ML20010E423

Technical Evaluation Rept:Electrical,Instrumentation & Control Aspects of Override of Containment Purge Valve Isolation & Other Safety Feature Signals.

ML20010E423
Person / Time
Site:	Brunswick
Issue date:	07/31/1980
From:	Udy A EG&G, INC.
To:
Shared Package
ML20010E420	List: ML20010E423
References
CON-FIN-A-6256 1179F, NUDOCS 8109040112
Download: ML20010E423 (11)

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1179F TECHNICAL EVALUATION REPORT ELECTRICAL, INSTRUMENTATION, AND CONTROL ASPECTS OF THE OVERRIDE OF CONTAINMENT PURGE VALVE ISOLATION AND OTHER SAFETY FEATURE SIGNALS BRUNSWICK STEAM ELECTRIC PLANT UNIT NOS.1 AND 2 Do c. e t No s. 50-3 25 and 50-3 24 .

July.1980 A . C . Ud y Reliability and Statistics Branch Engineering Analysis Division j

EG&G Idaho, In c .

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TAC Nos. 10184 and 10183 8109040112 810826 PDR ADOCK 05000324 P PDP .

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ABSTRACT Several instances have been reported where the automatic closure i

of the containment ventilation or purge isolation valves would not have occurred because the safety actuation signals were manually overridden or blocked during normal plant operations. This report addresses elec-trical, instrumentation, and control design aspects for these valves, and the ability of the unit containment ventilation system to isolate on several diverse parameters. Other related systems were audited to the same guidelines.

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FIN No. A6256 EICS Support ii

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, CONTENTS

1.0 INTRODUCTION

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2.0 EVALUATION OF BRUNSWICK STEAM ELECTRIC PIANT UdITS 1 AND 2 . . . . . . . . . . .. . . . . . . =. . . .. . 2

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. laview Guidelines . . . .. . . . . . . .-. . ... . .. . 2

.2 Containment Ventilation Isolation Circuits Design Description . *

. . . . . .. .. . . . . .. . ..... .. 3 2.3 Containment Ventila tion Isola tion System De sign Eva luat .on d

. . . . . . ..... . . . . . . .. . .. .. 5 2.4 other Related Engineered Safety Feature System Circuits . . . . . . . . ... . . . .... ... .... 6 i

3.0

SUMMARY

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4.0 REFERENCES

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TECHNICAL EVALUATION REPORT ELECTRICAL, INSTRUMENTATION, AND CONTROL ASPECTS OF THE OVERRRIDE OF CONTAINMENT PURCE VALVE ISOLATION AND OTHER SAFEIY FEATURE SIGNALS BRUNSWICK STEAM ELECTRIC PLANT UNIT NOS. 1 AND 2

1.0 INTRODUCTION

Based on the information supplied by Carolina Power and Light Company (CP&L), this report addresses the electrical, instrumentation, and control systems dasign aspects of the Containment Ventila tion Iso-lation (CVI) system and other related Engineered Safety Feature (ESF) sys tem functions for the Brunswick 1 and Brunswick 2 units. The Final Safety Analysis Report (FSAR) indicates that these systems are identi-cal in both units, and provides additional design information.

Several instances have been reported where the automatic closure of the containment ventila tion or purge isolation valves would not have occurred because the safety actuation signals were manually overridden or blocked during normal plant operations. These events resulted from a lack of proper management contro1s, procedural inadequacies, and circuit design deficiencies. These events also brought into question

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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.

As a follow-up of this Abnormal Occurrence, the NRC is reviewing the electrical override aspects and the mechanical operability aspe . i of containment purging for all operating reactors. On November 28, 1978, the NRC issued a letter, " Containment Purging During Normal Plant Op eration"1 to all Boi13.ng Wa ter Reactor and Pressurized Wa ter Reactor 2

licensees. CP&L responded on December 29, 1978 , January 19, 19793 ,

and May 1, 19794 .

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A plant visit was nade by NRC staf f members on June 11, 1979.

This revealed that the single failure criteria was not met. CP&L wrote 5

a Licensee Event Report'(L 3.) #2-79-023 . This gave some temporary

• circuit changes and revision of operating precedures and emergency instructions that eliminated the reported deficiencies, and reported that future permanent changes would be made. Details of these permanent changes were reported in letters of April 1,19806 and May 19,19807 '

2.0 EVALUATION OF BRUNSWICK STEAM ELECTRIC PLANTS UNITS 1 AND 2 2.1 Review Guidelines The intent of this evaluation is to determine if the following NRC requirenents are me t for the safety signals to all ESF equipment:

1. Guideline No. 1--In keeping with the requirements of General Design Criteria 55 and 56, the over-ridea of one type of safety actuation signal (e.g., radiation) shoold not cause the blocking of any other type of safety actuation signal (e.g. ,

pressure) for those valves that have no function besides containment isolation.

