ML20028D402
| ML20028D402 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 01/11/1983 |
| From: | Alexion T, Calvo J Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20027A776 | List: |
| References | |
| REF-GTECI-B-24, REF-GTECI-EL, REF-GTECI-ES, TASK-B-24, TASK-OR NUDOCS 8301190075 | |
| Download: ML20028D402 (2) | |
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ENCLOSURE 1 SAFETY EVALUATION REPORT DAVIS-BESSE NUCLEAR POWER STATION OVERRIDE OF CONTAINMENT PURGE ISOLATION Introduction Instances have been reported at nuclear pcwer plants where the intended automatic closure of the containment purge / ventilation valves during a postulated accident would not have occurred because the safety actuation signals were inadvertently overridden and/or blocked, due to design deficiencies. These instances were determined to constitute an Abnormal Occurrence (#78-5). As a follow-up action, NRR issued a generic letter requesting each licensee to take certain actions.
Evaluation The enclosed report " Override and Reset of Control Circuitry in the Ventilation / Purge Isolation and Other Engineered Saf.ejy Feature Systems" was prepared for us by Franklin Research Center as part of our technical assistance contract program. The report provides their technical evaluation of the design compliance with NRC' provided criteria.
The contractor's report states that the containment ventilation system portion of the safety features actuation system (SFAS) circuit design, as well as the SFAS in general, is not in conformance with Criterion 1.
Criterion 1 states that the overriding of one type of safety actuation signal should not cause the blocking of any other type of safety actuation signal. We agree with the contractor's findings in this regard.
The contractor's report states that the SFAS circuit design is not in conformance with Criterion 2.
Criterion 2 states that sufficient physical features should be provided to facilitate administrative controls. We agree with the contractor's findings for this aspect of the design.
1 The contractor's report also states that the intent of Criterion 3 is sa tis fied.
Criterion 3 states that system-level annunciation of the overridden status should be provided. The contractor's report recommends that although annunciation of the overridden status is not provided, sufficient indication of the bypass condition is provided so that the intent of Criterion 3 is met. The contractor based this recommendation mainly on the role played by the plant computer alerting the operator of the possibility that the actuation logic will no longer be tripped l
because an override has been applied. We disagree with the contractor's recommendation because this indirect method of annunciatir.g an override l
condition does not provide sufficient assurance that tr.e operability 8301190075 830111 PDR ADOCK 05000346 P
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status of the actuation system can be ascertained after an override signal was applied.
Furthermore, it is not clear whether the design of the actuation system has the capability to automatically return to the normal mode of operation after an initiating signal has cleared, when an override signal is present.
In order to clear the override signal, the local or remote reset switch must be manually depressed.
The contractor's report states that Criteria 4, 5 and 6 are satisfied.
We agree with the contractor's findings in this regard.
Concl usion Based on our review of the contractor's technical report, we conclude that the electrical, instrumentation and control design aspects of the override of containment purge valve isolation and other engineered safety features signals are acceptable except for the items listed below for which j
we recommend the following design changes:
1.
The SFAS should be modified so that the overriding of one type of
{
safety actuation signal does not cause the blocking of any other type of safety actuation signal as required by review Criterion 1.
I 2.
The block (override) push buttons on the SFAS initiation panel should be provided with special physica,1 features to facilitate administrative controls as required by review Criterion 2.
3.
System-level annunciation of the overridden status should be provided.
l This safety evaluation was prepared by T. Alexion and J. Calvo of the Operating Reactors Assessment Branch.
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