ML19296C978

Electrical,Instrumentation & Control Aspects of Override of Containment Purge Valve Isolation & Other Safety Feature Signals,Oconee Nuclear Station,Units 1,2 & 3, Informal Rept

ML19296C978
Person / Time
Site:	Oconee
Issue date:	11/30/1979
From:	Udy A EG&G, INC.
To:	Shemanski P Office of Nuclear Reactor Regulation
References
CON-FIN-A-6256 EGG-EA-5060, NUDOCS 8002290162
Download: ML19296C978 (11)

Text

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F or<V E G4 G 396 INTERIM REPORT Accession No.

Report No. EGG-EA-5060 Contract 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 & Other Safety Feature Signals, Oconee fiuclear Station, Unit. Nos.1, 2 & 3, Docket flos. 50-269, 50-270 and 50-287, TAC Nos. 10209,10208, and 10207 Type of Document:

Infonr.al Report Author (s): A. C. Udy Date of Document: flovember 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 f ull review and approval. Since there may be substantive changes, this document should not be considered final.

EG&G Idaho, Inc.

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Idaho Falls. Idaho 83401 gi __

H. P./Pearson, Supervisor

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A6256 INTERIM REPORT NRC Reshirc'i anEec' inia Amiehnce Report g c,z 8002200 t

EGG-EA-5060 November 1979 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 A. C. Udy U.S. Department of Energy Idaho Operations Office

• Idaho National Engineering Laboratory

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INTERIM REPORT Accession No.

Report No. EGG-EA-5060 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 arid 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 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 approval. Since there may be substantive changes, this document should nci t: considered final EG&G Idaho. Inc.

Idaho Falls, Idaho 83401 Prepared for the

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U.S. Nuclear Regulatory Commission and the U S Department of Energy idaho Operations Ofl ice NRC FIN No.

A6256 INTERIM REPORT NRC lesearch anc Tecimica

> Assistance Report

li50F TECHNICAL EVALUATION REPORT ELECTRICAL, INSTRUMENTATION, AND CONTROL ASPECTS OF THE OVERRIDE OF CONTAINMENT PURGE VALVE ISOLATION AND OTHER SArETY FEATURE SIGNALS OCONEE NUCLEAR STATION UNIT NOS. 1, 2, AND 3 Docket Nos. 50-269, 50-270, and 50-287 TAC Nos. 10209/10208/10207

. November 1979 A. C. Udy EG&G Idaho, Inc.

D

CONTENTS 1.0 ItiTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2.0 EVALUATION OF OCONEE NUCLEAR STATIvN UNITS 1, 2, AND 3 . . . . . 2 2.1 Review Criterion . . . . . . . . . . . . . . . . . . . . . 2 2.2 Containment Ventilation Isolation Circuits Design Description . . . . . . . . . . . . . . . . . . . . . . . . 3 2.3 Containment Ven ilation Isolation System Design -

Evaluation . . . . . . . . . . . . . . . . . . . . . . . . 4 2.4 Other Related Engineered Safeguards Protection System ,

Circuits . . . . . . . . . . . . . . . . . . . . . . . . . 5

3.0 CONCLUSION

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

4.0 REFERENCES

. . . . . . . . . . . . . . . . . . . . . . . . . . . 6 O

ii

TECHNICAL EVALUATION REPORT CLECIKICAL, INSTRUMENTATION, AND CONTROL ASPECTS OF THE OVERRRIDE OF CONTAINMENT PURGE VALVE ISOLATION AND OTHER SAFETY FEATURE SIGNALS OCONEE NUCLEAR STATION, UNIT NOS. 1, 2, AND 3 1.0 INfRODUCTION 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 circuit 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.

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 Operation" to all Boiling Water Reactor (BWR) and Pressurized Water Reactor (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 tells of modifications to the actuation signals of the purge valves.

1

2.0 EVALUATION OF OCONEE NUCLEAR STATION UNITS 1, 2, AND 3 2.1 Revies Criterion The primary intent of this evaluation is to determine if the fol-lowing requirements are met for the safety signals to all purge and ventilation isolation valves: .

(1) Criterion No. 1--The overridinga of one type of safety actuation signal (e.g., radiation) must not cause the blocking er any other type of safety actuation signal (e.g., pressure) to the isolation valves. Overriding of a system actuation signal composed of several types of actuation signals is not permitted.

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

key lock switches) are provided to facilitate ade-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:

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

(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 resettingb og the isolation actuation signal should not cause the automatic reopening of any isolation or purge valve.

