ML19322E282

Electrical Instrumentation & Control Aspects of Override of Containment Purge Valve Isolation & Other Safety Feature Signals, Informal Rept

ML19322E282
Person / Time
Site:	Salem
Issue date:	11/30/1979
From:	Udy A EG&G, INC.
To:	Shemanski P Office of Nuclear Reactor Regulation
Shared Package
ML19322E280	List: ML19322E282
References
CON-FIN-A-6256 EGG-EA-5048, RE-A-79-138, NUDOCS 8003270090
Download: ML19322E282 (10)

Text

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U ATTACHMENT

& EGnG ,, L FOAM EO4G 3ee INTERIM REPORT Accession No.

Report No. EGG-EA-5048 RE-A-79-138 Contract Program or Project

Title:

Electrical, Instrumentation and Control System Support Subject of this Document:

Electrical, Instrumentation and Control Aspects of the Override of Containment Purge Valve Isolation and other Safety Feature Signals, Salem Generating Station, Unit Nos. 1 and 2, Docket Nos. 50-272 and 50-311, TAC 08993 Type of Document:

Informal Report Author (s):

A. C. Udy Date of Document:

< November 1979 Responsible NRC Individual and NRC Office or Division:

Paul Shemanski, Division of Operating Reactors This document was prepared primarily for preliminary or internal use. it has not received full review and arc-' val. Since there may be substantlve changes this document should not be considerea smal.

EG&G Idaho, Inc.

Idaho Falls, Idaho 83401 Prepared for the U.S. Nuclear Regulatory Commission and the U.S. Department of Energy Idaho Operations Office NRC FIN No.

A6256 l

INTERIM REPORT

i 1060F TECHNICAL EVALUATION REPORT ELECTRICAL, INSTRUMENTATION, AND CONTROL ASPECTS OF THE OVERRIDE OF CONTAINMENT PURGE VALVE ISOLATION AND 0"'HER SAFETY FEATURE CIGNALS SALEM GENERATING STATION, UNIT NOS. 1 AND 2

, Docket Nos. 50-272 and 50-311 TAC 08993 s November 1979 A. C. Udy EG6G Idaho, Inc.

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CONTENTS

1.0 INTRODUCTION

. . . . . . . . ..............,.,, 1 2.0 EVALUATION OF SALEM GENERATING STATION UNITS 1 AND 2 . . . . . . 2 ,

2.1 Review Criteria . . . . .......... ........ 2 2.2 Containment Ventilation Isolation Circuits Design Description . . . . . . . . . . . . . . . . . . . . . . . . 3 2.3 Containment Ventilation Isolation System Design Evaluation . . . . . . ............... ... 4 2.4 Other Engineered Safety Feature System Circuits . ..... 6

3.0 CONCLUSION

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4.0 REFERENCES

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TECHNICAL EVALUATION REPORT ELECTRICAL, INSTRUMENTATION, AND CONTROL ASPECTS OF THE OVERRRIDE OF CONTAINMENT PURGE VALVE ISOLATION AND OTHER SAFETY FEATURE SIGNALS SALEM GENERATING STATION, UNIT NOS. 1 AND 2

1.0 INTRODUCTION

Based on the information supplied by Public Service Electric and Gas Corporation (PSE&G), this report addresses the electrical, instru-

, mentation, and control systems design aspects of the Containment Venti-lation Isolation (CVI) system and other Engineered Safety Feature (ESF) system functions for the Salem 1 and Salem 2 plants. PSE&G has verified that these systems are identical in both plants1 .

Several instances have been reported where the automatic closure

, of the containment ventilstion or purge isolation valves would not have I

occurred because the safety actuation signals were manually overridden or blocked during normal plant operations. These events resulted from a lack of proper management controls, procedural inadequacies, and circuit design deficiencies. PSE&G was one of the licensees who first '

reported a reportable occurrence of this type . It was found that, when the CVI system is reset without removing the isolation actuation signal, additional Safety Injection (SI) signals are prevented from l initiating containment isolation. Administrative controls were imposed i

until a design change could be incorporated.

l These events also brought into question the mechanical operability of the valves themselves. These events were determined by the Nuclear

. Regulatory Commission (NRC) to be an Abnormal Occurrence (#78-05) and accordingly, were reported to Congress.

