ML18100B191

Initial Part 21 Rept Re Deficiency in Signal Summators PM-505B & PM-506B Supplied by Westinghouse.Design Changes Implemented & Operators Made Aware of Affects of Power Supply Transient on Summator Operability

ML18100B191
Person / Time
Site:	Salem
Issue date:	06/30/1994
From:	Danni Smith, Thomson F Public Service Enterprise Group
To:	NRC
References
REF-PT21-94 NUDOCS 9407120141
Download: ML18100B191 (3)

Text

SENT BY= 6-30-94 ; 13:35 ; PSE&G LIC~Rf.G-i 301 8165151 :# 11 3 .

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e INITIAL 10CFR21 NO IFICATION HIGH STEAM LINE FLOW SI INSTRUMENTATION SIGNAL SUMMATORS PM- 05~ AND SOGB PUBLIC SERVICE ELECTR:C AND GAS CO.

SALEM GENERATING STATION:UNITS 1 ANO 2 The following is a summary of the re 'ults of PSE&G'S evaluation in accordance with 10CF.R21 concernin' a deficiency in signal summators PM-SOSB and PM-506B suppli 'd to PSE&G by Westinghouse.

These signal sumrnators were found to jsaturate high when the summators lose power and are then re 'nergized. These signal summators provide the setpoint signa i to high steam liile flow comparators that generate the high s earn line flow Safety Injection {SI) signal to Reactor Pro :ection System Trains A and B. SI actuation occurs as a result '.f high steam line flow coincident with Low-Low Tave or Low team Line Pressure.

Due t.o the recent spurious SI event '.n April 7, 1994, testing of signal summators PM*SOSB and 506B wa. initiated to determine if, on reactor t*rip, the signal summator : setpoint would undershoot below the 40% steam flow setpoint. :t was believed that the undershooting of the setpoint may ha ;e been a contributor to the inadvertent SI event on April 7 whic

• was initiated on High Steam Line Flow coincident with Low Low Ta :e. During this testing, it was identified that should the signa i summators lose power, upon reenergizing, the surnmators setpoint output would saturate high.

Technical Specifications define the igh Steam Line Flow setpoint at 110%, and following a reactor tri :, the setpoint is automatically reduced to 40%. As a esult of the setpoint output saturating to a setpoint significant greater than the setpoint limit allowed by Technical Specifica ions when power is lost, a high steam line flow SI signal would ct be generated by the flow comparators. The period of time tha the summators would saturate high following a loss of po er and subsequent reenergizing has not been estimated. tThe summators are powered from independent vital instrument bus~es (uninterruptable power supplies) and inverters.

In addition, each vital instrument bu and its inverter are required to be operable in accordance: with Technical Specification 3.B.2.l during Modes 1-:. Upon a loss of normal AC power to a vital instrument bus (i.e., LOP), the inverter is designed to transfer to the vital DC ower supply with no significant interruption in power to he bus loads. Should an inverter failure occ:u:r such that powe. is lost and not restored, the affected protection channel fails~in the safe position satisfying the High Steam Flow coinci:ence logic. However, should an inverter failure or power tFansient occur to the summator power supply, with power sub_equently restored, the signal summator would saturate which 'ould temporarily render the

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summator inoperable. Assuming that ~saturation of the signal swnmator pre-exists, in the event o  ! a design basis accident r:.hat would require the initiation of a S  ; signal on H.ig1: Steam Flow coinciderit with either Low Low Tave 'or Low Steam Line Pressure (e.g., Main Steam Line Break), this Eeactor protective function could be lost considering a single ctive failure in the remaining operable instrument chann ~-

Therefore, following a design basis transient, independent failures of the safety related unint.rrupt:able power supplies could occur resulting int.he SI sign,l on high steam flow t:o be adversely affected due to summator o~tput saturation. Evaluation by PSE&G has determined that this de iciency could seriously compromise the ability of the signalisummators t:o perform their designated safety function while con:idering a single active failure. PSE&G has concluded that t*is deficiency is reportable in accordance with 10CFR21. \.

Prior to restart of Salem Unit 1 foltowing the April 7 event, design changes have been implementedl:to correct this deficiency.

Por Salem Unit 2, procedure changes £-ve been made and operators have been made aware of the affects  :£ a power supply transient on summator operability thereby incr *aeing the detectability of the malfunction. Technical Specific:: 'tion surveillance requirements are performed to detec the output potential of the summators and thus their operability : If a channel is determined to he inop~rable due to saturation, echnical Specification Table 3

• 3 - 3 requires the affected channel *o be placed in the tripped condition until the channel is resto ed to operable. At the present time, the signal summators a e considered operable for Salem Unit 2, and this deficiency is therefore not an immediate safety concern.

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