ML19282B438
| ML19282B438 | |
| Person / Time | |
|---|---|
| Issue date: | 02/22/1979 |
| From: | Stolz J Office of Nuclear Reactor Regulation |
| To: | Sobon L GENERAL ELECTRIC CO. |
| References | |
| NUDOCS 7903150016 | |
| Download: ML19282B438 (5) | |
Text
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UNITED STATES
,0 O'a NUCLEAR REGULATORY COMMisslON h
j WASHINGTON, D. C. 20555
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FEB 2 2 B79 Mr. L. J. Sobon, Manager BWR Containment Licensing Containment Improvement Programs General Electric Company 175 Curtner Avenue San Jose, California 951cb
Dear Mr. Sobon:
SUBJECT:
GE REPORT NED0-24010-2 " BASIS FOR CRITERIA FOR COMBINATION OF EARTHQUAKE AND OTHER TRANSIENT RESPONSES BY THE SQUARE ROOT SUM 0F THE SQUARES METHOD " SUPPLEMENT 2, DECEMBER 1978 The NRC staff has reviewed your Report NED0-24010-2, Supplement 2, dated December 1978.
Our comments on the proposed criteria are enclosed.
We suggest that the Mark II Owner's Group meet with us and our consultants prior to your formal response to our comments.
Please contact us so that arrangements for a meeting can be made.
Sincerely, G
/n '
/
J(h F. Stolz, Chief L ht Water Reactors Branch No. 1 Division of Project Management
Enclosure:
Comments on NED0-24010 Supplement 2 700315 0 C /G
ENCLOSURE MECHANICAL ENGINEERING BRANCH COMMENTS ON NED0-24010 SUPPLEMENT 2 A.
For Criterion #1:
1.
The proposed criterion represents a fresh approach by utilizing characteristics of time functions,instead of attempting generic conclusions from a few case studies as done by others. Generally speaking, the criterion is simple, easy to apply, and may be able to achieve a high non-exceedance probability in most cases.
However, the criterion appears to be based on engineering judgement without the needed data basis to verify the claimed goal of achieving 84% non-exceedance probability.
2.
We are not certain the parameters used, such as number and level of high peaks, durations, etc., are sufficiently adequate to ensure a justifiable SRSS combination in all cases meeting the criterion.
For instance, one important condition to warrant the use of SRSS is that both time functions shall be rapidly varying.
Since " rapid varying" is a relative term, a comparison of frequency contents in time function may be necessary.
A search of parameters which control the characteristics of time functions in conjunction with sensitivity studies of those parameters may be helpful to verify the adequacy of the criterion.
2_
As an alternative, numerical examples associated with non-exceedance probability evaluation (i.e., use CDF) may be conducted to develop the dat.s base for verifying the assurance level of the proposed criteria.
3.
The proposed criterion indicated that the use of SRSS can be based on the characteristics of either the loading time functions, or the response time functions. We feel that combination of responses should be solely based on the character-istics of the response time functions.
Since the characteristics of the responses are effected by the structural dynamic properties, such as natural frequer.cies, damping values, etc. even the same loading can produce responses of various nature. Thus a loading time function meeting the criteria may not necessarily mean that the response time functions will also meet the criteria. We would require justification for the use of loading functions.
4.
It is rather difficult to determine whether two time functions are strongly correlated, or weakly correlated just by observation alone. Furthermore, judgement by opinion may vary from person to person. We have adequate confidence that the level of correlation among earthquake ground motion components is weak.
However, to determine the level of correlation among response time functions other than earthquake event may present a problem.
. Additional work of calculating the coefficient of correlation
[naybeneeded. The work will be compounded when an increased number of time functions are needed to be combined at one time.
5.
Many response time functions may not have a zero mean. No guidance is provided on how such cases would be handled.
B.
For Criterion #2:
1.
It was stated in the preamble of the report that the intent of the proposed criteria for response combinations is to achieve a nor-exceedance probability of 84% (+).
We feel that proposed criterion #2 may not achieve that goal if it uses SRSS based on a 50% (+) non-exceedance probability, since it appears to be inconsistent with the stated intent. Furthermore, the purpose and the basis in adding an additional requirement of 85% (+) non-exceedance probability at 1.2 SRSS is not clear, since the proposed value to be used is SRSS, not the 1.2 SRSS.
One of the many possible reasons for people to promote SRSS is because the method is simple and convenient.
If we go to the trouble of generating a CDF curve at the 84% non-exceedance probability then that value may be more justifiable than the SRSS value. Why bother to have two SRSS related vd ues?
% 2.
Since a CDF curve is used in the criterion, guidance to ensure the validity of the curve may be necessary.
Notice that CDF curve may not be unique due to following circumstances:
a.
Response time function is not unique.
b.
Durations of the strong motion portions taken for response combinations are arbitrary, c.
The probability density function assumed for defining phasing relationships among response functions is arbitrary.
Thus, how a bounding CDF curve is defined to ensure adequate coverage of all mentioned uncertainties is essential to the application of the proposed criterion #2.