ML20052F270
| ML20052F270 | |
| Person / Time | |
|---|---|
| Issue date: | 11/03/1981 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML19219B002 | List: |
| References | |
| FOIA-81-417 NUDOCS 8205120301 | |
| Download: ML20052F270 (3) | |
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DRAFT POSITION ON DIVERSITY FOR SDV LEVEL fNSTRUMENTATION BACKGROUND The safety function of reactor scram is a absolute necessary safety function -
its failure leads to unacceptable consequences (at least until ATWS fixes are made).
Therefore, it is extremely important that there be sufficient volume in the SDV for accepting a full reactor scram at all times.
There have been sources of water identified which could fill the SDV.
Given that water could be there, reliable instrumentation is necessary to detect water buildup and scram the reactor. The existing level instrumentation has experienced some failures. These failures have demonstrated the potential for common cause failures and therefore, common cause failures majbe the most significant contributor to this scram function unreliability.
Although it is now believed that the common cause failure (i.e., hydrodynamic forces) has been identified for the crushed floats, there is residual concern for other common cause failures such as ' human error (particularly during testing) or manufacturing errors.
Therefore, it is the staff's psoition that common cause failures should be addressed because of the potential consequences of the loss of the protective function and the experience to date with the level switches.
POSIT 10N' The BWR licensees should address single random failures as well as common cause failures with respect to the SDV level instrumentation provided for reactor scram. This instrumentation is part of the plant protection system I
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and, therefore, should :; wet all protection system requirements.
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8205120301 811103 PDR FOIA DIGNAN81-417 PDR
1 A.
With Respect to Single Failures (Random) 1.
Provide sufficient redundancy in the automatic scram level instrumentation to meet the single failure criterion on I
each instrumented portion of the SDV.
t B.
With Respect to Common Cause Failures Meet Either of the Following Two Al ternatives.
t Alternative 1:
1.1 Provide additional (or substitute) level sensing instrumentation for the automatic scram function to include diversity as well as-redundancy. The diversity should, as a minimum, be achieved by level sensors that employ different operating principles for measuring the water" level.
1.2 For the instrumentation selected for 1.1 above, demonstrate how common cause failures; such as those identified by operating history and those identified in the Foreward to IEEE 379-1975, will be prevented.
Alternative 2:
2.1 Utilize the existing type level sensors, i.e., float level switches, and 2.2 Provide a demonstration that the cause of the damaged floats has been identified and will be corrected, and 2.3 Provide a periodic test procedure (for on-line at power testing as well as for testing during and after shutdown) which helps
'i li ensure that testing induced human error is minimized, and il 2.4 Provide either:
ij.,
a) Additional (or substitute) level switches for automatic scram P
f which are made by a different manufacturer, or l
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b) Demonstrate tnat the indication provided to the operator by an ultrasonic system can provide adequate back-up protection if the level sensors (providing auto scram) should fail.
The ultrasonic system does not necessarily have to be classified as part of the protection system and not provide automatic scram.
However, its adequacy needs to be addressed considering:
- 1) The reliability of the information provided to the operator, specifically its redundancy and testing; and
- 2) The operator actions as a result of this information.
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