ML19309C471

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

ML19309C471
Person / Time
Site:	Oconee
Issue date:	02/29/1980
From:	Udy A EG&G, INC.
To:	Shemanski P Office of Nuclear Reactor Regulation
References
CON-FIN-A-6256 EGG-EA-5060, NUDOCS 8004080641
Download: ML19309C471 (12)

Text

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g POR*A AG4G ye INTERIM REPORT Accession No.

Report No. EGG-EA-5060 Rev. 1 Centract Program or Project

Title:

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

Electrical, Instrumentation & Control Aspects of the Override of Containment Purge Valve Isolation and Other Safety Feature Signals, Oconee Nuclear Station, etc.

Type of Document: Infonnal Report Author (s): A. C. Udy otte of Document: February 1980 R;sponsible 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 approval. Since there may be substantive changes, this document should not be considered final.

EG&G Idaho, Inc.

Idaho Falls, Idaho 83401 g g H.'P. Pearson, Supervisor Information Processing Prepared for the U.S. Nuclear Regulatory Commission i and the U.S. Department of Energy Idaho Operations Office Under contract No. EY-76-C-07-1570 NRC FIN No.

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EGG-EA-5060, Rev. 1 February 1980 ELECTRICAL, INSTRUMENTATION AND CONTROL ASPECTS OF Tile OVERRIDE OF CONTAINMENT PURGE VALVE ISOLATION AND OTilER SAFETY FEATURE SIGNALS, OCONEE NUCLEAR STATION, UNIT NOS. 1, 2 AND 3, DOCKET NOS. 50-269,

. 50-270 AND 50-287, TAC NOS. 10209, 10208 AND 10207 A. C. Udy U.S. Department of Energy Idaho Operations Office

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INTERIM REPORT Accession No.

Report No. EGG-EA-5060, Rev. 1 C ntract 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, Oconee Nuclear Station, Unit Nos. 1, 2, and 3, Docket Nos. 50-269, 50-270 and 50-287, TAC Nos. 10209, 10208 and 10207 Type of Document:

Informal Report Author (s):

A. C. Udy Dste of Document:

February 1980

. Rasponsible NRC Individual and NRC Office or Division:

Paul Shemanski, Division of Operating Reactors This document was prepared primarily for preliminary orinternal use. it has not received full review and approval. Since there may be substantive changes, this document should not be considered fmal.

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, .

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Ass: stance Reporty

1334F TECilNICAL EVALUATION REPORT ELECTRICAL, INSTRUMENTATION, AND CONTROL ASPECTS OF Tile OVERRIDE OF CONTAINMENT PURGE VALVE ISOLATION AND OTilER SAFETY FEATURE SIGNALS OCONEE NUCLEAR STATION UNIT NOS. 1, 2, AND 3 Revision 1 Docket Nos. 50-269, 50-270, and 50-287 TAC Nos. 10209/10208/10207 February 1980 A. C. Udy EG6G Idaho, Inc.

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E ABSTRACT Several instances have been reported where the automatic closure 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

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on several diverse pa'rameters. Other related systems were audited to the same guidelines.

FIN No.'A6256' EICS Support.

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Revision 1 L

CONTENTS

1.0 INTRODUCTION

. . . . . . . . . . .. . . .. ... . .. . . .. 1 2.0 EVALUATION OF OCONEE NUCLEAR STATION UNITS 1, 2, AND 3 . . . . . 2 2.1 Review Guidelines . . . .. .. . . . . . . . . ... ... 2 2.2 Containment Ventilation Isolation Circuits Design Description . . . . . . . . .. . . . . . .. . ..... . 3 2.3 Containment Ventilation Isolation System Design Evaluation . . . . . . . . ... . . . . - . . . .-. . .. . 5

. 2.4 Other Related Engineered '.fafeguards Protection System Circuits . . . . . . . . . .. . . . . .. . ... . . . . 6

3.0 CONCLUSION

S . . . . . . . . . . ... . . . . ... ... ... 6

4.0 REFERENCES

. . . . . . . . . .. ... . . . . . . . . .. . . . 7 e

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TECHNICAL EVALUATION REPORT ELECTRICAL, INSTRUMENTATION, AND CONTROL ASPECTS OF THE OVERRRIDE OF CONTAINMENT PUP.GE VALVE ISOLATION AND OIRER SAFETY FEATURE SIGNALS OCONEE NUCLEAR STATION, UNIT NOS. 1, 2, AND 3 Revision 1 1.0 IRTRODUCTION i

Based on the information supplied by Duke Power Company (DPC),

this report addresses the electrical, instrumentation, and control systems design aspects of the Containment Ventilation Isolation (CVI) system and other related Engineered Safeguards Protection System (ESPS) functions for the Oconee 1, Oconee 2, and Oconee 3 plants. DPC has verified that these systems are identical in all three plants .

