ML19344D893

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

ML19344D893
Person / Time
Site:	Arkansas Nuclear
Issue date:	04/30/1980
From:	Udy A EG&G IDAHO, INC., EG&G, INC.
To:
Shared Package
ML19344D887	List: ML19344D893
References
CON-FIN-A-6256 1607, NUDOCS 8008260275
Download: ML19344D893 (9)

Text

_ .. - - _ . . _ . . . . . .. _._ _ __

W [

Enclosure 1607.: l l

i I

TECHNICAL EVALUATION REPORT ELECTRICAL, INSTRUMENTATION, AND CONTROL ASPECTS OF

- THE OVERRIDE OF CONTAINMENT PURCE VALVE ISOLATION AND OTHER SAFETY FEATURE SIGNALS l

l ARKANSAS NUCLEAR ONE--UNIT 1 Docket No. 50-313 TAC No. 10212 April 1980 A. C. Ude .

EG&G Idaho, Inc.

1 i

b t

{

J S

8 0 08 26.0 - .J'_ - 2 7f.-_ -

- A CONTENTS

.................. I

1.0 INTRODUCTION

2.0 EVALUATION OF ARXANSAS NUCLEAR ONE--UNIT 1 . . . . . . . . . . . . . 2 2

2.1 Review Cuidelines . . . . . . ..... .. .. ........

2.2 Containment Ventilation Isolation Circuits Design 3

Description . . . . . . . . . . . . . . . . . . . . . . . . . .

2.3 Containment Ventilation Isolation System Design 4

Evaluation . . . . . . . . .. .......... ... .. .

2.4 Other Related Engineered Safeguards Actuation System 5

Circuits . . . . . . . . ......... .. ....... .

5 3.0

SUMMARY

6

4.0 REFERENCES

M 8

. _ . _ ._ . _ _ , . _ ,_ _. _ - . . , _ _ ~ , . _ , , . _ . .

o ,

- o TECHNICAL EVALUATION REPORT ELECTRICAL, INSTRUMENTATION, AND COSTROL ASPECTS OF THE OVERRIDE OF CONTAINMENT PURCE VALVE ISOLATION AND OTHER SAFETY FEATURE SICNALS ARKANSAS NUCLEAR ONE-UNIT 1

1.0 INTRODUCTION

Based on the information supplied by Arkansas Power and Light Company (AP&L) and information in the Final Safety Analysis Report, this report addresses the electrical, instrumentation, and control system design aspects of the Containment Ventilation Isolation (CVI) system and other related Engineered Safeguards Actuation System (ESAS) functions for Arkansas Nuclear One--Unit 1.

Several instances have been reported where the automatic closure of the containment ventilation or purge isolation valves would not have occur-red because the safety actuation signals were manually everridden or blocked during normal plant operations. These events resulted from a lack of proper i management controls, procedural inadequacies, and circuit design deficien-cies. 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.

As follow-up of this Abnormal Occurrence, the NRC is reviewing the .

electrical override aspects 1.sd the mechanical operability aspects of con-tainment purging for all operating reactors. On November 28, 1978, the NRC issued a letter, " Containment Purging During Norm 31 Plant Operation" to all Boil'ag Watar Reactor and Pressurized Water Reactor licensees. AP&L 2

responded to the letter by letters of December 29, 1978 , January 30, 3

j 1979 , and April 2, 1979'. A February 22, 1980 letter answered several additional concerns. A December 12, 1979 letter6 contained an -

1 interim committment to have the purge valves closed whenever Arkansas

[

Nuclear One--Unit 1 is in an operating me le.

l l

i I i

l l

i

, _ . . .. . ...-...-.--.r - - - . . - . . - - - ...

- - - , - .-. - ~ . _ - - - - , . - - , , , _ . - ,- , ,

~

2.0 EVALUATION OF ARKANSAS NUCI. EAR ONE-UNIT 1 2.1 Review Guidelines. The intent of this evaluation is to determine if the following NRC requirements are met for the safety signals to all ESA3 equipment:

1. Guideline No.1--In keeping with the requirements of General Design Criteria 55 and 56, the overridinga og one type of safety actuation signal (e.g., radiation) ~

should 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.

