ML20002E382
| ML20002E382 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 01/23/1981 |
| From: | Vincent R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| References | |
| TASK-02-02.A, TASK-2-2.A, TASK-RR NUDOCS 8101270691 | |
| Download: ML20002E382 (2) | |
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5 U1 Director, Nuclear Reactor Regulation Att Mr Dennis M Crutchfield, Chief Operating Reactors Branch No 5 U S Nuclear Regulatory Commission Washington, D C 20555 DOCKET 50-155 - LICENSE DPR SIG ROCK POINT PLANT - SEP TOPIC II.2.A -
SEVERE WEATHER PHENOMENA By letter dated December 17, 1980, the NRC provided its evaluation of SEP Topic II.2. A, Severe Weather Phenomena, for the Big Rock Point Plant site.
Consumers Power Company has reviewed this report and with two exceptions finds it to be consistent with our assessment of expected site conditions and recorded clima-tological data. The following comments are offered as our preliminary response on these issues:
- 1. There is a large difference between the design basis tornado described in Regulatory Guide 1.76 and the one based on actual occurrences near the site.
The NRC has elected to use the Regulatory Guide 1.76 design basis tornado because of the infrequent occurrence of tornadoes and the resulting small sample size. For the following reasons, we feel that a Regulatory Guide 1 76 design basis tornado is unnecessarily severe for the Big Rock Point site; and that a design basis tornado which is based on actual occurrences in the vicinity of Big Rock Point is more representative and sufficiently conservative for tornado wind loading analyses.
Meteorological and topographic conditions which influence the frequency of occurrence and intensity of tornadoes vary significantly throughout the state of Michigan. The small frequency of reported tornadoes in the vicin-ity of the Big Rock Point site is valid and should not be used in itself to question the data analysis results.
The wind and tornado loading analysis completed by Texas Tech University does not support the Regulatory Guide 1.76 design basis tornado, but rather one similar to that calculated from ac tual occurrences in the site region.
The tornado data used for this analysis includes tornado statistics from the lower portion of the state. Since tornado statistics from this region would give higher frequency and more severe classification than would be expected at the Big Rock Point site, the Texas Tech analysis is quite conservative.
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Mr. Dennis M Crutchfield 2
Big Rock Point Plant January 23, 1981 ANSI /ANS 2.3 Draft Standard " Guidelines for Estimating Tornado and Extreme Wind Characteristics at Nuclear Plant Sites" Draft 2, Revision 4 dated April, 1980, provides guidance which is more representative of the current level of knowledge on tornado and extreme vind characteristics than Regulatory Guide 3.76 and WASH-1300. Using this standard, a maximum tornado vind speed of 250 mph (annual probability 10-7) is indicated which closely agrees with the values indicated by data from actual tornado occurrences.
Finally, it must. also be noted that neither the staff evaluation nor ANSI /ANS 2.3 take into account the beneficial effect of Lake Michigan on tornadoes near a horeline areas such as the Big Rock Point site.
- 2. With respect to the extreme vinter precipitation snow load, Consumers Power Company is still in the process of verifying the stated value of 115 psf.
Although we do not yet have the results of this study, there is a possibility that this value may be slightly non-conservative. When our investigation is complete, we vill provide further information.
Robert A Vincent (Signed)
Robert A Vincent Staff Licensing Engineer CC Director, Region III USNRC NRC Resident Inspector - Big Rock Point
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