ML19318B352

Electrical,Instrumentation & Control Aspects of Override of Containment Purge Valve Isolation & Other Safety Feature Signals,TMI-1.

ML19318B352
Person / Time
Site:	Three Mile Island
Issue date:	06/30/1980
From:	Udy A EG&G, INC.
To:	Shemanski P Office of Nuclear Reactor Regulation
References
CON-FIN-A-6256 EGG-EA-5167, NUDOCS 8006260004
Download: ML19318B352 (8)

Text

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. m:a= soao-ase (me, itJs INTERIM REPORT Accession N: B0062600%

Report No. EGG-EA-5167 Contract Program or Project Tit!s:

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, Three Mile Island - Unit 1, Docket No. 50-289, TAC No. 10205 Type of Document Informal. Report Author (s):

A. C. Udy Det) of Document June 1980 Responsible NRC Individual and NRC Office or Division:

. Paul C. Shemanski, Division of Operating Reactors This document was prepared primarily for preliminary or internal use. it has not received full review and approval. Since there may be substantive changes, this document shouf d not be considered final.

EG&G Idaho, Inc.

Idaho Falls, Idaho 83415

. Prepared for the U.S. Nuclear Regulatory Commission Washington, D.C.

. Under DOE Contract No. DE-AC07-761D01570 NRC FIN No. A6256 INTERIM REPORT ur n n ' '

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June 1980 ELECTRICAL, INSTRUMENTATION AND CONTROL ASPECTS OF i

l THE OVERRIDE OF CONTAINMENT PURGE VALVE ISOLATION AND l

OTHER SAFETY FEATURE SIGNALS, THREE MILE ISLAND -

, UNIT 1, DOCKET NO. 50-289, TAC NO. 10205 A. C. Udy U.S. Department of Energy Idaho Operations Office

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4 TECHNICAL EVALUATION REPORT

- ELECTRICAL, INSTRUMENTATION, AND CONTROL ASPECTS OF-THE OVERRIDE OF CONTAINMENT PURGE VALVE ISOLATION AND OTHER SAFETY FEATURE SIGNALS 4

THREE MILE ISLAND NUCLEAR STATION, UNIT NO. 1 Docket No. 50-289 TAC No. 10205 a

June 1980-

- A. C. Udy Reliability.and Statistics Branch Engineering Analysis Division EG&G Idaho, Inc.

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s ABSTRACT

, 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 overridden or_ blocked during normal plant. operations. This report addresses electrical, instru -

men.tation, and control design aspects for these valves, and.the ability of the unit containment ventilation system to isolate on-several diverse param-

-eters.. Other related systems were' audited to the same guidel'ines.

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FIN No. A6256-EICS Support ii

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, ,.,: - CONTENTS

' 1.0'-[ INTRODUCTION'-.'..'. . . . - . . . -. .. . . . . . . . . . . . . . . . . . . .

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220 EVALUATION 0F THREE MILE ISLAND NUCLEAR STATION, UNIT 1 . . . . . . 2 2.1 Review' Guidelines'. '

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= 2.2: Containment Ventilation Isolation Circuits Design

. , 1 Description . . . .. .. . . . . . . . . . . . . . . . . . . . . . . . 3 2.3- Containment Ventilation Isolation' System Design Evaluation' -. - - . . - . . . . .

. . . . . . . . - . . . . . . . . . . . 5 2.4 Other-Related Engineered Safeguards Actuation System Circuits. . . . . . . . .. .. . . . . . .. . . . . . . . .

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, 7 3.0

SUMMARY

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.4.0- REFERENCES . . ' . . -

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. [ TECHNICAL ~ EVALUATION; REPORT _

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ELECTRICAL, INSTRUMENTATION, AND CONTROL ASPECTS' OF -

THE- OVERRRIDE OF L CONTAINMENT PURGE VALVE ISOLATION -

AND OTHER SAFETY FEATURE' SIGNALS'

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THREE MILE ISLAND NUCLEAR STATION, UNIT NO. 1_-

1.0~ INTRODUCTION 1 Based on the 'information supplied by: General Public Utilities (GPU),

' this. report addresses the: electrical, instrumentation,.and control systems design ~ aspects of the Containment Ventilativa Isolation ;(CVI) system andL ather related Engineered ~ Safeguards Actuation Syste'm!(ESAS) functions'for.

Three Mile Island--Unit ~ 1.

.Several. instances have been reported where the automatic closure of Ethe. containment ventilation or' purge isolation valves would not have occur-red because the-safety 1 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 deficien-

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. 'cies. .These events'also brought-into question the mechanical operability ~

, of the-valves themselves. These events were determined by the Nuclear

, Regulatory Commission 1(NRC) to be an Abnoanal Occurrence (#78-05) and accordingly', were reported.to Congress..