2. Guideline No. 2--Sufficient physical features (e.g.,

key lock switches) are to be provided to facilitate adequate ad=inistrative controls.

3. Guidelin. fl. . . 3--A system level ann. .. i4 tion of the overridden status should be pr;vided tor every safety system impacted when any override is active. (See -

R.C. 1.47.)

Incidental to this review, the following additional NRC design guide-lines were used in the evaluation:

1. Guideline No. 4--Diverse signals shoeld be provided to initiate isolation of the containment ventilation system. Specifically, containment high radiation, saf ety injection actuation, and contain=ent high pres-sure (where containment high pressure is not a portion of safety injection actuation) should automatically initiate CVI.

j I

2. Guideline No. 5--The instrumentation and control systems l provided to initiate the ESAS should be designed and l

qualified as safety grade equipment.

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 per-form a function contrary to the signal.

l 2

96 6 6 e e e

~

- o

. 3. Guideline No. 6--The overriding or resetting' of the ESAS actuation signal should nct cause any valve or da=per to enange position.

Guideline 6 in this review applies primarily to other related ESF systems because implementation of this guideline for containment isolation will be reviewed by the Lessons Learned Task Force, based on the recommend-ations in NUREG-0578, Sec tion 2.1.4. 'n' hen containment isolation is not involved, consideration on a case-by-case basis of automatic valve reposi-tioning upon reset may be considered acceptable. Acceptability would be dependent upon system function, design intent, and suitable operating procedures.

2.2 Containment Ventilation Isolatisn Circuits Design Description.

Arkansas Nuclear One--Unit I has two ESAS' trains which close independently and separately the inbeard and cutboard containnant ventilation isolation (CVI) valves . The, valves can only be opened by manual control swi;ch.

High containment pressure (4 psig)' or low reactor coolant system (RCS) pressure5 will automatically initiate isolation of the CVI valves.

The actuation signal resulting from the automati: initiation signal cannot be reset or overridden. However, ance the initiating condition is gone, the high containment pressure or the low RCS pressure signal can be reset to allow =anual opening of the CV1 valves.

Manual control of the CVI valves is oy rotary, spring return to neutral position switches. The control system prevents valve opening except when

( the switch is rotated to the "open" position, thus preventing reopening of the valves when the automatic closure sigTal is manually reset. Loss of power to the control system or loss of air to the-solenoid valve closes the solenoid-operated isolation valves while socor-operated valves remain in their last position. Valve position lights, "open" and " closed," are pro-vided on the control console.

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

Reset: The signal has co=e and gone, and the circuit is being cleared in order to return it to the nor=al condition.

3 r-- em - --w__ m e* wee ,m.

~

a n Sinco AP&L has not yet d2:enstratsd valvo opzrobility during i .tet ign f

basis accident, the utility has committed 6to maintain the purge valves in a closed position whenever the reactor is in an operating mode. This committment is only until the utility demonstrates the operability of the valves.

1 2.3 Containment Ventilation Isolation System Design Evaluation.

1 Guideline 1 requires that no signal override can prevent another safety actuation signal from functioning. The CVI system has no override capabil-

. ity and is, therefore, in compliance with this guideline.

t

! Guideline 2 requires that any reset or override switches have physical provisions to aid in the administrative control of the switches. AP&L has

. shown no evidence that additional physical provisions exist for reset swit-ches (there are no override switches). The lite. I requirements of guide-line 2 are not met; however, the NRC has found this design acceptable where the reset switch serves only to reset logic after an actuation condition is cleared (see the Safety Evaluation Report for Millstone, Unit 2, same topic). On this basis, Arkansas Nuclear One--Unit I has acceptable reset switch provisions.

