ML17174A224
| ML17174A224 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 11/29/1979 |
| From: | Janecek R COMMONWEALTH EDISON CO. |
| To: | Oconnor P Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML17174A225 | List: |
| References | |
| TASK-03-06, TASK-3-6, TASK-RR NUDOCS 7912070417 | |
| Download: ML17174A224 (9) | |
Text
e Commonweal.dison One First National Plaza. Chicago, Illinois Address Reply to: Post Office Box 767 Chicago, Illinois 60690 No~e~ber 29, 1979
- Paul O'Connor, Project Manager Operating Reactors-SEP Branch U.S. Nuclear Regulatory Commission Washington, D.C. 20555
Subject:
Comments on the LLL/TERA Reports NRC Docket 50-10/237
Dear Mr. O'Connor:
Commonwealth Edison requested Fugro to review the LLL/TERA reports and to provide their comments.
Attached are Fugro's general comments on the LLL/TERA reports.. In addition to the Fugro comments, Commonwealth Edison's general comments are provided in the following paragraphs.
In the type of study performed by LLL/TERA, the use-fulness of the results is directly related to the cbnsistancy of the expert opinions.
This survey is attempting to determine the state of knowledge on the expected maximum seismic event to occur at a given site.
If the expe~t opinion varies significantly the reasons for. the variation must be understood before the opinions can be used.
In the LLL/TERA report there is a wide variance in the
~pinions generated by the experts polled by LLL.
Due to the wide variance in the opinions the output of the LLL/TERA program appears to be wrong.
As a result, the output is unusable.
We believe the three basic reasons for the wide variance in.the opinions are:
- 1)
It appears not all the experts properly understood the questions in the survey, 2) the experts were not allowed sufficient time to provide required responses and, 3) in some cases, the experts were commenting.on tectonic areas they were not intimately familiar with as to it's seismologic, history.
Commonweal th.Edison *believes for the methology developed by LLL/TERA to be useful, LLL/TERA must go back and examine.the*
causes of the variances in the expe~t opinion and resolve those aieas they find questionable.
They should then obtain expert opinion
- about a particular tectonic area from the"expert most familiar with the area.
In addition, a feedback mechanism s.hould be established to make certain the experts understand the questions and that they have sufficient time to provide the required answers.
Ao~8 s
I' 7912010 4(1/J
Please address any questions you may have concerning the matter to this office.
One (1) signed original and thirty-nine (39) copies of this transmittal have been provided for review.
)
- 10-~P-T/'-~V.Jl-C,£
~. F. *Janecek Nuclear Licensing Administrator Boiling Water Reactor
CRITIQUE OF LLL/TERA REPORTS ON SEISMIC HAZARD ANALYSIS Prepared for:
NUCLEAR SERVICES CORPORATION.
1700 Dell Avenue Campbell, California 95008 Prepared by:
FUGRO, INC.
Consultirig Engineers and Geologists 3777 Long Beach Boulevard Long Beach, California 90807 October 26, 1979
INTRODUCTIO_N At the request of Commonwealth Edison and Nuclear Services Corporation, F~gro h~s reviewed the following three draft reports prepared by Lawrence Livermore Laboratory (LLL) and Te~a Corporation on Seismic Hazard Analysis:
o "Seismic Hazard Analysis:
A Methodology for the Eastern United States," Tera Corporation, August 23, 1979.
o "Seismic Haza~d Analysis:
Solicitation of Expert Opinion,"
Tera Corporation, August 23, 1979.
o "Seismic Hazard Analysis:
Site Specific Response Sectra Results," by D. L. Bernreuter (LLL), C. P. Mortgat (Tera) and L. H. Wight (Tera), August 23,.1979.
These reports were submitted to the Nuclear Regulatory Commission (NRC) as part of their Safety Evalu~tion Program (SEP) of older nuclear power plants.
- Thi~ document presents a critique of these reports.
Because of the large amount of material contained in these reports and the limited amount of time available for review, the comments below are mostly general* in nature.
CRITIQUE General.
The three LLL/Tera reports basically present:
(1) a 1
probabilistic model for estimating uniform risk spectra at a site, (2) the solicitation of expert opinions and the interpre-and incorporation of these opinions in the probabilistic model, 1
Uniform risk spectra are response ~pectra whose ordinates h~ve the.same probability of being exceeded during some time period.
-pi.aRD
- 1'"
2 and (3) tlte results of th~ application of this model to nine nuclear power plant sites included in the NRC's SEP.
Th l
f f
f
... f.
. lk
. e resu ts or each site consist 6 a set o.uni orm ris spectra, each spectrum derived using one expert's opinio1** and an overall spectrum representing t~e synthes~s of all exrert's opinions.
Comparisons are also made between the synthesized spectrum and spectr~ obtained from more deterministic apiroaches.
I The reports make no recommendations as to which spectra are to be used in the SEP or the corresponding p~rformante critlria of structural components and local soils.
However, sbme discussion is given*on the merits and limitations of the use of each type of spectrum.
An important criticism of uniform risk spjctra
. I that was ~entioned is that the spectra essentially represent the contribution of all possible earthquakes in the sit~ region. ~
On the other hand the facility has to resist the shaking from only one earthquake at a time.
Therefore, the uniform tisk I..
spectra may be overly conservative in this regard, and other types of spettra may be more appropriate for the SEP.
