ML13330B106
| ML13330B106 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 11/26/1980 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML13330B105 | List: |
| References | |
| TASK-06-04, TASK-6-4, TASK-RR NUDOCS 8012180346 | |
| Download: ML13330B106 (10) | |
Text
ENCLOSURE SAFETY EVALUATION REPORT SAN ONOFRE UNIT 1 NUCLEAR GENERATING STATION OVERRIDE OF CONTAINMENT PURGE ISOLATION AND OTHER ENGINEERED SAFETY FEATURE ACTUATION SIGNALS Introduction As a result of Abnormal Occurrence #78-5, the NRC issued a generic letter requesting each licensee to take certain actions.
Evaluation The enclosed report was prepared for us by EG&G, Idaho, as part of our technical assistance program for SEP. This report provides a technical evaluation of the electrical, instrumentation and control design aspects of the override of containment purge valves isolation and other engineered safety feature actuation signals and is based upon review of these design aspects against the six NRC criteria provided for the review. The technical evaluation concludes that the present design does not conform with the review criteria.
Conclusion Based upon our review of the consultant's technical evaluation, we conclude that the electrical, instrumentation and control design aspects of the override of containment purge valves isolation and other engineered safety feature actuation signals are not acceptable. The licensee must modify his designs such that:
- 1. The safety injection actuation signal and the high containment pressure signal for containment isolation can not be overridden by a single switch movement.
- 2. The containment isolation and spray override switches should be provided with suitable mechanical features (such as key locks) to augment administrative controls.
- 3. Audible alarm are activated when the safety injection low pressurizer pressure signal or containment spray is blocked. Visual indications should indicate that contain ment isolation and control ventilation isolation or contain ment spray is bypassed.
- 4. We also require that the licensee commit to replace the containment radiation channels that initiate containment isolation when Regulatory Guide 1.141 is approved by the NRC.
These changes should be completed by the end of the next refueling outage.
The contractor's concern with regard to General Design Criterion 56 will be pursued as part of SEP Topic 111-7.
80.121 083 7'W
4976N SEP TECHNICAL EVALUATION TOPIC VI-4 ELECTRICAL, INSTRUMENTATION, AND CONTROL ASPECTS OF THE OVERRIDE OF CONTAINMENT PURGE VALVE ISOLATION FINAL DRAFT SAN ONOFRE NUCLEAR GENERATING STATION, UNIT NO. 1 Docket No. 50-206 November 1980 A. C. Udy Reliability and Statistics Branch Engineering Analysis Division EG&G Idaho, Inc.
Draft 11-6-80
CONTENTS
1.0 INTRODUCTION
- 1.
2.0 EVALUATION OF THE SAN ONOFRE NCULEAR GENERATING STATION, UNIT 1..
2 2.1 Review Guidelines.........
2 2.2 Containment Ventilation Isolation Circuits Design Description.
3 2.3 Containment Ventilation Isolation System Design Evaluation
- * * * * * * *
- 4 2.4 Other Related Engineered Safety Feature System Circuits 5
3.0
SUMMARY
5
4.0 REFERENCES
6
- 1
SEP TECHNICAL EVALUATION TOPIC VI-4 ELECTRICAL, INSTRUMENTATION, AND CONTROL ASPECTS OF THE OVERRRIDE OF CONTAINMENT PURGE VALVE ISOLATION SAN ONOFRE NUCLEAR GENERATING STATION, UNIT NO.
1
1.0 INTRODUCTION
Based on the information supplied by the Southern California Edison Company (SCE) this report addresses the electrical, instrumentation, and control systems design aspects of the Containment Ventilation Isolation (CVI) system and other related Engineered Safety Feature (ESF) functions for San Onofre 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 overridden or blocked during normal plant operations. Lack of proper management con trols, procedural inadequacies, and circuit design deficiencies contributed to these instances. 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.
The NRC is now reviewing the electrical override aspects of contain ment purging and venting for all operating reactors.
On November 28, 1978, the NRC issued a letter, "Containment Purging During Normal Plant Opera tion" 1 to all Boiling Water Reactor and Pressurized Water Reactor licensees.
This required a review of these systems by the licensee.
SCE 2
3 4
responded on January 9, 1979, December 14, 1979, January 15, 1980,
5 6
and June 23, 1980.
On October 2, 1980, SCE clairified information requested by an earlier telephone conference and submitted Control Logic Diagram No. 235234-0. The Final Safety Analysis Report (FSAR) also con tains design information reviewed for this report.
1
2.0 EVALUATION OF THE SAN ONOFRE NUCLEAR GENERATING STATION, UNIT 1 2.1 Review Guidelines. The intent of this evaluation is to determine if the actuating signals for the ESF equipment meet the followingNRC requirements:
- 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) 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 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.
Additionally, this review uses the following NRC design guidelines:
- 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 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 ESF should be designed and qualified as safety grade equipment.
- 3. Guideline No. 6--the overriding or resettinga of the ESF actuation signal should not cause any valve or damper to change position.
- a. The following definitions are 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.
Reset:
the signal has come and gone, and the circuit is being cleared in order to return it to the normal condition.
2
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, Section 2.1.4. When containment isolation i's 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.
Automatic closure of containment purge and vent isolation valves will occur on any of the following conditions2
- 1. High containment pressure (2 psig).
- 2.
High containment radiation. 6
- 3. Safety injection actuation (through the safety injection sequencer).
SCE has indicated 5, that these signals are derived from safety grade equipment. However, in discussing the qualifications of the radiation monitors they state that these monitors are "considered to be qualified based on experience."