Guideline 3 requires system level annunciation whenever an cver ride effects the performance of a safety system. The AP&L design has no over-ride for the CVI system; therefore, compliance with this guideline is inherent.

Guideline 4 requires that isolation of the CVI system be actuated by several diverse signals. Arkansas Nuclear One--Unit 1 provides for CVI on high containment pressure or low RCS pressure. The unit FSAR indicates that these same signals actuate safety injection. This is acceptable.

Husever, additional actuation signals derived from high radiation levels (gaseous, particulate, and iodine) in the unit vent and in the containment i atmosphere are needed if the purge valves are ever to be open when the unit is in an operating mode. The NRC should require AP&L to provide either the needed radiation monitors a r technical specification requirements that the purge valves be securely closed when the unit is in an optrating mode .

4 e..au.. .e==* -= e.. *~ee e. . . .-...ee.. .e =#- - e- .e -.g..

l

. s Guid21 ins 5 requires thct th2 isolation signals ba d2 rived from safety

. grade instruments. The present actuation signals are derived from safety grade equipment in compliance with this guiceline. The NRC should require that the additional high radiation signals used are derived from safety grade equipment.

Guideline 6 requires that no resetting of isolation logic will, of itself, automatically open the isolation valves. The present control cir-cuits conform to this guideline.

2.4 Other Related Engineered Safeguard Actuation System Circuits.

The Arkansas Nuclear One--Unit 1 Emergency Core Coolant System (ECCS) has bypass capability to allow normal shutdown. This bypass requires a permissive condition to be entered (on controlled RCS pressure decrease) and is automatically remcved on a teturn of RCS pressure to approximately 250 psig above the bistable setpoint. This bypass prevents " actuation of high and low pressure injection, isolation, and cooling systems during a normal shutdown."5 This bypass does not c:mply with the literal requirements of guidelines 2 or 3; however, the bypass is automatically removed if the permissive condition necessary to enter the bypass is removed. Physical provisions for the bypass switches are served by permissive circuits.

Annunciation is not deemed necessary when automatic removal of the bypass exists.

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

3.0

SUMMARY

l The electrical, instrumentation, and control design aspects of the containment ventilation isolation valves and other related ESAS signals for Arkansas Nuclear One--Unit I were evaluated using the design guidelines 5

, , , , , _ , , , , a weem + w emmee - - w *w w e myee

stated in Section 2.1 of this report. The CVI system meets the 14KC guide-li,nes except that high radiation levels do not initiate isolation of the CVI valves. Should the purge valves be opened when the unit is in an operating mode, the NRC should ensure that class 1E radiation level trips will isolate the containment atmosphere. Alternatively, AP&L should be required to incorporate in the the Arkansas Nuclear One--Unit 1 technical specifications requirements that the purge valves be securely closed whenever the unit is in an operating mode.

f a

4.0 REFERENCES

/ NRC/ DOR letter (A. Schwencer) to all BWR and PWR licensees, "Contain-1.

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

2. AP&L letter (Daniel H. Williams) to Director of Nuclear Reactor Regu-lation, NRC, " Containment Purging During Operation," dated December 29, 1978, Serial 1-128-9.

3. AP&L letter (Daniel H. Williams) to Director of Nuclear Reactor Regu-lation, NRC, " Containment Purging During Operation," dated January 30, ,

1979, Serial 1-019-17.

4. AP&L letter (Daniel H. Williams) to Director of Nuclear Reactor Regu-lation, NRC, " Reactor Building Purging During Operation," dated April 2, 1979, Serial 1-049-2.

s

5. AP&L letter (David C. Trimble) to Director of Nuclear Reactor Rega-lation, NRC, " Reactor Building Purge System," dated February 22, 1980, Serial 1-020-17.

6. AP&L letter (David C. Trimble) to Director of Nuclear Reactor

! Regulation, NRC, " Reactor Building Purging During Normal Operation,"

l dated December 12, 1979, Serial 1-129-8.

l e

6 l

l l

l .

- ~ ~-~ ~~

• - _ r':-___z:__ r