ML20052A003
| ML20052A003 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 01/25/1982 |
| From: | Pomeroy P RONDOUT ASSOCIATES, INC. |
| To: | Griesmeyer J Advisory Committee on Reactor Safeguards |
| Shared Package | |
| ML20052A001 | List: |
| References | |
| NUDOCS 8204260421 | |
| Download: ML20052A003 (4) | |
Text
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.s ROwoOu1 ASSOCIATES,
" [NCORPOEATED P.O. Ba 224, Stone Pddge. New York 12454 I
nts re;ut may cid21 FW *ph January 25, 1982 w other 1: term 23cn *MB
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p,eA1 act te talt::td satil a tenew d me tasment his tccc empletes.
RECEIVED NC 0 55 u S S R.C.
FEB 2 1982 au kllI21234k 4
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.3.i i Dr. J. Michael Griesmeyer Advisory Comnittee on Reactor Safeguards U.S. Nuclear Regulatory Co=nission Washington, D.C.
20555
Dear Dr. Griesmeyer:
In accordance witn your letter of December 21, 1981, I have reviewed the appropriate sections of the Zion PRA
. and a copy of my remarks which I forwarded to Prof. Okrent, is attached.
I have also enclosed a signed Form 148 for one day consulting fee.
Can you arrange for processing of this billing?
~
Thank you.
Sincerely yours, mM f.d.d%
3 Paul W. Pomeroy
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PWP:gla Attachments l
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Co.ments en the Probabilistic Assessment of the Seismic Ground Motion Hazard at the Zion Nuclear Power Plant, t.ake County, Illinois I have dealt alrost exclusively with Section 7.9.1 entitled ' Seismic Ground Motion Hazard at Zion Nuclear' Power Plant Site' since 1) that portion of the re-port falls within my area of expertise and 2)-the conclusions of that portion have profound effects on the later probabilistic analyses.
Section 7.9.1 was, prepared by the Golden, Colorado office of Dames & Moore presumably under the direction of Dr. Robin McGuire with Prof. Otto Nuttli serving as a seismological consultant.
In general, the me5cdology applied in the analysis in Section 7.9.1 con-forms to the present state of the art and, in my estimation, the conclusions are not inappropriate for this type of approach.
However, there are so many assump-tions in the analyses that I question the usefulness of the report as an input to the scientific decision making process.
The implications of.the assumptions are not discussed nor are implications of possible alternative assumptions. Some of the assumptions have been dealt with in other ACRS deliberations while others have not.
I will try to list the assumptions and indicate areas that require further calucidation.
I have underlined the assumptions taken from the text.
A.
Page 3-1st paragraph--basic assumptions of the seismic hazard model.
1.
Zones of potential future earthouakes are delineated by seismicity and tectonic evidence.
While this statement is almost an act of faith arong the seismological community, there is certainly evidence that previous seis-micity alone does not delineate future active zones and, while tectonic evi-dence of ancient faulting is abundant, its relationship to present day seis-micity is far from clear.
If this assumption were not made, what are the im-plications for probabilistic seismic risk analyses?
2.
The relative frecuency of earthouake magnitudes in seismogenic zones can be represented by a truncated exponential distribution.
What is the evi-dence that a truncated exponential is appropriate? What are the implications of a non-truncated exponential distribution?
j B.
Page 4, Seismogenic Zones.
1.
The report indicates that all the seismogenic zones of Nuttli and Hermann were included in the analyses and that except for N. Illinois and the central stable region, they are not important.
It would be useful.to see how they are non-important if the assumptions below happen to be wrong.
O e
- A
/
2.
Thre ralternative hycotheses were exami'ncd for seismoo:.nic zones in the vicinity of the site and these hypotheses are assicned a subjective (!) -
probability of 0.2, 0.5, and 0.3.
What if these subjective probabilities are completely incorrect? What is the effect on the analyses? Who defined the Wisconsin Arch Zone and the Wiconsin Arch-Michigan Basin Zone? Certainly not Nuttli and Hermann who only defined a Northern Illinois zone and the Central Stable region.
How does the area of the Nuttli-Hermann zone. compare with the are of the Wisconsin Arch Zone? If there is a difference, how does that effect the analyses? Are the boundaries of the Wisconsin Arch Zone and the Wisconsin Arch-Michigan Basin Zone real and, if so, why?
3.
Page 5--While oEher seiscogenic zones 'might be defined which would indicate larger (or smaller) suismic hazard at the site, it is felt (!) that t
no such zones can be justified on a geological basis....
None of these zones, including the ones used in the analysis, can be justified on a geological basis.
Why exclude some arid include others?
C.
Page 6, Seismicity Parameters.
How is seismic activity rate determined?
It would be impossible for a non-specialist to figure it out from the discussion in this section.
I.' Several rcdifications were made to the activity rates reported by Huttli and Hermann.
Other than No. 1 on page 6 which is a valid correction, why?
In No. 2 on page 6 where the activity rates for this report are calcu-lated for m t 4 because earthquakes of smaller magnitude rarely cause structural b
dama ge.
What does that have to do with activity rates? What is the effect of uncertainty in activity rates? In eg 1 on page 2, usually n is the cumulative number of events greater than or equal to a given m.
Is there a purpose in b
defining n as the annual number of earthquakes of body wave magnitude m and, b
if so, what is it? What is the effect on this study of variation in b values?
was assigned using 2.
Page 7, paragraph 3--Maximum body wave magnitude ab Dr. Nuttli's subjective (!) judgement. What is the evidence that there is a ab rax for any of these zones? I know the arguments that'Dr. Nuttli has advanced but he,could be wrong. What is the effect on this analyses if there is no mb max? A double triangular probability distribution was chosen to represent un-ver the range 5.4 to 6.2.
What is the effect on the analy-certainty in m mx b
sis of this distribution? Why this and not another distribution?
Page 8, paragraph 1--A simolifying assumption was made that low b 3.
max. This produces a wider range values are perfectly correlated with high mb of hazard curves than less-than perfect correlation but it is not important since'heuncertaintyinshismogeniczorescausesthecredominantspreadin
4 se'ismic hazard curves.
The simplifying assumation was judged (!) to be appropri-ate.
By whom?
D.
Page 9, Estimation of Ground Motion.
Nuttli's theory estimates a sustained level of acceleration corresponding to the third hichest oeak in the acceleration time history. What is the valid-ity of the ' theory' of ' sustained' level of acceleration? Why was the value 1.37 used at all magnitudes?
On page 10, a factor of 0.9 is introduced as a correction for a random oriated acceleration. What is the derivation of that factor?
On page 12, a further modification is made,to ' account for the hypotheses' that effective peak acceleration may be limited and limits are chosen as follows:
8 max probability 0.5g 30%
0.8g 50%
00 20%
What is the effect if the hypothesis is completely wrong and an infin.ite a
has an associated probability of 100%7 mn On page 13, paragraph 3, certain considerations outlined led the Dames &
Moore investigators to reject formal application of the TERA curves and use re-sults based solely on the Nuttli estimates.
Nuttli estimates or modified Nuttli estimates? What happens to the analysis if TEPA curves are used?
To sum.arize, the coraents outlined here suggest that while the methodology-
[
is ' state of the art', there are so many assumptions and judgements (subjective or other) that are made that'the usefulness of this analysis is open to question.
Apparently, the other parts of the Zion PPA rely heavily on this input data.
A much more detailed, systematic account of the analysis, as well as its assump-
[
tions and their effects should be obtained. The report is incomplete.as it i
i stands and its unqualified acceptance is not warranted although its conclusions may be valid.
1 e
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