-As a follow-up of this Abnormal Occurrence, the.NRC is reviewing the' Jelectrical override; aspects and .the mechanical operability aspects of con- -

tainment purging for all operating reactors.- On November 28,-1978, the NRC issued.a letter, " Containment Purging During Normal Plant Operation"I to all Boiling Water Reactor and Pressurized Water Reactor licensees. GPU 2

responded to the~. letter by.a-letter of January 4, 1979 . After discus-sions between GPU.and the NRC, GPU' issued-another letter on this subject on-

! ' April- 3', ~ 1980.3 Additional information is-taken from the Three Mile

-Islan'd--Unit *1 restart report 4 'Section 2.1.1.5, and the Final-Safety (j -

Analysis Report 1(FSAR). A telephone conference call5 on May 7, 1980,

,. 1 discussed the April'3, 1980-letter.

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~ 2.0. : EVALUATION OF THREE MILE ISLAND NUCLEAR STATION, UNIT :1 .

.2.1 LReviewfG uidelines 1The intentT of this~ evaluation is to determine if the following NRC requirements are met for the safety signals to all ESAS 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 ithat 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 administrative controls.

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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 guide-lines were used in the evaluation: -

'l. 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 pres .

sure (where containment high pressure is not a. portion of safety injection actuation) should automatically initiate CVI.

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

3. . Guideline No. 6--the overriding or resetting a of the ESF actuation signal should not cause any valve or damper to change position.

o - 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 i

perform a function contrary to the signal.

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. ' Guideline 6 in th'is review applies primarily to other related ESAS circuits 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, Section 2 1.4. When 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 Isolation Circuits Design Description Three Mile Island--Unit I has two ESAS trains which close, indepen-dently and separately, the inboard and' outboard isolation valves. Each valve can only be opened by a manual control switch if a key-operated per-missive switch has been operated. ' The key is removed once the valve is opened.5 The control system is such that the automatic closure signals will close the valves'even if the control-switch is held in the "open" position.

The resetting of the isolation signal does not cause the opening or repo-sitioning of . any CVI valve.4 Loss of power to the control system or loss of. air to'the solenoid valve closes the solenoid-operated isolation valves.

Motor-operated valves remain in' their last position. Valve position lights, "open" and " closed", are provided on the control console. .

The initiating signals which will close the valves are listed below and in Table 2.1-l':

1. Containment pressure high (4 psig)

a. ' The following definition is given for clarity of use in this evaluat'.on:

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. ' Reactor. building.exhau'st monitors of radioactivity .

~ level _as. called out in the unit FSAR:

a. : Air lparticlemonitor

b. , Iodine monitor

c. 1 Radioactive gas monitor -

3. ' Reactor trip".

The actuation signal resulting from the automatic initiation signal can be reset,_once'the initiation signal is gone, at the ESAS panel or at a

- benchboard to allow manual ~ opening"of the CVI valves. The permissive key

' switch will still'need to be operated before the valves can be opened.

Individual initiation signals can be overridden. An override condition can_only he' established when an accident signal exists, and is automatically

' removed'when the accident signal _is gone. An audible signal informs the operator that his action'has established an override condition.

The inboard and the . outboard CVI valves are controlled by separate ,

ESAS trains,.with the three radiation monitoring channels also able to close<both the inboard and the outboard valves. Once a closure signal has-been received,Jthe valves.cannot be opened until the initiating signal is either overridden or gone'(and the logic then reset by a manual pushbutton switch). There is provision to override an actuation signal-from the radi-2 ation _ channels; this override is annunciated , -A reactor' trip actuation signal can also be overridden, as can the containment pressure signal, to' permit valve opening. These_ override conditions cause an audible signal when established, and are automatically removed when tne initiating condi-

-tion isLgone, i

~The-reactor' trip-signal, defined in Section 2.1.1.5.34 as "antici-

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patory of SFAS and occurs prior .to SFAS initiation," occurs at 1900'psig

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reactor coolant syst'em'(RCS)-pressure, while the SFAS initiation occurs at 1600.psig-RCS; pressure.

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. .: To-reopen ~theipurge valveslwhen an' isolation condition is present,

- theee actionszarelnecessary for each redundant valve. 1The operator must

~a< tuate the override ~ switch, operate the permissive key switch, and operate.

tha' valve control switch.'

- 2.3 -containment ventilation' Isolation System Design Evaluation E .. .

