ML20043D731
| ML20043D731 | |
| Person / Time | |
|---|---|
| Issue date: | 01/29/1990 |
| From: | Mark C Advisory Committee on Reactor Safeguards |
| To: | Seiss C Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-CT-1958, NUDOCS 9006110120 | |
| Download: ML20043D731 (2) | |
Text
tr-/958 l 4900 Sandla Drive py er%//9M Los Alamos. New Mexico 87544 January 29,1990 Crater Stess. ACRi gg 69 Dear Chet g
r, gg Her e are tome comments on the Structural Enalneerina Subcommittee meeting of January 24-25. I am aware that they are rather obvious, but hope ther may be of some use.
1 First. wtth resoect to the 5 S L Study of Selsmic Threat to Containment Ir t yrit:,
J0r.n Stevenson haI stated that he considers this to be an excellent re le.,. ar.; in his opinicn it is likely to beco,me a '0eilnitiVC r0f 0rence and itandfard' This ma, be partiv because of the expectation that no further it J s 32 ccmt'ehensive a3 this will ever ue undertaken of the seismic i
cra;itv of the.:cntattments. Should such an outcome seem likely there wcald appear to be a real need for some independent review of the study.
l
- v. tether this should te a full-dress " Deer review'(whatever that is) or not. It ihould be suf ficient to Drovide an authoritative independent con-firmation that
- the methods and a?Droximations employed are judged to be Sultable. and that
- the selection of " direct limits states" and their f ailure criteria are adeouate for the purpose.
At a separate point, it may be noted that in at least three of the four plants covered in the study the smallest seismic margins were associated with the so-called " indirect limit states
- These are site-specific. and will require the exercise of insight and careful examination before results from this study can be applied to any plant other than the four addressed.
Admittedly. there are plenty of caveats throughout the body of the report to the effect that the specific ' indirect limit states" will require consideration. But. at least in my view, this point should be much more prominantly emphasized in the Executive Summary than I find it to be --
where, for example, the conclusion is given that the four major types of
" containments evaluated in this study have selsmic capacities at least three times higher than their design - basis shutdown earthquakes.'
l DESIGNATED ORIo111AL f()
900611o1:o 90o129 mm., o Sw;,.e g
w enc
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On another point, there are many references in the report to possible future studies or possible improvements in the estimates provided for the margins available with respect to partitular direct limit states, by carrying out more elaborate analyses I do not find the need for these at all compelling, particularly in the f ace of the evident need f or searching out and assessing the margins applying to the indirect limit states. The studv would appear to have established that pelg the four containment types are tuf ficientiv rugged Letond. wtth respect to_the final presentation at the meeting, which I
had to de with the ef fects of a reduced stif fness for concrete.
I suppose LMt once proper values for the stiffness parameter are decided on this matter will pass from the hands of the structural engmeerIng subcommittee But the consequences of the presently indicated changes seem likely to warrant a large amount of new work wht:h I would hope will be provided for, incidentally, does the work on concrete stif fness represent an instance in which research outside the range of that SDecifically called f or and endorsed by NRR will have demonstrated its importance?
Yo e truly,
- e Larson Mark l
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