The following definitions are given for clarity of use in this evaluation:

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

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

2

2.2 Containment Ventilation Isolation Circuits Design Description tach of the Oconee units has two ESPS trains which close indepen-deutly and separately the inboard and outboard isolation valves. The valves can only be opened by manual control switch. The initiating signals which will close the valves are listed below:

(1) Bistable signals which comprise tha liigh Pressure Coolant Injection signal 6.

(a) Containment pressure high (4 psig)

(b) Low reactor coolant pressurea (1500 psig).

(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 actuation signal resulting from the automatic initiation signal can be reset, once the initiating signal is gone, at the ESPS panel or at a benchboard to allow manual opening of the CVI valves.

Manual control of the inboard, motor-operated valves is by rotary, spring-return-to neutral position switches. Manual control of the outboard pneumatic-operated valves is by maintained-contact, rotary awitches. The control system is auch that the automatic closure sig-nals will close the valves even if the switch is in the "open" posi-tion. The control system prevents valve opening except when the switch is rotated to the "open" position, thus preventing reopening of the motor operated valves when the automatic "close" initiating signal is

a. The Oconee units are being modified to have low reactor coolant system pressure as an additional actuation signal to the CVII .

This modification is expected to be completed for all three units by January 1, 1980.

3

manually reset. Loss of power to the control system or loss of air to the solenoid valve closes the solenaid-operated isolation valves.

Motor-operated 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 close the outboard valves. The radiation channels will initi-ate closure of the outboard CVI valves should any of the radiation monitors trip or lose power. Once a closure signal has been received, toe valves cannat be opened until the initiating signal is gone and the logic then reset by a manual pushbutton switch (these switches are located i.nside ESPS cabinets or have covers where mounted on a bench board). There is no provision to override an actuation signal.

2.3 Containment Ventilation Isolation System Design Evaluation Criterion I requires that no signal override can prevent another ,

safety actuation signal from functioning. The CVI system has no provi-sions to override a safety actuation signal, and is in conformance with -

this criterion.

Criterion 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 criterion is met.

Criterion 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 criterion is satisfied.

Criterion 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:

4

(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 cicaure 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. We recommend that DPC modify the inboard valve control circuits so that detection of high radiation levels will close both the inboard and outboard valves.

Criterion 5 requires that the isolation actuation signals be derived from safety grade instruments. The Oconee plants do not have safety grade radiation channels, and do not satisfy this criterion. We recommend that DPC upgrade their systems to provide safety grade radi-

~

ation equipment for CVI.

Criterion 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 criterion. However, the out-board, pneumatic operated valves have maintained contact control swit-ches, 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 confor-mance to criterion 6 is expected by January 1, 1980.

2.4 Cther Related Engineered Safeguard Protection System Circuits As with the CVI valves, other safety actuation circuits do not have manual override capabilities. Criterion 6 is not complied with in otner portions of containment isolation, because the same circuits that the CVI valves have are used. We rectamend that DPC provide sufficient features to prevent automatic valve movement when the isolation actu-ation logic is reset.

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3.0 CONCLUSION

S The e lec t rica l, instrumentation, and control design aspects of the containment ventilation isolation valves and other related ESPS signals for the Oconee units were evaluated using the design criteria stated in Section 2.0 of this report. We determined that:

(1) Criterions 1, 2, and 3 are complied with -

(2) Criterions 4, 5, and 6 are not complied with.

DPC is in the process of modifying the valve control circuits to ensure that, when the isolation logic is reset, the valves do not change state. DPC is also providing an additional signal to actuate the CVI; thus, any automatic SI actuation will actuate the CVI. The Oconce units are expected to be in compliance with criterions 4 and 6 by January 1, 1980. tiowever, we recommend that the NRC ensure that all pneumatic isolation valve control circuits are modified to meet criterion 6. -

We recommend that DPC be required to submit plans to provide safety grade radiation monitor signals to the CVI valve logic in conformance to criterion 5, and to have both inboard and outboard valves respond to high radiation level trips.

We recommend that DPC be required to submit plans to bring Oconec Unit Nos. 1, 2, and 3 into conformance with criterions 4, 5 and 6 as stated in Section 2.0 of this report; and that DPC confirm that the modifications scheduled to be completed by January 1, 1980, are completed.

4.0 REFERENCES

1. Telecon, R. L. Gill, DPC, A. C. Udy, EG&G Idaho, October 10, 1979.

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

6

3. DPC letter, W. O. Parker, Jr. to H. R. Denton, NRC, "Oconee Nuc-lear Statia.1, Docket Nos. 50-269, 50-270, 50-287", January 5, 1979.

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

5. Telecon, R. L. Gill, DPC, A. C. Udy, EC&G 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.

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