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Guideline Nc. 2--Suf ficient physical features (e.g. ,

key lock switches) are to be provided to facilitate adequate administrative controls.

3. Guideline No. 3--A system level annunciation of the overridden status should be provided for every safety system impacted when any override is active.

Incidental to this review, the following additional NRC design guidelines 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. Guideline No. 4--Diverse signals should be provided to initiate isolation of the containment ventilation system. Specifically, containment high radiation, safety injection actuation, and containment high pressure (where containment high pressure is not a portion of safety injection actuation) should auto-matica11y initiate CVI.

2. Guideline No. 5--The instrumentation and control systems provided to initiate the EST should be designed and qualified as safety grade equipment.

3. Cuideline No. 6--the overridia.g or resettinga of the ESF actuation signal should not cause any valve or damper to change position.

Guideline 6 in this review applies primarily to other related ESF systems because implementation of this guideline for containment isola-tion will be reviewed by the Lessons Isarned Task Force, based on the recommendations in NUREG-0578, Section 2.1.4. When containment isola-tion is not involved, consideration on a case-by-case basis of automatic valve repositioning upon reset may be considered acceptable. Accept-ability would be dependent upon system function, design intent, and suitable operating procedures.

2.2 Containment Ventilation Isolation Circuits De sign Description

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Automatic closure of containment isolation valves will occur on j any of the following conditions:

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l 1. TVc drywell pressure high (2 psig) signals and two reactor vessel water level low (12.5 in.) signals are combined to form a hybrid one-out-of-two-taken-twice logic for isolation of each valve train.

l These signals are of safety grade, and also actuate high pressure coolant injection (safety injection).

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

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

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2.

Two radiation detectors in the reactor building ventilation exhaust duc t provide inputs to two separate channels of radiation monitors that initi-ate isolation of both valve trains. De licensee has stated that these channels satisfy the requirements of IEEE Standard 279 6 , y,1ye closure is initiated should either radiation channel trip (at 11 mr/hr) .

As modified,6 the control of the solenoid-op'erated and of the motor-operated CVI valves are similar with spring-return to neutral control switches .

Valve position lights show the actual valve position. Be solenoid valves fail closed on loss of air or loss of power. Should a motor-operated valve control circuit lose power, the las t position is maintained.

Prior to the NRC visit and subsequent LER,5 a single override '

i switch could override all unit safety actuation signals for all CVI valves. Each plant now has one manual two position override switch that can bypass all automatic closure relay contacts for the inboard valves. A separate switch has been provided for the override of the isolation signal to the outboard valves. Dese switches are adjacen t to indicator lights that indic~ ate the status of the override, and will be changed to keylocked switches during 1980 in both units.7 his modification wi.'. ) also provide an automatic cancellation of the override should any isolation siF'ai occur af t er the override is established.6 There is no provision for manual reset of the safety actuation signal; it is removed automatically when the initiating condition is gone. We CVI valves are preventad from changing position on either an automatic reset of the actuation signal or when a override condition is, manually established.

2.3 Containment Ventilation Isolation System Design Evaluation Guideline 1 requires that no signal override can prevent another safety actuation signal from functioning. The Brunswick units have two trains of valve override logic which could override all safety actuation signals for (separately) the inboard and the outboard valves. Re fe r-ence 5 reports that the override capability was removed and that oper-ating procedures and emergency instructions were revised to show this.

Reference 6 (ndicates that the original override control was modified and separated into two override ch'annels, each override switch bypas-sing all actuation signals. A future modification will defeat this override for subsequent isolation signals 6 This modification will be installed in both units during the year 19807 , and af ter instal-lation, the Brunswick station will be in conformance with guideline 1.

Guideline 2 recuires that reset and override switches have physical provisions to aid in the administrative control of these switches. The

, override switches, at present, have no such provision. CP&L is commit-ted to changing these switches,7 during 1980, to keylocked switches so that this guideline is satisfied. The CVI systems in the Brunswick units do not have reset switches.

