ML20052F141
| ML20052F141 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 05/05/1982 |
| From: | Vincent R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| References | |
| RTR-REGGD-01.060, RTR-REGGD-1.060 NUDOCS 8205120157 | |
| Download: ML20052F141 (3) | |
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1 Consumem l
Power Company General offices: 1945 West Parnall Road. Jackson, MI 49201 * (517) 788 0550 May 5,'1982
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k Dennis M Crutchfield, Chief
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Operating Reactors Branch No 5 Nuclear Reactor Regulation US Nuclear Regulatory Commission
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Washington, DC 20555 4
p DOCKET 50-155 - LICENSE DPR BIG ROCK POINT PLANT - SEP III-6, SEISMIC DESIGN CONSIDERATIONS By letter dated June 8, 1981 (reissued June 17, 1981) the NRC issued a site-specific seismic response spectrum for the Big Rock Point Plant site. Attach-ment 2 to that letter stated,
"...it is our position that the recommended spectra represent the appropriate levels of free field ground motion to be used in the SEP for the purpose of evaluating the seismic design adequacy of the-selected plants." The adequacy of the site-specific spectrum for Big Rock Point, however, recently has been questioned. The purpose of this letter, therefore, is twofold. First, it transmits a seismic spectrum for Big Rock
. Point'which was derived by Consumers Power Company independently from the NRC efforts in this area, and second, it discusses the current status of the SEP seisnic analyses for the plant.
Early in the SEP Consumers Power Company made a decision to develop a seismic response spectrum for the Big Rock Point site independent of any programs the NRC chose to undertake. The product of that effort, Weston Geophysical Corporation report, " Site Specific Response Spectrum for Big Rock Point Nuclear Power Plant," (May 1982) is enclosed as Attachment 2.
For convenience, Attachment 1 shows a plot of the spectra resulting from the Weston work as well as a.12g Reg Guide 1.60 spectrum and the site specific spectrum issued by the NRC (letter of June 8, 1981). As you will note, the peak acceleration values derived deterministically by Weston agree well with the other spectra.
It is important to emphasize that the Weston spectra implicitly include consideration of the local Big Rock Point site geology.
Since the appropriate spectrum for SEP purposes should be the Weston mean, it is readily apparent that the existing NRC site-specific spectrum which considers Big Rock Point as a soil site is conservative.
Likewise, it is also important to note that a.12g Reg Guide 1.60 spectrum is conservative even when compared to the 84th percentile spectrum from Weston. This fact directly oc0582-0004a142 0
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D M Crutchfield, Chief 2
Big Rock Point Plant SEP III-6 May 5, 1982 supports the conservatism of previous plant analyses which were performed to the.12g Reg Guide 1.60 spectrum.
We would be pleased to meet with the staff to discuss the Weston report. Such a meeting would be considered highly desirable to facilitate a rapid resolu-tion of this issue. We will contact the staff separately within the next few days to discuss a possible meeting.
As a second item, it has been Consumers Power Company's intent to use the NRC-issued site specific spectrum as the basis for other analyses performed under SEP Topic III-6.
To date the large models of major plant structures have been reanalyzed using the NRC spectrum as input, and new floor response spectra for various locations have been generated. Other analyses have been or were about to be performed with these new floor response spectra. Because the adequacy of the NRC-issued spectrum, and even the conservatism of a.12g Reg Guide 1.60 spectrum, have now been questioned, we consider it inadvisable to continue this work.
Accordingly, we have suspended all plant SEP analyses which are dependent on the seismic input spectrum. As stated previously, we believe the NRC site specific spectrum to be fully adequate if not conservative for the Big Rock Point site.
In view of the current level of uncertainty and the expense associated with the analyses, however, suspension of the work is our only logical choice. When a final documented conclusion is reached on the acceptable seismic spectrum for the site, our analyses will be restarted on a suitably adjusted schedule.
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Robert A Vincent Staff Licensing Engineer CC Administrator, Region III, USNRC NRC Resident Inspector-Big Rock Point Attachment oc0582-0004a142
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Response Spectrum for Big Rock Paint iiuclear Power Plant, Lomparea n'itu Reg. Guice 1.60 Spectrum at.12g und SEP Spectrum (t;RC Letter of June 8, 1981) 5% Damping weston Geoohysical
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