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l As a follow-up of this Abnormal Occurrence, the NRC is reviewing the electrical override aspects and the mechanical operability aspects of containment purging for all operating reactors. On November 28, 1978, the NRC issued a letter, " Containment Purging During Normal Plant 1

i Operation" to all Boiling Water Reactor (BWR) and Pressurized Water 4

Reactor (PWR) licensees. PSE&G responded to the letter saying that, " Manual override circuitry has been changed to prevent the by-passing of the safety signal." Howevar, Reference 5 reported another reportable occurrence where a radiation channel alarmed but did not initiate containment isolation. This was attributed to failure to reset another radiation channel alarm prior to resetting the CVI system.

l PSE&G states in Reference 6 that "Our design is no longer subject to override conditions which could prevent automatic valve closure during a LOCA." l 2.0 EVALUATION OF SALEM CENERATING STATION UNITS 1 AND 2 2.1 Revicw Criterion a

The primary intent of this evaluation is to determine if the fol-loving requirements are met for the safety siF nals to all purge and ventilation isolation valves:

(1) Criterion No. 1--The overridings of one type of -

safety actuation signal (e.g., radiation) must not cause the blocking of any other type of safety actuation signal (e.g., pressure) to the isolation valves.

(2) Criterion No. 2--Sufficient physical features (e.g.,

l key lock switches) are provided to facilitate ade-I quate administrative controls.

(3) Criterion No. 3--A system level annunciation of the overridden status is provided for every safety system impacted when any override is active.

Incidental to this review, the following additional NRC design criteria were used in the evaluation:

(a) The following definition is given for clarity of use in this evaluation:

Override: The signal is still present, and it is blocked in order to perform a function contrary to the signal.

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(1) Criterion No. 4--Diverse signals should be provided l to initiate isolation of the containment ventila- i tion system. Specifically, containment high radi-ation, safety injection actuation, and containment high pressure should automatically initiate CVI.

l (2) Criterion No. 5--The instrumentation and control systems provided to initiate CVI should be designed and qualified as safety grade equipment.

(3) Criterion No. 6--The overriding or resettinga og the isolation actuation signal should not cause the automatic reopening of any isolation or purge valve.

2.2 Containment Ventilation Isolation Circuits Design Description Each of the Salem units has two ESF trains which close indepen-dently and separately the inboard and outboard isolation valves. The valves are opened by manual control only. The initiating signals which j o override any opening signal are listed below:

Manual

1. Pressing either of two momentary pushbuttoa switches will actuate both trains of contaiment isolation phase A (all non-essential process lines) and CVI.

2. Simultaneous pressing a single pair (of two pairs) of momentary pushbutton switches will actuate both trains of containment spray and CVI.

Either of the above two signals, once initiated, will continue until manually reset by a separate momentary pushbutton switch. (A single switch per train resets either signal.)

Automatic 1

1. Any of the following containment radioactivity levels exceeds its setpoint:

(a) The following definition is given for clarity of use in this

. evaluation:

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' Reset: The signal has come and gone, and circuit is being cleared in order to return it to the normal condition.

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a. Air particle monitor

b. Iodine monitor

c. Radioactive gas moc' tor

2. SI signal, which may be initiated by any of the following

a. Pressuriser level and pressure low

b. Containment pressure high

c. Steam line differential preseure high

d. Steam line flow high coincident with either Tay, low or steam line pressure low.

The actuation signal resulting from the automatic initiation signal can be reset from the ESF panel to allow manual opening of the CVI valves.

Manual control of the valves is by momentary contact pushbutton

( switches. The control system is such that the automatic closure sig-e nals will close the valves even if the "open" pushbutton is depressed.

The control system also prevants valve opening except when the "open" pushbutton is erercised, thus preventing reopening of the valves when the "close" signal is removed. Loss of power to the control system or ,

loss of air to the solenoid valve closes the isolation valves. Valve position lights, open and closed, are provided on the control console.

2.3 Containment Ventilation Isolation System Design Evaluation Each train of CVI in the solid state ESF has a retentive memory with " manual reset." Briefly, sM uld an actuation signal be present, I

and then a " manual reset" perfor d, the " manual reset" signal remains present as long as the actuation signal is present, thus functioning as a signal override, as defined in Section 2.0 of this report.

Each CVI train is automatically actuated by either a high radiation l .

signal or a safety injection signal through an "0R" gate. If either l

l signal actuates the CVI and then is overridden, the other signal then l

could not possibly actuate the CVI until after all actuation signals 1

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are gone. The fact that an actuation signal is overridden is not annunciated. Both the signal blocking and the non-annunciation is not l in conformance with NRC criteria.

After the first reportable occurrence , a spare SI actuation  :

relay contact was placed in series with the solenoid valve control l power for Salen Unit 2, in addition to the connection through the "OR" )

gate. This was also recently completed for Salem Unit 1 . This permits any SI actuation signal to additionally actuate the CVI regard-less of the condition of the radiation signal and override. Blocking of the SI signal to deenergize safety injection and to allow opening of the CVI valves will not prevent the radiation channels from initiating l isolation nor will this action open the CVI valves as these can be  !

