ML19301F089

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AEOD/T513, Flooding of Safety-Related Valves in Pits, Technical Review Rept.No Further AEOD Action Planned
ML19301F089
Person / Time
Site: North Anna Dominion icon.png
Issue date: 11/07/1985
From: Zukor D
NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD)
To:
Shared Package
ML19301F083 List:
References
TASK-AE, TASK-T513 AEOD-T513, NUDOCS 8603120307
Download: ML19301F089 (6)
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{{#Wiki_filter:. AEOD TECHNICAL REVIEW REPORT

  • UNIT:

North Anna Unit 1 TR REPORT NO. AEOD/T513 DOCKET NO.- 50-338 DATE: November 7, 1985 LICENSEE: Virginia Power EVALUATOR / CONTACT: D. Zulor NSSS/AE: Westinghouse / Stone & Webster

SUBJECT:

FLOODING OF SAFETY-RELATED VALVES IN PITS EVENT DATE: Ja nua ry 28, 1985

SUMMARY

Between February 15 and 18, 1985, testing of the recirculation spray valves indicated that one of these valves was sticking in the 757 open position. Maintenance personnel found mineral deposits on the valve yoke nut and valve stem which prevented the valve from operating properly. The valve was Groundwater submerged and impurities in the water had solidified on the valve. infiltration is a chronic problem at the North Anna site. This particular problem does not appear to have generic implications. It can, however, have safety implications for specific sites. The resident inspector is tracking North Anna's resolution of the problem. INTRODUCTION AEOD identified an event which could cause a common mode failure of safety-related equipment at North Anna Units 1 and 2. Due to groundwater infiltration into the valve pits containing the outside containment recirculation spray pump suction valves, the valves in the pits frequently remain submerged for prolonged periods and impurities in the water solidify on tne valve stem rendering the valve inoperable. The purpost of this review is to determine if this problem is widespread and/or generic among other nuclear power plants. DISCUSSION On January 28, 1985, the licensee found that eight checi valves in the hydrogen removal system were not being tested as required by the station valve inservice testing program (Ref. 1). As a result, the licensee reviewed its inservice testing program and found six other vah es that were rot beino tested at the These valves correct frequency because the procedures had not been revised. included the following: two outside recirculation spray pump suction valves (MOV-RS-155A,B), two outside recirculation spray pump discharge valves (MOV-RS-156A,B), and two low head safety injection pump discharge valves (MOV-SI-1890C,D) to the reactor coolant system (RCS). The recirculation spray (PS) subsystem is an engir cered safety feature (ESF) used to remove heat from the containment followino a l0CA or a main steam line break (Pef. 2). Each RS subsystem is corprised of a recirculatinn spray pump, a recirculation spray cooler. and a 180-degree spray rina header. Each PS sub-system has a 50 percent capacity. Followinc a LOCA, water flows into the 6603120307 851109 PDR ADOCK 05000338 PDR g This report supports ongoing AEOD and NPC activities and does not represent the position or requirencnts of the er(;trsible NPC program office.

-7 containment sump. Once the recirculation mode of safety injection is actuated, the containnent sunp provides the suction points for the four recirculation sptay pumps -- two inside and two outside containment. The heat from the con-tainment sump water is removed by service water when it is pumped through the recirculation spray coolers. A drawing with the indicated flow paths of the RS subsystem may be found in Figure 1. Both suction isolation valves to the two outside recirculation spray pumps are in one valve pit and are separated by a baffle. The arrangement of the outside recirculation spray pumps is such that a break in the suction piping of the pumps does not affect the operation of the system. If a break in the suction piping occurred between the containment isolation valve and the pump, the valve could be closed and the redundant recirculation spray pump would be used. If a breat occurred in the piping between the con-tainnent and the valve, the pump could take suction directly from the floaded pit. No motion of the valves is necessary following a LOCA. The valves are only needed if a break occurs at a specific place in the suction piping and containment isolation is necessary. During power operation, these six valves remain open and are given a signal to open following an accident so no change of valve positicn is required for them to perform their safety function. These valves are tested quarterly as required by technical specification 3/4 6.3. The technical specification also requires that each unsecured valve in each recirculation spray subsystem be verified for correct position every 31 days. During the surveillance testing of the Unit I recirculation spray valves, the outside recirculation spray pump sucticn valve (MOV-RS-155 A), which is a 12-inch Velan gate valve, stuck in the three quarters open position when it was cycled. None of the other valves experienced similar problems. Upon examining the failed valve, maintenance personnel discovered mineral deposits on the valve yoke nut and valve sten which had caused the valve to malfunction. The motor operators for these salves were not submerged because they are located high above the valves themselves. The North Anna site has severe groundwater infiltration problems and the valve pit sumps cannot be kept drained. Consequently, the outside recirculation spray valves renain submerged a large percentage of the time. Temporary sump pumps are currently being used to keep the water level in the valve pits at a minimum. Keeping the basemat sump water level low seems to c!1eviate the probler somewhat. An improved dewatering systen for the site is being considered. All four outside recirculation spray pump suction valves were replaced during the 1984 Unit I and 2 refueling outages. The licensee's review of the mainte-nance histories of these valves since replacenent included three failures on Unit I and one failurt on Unit 2. TFese failures were not fcund in the SCSS or NPPDS data bcses. At The data bases were first searched for other events occurring at pWPs. (Pef. 3). Surry, the valve pits used to flood routinely due to maintenance worf Surry has since solved this problen and has not bad any events since 1983 when

