Probabilistic Evaluation of OBE for Nuclear Plants

by John T. Christian, (M.ASCE), Consulting Engr.; Stone & Webster Corp., Boston, Mass.,
Philip T. Tringale, (A.M.ASCE), Engr.; Stone & Webster Corp., Cherry Hill, N.J.,
Ralph W. Borjeson, (A.M.ASCE), Sr. Soils Engr.; Stone & Webster Engrg. Corp., Boston, Mass.,

Serial Information: Journal of the Geotechnical Engineering Division, 1978, Vol. 104, Issue 7, Pg. 907-919

Document Type: Journal Paper


The Operating Basis Earthquake (OBE) governs the design of many components of a nuclear plant. Probabilistic analyses were performed to determine the OBE for the Koshkonong Nuclear Plant in southern Wisconsin. The area has very sparse seismicity, so the data are quite scattered. Parametric studies indicated the effects of different recurrence rates, attenuation laws, and maximum epicentral intensities. An OBE of intensity VI (Modified Mercalli) with a corresponding peak acceleration of 0.06g is justified. A simple analysis of the probability of recurrence of an event shows that multiple occurrences have significant probabilities when the return period of the earthquake is close to the life of the plant. The present OBE has an expected return period of about 1,000 yr; for very conservative assumptions, the return period is a few hundred years.

Subject Headings: Probability | Earthquakes | Seismic design | Light rail transit | Seismic tests | Seismic effects | Parameters (statistics) | Lifeline systems | Wisconsin | United States

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