ML20059L751
| ML20059L751 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 11/10/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20059L736 | List: |
| References | |
| NUDOCS 9311170359 | |
| Download: ML20059L751 (2) | |
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO ACCUMULATOR PRESSURE AfiD VOLUME INSTRUMENTATION RELAXATION OF REGULATORY GUIDE 1.97 ENVIRONMENTAL OVALIFICATION RE0VIREMENTS COMMONWEALTH EDISON COMPANY ZION NUCLEAR POWER STATION. UNITS 1 AND 2 C0CKET NOS. 50-295 AND 50-304
1.0 INTRODUCTION
Section 6.2 of Generic Letter 82-33 requested that each licensee report on its implementation of Regulatory Guide (RG) 1.97, Revision 2, and methods for complying with the Commission's regulations, including a supporting technical justification of any proposed alternatives or deviations. A review 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 Regulatory Guide for each post-accident monitoring (PAM) variable except for the variables identified in the SE.
Exceptions were identified for the accumulator level and pressure monitoring.
A large nember of the exception requests were to relax the equipment qualification (EQ) requirement from a Category 2 to a Category 3 qualification that allows commercial grade instruments to be used in certain applications.
However, none of the submittals requesting the exceptions provided sufficient justification to grant the exception. These requests were denied to licensees whose RG 1.97 compliance SEs.were issued by the staff before 1987.
Since 1987, exceptions for the accumulator instrumentation have been 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, in 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 RG 1.97, Revision 2.
The RG identifies the accumulator instrumentation as a type D variable that provides information to indicate the operation of individual safety systems and other systems important to safety, to help the operator in selecting appropriate mitigating actions. The RG lists Category 2 qualification for the accumulator instrumentation. The Category 2 qualification criteria require the instrumentation to be qualified i
in accordance with RG 1.89 and the methodology described in NUREG-0588.
Additionally, instrumentation with a Category 2 qualification should be energized from a high reliability power source, not necessarily standby power.
9311170359 931110 PDR ADOCK 05000295 p
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$ 3 In contrast to this, the Category 3 qualification criteria require only an off-site power source and the instrumentation to be 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 the qualification category of a RG 1.97 variable are 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 barated water and pressurized with nitrogen gas. They are a passive system that provides a fast acting, high flow rate, cold leg injection during the injection phase of an Emergency Core Cooling System (ECCS) operation.
Both volume and pressure are monitored to ensure that the accumulator functions in accordance with the Updated Final Safety Analysis Report. To prevent inadvertent isolation of an accumulator from the Reactor Coolant System (RCS) during normal power operatiqn, each accumulator's motor operated isolation valve (MOV) is open with its power removed, and the status of the MOV is ensured by the Technical Specifications surveillance requirements. During normal power operation, two swing check valves in series isolate the accumulator from the RCS.
If the RCS pressure decreases below the accumulator pressure (as during a loss-of-coolant accident), the check valves open and the nitrogen gas pressure forces the borated water into the RCS. Thus, 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.
3.0 CONCLUSION
Based on its review, the staff has concluded that post-accident monitoring of the accumulator volume and pressure does not serve a safety function and no operator actions are based on the information that would require Category 2 i
qualification of the instrumentation. Therefore, in lieu of Category 2 i
qualification, Category 3 qualification of this instrumentation is acceptable.
Principal Contributor:
- 1. Ahmed Date:
November 10, 1993