THE MID NIIGATA EARTHQUAKE AND ASEISMIC DESIGN OFKASHIWAZAKI-KARIWA NUCLEAR POWER STATION

摘要

The magnitude 6.8 Mid Niigata Earthquakern(MNE) on October 23, 2004, centered in the ChuetsurnRegion of Niigata Prefecture at a depth of 13km,rnproduced peak ground acceleration of about 1,722Galrnin Kawaguchi Town, Niigata. This earthquake, arntypical result of near-fault strong motion, causedrnhouses to collapse and landslides to occur, mostly inrnand around Kawaguchi town and Ojiya City, andrncaused 40 deaths. Additionally, a characteristic of thisrnearthquake is that major aftershocks continued forrnmore than two weeks afterward.rnThe Kashiwazaki-Kariwa Nuclear PowerrnStation (KKS) of Tokyo Electric Power Companyrn(TEPCO) is located about 28km northwest from thernepicenter of this earthquake. During the mainrnearthquake, response acceleration of about 54Gal wasrnrecorded on the base mat of the reactor building,rnwhile the SCRAM acceleration is 120Gal. Under thernmain earthquake and aftershocks, the facilitiesrnmaintained plenty of structural integrity. The sixrnreactor units continued to operate during the mainrnearthquake (No.4 unit was under a periodicrninspection), but during one of aftershocks the turbinernprotection interlock activated in No.7 unit, causingrnthe unit to shut down (the unit restarted soon after).rnThe main reasons being that magnitude of 6.9rnearthquake, larger and nearer than the MNE, isrnconsidered as design basis earthquake for KKS, inrnaddition, nuclear power plants should be constructedrnon a bedrock without remarkable amplification ofrnearthquake motion, based on the aseismic designrncriteria.Generally, Japanese reactor buildings andrnfacilities are designed with significant safety marginsrnin the event of an earthquake. During this event, nonernof this safety was compromised, and performancernagainst an earthquake of a nuclear power plant wasrnshown sufficiently.rnHowever, on the basis of essences of thisrnearthquake, a detailed survey was carried outrnincluding influence of the aftershocks and suitabilityrnof design basis earthquake settings.