I The critiques of each of the three reports are given below~
Solicitation of Expert Opihion.
Ten experts in the fields of seismology and tectonics responded to specific questions in the~e ar~as in ord~r to provide the necessary inputs to the probabilistic model *. ideally, the experts should be ~ery knowledgeable in all tpe problem areas **and haye plenty of time to seriously study the questions and all of the relevant data
"'fUGRD
,i,'*-:*
3 and respond in an unbiased and objective manner.
However, for various reasons, it appears that these ideals were not a~hieved.
I.
The experts generally were seismologists with some experrise in tectonics.
To our knowledg~ none of the experts has rone exterisive research on the attenuation of strong ground motion or the respons~ of local soils during earthqu~ke shakinJ, two important considerations in any site-specific analysis.
The limited expertise in the latter area was evidenced by the response to Question 4-20 (p.
11-10~), which asked what was the maximum acceleration that vario~s types of soil ~eprsits could s~stain.
Only three experts responded and their answers I.
indicated a limited knowledge in this area.
Some of th~ experts emphasized their low confidence in their answers.
Even within their fields of expertise, the exberts are usually most knowl-edgeable about the seis~icity and tect6nics in the region in which they are located.. In this regard it appeared th+ the experts concentrated their efforts on the data they wer/e most familiar with and spent little time with other data.
,om~times only two or three experts n:*sponded to a particular question or I
I More feedback between the expert$ and LLL/Tera would hrve been desireable during the cours~ of the. study.
The experts did not I
have a chance to judge the reasonableress of the LLL/Tera
- interpretations of their responses. to the' questions, nlr did I
the experts review the methodology or the results.of the Tera/LLL probabilistic analyses for *each site.
~~e experts may/ well have.
group of questions.
-rGRO
4 modified their responses to some questions if they had understood the way in which those responses were going to be used.
The methdd of self-ranking of the experts' opinions and the
.1 I inclusion of the information by LLL/Tera to weight all of the experts' opinio~s is questionable.. The resulting synthelized spectrum f~orn the applicatioh nf t~e weighting techniiue is biased to~ard experts who have a high degree bf confidence in I -
their opinions.
A high self-confidence in one's answ~r aces not necessarily mean. that that answer *is likely. to be co~rect, Conversely, a lower* self-confidence. ranking does not neclessar ily reflect ~ lesser understanding of the problem.
Some tyfie of I
cross-ranking b~tween the experts might have established whose opinions were most respected.
Methodology for the Eastern United States.
The major c0ncern
. I with the methodology was the treatment-of the uncertainties
. I.
associated with input parameters of the probabilistic model, I
and the impact of these uncertainties 6f the results.
A detailed I
~nalysis of the ~ncertainti~s in order to ~ully ev~luatie their
- ?"
impact was not given.
However, LLL/Tera did question lhether or not th~ rather large uncertainties in the attenuation,elations based on statistical analysis of empirical data and the uncertain-t.
d
. h.th t I I
ies associate wit
. e exper *s opinion were accurate represen-tations of reality.
Limited sensitivity studies perfoirned on the. attenuation uncertainty showed.. in one particular elarnple that an 80 percent increase in the~s~a~daid~eviation had a/ similar
. I increase in the spectral 1eve1 for a given return peril°d.. Although.
I
~~ '*..
I
5 the uncertainty in the final probabilistic distribution for the I
I response. spectral ord ~na tes ~a~ not estimated~ i ~ is imporlt~nt to know 1f the model is comb1n1ng the uncerta1nt1es of the input
. I parameters in such a way so.as to produce a grossly overes~imated uncertainty in the final distribution.
If the model is d~ing this, then at long return. periods the corresponding unifo+ risk spectra will be overesUmated.
I Site Specific Res~onse Spectra Results.
The reasonableness of I
the results could be better evaluated if a more complete docu-1 mentation were given on the effects the various input pardmeters h d 1
1 1
- b *I f
a on the.resu ts.
For examp e, the re at1ve contr1 ut1ons o I
the various earthquake magnitudes,* in addition to the seismic I
I sources, would have been.useful~ More analysis of the effects I
I of the uncertainties of the input parameters, through formal I
statistical methods and sensitivity studies, would also be useful.
I.
I A review of the results for the Dresden nuclear power plart was made based on our knowledge of the seismicity and tectonibs of that site region.
The LLL/Tera results shbwed that the Nlw Madrid seismic ~one contributed anywhere from 35 to 47 percent tl the 1000-year peak ground acceleration while the Central Stable Region seismic source contributed 45 to 61 percent.
The relative I
contribution from the New Madrid zone seems unreasonably !high.
simply because the zone is 300 to 500 kITJ. from the site <4epending I
on the expert's choice of the appropriate northern boundary) at I
I its closest approach.
Expected peak ground a*ccelerat1ons. at these distances from an earthquake of :epicentral intensi~y equal I
h...
~.*,
to XII (MM*) should be less than 0. Olg according to the I formula given on Table 5-5 (p. 5...-21) of the LLL/Tera report, "Site Specific Response Spectra Results."
The report offers no concrete explanations or ~resents any analysis to explain why 6
I the New Madrid seismic zone should contribute so heavi[y to the results and~ until this is investigated, the reslts fol Dresden should be interpreted with reservations.