Guideline 3Erequires system level annunciation whenever an over-ride affects the performance of a safety system. While status lights are provided; the Brunswick units are not in compliance with the literal requirement to provide annunciation. Af ter toe modification to automatically defeat the override on subsequent isolation signals, annunciation may not be needed since the CVI valves will isolate on any subsequent isolation signal.

I Guideline 4 requires that isolation of the CVI vsives be actuated by several diverse signals. The Brunswick units meet this requirement i.

in that:

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1. The same signals that initiate safety injection also initiate CVI sys tem isolation

2. The reactor building pressure .is a portion of this .

signal

3. Radiation trips on high radiation. level in the reactor building ventilation exhaust ducts will initiate isolation.

Guideline 5 requires that isolation actuation signals be derived from safety grade equipment. The Brunswick units meet this requiremen t.

Guideline 6 requires that no reset of isolation logic will, of itself, automatically open the isolation valves. The Brunswick units comply with this guideline.

2.4 Other Related Engineered Safety Feature System Circuits -

Reference 3 states that, of all the safety actuation signal cir-cuits, manual overrides which additionally override safety actuation signals exist only "for those controlled by plant procedures." CP&L clarified this to be the ability to turn off individual residual heat removal pumps and core spray pumpsI4 Indicator lights indicate when a pump has been stopped. The pumps are started automatically. The ability to shut down an individual pump is in agreement with the NRC -

position of establishing manual control as the accident progresses.

No other manual override capability has been identified in the review of the material submitted by CP&L for this audit.

3.0

SUMMARY

The NRC issued a letter, " Containment Purging During Normal Plant Operation," which requested CP&L to review purging requirements, con-trols, and procedures for purging at the Brunswick station.

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f During the course of the NRC review of this topic, CP&L has modified the CVI valve control and override circuits to eliminate a potential single failure that could result in opening all CVI valves f rom an isolated condition and to prevent any valve motion except those initiated by an operator. The modifications prese.. ..y completed are:

(a) A second switch was added to control the override of the outboard CVI valves. This function was removed from the switch that now controls the inboard CVI valves.

(b) Valve control switches and circuits were changed to require operator action each time a CVI valve is opened.

Further modifications to be made in 1980 that were also identified as part of this review are:

(a) Installing keylocked switches in place cf the present override switche s.

(b) Providing an automatic cancellation of an override should any isolation condition occur af ter the override is established.

The electric 31, instrumentation, and control design aspects of the contain=ent ventilation isolation valves and other related ESF signals for the Brunswick plants were evaluated using the design gudelines stated in Section 2.1 of this report.

CP&L has not provided annunciation for when an override is established for the CVI valve; however, status lights are provided.

This is not in strict conformance with NRC Guideline'3.

With this exception, the CVI system will comply with the NRC guidelines af ter the unit modifications are completed during 1980.

These modifications are scheduled to be done during the 1980 refueling 7

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outage for Unit 1, and at the first available outage o f suf ficient length after August 1, 1980, but in no case af ter December 31, 1980, for Unit 2.7 ,

4.0 REFERENCES

1. NRC/ DOR letter (A. Schwencer) to CP&L and all BWR and PWR licen-see s, "Containmen t Purging During Normal Plant Operation," dated Nov emb er 28, 1978.

2. CP&L le tter, E. E. Utley to T. A. Ippolito, NRC, " Containment Purging During Normal Plant Operation," dated December 29, 1978, serial CD-78-4411.

3. CP&L le tter, E. E. Utley to T. A. Ippolito, NRC, " Containment Purging During Normal Plant Operation," dated January 19, 1979, s erial GD-7 9-187.

4 CP&L letter, E. E. Utley, to T. A. Ippolito, NRC, " Containment Purging During Normal Plant Operation," dated May 1,1979, seri- ,

al GD-7 9-1159.

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5. CP&L le tter, B. J. Furr to J. P. O 'Reilly, NRC, " Licensee Event Report 2-79-023," dated June 22, 1979, serial GD-7 9-1623.

6. CP&L letter, E. E. Utley, to Of fice of Nuclear Reactor Regulation, NRC, " Response to Request for Additional Information on Contain-ment Purging," April ! .1980, Serial NO-80-519.

7. CP&L letter, E.,E. Utley, i s Of fice of Nuclear Reactor Regulation, NRC, " Response to Request fo

• Additional Information on Contain-men t Purging," May 19, 1980, Serial No. NO-80-750.

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