1 opened only by pushbutton switch. These features are now in conform- l ance with NRC criteria.

b bovever,usingthemanualresettooverrideoneradiationsignal overrides the other five signals also. Since the same type signal is involved, this is in conformance with the NRC criteria. Each radiation signal is annunciated separately, as is the operational bypass. This will alert the operator of potential problems. .

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Additionally, should the SI signal be overridden at the CVI reten-tive memory instead of the normal "SI blocked function," the radiation signals would be bypassed. Administrative controls are required here.

The four signals for SI actuation (as listed in Section 3) agree I with the NRC position that inputs to safety actuation circuits should be diverse.

Additionally, the CVI circuit monitors the status of two channels

, or a.ontainment radiation level adding further diversity to CVI actua-tion 1. Each radiation channel monitors (a) particulate level, (b)

. iodine level, and (c) radioactive gas level. One channel monitors the containment, while the other channel monitors the plant stack, both via 5

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sample lines which are blocked in the event of high pressure (the pres-surs signals are independent of those for the SI actuation). Should any one of the six radiation levels (two locations, three variables jach) be high, CVI is initiated on both trains. These radiation moni-tors are not located inside of containment, and are not relied on to monitor containment radiation in a post-accident condition (since the sample lines are isolated from containment on a high pressure signal).

Isolation status lights for the radiation monitoring system are adja-cent to the radiation readouts to indicate if the monitor sample streams are functional. The monitors are seismically qualified and testable, and are powered by vital AC power buses.

l The criteria that sufficient physical features be present to pro- l vide for adequate administrative controls is not met as the pushbutton  !

switches for actuating resets, overrides, and valve opening are not protected from accidental actuation.

2.4 Other Engineered Safety Feature System Circuits The CVI is the only portion of the ESF where two signals were "0R"ed together to a common retentive memory with manual reset. This .

reset affects no other portion of the ESF system. Other ESF circuits are not prone to the same failure mechanism.

3.0 CONCLUSION

S The electrical, instrumentation, and control design aspects of the containment ventilation isolation valves and other ESF signals for the Salem plants were evaluated using tne design criteria stated in Sec-tion 2.0 of this report. We determined that (a) the ESF system is.not now prone to overriding actuation signals should another signal be

, overridden to establish manual control (per criteria 1), (b) suffici-

. ently diverse actuation signals are present to actuate CVI, and (c) the overriding of or the release from an isolation actuation signal will not cause automatic reopening of the isolation valves.

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Provided that (a) spring loaded transparent covers are installed on the pushbutton control and override switches, (b) provisions for system level annunciation of overridden actuation signals are made, and (c) the radiation channels be qualified as safety grade equipment, the Salem 1 and Salen 2 plants would be in full compliance with the NRC criteria and guidelines. These items have been discussed with the licensee . PSE&G has not voluntarily agreed to these changes; how-ever, the licensee has expressed willingness to make the changes if they are required by the NRC.

We recommend that PSE&G be required to submit plans to bring Salem Unit Nos. I and 2 into conformance with Criterions 2, 3, and 5 as stated in Section 2.0 of this report.

4.0 REFERENCES

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1. Telecon, J. T. Beard, NRC-DOR, J. Gagliardi, PSE&G, A. C. Udy, EG&G Idaho, September 9, 1979.

2. PSE&G 1etter, F. P. Labrizzi, to B. H. Utier, NRC license No. DPR-70, Docket No. 50-272, Reportable Occurance 78-61/01T, September 19, 1978.

3. NRC/ DOR letter (A. Schwencer) to all BWR and PWR licensees,

" Containment Purging During Normal Plant Operation," dated November 28, 1978.

4. PSE&G 1etter, F. P. Librizzi to A. Schwencer, NRC, " Containment Purging During Normal Plant Operation," Salem Generating Station, Unit No. 1, Docket No. 50-171, December 21, 1978.

5. PSE&G letter, F. P. Librizzi to B. H. Grier, NRC, License I N3. DPR-70, Docket No. 50-272, Reportable Occurrence 79-11/01T, January 30, 1979.

6. PSE&G 1etter, F. P. Librizzi to A. Schwencer, NRC, " Containment Purging During Normal Plant Operating, Salem Generating Station, Unit No. 1, Docket No. 50-272, Jrnuary 30, 1979.

7. Telecon, J. T. Beard, NRC-DOR to J. Gagliardi, PSE&G, September 13, 1979.

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