ML20043D750
| ML20043D750 | |
| Person / Time | |
|---|---|
| Issue date: | 02/07/1990 |
| From: | Etherington H Advisory Committee on Reactor Safeguards |
| To: | Shewmon P Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-CT-1961, NUDOCS 9006110132 | |
| Download: ML20043D750 (5) | |
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MEMORANDUM FOR:
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G.
Shewmon, ACAS Member M.hw Et,heri(hgton, ACRS Consultant
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FROM:
Harold L$' EVALUATION FOR REACTOR VESSEL STEELS W K
SUBJECT:
CHARPY UPPER SHELF ENERGY (USE)
Now that very low value of Charpy USE are anticipated for some reactor vessels, I feel that I must reiterate my long-standing belief that ASME Code,Section XI, Appendix A, Fig. A-4200-1 is unconservative for low USE steels.
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l Summary of my Contention
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In Figure 1, the ASME curve is assumed to give a conservative value of K for any reactor steel, unirradiated or irradiated, rc and upper shelf temperature, at any temp *erature between RT[ will be not less than about 100 e.g. at 100 F. above RT Ksi E for any steel. The Nrve must therefore envelope the transition curves for all reactor vessel steels.
Actually, the Appendix A curve will envelope transition curves l
for high fracture toughness, t.,tsels, but will not do so for steels l
of low fracture toughness, and the curve becomes increasingly unconservative with decrease in Charpy-upper shelf energy.
The NRC Staff Position The NRC staff has consistently refused to discuss this matter in a meaningful way.
However, there have been a few chinks in the
-monolithic front.
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1.
In January 1986, in response to specific questions in my second memorandum on this subject, Mr. Knight conceded that "Mr. Etherington may have a point."
L 2.
At the subcommittee meeting last summer, an Oak Ridge i
delegate said, in personal conversation, (as nearly as I remember) "You are right, and after your discussion at Oak Ridge, the-Commission spent $2,000,000 exploring the concern.
It was found, however, that.the ASME curve is so conservative that it still bounded data for steels of low fracture toughness."
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Shewnon, ACRS Member 3
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Figure 2 (a handout at the 1989 subcommittee meeting) could be interpreted to indicate the presence of at least one free-thinker in the ORNL contractor group.
4.
Figure 3 (another handout) shows clear evidence of erosion of conservatism for the irradiated steel, even though the fracture toughness remained exceptionally high.
Recommendation I know that ACRS cannot follow up on every personal opinion, but in this case I am suggesting that uso of unconservative data may lead to operation of one or more reactors that should be decommissioned or shut down for heat treatment of the vessel.
I think ACRS should make an immediate in-house review, terminating in a short report to assure the subcommittee in establishing a position.
The review should include a study of the proceedings that led to formulation of the ASME Appendix G (Section III) and Appendix A (section XI) curves, as well as appraisal of the current problem.
I don't know how this can be done.
Clearly, the ACRS staff cannot take time out to do this, but perhaps one of the fellows could be assigned to it.
or perhaps, John McKinley could be persuaded to put in a week (or two) revising the background.
Finally, an expert opinion (e.g. Herb Corten) might be sought, i
Attachments:
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