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NUCLEAR REGULATORY COMM!SSION 2[fM
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July 7, 19E3
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j 7,,. a MEMORANDUM FOR:
Chairman Palladino
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fy Comissioner Gilinsky 0:. E ; m r.2 a.c Comissioner Roberts U
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chn Zerbe, Director 74E40Ly,1,y,/,y,d Office of Policy Evaluation OPE COMMENT ON THE STATUS OF THE CHARLESTON EARTHQJAK SU5 JECT:
ISSUE As recussted by Comissioner Gilinsky, we have looked into the statt.s of the staff's re-evaluation of the Charleston earthquake.
Nuclear power plants in the region east of the Rocky Mountains have been controlled in their seismic design by the maximum historical earthcuake not associated with a geologic structure, typically a Modifiec Mercaili Intensity (M'41) Vil or VIII, whereas the Charleston earthouake was estimated at MMI X.
The USGS letter of November 18, 1982 had concluded that the historical record is not, of itself, sufficient grounds for ruling out the occurrence elsewhere l
along the eastern seaboard of strong seisgc ground motions similar to those experienced near Charleston, SC in 1886.
(Enclosure 1).
19,1982(Enclosure 2)
The staff's memorandum to the Commission on November outlined a preliminary plan to address the revised USGS po for new efforts both probabilistic and deterministic.
The staff's current position is sumarized in Enclosure 2 of an NRR The plan now memoranum of March 2, 1983 (Enclosure 3 of this memorandum).
consists of a short.-tem probabilistic assessment utilizing an extensive new seismic hazard study currently being developed by Law on long-range RES resear.ch, with the possible need for utility-sponsored investigations at some locations af ter an assessnent of the long-term ag In addition, the staff recomended that an g
n-research results.
0 industry-sponsored seismic hazard study be sclicited.
o od' It is our understanding that there are approximately 33 commercial power l
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reactors either in operation or in some stage of construction on the j
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The staff expects that deteministic studies would reduce uncertainties by better identifying (1) the causal mechanisms of large Charleston-like earthquakes, and (2) the potential for the occurrence of such lagge earthquakes throughout thq eastern seaboard.
Probabilistic studies would f
determine any differences between the probabilities of seismic ground motion exceeding design leve',s on the eastern seaboard (i.e., as affected by the revised USGS position on the Charleston earthquake) and those elsewhere in the central and eastern U.S.
The staff's position statement concludes with the following:
"Given the speculative nature of the hypotheses with respect to the recurrence of large Charleston-type earthquakes as a result of our limited scientific knowledge and the generalized low probability associated with such events, we do not see a need for any action for specific sites at this time.
It is our position, as it has been in the past, that f acilities should be designed to withstand the recurrence of an earthquake the size of the 1886 earthquake in the vicinity of Charleston. At tha conclusion of the shorter-term probabilistic program and during the longer-tem deterministic studies, we will be assessing the neea for a modified position with respect to specific sites."
(Underlined for emphasis.)
Enclosure _4,is a copy of an EPRI report that proposes a parallel program by
'the utifities in response to the clarification in position taken by NRC and the USGS. We understand that such an industry undertaking would cost some $3 million. Apparently, the EPRI approach would emphasize tectonic models while NRC's program would place more emphasis on the consensus of expert opinions.
Finally, in its memorandum of January 11, 1983 to the Chairman,_when it listed programs that might be conducted over the next two to four years in connection with the iss.ue of quantifying seismic design margins, the ACRS referred to a " Charleston-like earthquake in the Eastern United States":
"The ongoing U.S. research program on geology, seismicity and geophysics should continue to receive strong support from the NRC.
The recent re-evaluation by the U.S. Geologic Survey of the possible causes and potential of a Charleston-like earthquake in the Eastern United State.1 results in large part from such studies and gives strong support to the likely importance of a probabilistic examination of seismic design. The NRC research program in this area should attempt to develop an improved motion which may have a return frequency in the range of 10-4groundt capability for estimating the severity of earthquake-induced per year at reactor sites."
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6 The staff believes that its program as described in the March 2, 1983 memorandum, addresses the concerns in seismology described in the January 11,
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1983 letter from the ACRS to the Chairman.
Enclosures:
As stated cc:
S. Chilk H. Plaine W. Dircks H. Denton l-R. Minogue R. Fraley i
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