ML19209C917
| ML19209C917 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 06/13/1979 |
| From: | Michelson C Advisory Committee on Reactor Safeguards |
| To: | Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-CT-1124, NUDOCS 7910180473 | |
| Download: ML19209C917 (2) | |
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UNITED STATES 5 }* ",,f'g'o NUCLEAR REGULATORY COMMISSION y
E ADVISORY COMMITTEE ON REACTOR SAFEGUARDS e
I WASHINGTON D. C. 20555 o
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TO:
ACRS MEMBERS C. Michelson, ACRS Consultant,hlff FROM:
SUBJECT:
Failure of Feedwater Flow ctraightner at San Onofre Nuclear Station, Unit 1 LER 78-013 for the subject incident brings into focus a related concern which needs to be addressed for all piping systems containing internal I
appurtenances such as flow straightening devices.
The concern is that such devices might have to be designed to withstand blowdown flow load-ings in addition to normal loadings.
Consideration should be given to the possible consequences of an internal appurtenance being dislodged by the blowdown flow. Of particular concern would be the case of a straightening vane which might become lodged in a valve whose closure is an essential mitigating step following an accident.
If such a consequential failure is unacceptable, the supporting attach-ment scheme for the appurtenance must be designed for the blowdown load-ings including the degradation effects of cyclic fatigue.
It should also be recognized that blowdown flow might be in either direction. This could affect the severity of loading for norsymmetrical arrangements.
When considering the consequential effects of an internal appurtenance failure, consideration should also be given to possible steam generator tube damage. Of particular concern would be a primary or secondary side piping failure whose blowdown consequences might include the generation of internal debris due to one or more consequential failures. This could lead to multiple steam generator tube failures including, perhaps, both steam generators.
The present design basis for PWR plants does not take into account the possibility of such a combined primary / secondary side blowdown into containment or the possibility of a blowdown outside of containment if the debris should aisc prevent isolation valve closure.
There are a number of internal appurtenances which need to be examined from this viewpoint. Typical examples are flow orfices, flow eler.ents,
thermocouple wells, straghtening vanes, flow scoops, flow tubes,
diffusers, and thermal sleeves. The plant Safety Analysis Report draw-ings may not clearly identify such appurtenances for review.
It might be interesting to find out how this problem is being handled by the NRC.
1176
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h 2-In my opinion, this LER is a good example of the type of safety question which might be uncovered by a proper examinatiot, of plant failures during normal operation.
Equipment weaknesses revealed during the generally less severe loading conditions of normal operation could be important indicators of how the equipment and systems might be expected to perform under potentially more severe accident loading conditions during which such consequential failures might not be aceae:able.
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