APPLICABILITY OF THE SEISMIC BASE ISOLATION TO A MODULAR HIGH TEMPERATURE REACTOR

摘要

Structural applicability of a modular high temperaturernreactor in high seismic regions like Japan was examined. Thernmodular HTR designed by Siemens in Germany was used as arnreference model.rnThe dynamic responses of the reactor building and thernprimary vessels against two artificial seismic waves withrnextended period components were obtained using the two andrnthree dimensional idealization. Two soil conditions with thernshear wave velocity of 400 and 1500 m/s were applied. Nonlinearrnspring idealization was used to model the seismicrnisolator. The vessel supports stiffness are also treated as arnparameter.rnThe main preliminary results obtained can be summarizedrnas follows.rn1. At sites with soft soil, increase of the vessel responses arernwithin a factor of 2~3 because responses are mitigated due tornthe high damping of the soil. The reference model or the nonisolatedrnmodel can be accepted if the problem of the soilrnstability is cleared. Seismic base isolation may not bernnecessary at sites with soft soil.rn2. At sites with hard rock, the reference model shows a ratherrnpoor behavior in respect to the lifting of the building duringrnearthquake. Improvement such as lowering of the center of therngravity, increasing of the width of the foundation orrnintroduction of a seismic base isolation may be necessary.rn3. Seismic base isolation is very effective at sites with hardrnrock sites.rn(1) For horizontal seismic waves, increase of the vesselrnresponses are large by a factor of ten at hard rock sites, so thernreduction of the building responses itself is indispensable inrnthis case because the strength of the HTR core seems to bernlimited mainly by the strength of the structural graphite,rnwhich is difficult to be improved so much.rn(2) Reaction against vertical seismic waves are not explicitlyrncarried out in this study but such modification as an increase ofrnvessel support stiffness together with a base isolation may bernnecessary to limit the stress of core components within limits.rn4. If the seismic base isolation devices are adopted, thernoriginal M-HTR design for soft rock sites can easily be appliedrnto hard rock sites without big modifications of therncomponents' design.