Several instances have been reported where the automatic closure 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. These events resulted from .

a lack of proper management controls, procedural inadequacies, and

, c ircuit design deficiencies. 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.

i 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, l 1978, the NRC issued a letter, " Containment Purging During Normal Plant

, Operation" to all Boiling Water Reactor (BWR) and Pressurized Water l Reac tor (PWR) Licensees. DPC responded to the letter by letters of January 5, 1979 and September 25, 1979.' Portions of these were clarified in telephone conversations of October 10, 1979 and October 11, 1979'. An additional letter of October 19, 1979 0 tells l

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. 4 of modifications to the actuation signals of the purge valves. An '

additional telephone conversation on December 26, 1979 clarified proj ec ted s chedules.

2.0 EVALUATION OF OCONEE NUCLEAR STATION UNITS 1, 2, AND 3

't 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 ESF equipment:

1. Guideline No. 1--In keeping with the requirements of General Design Guidelines 55 and 56, the over-ridinga of 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. Guide line No. 2--Su fficient 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. .

(See R.G. 1.47.)

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

1. . Guideline No. 4--Diverse signals should be provided '

to initiate isolation of the containment ventilation system. Specifically, containment high radiation, I safety inj ec tion actuation, and containment high pressure (where containment high pressure is not a ,

portion of safety inj ection actuation) should auto-

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matically initiate CVI. ,

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

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

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2. Guideline No. 5--1he instrumentation and control systems provided to initiate the ESF should be designed and quali fied as safety grade equipment.

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

Cuideline 6 in this review applies primarily to other related ESF

, systems beciaise implementation of this guideline for containment isola-tion will be reviewed by the Lessons Learned Task Force, based on the reconenendations in NUREG-0578, Sec tion 2.1.4. When containment isota-

! tion is not involved, consideration on a case-by-case basis on automatic va lve 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 D.* sign Description Each of the Oconeo unita has two ESPS trains which close indepen-deut ly and separately the inboa rd and ou t boa rd isolation valves. The

, valves can only be opened by manual control switches. The initiating I signals which will close the valves are listed below:

1. llistable signals which comprise the liigh Pressure Coolant Injection signa 16;

n. Containment pressure high (4 psig)

b. Low reactor coolant pressureb (1500 psig).

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

Resett the signal has come and gono, inx! the circuit is being cleared in order to ret u rn it to the normal condition.

b. The Oconee units are being modi fied to have low reactor coolant system pressure as an additional actuation signal to the CVI I. This malification is expec ted to be completed bef ore startup from refueling for Units 1 and 2, and at the first available forced outage for Unit 3 7, 3

Revision 1

2. In addition to the above initiating signals, any of the following containment vent radioactivity levels exceeding its setpoint will close the outboard valves:

a. Air particle monitor

b. Iodine monitor

c. Radioactive gas monitor.

The valve closure signal resulting from the automatic actuation signal <

can be re se t , once the initiating signal is gone, at the ESPS panel or at a benchboard to allow manual opening of any of the CVI valves.

Manual control of the inboard (motor-operated) valves is by rotary spring return to neutral switches. Manual control of the outboard pneumatically operated valves is by maintained-contact, rotary switches.

The control system is such that the automatic closure signals will close the valves even if the switdi is in the "open" position. The control system prevents valve opening except when the switch is rotated to the "open" pos ition, thus preventing reopening of the motor-operated valves when the automatic "close" initiating signal is manually reset.

Loss of power to the control system or loss of air to the solenoid

• valve closes the solenoid-operated isolation valves. Mo to r-ope rated ,

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

Both the inboard and the outboard CVI valves are controlled by separate ESPS trains, with the three radiation monitoring channels also able to c lose the outb oa rd va lve s . The radiation channels will initi-ato closure of the outboard CVI valves should any of the radiation mon i t ors trip or lose power. Once a closure signal has been received, the valves cannot be opened until the initiating signal is gone and the ,

logic then reset by a manual pushbutton switch (these switches are located inside ESPS cabinets or have covers where mounted on a bench -

b oa rd ) . The re b no provision to override an actuation signal.

