the spring from valve 1BFHV-F011, and measuring the physical dimensions, spring rate and selected material properties, and (3) confirming that the spring and spring adjuster design are adequate to maintain spring compression for valve closure. Items 1 through 3 above will be completed prior to restart of Hope Creek from the current refueling outage presently scheduled for February 6, 1996. The results of Items 1 through 3 will be used to complete the root cause determination, and the evaluation to determine if this condition is reportable under 10CFR21. The final determination of reportability will be completed prior to restart. Page 4 of 5 LR-N95244 ATTACHMENT To prevent the spring adjuster from backing off the spring resulting in loss of spring compression, PSE&G will also install a locking device for the spring adjuster on the SDV vent and drain valves. This modification will also be completed prior to restart. Page 5 of 5 *** END OF DOCUMENT ***

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