ML20056C517
| ML20056C517 | |
| Person / Time | |
|---|---|
| Issue date: | 04/10/1993 |
| From: | Ward D Advisory Committee on Reactor Safeguards |
| To: | Kress T Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-CT-2069, NUDOCS 9306240365 | |
| Download: ML20056C517 (2) | |
Text
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/cc Dean Houston fpf 6/m/93 '
April 10,1993 To:
Tom Kress, Chairman ACRS Severe Accidents subcommittee L.
From: Dave Ward, 1
ACRS consultant
Subject:
Comments on meeting of March 18 on review of ABWR design and severe accident considerations j
You asked to be provided comments or what ACRS should hear next on the subject.
j I suggest it would be useful for the Committee to learn more about the following:
1] ATWS GE opted to incorporate a diverse scram system rather than credit, through analyses, a j
possible benign system response to an ATWS. ACRS had suggested that the latter would be acceptable and the Staff and Commission had agreed. Why did GE opt for i
the added system? Was the calculated system response not benign?
2 Unnecessaryreouirements i
A] number of features are being included in the ABWR design, even though they not be warranted by severe accident concerns, because GE says they are easily accommodated. This may establish a precedent that these things are actually necessary in other future designs or in possible future ABWR modifications. These include:
GE said the hydrogen recombiners "r uired" by RG 1.97 will cost "only a few million dollars". Recombiners do no for severe accidents, is there really a need for them? Good DBAs should surrogates for the things that really might l
happen. What does RG 1.97 have in mind? [A million here, a million there; pretty soon it adds up to real money -- to paraphrase Everett Dirksen.]
Why are both the belt and suspenders of venting and cavity design required for
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the rare events leading to DCH. The Staff says DCH is a risk-dominant sequence.
Is that true for ABWR7 Would it be with only the belt?
j PCT > 2200 F as a de6nition of core damage appears to be unnecessaril con 3ervative. Apparently GE can tolerate this, but is it a good precedent? y
/q 3l The so-called deteiWinc containment reouirement I ow does the determrnstic criterion for containment, "Sennce Level C", etc. have on p. 7 of its presentation charts? phenomenological behavior, as the St to about uncertainties in, e.g.,
clai 4' Hvdrooen detonation and 8tra65cetion The Staffclaims [p.20 of diarts] that using 10% rather than 13% as a datonation o
threshold provides sufficient margin for concems about high local concentrations of p-y hydrogen, especially as caused by stratification. This should be explained and justified.
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5]MAAP 3
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Some examples of MAAP calculations, perhaps compared with anything MELCOR
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9 has done, should be shared with ACRS. Especial ofinterest would be calculations 1
M which influenced dp about whether an AB feature was acceptable or not.
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6] Stradlicadon and high temperatures One of the items suggested for consideration in the ACRS letter on May 1991 were
. i possible detriments to containment insegnty that might result from local temperature
'l extremos due to stratification of hot spes in an accident, perha This seems not to have been cons,c ered in the ABWR review. ps even in a LOCA.
i The Staff should explain why they consider N unnecersary.
7 IS-LOQA T% intersystem LOCA issue is still open. ACRS should hear about its resolution.
8] How much metalis available?-
GE said that 100% of cladding in contact with the fuel amounts to about 30% of the total metal in the core area.- This 100% is often presented as if it is a conservative upper limit..
H If there is some reason to believe the reraamin; 70% is categoricall produce hydrogen, GE or the Staff should expain that. Otherwise,y less likely to.
they should justify-i use of the 30% value.
9 MCCI and 0.02 so ml MWt This is not resolved and ACRS should hear more.
On other subjects:
- It seems to me that the steam explosion issue for ABWR has been adequately.
resolved.
The fact that NRR has combmed severe accident and containment issues into one -
branch shows real progress. - For too long, the Staff behaved as if these were almost -
unrelated subjects. They havent yet gone the full distance to a rabonal perspective, however. Charts 5 and 6 retain some muddle in the PURPOSE sections, although the guidelines and requirements are not bad.: SECY-92-070 still maintains that SA and
- DBA "should be kept separate".' if this means separate in the sense that design requirements are different, as summanzed on charts 5 and 6, that is good. But, if they -
retain the idea that SA should not be a bases for designs, that is not good.
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