ML20049A461
| ML20049A461 | |
| Person / Time | |
|---|---|
| Issue date: | 02/20/1981 |
| From: | Murley T Office of Nuclear Reactor Regulation |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19219B002 | List: |
| References | |
| FOIA-81-417 NUDOCS 8103230682 | |
| Download: ML20049A461 (3) | |
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FEB 20 1981 MEMORANDUM FOR: Harold R. Denton, Director, Office of Nuclear Reactor Regulation, NRR FROM:
Thomas E. Murley, Director, Division of Safety Technology, NRR
SUBJECT:
UPDATE OF DST REVIEW OF ?!RC STAFF SAFETY EVALUATIOff REPORT CH BWR SCRAM DISCHARGE SYSTEM
References:
1.
Memorandum for G. Lainas, T. Novak, R. Tedesco, USNRC from P. Check, USNRC, "BWR Scram Discharge System Safety Evaluation," December 1,1980.
2.
f'emorandum for Harold R. Denton, USNRC, from Thcmas E.
i'urley, USNRC, " DST Review of imC Staff Safety Evaluation Report on BWR Scram Discharge System", January 28, 1981.
The staff prepared a Safety Evaluation Report (SER) on the BWR Scram Discharge System (Reference 1). The Division of Safety Technolocy (DST) previously reviewed this SER and agreed with all the criteria proposed in. that SER and with the methods of " acceptable compliance" with those criteria with one exception
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(See Reference 2, enclosed).
Safety Criterion 3 of the staff SER states:
The scram discharge system instrumentation shall be designed to provide redundancy, to operate reliably under all conditions, and sh611 not be adversely affected by hydrodynamic forces or flow characteristics.
The " acceptable compliance" of the staff SER (Reference 1) expanded this criterion to consider not only redundancy but also diversity. Two alternatives for accept-able compliance to meet the diversity requirement were given. These were:
Alternative 1:
(a) 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; (b) For the instrumentation selected, demonstrate how common-cause failures; such as those identified by operating history and those identified in the Foreward to IEEE 379-1977 (Reference 21), will be considered.
Alternative 2:
(a) Utilize the existing type level sensors, i.e., float level switches; (b) Provide a demonstration that the cause of the damaged floats has been identified and will be corrected or compensated for;
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Harold R. Denton.
(c) Provide a periodic test procedure (for on-line at power testing as well as for testing during and after shutdown) which helps ensure that testing-induced human error and adverse environmental factors will be minimized (requirement under surveillance criteria); and (d) Provide either:
i.
Additional (or substitute) level switches for automatic scram which are made by a different manufacturer; or fi. Demonstrate that the diverse indication of SDV water accumulation provided to the operator by an alarmed continuous monitoring system can provide adequate backup protection if the level sensors (providing auto scram) should fail (note that operator's response to a fast SDV fill event must be considered, i.e., automatic air dump on loss of air).
Our previous evaluation (Reference 1) found that Alternative 2 with option (d)ii (operator action in response to diverse level sensing indications) was undesir-able, and we still consider this to be the case for the long term solution to the problem. However, at a subsequent meeting of members of th.e. staff of both NRR and IE, information from the operating BWRs concerning the operation of water level measuring methods other than floats was discussed. This information appears to show that the reliability of the level measuring methods based on different operating principles is not as great as we had anticipated. Therefore, DST now recommends that Alternative 2 with option (d)i (which we had also pre-viously considered as not desirable) now be offered as a choice to licensees and applicants along with Alternative 1.
We suggest that Alternative 2 with option (d)i be reworded to clarify that the overall float assembly, not merely the switch, must be made by a different manufacturer.
Our original objection to Alternative 2 with option (d)i, was based on our judge-ment that the amount of diversity offered by Alternative 2 with option (d)1 was not as great as that offered by Alternative 1.
While we still consider this to be the case, the new information shows that Alternative 1 is not as favorable in comparison with Alternative 2 with option (d)i as we had thought at the time we wrote our first evaluation (Reference 1). Many problems have occurred with the ultrasonic measuring devices and it is not clear that d-p cells, another possible choice, are any more likely to survive hydraulic pressure or flow tran-sients than the level switches.
Therefore, by allowing the choice of either Alternative 1 or Alternative 2 with option (d)i, it is our opinion that the licensee will be better able to maximize the reliability of the automatic level sensing system for his reactor.
wh Thomas E. Murley, i~ ctor Division of Safety Technology Office of Nuclear Reactor Regulation
Enclosure:
Reference 2 ces w/ enclosure: See page 3
Haro'id R. Denton 3-FEB 20 1981 ccs:
T. Murley P. Check S. Hanauer R. Baer D. Ross A. Thadani D. Eisenhut R. Lobel R. Vollmer J. Hannon M. Ernst V. Panciera B. Mills O
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