ML20210Q716
| ML20210Q716 | |
| Person / Time | |
|---|---|
| Site: | 05000000, Davis Besse |
| Issue date: | 08/08/1985 |
| From: | Schrock V CALIFORNIA, UNIV. OF, BERKELEY, CA |
| To: | Boehnert P, Ward D Advisory Committee on Reactor Safeguards |
| Shared Package | |
| ML19301C663 | List: |
| References | |
| FOIA-86-110 NUDOCS 8605150062 | |
| Download: ML20210Q716 (5) | |
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.' l UNIVERSITY OF CALIFORNIA, BERKELEY SANTA RARBARA e SANTA OtCE 3"*" rv
- D4vis
- IRVD8E
- 108 ANCELES
- RIVERSIDE
- SAN DIEGO
- SAN FRANOSCO l
BEREELEY, CAUTORNIA 94720 COLLEGE OF ENCINEER1NC DEPAPTMENT OF NUCLEAR ENCINEERI%C l
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i David Ward, Chairman ECCS Subcommittee Advisory Committee on Reactor Safeguards l
U.
S. Nuclear Regulatory Commission Washington, D.
C.
20555
Dear Dave,
Attn: Paul Boehnert 1
I am enclosing my comments on the topics covered at the July 31, l
1985 meeting of the EECS Subcommittee.
Sincerely, f'
Virgil E.
Schrock Professor 8605150062 860421 PDR FOIA f){p PDR PEDRO 86-110
Augunt @, 1995 To: David Wcrd Att'n Paul Boehnert From Virgil Schrock RE: ECCS SUBCOMITTEE MEETING July 31, 1985 A. Comments on Appendix K Revision
- 1. I am generally supportive of the approach the NRC staff has chosen for revision of licensing calculation rules.
The use of best estimate calculations and avoidance of specific correlations and unrealistic ad hoc " conservative assumptions" such as disallowing the effect of steam cooling, etc., is a great step forward from the approach in the present Appendix K.
Providing the necessary conservatism by taking the "best estimate" at the 95 percent confidence level is a sound and defensible approach, in principle, and one that must most certainly be more satisfactory to the technical community.
I continue to see a need for a greater emphasis to be given to the documentation of many aspects of the technical problems involved.
The document that Drs Beckner and Zuber are editing will be extremely critical to the success of the new licensing procedure in the sense that it will endure the critical examination to which it will likely be exposed.
So far we have reviewed only an outline of the report.
While it appears to be rather complete in scope there remain many technical issues to be examined in detail in order to complete the report.
Probably the most important general aspec't to be addressed by this document (and the companion REG GUIDE) is the technical basis for determining the 95 percent confidence level in calculated quantities that are a part of the acceptance criteria (peak clad temperature, clad oxidation, )
l In Brian Sheron's presentation, a philosophy of "less interest in l
individual models than in the right answer" was put forward.
The inference is that the right result can be expected from a collection of inaccurate component models by f ortuitous compensation of errors.
In my view, this faulty reasoning has been an impediment to good code assessment.
I think this is the wrong approach both to " selling" che new rule and to implimenting it.
We do not have the richt answer.
The technical basis must 1 -
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show that we have tha cbility to cesean tha 95 percent confidenco 1
level.
This can only be done by showing that (a) we can evaluate the uncertainty in the result of our best estimate calculation via error propagation analysis and (b) by demonstration that the effect of scale, going from experimental data to the full scale plant does not invalidate the assessment of the uncertainty in )he final application.
This is not a simple task but it must be done if the procedure is to be accepted.
It will agi be done if the philosophy mentioned above is pursued.
One example of what I mean is the decay heat evaluation and its role in the final results.
Decay power with eccuracy of the order of a f ew percent depends upon the f uel composition and operating power history of the fuel.
In general these parameters vary spatially within the core and with time.
The ability exists to do the evaluation of local decay power histories and to estimate the time dependent uncertainty for each point in the reactor for selected sets of the parameters, however this is an overwhelming burden in computational time.
The simplifying procedure developed by General Electric Co. has the potential to provide adequate results in the context of 95 % confidence in PCT and clad oxidation but the staf f has not had the time to document how they I don't have satisfied themselves that this is indeed the case.
see how ACRS can endorse the final procedure unless details are made known to it.
s With regard to the REG GUIDE, there is a new problem that arises.
aspects that are essential to an acceptaole calculation have Some been lef t to cover in the REG GUIDE.
Thus the necessary language The draf t REG GUIDE consistently is avoided in many instances.
I talks about what should be done rather than what,gggt be done.
understand that this an administrative issue but in my opinion it l
needs to be settled bef ore the final division of material between l
i the " rule" and che REG GUIDE can be made.
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approve codes such as SAFER as being in the category of NRR will best estimate.
From what I have heard at this and previous they do not commit themselves to using NRC's own best
- meetings, codes to assure themselves that such codes accomplish predictions that have 95 % certainty.
In summary, I am in f avor of the ht\\0
intended use of the 95 % confidence approach but I hnvo an unOcoy feeling that at worst its achievement will be only a claim not a reality or at best lacking in supporting technical details.
ACRS should press for a sound approach and better supporting docmuentation.
The ECCS Subcommittee should review further both the RES
" Technical Basis" and the REG GUIDE as well as the White Paper.
B.
RC PUMP TRIP STRATEGY Both CE and B&W are doing EM or mixed bag calculations to justify their selection of pump trip procedures f or SBLDCA.
In my opinion should be more insistent upon best estimate calculations the staff to support choices of operating procedures.
It is just plain These comments should apply sloppy engineering to do otherwise.
to be provided by to plant specific supporting calculations still the W plants.
C.
DAVIS BESSE EVENT The event revealed several common mode failures that could and The fact that the operators should have been understood long ago.
were able to restore auxiliary feedwater in time to save the plant in part due to post TMI emphasis upon improving was no doubt operator knowledge of plant transietits on the other hand it is that owners need to be f orced to do,. more to identif y such clear problems and take corrective action bef ore a plant is put in such It will take a precarious position as occurred at Davis Besse.
additional study of NUREG-1154 (advance copy distributed at the My first to fully assess the significance of the event.
meeting) is that the NRC investigation of the event was quite reaction thorough and suggests that we still have serious generic weaknesses in the safety of operating plants that call for a major reassessment.
D. Seismic Risk to Instrument Tubes It was not razy to follow the logic of the NRR assessment of the potential problem.
It was suggested that these lines may be vulnerable at the seal table.
Available old calculations f or
-s-f0l0
breake et tha roactor voo001 wero used to try to GStablish thct even for this extreme case there is not a major risk.
I would like to see some calculations based upon more up-to-date codes together with a more serious examination of the possibilities of f ailure propagation moving the break location f rom the table toward the reactor vessel and increasing the number of broken I was not convinced that this is a "non-problem" although tubes.
it may well be.
E.
LOCA MODEL ERROR CORRECTIONS It appears that the staff is persuing this situation and has established that there is no saf ety issue f or operating plants involved as a consequence of the recently discovered errors in some licensing code models.
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