ML20044C391
| ML20044C391 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 03/11/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20044C386 | List: |
| References | |
| NUDOCS 9303220402 | |
| Download: ML20044C391 (2) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION c
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E-WASHINGTON. D. C. 20586 l
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION PRESSURIZED WATER REACTORS ACCUMULATOR PRESSURE AND VOLUME INSTRUMENTATION.
RELAXATION OF REGULATORY GUIDE 1.97 ENVIRONMENTAL'00ALIFICATION REDUIREMENTS a
1.0 INTRODUCTION
Section 6.2 of the Generic Letter 82-33 requested licensees to provide a report on their implementation of Regulatory Guide (RG) 1.97 (Rev.2), and methods for complying with the Commission's regulations including a supporting.
technical justification of any proposed alternatives or deviations. A review i
of the licensees' submittals was performed by the staff and a safety.
evaluation (SE) was issued for each plant. These SEs concluded that the licensees either conformed to, or adequately justified deviations from, the -
guidance of the RG for each post-accident monitoring (PAM) variable except for j
the variables identified in the SE.
Exceptions were identified for the accumulator level and pressure monitoring.
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A large number of the exception requests were for relaxing the equipment l qualification (EQ) requirement from Category 2 to Category 3 qualification that allows commercial grade instruments to be used,in certain applications However, none of the submittals requesting the exceptions provided sufficient 4 -
1 justification for granting.the exception. These requests were denied to.the-licensees and applicants whose RG 1.97 compliance SEs were issued by the staff' before 1987. Since 1987, exceptions for the accumulator, instrumentation were considered by the staff as an open item until a generic resolution could be found.- Thirty-two plants requested relaxation of EQ requirements from Category 2 to Category 3 for the accumulator level and pressure instrumentation.
2.0 EVALUATION The Code of Federal Regulations 10 CFR'50.49 requires licensees to establish a program for qualifying certain post-accident monitoring equipment for which ~
specific guidance concerning the types of variables to be monitored-is provided in Revision 2 of RG 1.97.
This. guide. identifies the accumulator instrumentation as type D variable that provides information to indicate the operation-of individual safety systems and other systems important. to safety, i
to help the operator in selecting appropriate mitigating actions. The guide lists Category 2 qualification for this instrumentation. The' Category 2-a qualification criteria-require the instrumentation to be qualified in accordance with RG 1.89 ' Environmental Qualification of Certain Electric Equipment Important to Safety for Nuclear Power Plants," and the methodology-described in NUREG-0588,'" Interim Staff Position Engineering Qualification of i
Safety Related Electrical Equipment." Additionally, the instrumentation with
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Category 2 qualification should be energized from a high-reliabil.ity power i
source, not necessarily standby power.
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, In contrast to this, the Category 3 qualification criteria require only'an off-site power source and the instrumentation to be only of high-quality commercial grade to withstand the specified service environment (mild environment as defined in 10 CFR 50.49, paragraph c).
Qualification criteria for instrumentation are established based on the safety function of the system whose variables are being monitored. The selection criteria for RG I.97 variables qualification category is based upon whether monitoring of system parameters is needed during and following an accident and whether subsequent operator actions in the operating procedures are dependent on the information provided by this instrumentation.
The accumulators are pressure vessels filled with borated water and pressurized with nitrogen gas.
Being a passive system, it provides a fast acting, high flow rate, cold leg injection during the injection phase of an ECCS operation. Both volume and pressure are monitored to assure the accumulator's function in accordance with the Final Safety Analysis Report (FSAR) safety analysis. During normal operation, the accumulator is isolated from the reactor coolant system (RCS) by two check valves in series. To prevent inadvertent closing, each accumulator's motor operated isolation valve (MOV) is normally open with its power removed, and the status of the H0V is
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assured by the technical specification surveillance requirements. Should the RCS pressure decrease below accumulator pressure (as during a LOCA), the check valves open and the nitrogen gas pressure will force the borated water into the RCS. Thus, a mechanical operation of the swing-check valves is the only action required to open the injection path from the accumulator to the reactor core. No external power source or initiating signal is needed for the accumulator to perform its safety function. The operator can only control the operation of the motor operated valve which is used to isolate the accumulator from the RCS.
Isolation from the RCS is not a safety function of the accumulator. Additionally, the accumulator is not designed to perform any post-accident safety function.
The above discussion establishes that the accumulator instrumentation does not perform a safety function during or in a post-accident environment and operator actions to mitigate the effects of an accident do not depend on the information provided by the accumulator instrumentation. Additionally, successful performance of core cooling systems can be inferred from environmentally qualified instrumentation.
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3.0 CONCLUSION
Based on our review, the staff concludes that the post-accident monitoring of the accumulator volume and. pressure does not perform a safety function and no l
operator action is based on the information that will require Category 2 qualification of the instrumentation.
In lieu of Category 2 qualification, Category 3 qualification of this instrumentation is acceptable.
Principal Contributor:
I. Ahmed Date:
March 11, 1993 l