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seven out of eight valves failed to open to admit service water to the recir-culation spray coolers (Ref. 4). Many events attributing valve inoperability to moisture intrusion or corrosion were found at other plants but it was not possible to determine whether this was due to actual immersion of the valve in water or the humid atmosphere surrounding the valve. Many events were due to electrical shorting of the notor operator. Tne search was then expanded to include events at EWRs. The events were similar to those described above for PWPs. Most of the events described rust or corrosion on the valves due to packing leals. Sone of the events attributed valve inoperability to the surrounding humid atmosphere which rusted the valve and caused corrosion on electrical parts of the motor operator. As mentioned above for PWRs, noisture intrusion or corrosion was frequently given as the cause of valve failure, and it was not possible to deternine whether or not the valve was cctually inmersed in water. No cases of external valve flooding which caused valve inoperability could be found for BWRs. The North Anna event would not have been reportable had a surveillance test not been nissed. Since single failure events have not been reportable as LERs since January 1,1984, some other plants were polled to see if they had or knew of plants that had similar flooding problems. No other similar problems were found. Followinc the February 9,1983 event at Surry Units 1 and 2 where seven out of eight valves failed to open to admit service water to the recirculation spray coolers due in shorted notor operators and corroded valves, the follow-up of the electrical portion of this event was made part of multi-plant action (MPA) B-60 review ior Surry (Pef. 5). The cperability of class lf electrical equipment, which includes the motor cperators of safety-related valves, is being studied as part of the resolution of USI A-24* which is being implemented as MPA B-60. The flooding of safety-related equipment at plants licensed prior to the implenenta-tion of the SRP is being studied unde; Generic Issue (GI) 77.** GI 77 will consider flooding of safety-related equipment due to groundwater seepage, rivers, lal< s, and rainfall for plants licensed prior to the fornalization of the standard review plan (SFP). Thus, GI 77 will not include consideration of the t' pes of problers ncticed at Surry or North Tnna. IINDINGS A review of the creratinc data indicated + hat nost of the events involving water affectinG the cperability of tho valves was a result of wett'nq the electrical componerts associated with the valve. Sone events were due u corrosion of the valve internals due to packing leaks. Very few events were found where external flooding of the valve caused valve inoperability. Thus, this problem does not appear to bt generic. USI A-24: Quelificaticn of Clas; IE O foty Pelated Equipment GI 77: Flooding of Saf ety Equir ient Corp 3rtront hy Eack-Flow Through Floor Drairs.

- The valve which failed at North Anna is a containment isolation valve and niust be available to close when called upon. The frequent immersion of this valve in water adversely affects its operability and its safety function. The licen-see is evalcating the situation to deternine if reliability of these va'.es can be improved. CONCLUSIONS AND SUGGESTIONS Although failures of motor operators are being considered as a generic issue, no evidence for widescale failures of safety-related valves themselves due to external flooding could be found. Therefore, the problem of flocding of valves in pits does not appear to be a generic problen. It could, however, be a site-specific problem depending upon the containment's location relative to the water table of the area and the capacity of the dewatering system at the site. Resolution of these problems should be handled on a plant by plant basis. The North Anna site appears to have a difficult time keeping the groundwater out of their plant sumps. Their use of temporary sump pumps to keep up with the problem may not be an adequate solution. The resident is tracking the licensee's actions to assure an adecuate resolution of this problem. No further AEOD action on this issue is planned.

REFERENCES:

(1) Licensee Event Report 85-002, Virginia Power Company, Porth Anna Unit 1, Docket No. 50-338, dated February 27, 1985. (2) Virginia Power Co., " Updated Final Safety Analysis Peport," Docket 50-338 and 50-339. (3) AEOD, " Valve Flooding Event at Surry," E303, February 16, 1983. (4) IE Infomation Notice No. 83 46, " Common-Pode Failures Degrade Surry's Recirculation Spray Subsystem," July 11, 1983. (5) U.S. Nuclear Regulatory Conrnission, " Unresolved Safety Issues Summary," NUREG-0606, Vol. 7, No. 2, May 17,1985. Available for Purchase from . National Technical information Service, Springfield Virginia 22161.}}

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