. ' Guideline ~l~ requires:that-no signal ovarride:can preventfanother safety actuation signal from' functioning. 'The signals can be individually over-J 1 ridden with no affect on'the other. actuation signals;~this conforms-with l this - guideline .

Guideline 2. requires that ~ any reset cn: override switches have physical provisions to aid'in'the' administrative' control of the' switch'es. With key-locked' permissive switches installed in the CVI valve opening logic,

'this guideline is satisfied. The override switches do not' meet the literal intent of this guideline; however, an override can only be established and

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. maintained when an accident condition-exists. Once the override is-estab-lished, the purge valver cannot be opened without using a key permissive 1'-  : switch. This is deemed sufficient to facilitate administrative control.

Guideline T requires: system level annunciation whenever an override-affects the performance of a safety system. Annunciation is provided when

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a radiation channel is' overridden. Overrides of ESAS signals cause an audible signal'when the override is established. While not in full compli-

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< ance with the guideline, in- all casesi the operator is -informed by the control system that an override has been established. The override itself 4 does not allow the purge' valves to be opened. A key-locked permissive switch still needs to be operated. Additionally,.the override is automati-4 cally removed when'the' actuating conditiot. is gone Annunciation,.in addi-

-. tion to these design features,-is notLdeemed necessary.

4 Guideline 41 requires that isolation of the CVI system be actuated by

. several diverse signals. -Three Mile ~-Island--Unit I uses a reactor trip

-signal as-anticipatory of a safety-injection. This is acceptable. -With i

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" high radiation.. signals and high containment pressure signals in addition'to -

jthe1 reactor trip signals, this guideline is~ satisfied.

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... - Guideline 5 requires _that_th'e!-isolation actuation signals be: derived

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afrom safety grade. instruments.; Three Mile: Island--Unit 1 actuates' closure fof(thelpurgetvalve's;by'use of signals' derived from safety grade equipment,3 _

except forinon-safety grade radiation channels4 ,5 The'NRC should require

.the_use'of safety grade. radiation channels to initiate. isolation of the.

purge val'vesiat-Three_Mileelsland--UnitJ1.

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GuidelineL6' requires that no resetting of' isolation logic will, of 2

-itself, automatically open th'e is'lation_ valves. The CVI valves have bIeen

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- modified'as Section 2.1'.1.5.3 0 states: " deliberate operator action shall be required.-to reopen selected individual valves." Guideline 6 is satisfied.

.2.4 OtherJRelated Engineered Safeguard Actuation System Circuits

~0ther ESAS circuits have manual override capabilities. Table 2.1-1 sh'ows these? overrides. Applicable guidelines are complied with for these

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' circuits.

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j< No other. manual-overrides have been identified in the review of the material submitted?for this-audit.- -

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3.0 . .

SUMMARY

i l- ' The1NRC . issued a letter, " Containment Purging During Normal Plant

, Operation," which; requested:GPU to review' purging requirements, controls,

! , and } procedures ~ for^ purging at the Three Mile Island station.

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'Thel electrical, instrumentation, and control design aspects of the f

containment' ventilation isolation valves and other related ESAS signals for'-

LThree' Mile < Island--Unit l~were= evaluated using the-design guidelines stated- -

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'in.Section.;2l^of this report. 1&nt unit. design. meets the NRC guidelines ~

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i except that.non-safety grade rzdiation channels are used for automatic

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closure of the purge valves.

The NRC should require GPU to' submit plans to supply.Three Mile Island--Unit I with safety' grade' radiation channels that will initiate closure of the CVI valves.

. ThelThree Mile Island--Unit'l CVI system is-not in compliance with the literal requirements of guidelines 2 and 3, which require protective covers

. or other - features for the override switches and annunciation when an over-ride is established. The.NRC should accept the present design as adequate as pointed out in Section 2.3 of this report.

4.0 REFERENCES

1. NRC/ DOR letter (A. Schwencer) to all BWR and PWR licensees, " Con-tainment Purging During Normal Plant Operation," dated November.28, 1978.

- 2. Met Ed letter (J. G. Herbein).to Director of Nuclear Reactor Regu-lation, "Three Mile Island Nuclear Station, Unit 1 Containment-

. Purging," January 4, 1979, GQL 0007.

. 3. Met'Ed letter (J. G. Herbein) to Director of Nuclear Reactor Regu-lation, " Purge Valves," April 3, 1980, TLL 157.

4. Three Mile Island Nuclear Station, Unit 1 Restart Report, Sec-tion 2.1.1.5 and response to NRC question 26. -

5. Telecon,'A. C. Udy, EG&G Idaho, Inc., Dominic Dilanni, NRC, G. Sen, J. Korea, and D. Chisholm, GPU, May 7, 1980.

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