ML19305A398
| ML19305A398 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 04/14/1979 |
| From: | Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | Herbein J METROPOLITAN EDISON CO. |
| References | |
| NUDOCS 7905020377 | |
| Download: ML19305A398 (1) | |
Text
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NUCLEAR REGULATORY COMMISSION REGION I o
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April 14,1979 Docket No. 50-289 Metropolitan Edison Company ATTN: Mr. J. G. Herbein Vice President - Generation P. O. Box 542 Reading, Pennsylvania 19640 Gentlemen:
The enclosed Bulletin 79-07 is forwarded to you for information.
No written response is required at this time.
If you desire additional information regarding this matter, please contact this office.
Sincerely,
{
Boyce H. Grier
' Director
Enclosure:
IE Bulletin No. 79-07 with Enclosures cc w/encls:
E. G. Wallace, Licensing Manager J. J. Barton, Project Manager L. L. Lawyer, Manager - Generating Operations G. P. Miller, Manager - Generating Station - Nuclear J. L. Seelinger, Unit 1 Superintendent W. E. Potts, Unit 1 Superintendent - Technical Support I. R. Finfrock, Jr.
Mr. R. Conrad G. F. Trowbridge, Esquire Miss Mary V. Southard, Chainnan, Citizens for a Safe Environment 7905020772
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UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C.
20555 IE Bulletin No. 79-07 Date: April 14, 1979 Page 1 of 3 SEISMIC STRESS ANALYSIS OF SAFETY-RELATED PIPING Description of Circumstances:
In the course of evaluation of certain piping designs, significant discrepancies were observed between the original piping analysis com-puter code used to analyze earthquake loads and a currently acceptable computer code developed for this purpose.
This problem resulted in the Nuclear Regulatory Comission order to shutdown five power reactors whose design had involved the use of the suspect computer codes (IE Infor: nation Notice No. 79-06).
The difference in predicted piping stresses between the two computer codes is attributable to the fact that the piping analysis code used for a number of piping systems uses an algebraic sumatien of the loads predicted separately by the computer code for both the horizontal components and for the vertical component of seismic events.
This is an incorrect treatment of such loads and was not recognized as such at the time the original analyses were performed.
Such codirectional loads should not be algebraically added (with predicted loads in the negative direction offsetting predicted loads in the positive direction) unless certain more complex time history analyses are performed.
Rather, to properly account for the effects of earthquakes on systems important to safety, as required by " Design Bases for Protection Against Natural Phenomena," General Design Criterion 2 of Appendix A to 10 CFR Part 50, such loads should be combined absolutely or, as is the case in the newer codes, using techniques such as the square root of the sum of the squares.
These combinations of loads conform to current industry practice.
The inappropriate analytical treatment of load combinations discussed above becomes significant for piping runs in which the horizontal seismic excitation can have both horizontal and vertical components of response on piping systems, and the vertical seismic excitation also has both horizontal and vertical components of response. It is in these runs that the predicted earthquake loads may differ significantly.
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