ML18095A403

Part 21 Rept Re MSIV Design Deficiency at Plant.Design Spec Provided by Westinghouse Did Not Specify Requirement to Provide Seal in Capability & Util Design Process Failed to Recognize Deficiency

ML18095A403
Person / Time
Site:	Salem
Issue date:	08/02/1990
From:	Crimmins T Public Service Enterprise Group
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
REF-PT21-90 NLR-N90160, NUDOCS 9008100211
Download: ML18095A403 (4)

Text

• Public Service Electric and Gas Company Thomas M. Crimmins, Jr. Public Service Electric and Gas Company P.O. Box 236, Hancocks Bridge, NJ 08038 609-339-4700 Vice President - Nuclear Engineering AUG O2 1990 NLR-N90160 U.S. Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20555 Gentlemen; 10 CFR 21 REPORT REGARDING MSIV DESIGN DEFICIENCY SALEM GENERATING STATION UNIT NOS. 1 AND 2 DOCKET NOS. 50-272 AND 50-311 Public Service Electric And Gas (PSE&G) hereby submits, in accordance with the requirements of 10 CFR 21.21, a description of the circumstances contributing to the recently identified design deficiency in the Main Steam Isolation Valve (MSIV) closure circuitry. Attachment 1 to this transmittal contains a summary of the information obtained to date rel~tive to this condition. A verbal report was communicated to NRR and NRC Region I personnel on July 19, 1990 at 3:30 pm. On July 25, 1990, PSE&G informed NRC that this written follow-up was being delayed due to additional concerns pertaining to MSIV operation.

Those issues are still under review and as such, are not specifically addressed in this submittal.

If you should have any question regarding the attached information, please feel free to contact us.

Attachment

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Document control Desk 2 AUG 0 2 1990 NLR-N90160 c Mr. J. c. Stone Licensing Project Manager Mr. T. Johnson Senior Resident Inspector Mr. T. Martin, Administrator Region I Mr. Kent Tosch, Chief New Jersey Department of Environmental Protection Division of Environmental Quality Bureau of Nuclear Engineering CN 415 Trenton, NJ 08625

Background

• ATTACHMENT 1 On June 28, 1990, Salem Unit 2 experienced a reactor trip.

During the transient, control room operators attempted to close the 4 Main Steam Isolation Valves (MSIV) by use of the momentary push-buttons on the Safety Injection console. The initial attempt resulted in closure indication only two of the four MSIVs. A subsequent attempt was successful in closing the remaining valves when the operator depressed and held the closure push-button. Subsequent review of the event and the closure circuitry identified; 1) the 2 valves which failed to close had drifted off the open limit switch, and 2) with the valve off the open limit switch, the closure circuitry does not seal in the closure signal. This latter condition is a deviation from the requirements of IEEE 279, which states that once actuated, the actuated function should continue to completion.

The design of the closure circuit was developed by PSE&G on the basis of design specifications provided by Westinghouse via PSE-300/8 dated September 12, 1969. This document and the corresponding Logic Diagram (5651Dll, sheet 8), did not specify a requirement to provide seal-in capability for the MSIV closure circuit. Other RPS signals delineated in these documents did contain specific requirements for seal-in capability. In a May 1971 revision to the Westinghouse generic design specification (CPA4-300/8), specific requirements for seal-in capability for MSIV closure were specified. PSE&G has been unable to determine if the revised specification was transmitted by Westinghouse to PSE&G. It is clear however, that the revised design requirements have, as yet, not been incorporated into the referenced logic diagram.

Based on the above discussion, we have concluded that the ambiguity in the Westinghouse specification contributed to the

_design deficiency in the MSIV closure circuit and the PSE&G design process failed to recognize this deficiency and provide the required seal-in capability. The MSIV, Westinghouse design specification and the PSE&G design activity are considered a "Basic Component" under 21.3.(1) and 21.3.(3). A "defect" as defined in 21.3.4.(d).(1) exists in that, had this design deficiency remained undetected, the potential existed for a common mode failure of the MSIVs to close. A common mode failure of the MSIVs would create a "Substantial Safety Hazard" in that the consequences associated with main steam line breaks inside and outside containment would be substantially more severe than previously predicted.

• This deficiency exists for the closure circuits of the MSIVs at Salem Units 1 and 2. We have determined that electrical seal-in of a closure signal does not occur under the following conditions; 1) an automatic actuation signal is received when the valve is less than full open, or 2) manual closure is initiated from the momentary push-buttons on the Safety Injection console with the valve less than full open.

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• • f.

As such, the potential for common mode failure exists only when the valves are in mid-position.

PSE&G has completed a review of applicable accident scenarios and determined that seal-in of the circuit will be accomplished inherently (i.e. the duration of the signal exceeds the closure time of the MSIV) for all MSLB scenarios except the rupture of a main steam line outside containment. For this scenario, the initiating signal is the high steam flow coincident with either low Tavg or steam line pressure. As the MSIV closes, the signal will reset at 40% of rated steam flow. An engineering analysis of valve closure capability for this condition was indeterminate.

As such, a modification to the circuit is being made to assure that the closure signal for this scenario seals-in. This modification would cause the closure signal to seal-in and thereby maintain the vent valves open until the MSIV is in the fully closed condition, at which time the vent valves will reset.

As was mentioned previously, the initial identification of this problem resulted from two valves having drifted from the full open position. A review of the MSIV operating history for both units indicates that the frequency of drift on Salem Unit 2 was substantially higher than that for Unit 1. An investigation into the root cause of the drift identified several maintenance issues which have been addressed on Unit 2 as part of the present forced outage. Inspections have been conducted at Salem Unit 1 to assure that similar maintenance problems do not pose an immediate concern. Required maintenance is being performed as part of the present forced outage of Unit 1.

NLR-N90160 2