ML20027C904
| ML20027C904 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 02/23/1982 |
| From: | Trifunac M Advisory Committee on Reactor Safeguards, SOUTHERN CALIFORNIA, UNIV. OF, LOS ANGELES, CA |
| To: | Griesmeyer J Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-CT-1424A, NUDOCS 8210270408 | |
| Download: ML20027C904 (3) | |
Text
n W M e f0 f s
- W UNIVERSITY OF SOUTHERN CALIFORNIA fe W
\\
[
UNIVERSITY PARK IDS ANGE!IS, CAIJFORNIA poesy p
,a SCHOOL OF ENGINEERING DEPARTMENT OF CIVIL ENGINEERING February 23, 1982 Mr. J. Michael Griesmeyer Staff Engineer A.C.R.S.
U.S.N.R.C.
Washington, D.C. 20550
Dear Mr. Griesmeyer:
I have now completed my review of the material you mailed to me on December 21, 1981 and regarding the Zion probabilistic assessment.
I will first state a number of general comments and follow this with some mere detailed remarks.
The general methods and principles employed in the analysis of possible earthquake shaking and Zion si.e appear to apply the modern state of the art techniques.
In reviewing the specific steps involved in this analysis, I found that:
1.
The overall level of seismicity,3namely what I infer to be MM yr/ 10 km2 for the Wisconsin arch-log 1gN a -0.58 - 0.59 I
/
Michigan basin is not in obvious disagreement with what might be expected in this area.
I tested this seismicity using literature at my disposal and found no difficulties. When I receive from you the paper by Nuttli and Hermann (1978), I can review this question again. The maximum cut off magnitude (intensity) for this area has been assumed to be 5.6 to 6.0
(~VII to ~VIII). This again appears reasonable, but except for the general historic record, I wish I found other more physical support for this cut off range.
I wonder whether sensitivity studies were carried out for MMI=IX cut off?
2.
I calculated the approximate probabilisties of exceeding peak acceleration (analogous to the results presented in Figure 10 of Dames and, Moore report) and found that the solid curve in Figure 10 for Wisconsin Arch - Michigan basin (using Nuttli modified attenuation) appears to give good results. The curves based on TERA (1979) attenuation should not be used since there is evidence that this correlation may be biased towards smaller peak accelerations. For smaller peak accelerations mainly resulting from more distant earthquakes, the Nuttli attenuation seems to give reasonable results. However, the results for
~
~
closer earthquakes may be g o g o8 820223
~
CT-1424A PDR
Mr. J. Michael Griesmeyer o
February 22, 1982 Page Two highly suspect. Figure II.7-1 clearly shows this to result from an assumption that the acceleration versus distance levels off at a constant acceleration and for the assumed maximum magnitude. The abrupt cut off of all curves in Figure II.7-1 at ~.45, ~.55 and ~.65 g is a consequence of certain assumptions which at present cannot be supported by the strong-motion observations. Even though the hypothetical arguments supporting such abrupt cut-off may be reasonable, the continuity of the physical nature of the problem and the lack of conclusive data strongly argue against introducing such hypothetical and theoretical assumptions into an engineering decision process.
In any case, why not consider other alternatives? Especially when one is aware of the approximate Median Fragility Distribution shown in Figure II.7-1.
Even to an uninitiated reader, the rather unlikely event that the " upper bound of seismic transmissibility" just happens to be where the number of affected items begins to increase, would seem very unlikely (Figure II.7-8).
3.
The analysis of the " conditional probabilities of siesmic induced failures for structures and components for the Zion Nuclear Generating Station" by S.M.A. is very difficult to evaluate.
It is just impossible to review and check this work without structural drawings and details.
Furthemore, such checking would be very time consuming and thus expensive.
I would reconnend some serious spot checks to be made by a very experienced structural design engineer.
Selected Detailed Comments:
Page II.7-6.65g is used as "the upper acceleration bound". What is the basis for this estimate?
Pages 11.7-20 and 11.7-21: These conclusions are based on the l
assumption that 0.65 g is the upper limit for the acceleration. How can these conclusion be made when it was not demonstrated that.65g is indeed the upper limit?
Page 7.2-2.
The idea of a sustained peak acceleration (corresponding to the third largest peak of the acceleration time history) may be appealing to a time series analyst interested in simple yet stable scaling parameters for a random like function, but is neither an accepted measure of ground accelerations in engineering design, nor it has some general physically meaningful basis in the analytical dynamic response analysis.
Page 4-18 Reductions of 0.90 for the reactor building and o.85 for the auxilliary building are assigned to the
Mr. J. Michael Griesmeyer Februa ry 22, 1982 Page Three embedment effects. However, other consequences of the embedment, like rocking excitation for Rayliegh waves and torsional excitation for Love and SH waves are ignorad? It is not clear then how the factor of safety 1.2 follows from this?
If you find any of these comments not to be clear, or if you have other specific questions, please let me know.
Sincerely, Id,0Xv.4- ~
M.D. Trifunac Professor MDT:mdm
__.