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,e 2.3 Containment Ventilation Isolation System Design Evaluation Guideline I requires that no signal override can prevent another I safety actuation signal from functioning. The CVI system has no provi-sions to override a safety actuation signal, and is in conformance with this guideline.

, Guideline 2 requires that any reset or override switches have physical provisions to aid in the administrative control of the swit-ches. With no override switches and with reset switches inside the ESPS cabinets or covered, this guideline is met.

Guideline 3 requires system level annunciation whenever an over-ride effects the performance of a safety system. With no provision for overriding a safety signal, this guideline is satisfied.

Guideline 4 requires that isolation of the CVI system be actuated by several diverse signals. Upon the inclusion of the low reactor coolant system pressure trip as a CVI actuation signal, the Oconee

, units will meet this requirement in that:

1. The same signals that initiate safety injection also initiate CVI valve closure

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

3. Radiation high signals will actuate closure of the outboard valves.

With the present design, radiation signals do not initiate closure of the inboard valves, therefore, the single failure of an outboard valve to close on a high radiation signal (such as might occur with a refueling accident) would prevent containment isolation. It is recom-

. mended that DPC modify the inboard valve control circuits so that

' detection of high radiation levels will close both the inboard-and outboard valves.

5 Revision 1

r-Cuideline 5 requires that the isolation actuation signals be 4 derived from safety grade instruments. The'Oconee plants do not have safety grade radiation channels, and do not satisfy this guideline. It is recommended that DPC upgrade their systems to provide safety grade radiation equipment for CVI.

Cuideline 6 requires that no resetting of isolation logic will, of

• itself, automatically open the isolation valves. The inboard, motor operated valve controls conform to this guideline. However, the out-board, pnemmatically operated valves have maintained contact control switches, and the control system will permit these valves to open (with the control switch in the open position) when the isolation logic is reset. DPC is designing a modification to correct this deficiency, and conformance to guideline 6 is expected (see footnote b on page 3). L 2.4 Other Related Engineered Safeguard Protection System Circuits The material submitted by DPC was identified as tyical of the ESPS actuation circuits for the Oconee units. DPC has stated that no manual override features exist in these circuits. No manual overrides have ,

been identified in our review of the material submitted for this audit.

Guideline 6, however, is not complied with in other portions of containment isolation, because the same circuits that the CVI valves have are used. DPC has identified those pneumatically operated valves that would be susceptible to automatic motion on reset of valve actua-tion logic, and will modify these as with the CVI valve logic7 . The scheduled completion is the aame as identified in footnote b on page 3.

This same modification will include the addition of the low reactor coo l ant pressure signal as an actuation signal.

3.0 CONCLUSION

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The electrical, instrumentation, and control design aspects of the j ' containment ventilation isolation valves and other related ESPS signals f-for the Oconee units were evaluated using the design guidelines stated 1

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1 in Section 2.0= of this report. With the completion of the modifications that DPC is presently' committed to, the CVI complies.with the review-quidelines except for the radiation monitors used to provide one of the.

diverse acutation signals. These radiation monitors'are not class.lE equipment and do not cause closure of the inboard valves. It is recom-mended that the NRC require that both the inboard and the outboard valves be actuated to close by class IE radiation channels for all-

, three Oconee units.

Other containment isolation valves have been determined to have the capability to change state upon reset of the. isolation logic. DPC is committed to modify the control circuits for these valves before restart from the current refueling outage for Units 1 and 2, and as soon as a forced outage of sufficient length occurs for Unit 3. D2is modification will prevent containment isolation valve motion on the reset of the actuation logic.

4.0 REFERENCES

e 1. Telecon, R. L. Gill, DPC, A. C. Udy, EG6G Idaho, October 10, 1979.

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

3. DPC letter, W. O. Parker, Jr. to H. R. Denton, NRC, "Oconee Nuc-Icar Station, Docket Nos. 50-269, 50-270, 50-289", January 5, 1979.

4. DPC letter, W. O. Parker, Jr. to H. R. Denton, NRC, "Oconee Nuc-Icar Station, Docket Nos. 50-269, 50-270, 50-287", September.25, 1979.

5. Telecon, R. L. Gill, DPC, A. C. Udy, EG6G Idaho, October 11, 1979.

6. DPC letter, William O. Parker, Jr. to Harold R. Denton, NRC, "Oconee Nuclear ~ Station, Docket Nos. 50-269, 50-270, 50-287,"

October 19, 1979.

~7. Telecon R. L. Gill, DPC, R. F. Scholl, Jr., NRC-DOR, A.-C. Udy, EG&G Idaho,. December 26, 1979. {

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