The control of the solenoid-operated purge and vent valves use spring return to neutral control switches. Valve position lights show the actual valve position. The solenoid valves fail closed on loss of air or on loss of power.
The automatic vent valves are located both inside and outside contain 3
ment3.
The purge valves are located outside containment, one automatic valve with a manual backup valve2 on each purge line.
There is provision for manual override of the purge and vent valve actuation signals (except for radiation level), and there is a safety injection manual override which is used to prevent inadvertant operation of 3,4 the Safety Injection System on planned depressurization.
The CVI 3
valves are prevented from changing position on either a reset of the actu ation signal, an override of the actuation signal, or when the safety injection 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. One signal that can be overridden is the low pressurizer pressure safety injection signal. This override is automatically removed on a pressurizer pressure increase above 1900 psig 2.
This override is used to prevent inadvertant safety injection on a planned cooldown. This override does not affect the other actuation signals and is in conformance with this guideline.
Override of the containment isolation signal (safety injection or high containment pressure but not high radiation) is also possible. Since a single action overrides both signals, this guideline is not met.
Guideline 2 requires that reset and override switches have physical provisions to aid in the administrative control of these switches. The Safety Injection System override switches are pull-to-allow momentary rotation that comply with this guideline. The override of the contain ment isolation signal is established by a manual alternate action switch. Having no features to facilitate administrative control, they are not in conformance with this guideline.
Guideline 3 requires system level annunciation whenever an over ride affects the performance of a safety system. The use of either override is annunciated in conformance with this guideline. However, the effect of tne safety injection block is not annunciated for the containment isolation valve system or the containment spray. This is not in conformance with this NRC requirement.
Guideline 4 requires that isolation of the CVI valves be actuated by several diverse signals.
This requirement is met in that:
- 1.
Safety injection actuation will initiate isolation, 4
- 2.
High reactor building pressure will initiate isola tion, and
- 3. High radiation level will initiate isolation.
Guideline 5 requires that isolation actuation signals be derived from safety grade equipment. San Onofre Unit 1 meets this requirement, except for the radiation monitors.
Guideline 6 requires that no reset of isolation logic will automati cally open the isolation valves.
San Onofre Unit 1 complys with this guideline.
Additionally, General Design Criteria 56 does not permit both valves on a single purge line to be outside of containment. San Onofre Unit 1 does not conform to this criteria.
2.4 Other Related Engineered Safety Feature System Circuits. A review of other related ESF circuits was also made. Unguarded push buttons in the control room allow individual components of the containment spray system to be removed from service. 2 This override of a piece of equipment is not annunciated. Guidelines 2 and 3 are not satisfied for these override circuits.
No other manual overrides have been identified in the review of the material submitted for this audit.
3.0
SUMMARY
The NRC issued a letter, "Containment Purging During Normal Plant Operation," which requested SCE to review purging requirements, controls, and procedures for purging at the San Onofre station.
The electrical, instrumentation, and control design aspects of the containment ventilation isolation valves for San Onofre Unit 1 were evaluated using the design gudelines stated in Section 2.1 of this report.
These guidelines are satisfied except as follows:
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- 1.
The CVI actuation signals from both the safety injection actuation and the high containment pressure are over ridden by a single, unprotected switch.
The NRC should require SCE to install a single switch per overridden actuation signal, and that these switches be either keylocked or covered.
- 2.
SCE has not provided an annunciator for the containment isolation (or CVI) system when the Safety Injection System (low pressurizer pressure signal) is blocked.
The NRC should require SCE to install the required annunciation at San Onofre Unit 1.
- 3.
SCE has not supplied acceptable equipment qualifica tions for the radiation monitors that initiate contain ment purge and vent system isolation. The NRC should require SCE to either provide upgraded equipment (to class 1E requirements) to perform this function, or to upgrade the existing equipment to this standard.
The NRC should require that these deficiencies be corrected. Other ESF systems have deficiencies as outlined in Section 2.4. The NRC should also require that these be corrected.
There is only one automatic purge valve per purge line at San Onofre Unit 1. Each automatic valve has a manual backup valve. Both valves are located outside of containment.
This design is not acceptable per General Design Criteria 56 which requires one valve inside containment and one valve outside containment.
The NRC should determine if this unit should be allowed to operate in exemption to this General Design Criteria.
4.0 REFERENCES
- 1.
NRC/DOR letter (A. Schwencer) to CP&L and all BWR and PWR licensees, "Containment Purging During Normal Plant Operation," dated November 28, 1978.
- 2.
SCE letter, K. P. Baskin, to Director of Nuclear Reactor Regulation, U. S. NRC, "Containment Purging," January 9, 1979.
- 3.
SCE letter, K. P. Baskin, to Director.of Nuclear Reactor Regulation, U. S. NRC, "Containment Purging and Venting," December 14, 1979.
- 4.
SCE letter, K. P. Baskin, to Director of Nuclear Reactor Regulation, U. S. NRC, "Containment Purging and Venting," January 15, 1980.
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- 5.
SCE letter, K. P. Baskin, to Director of Nuclear Reactor Regulation, U. S. NRC, "Systematic Evaluation Program," June 23, 1980.
- 6.
SCE letter, K. P. Baskin, to Director of Nuclear Reactor Regulation, U. S. NRC, "Systematic Evaluation Program," October 2, 1980.,
- 7.
SCE Drawing 235234, Revision 0, "Control Logic Diagrm, Containment Isolation Valves, POV-9, POV-10."
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