DEVELOPMENT OF EVALUATION METHOD FOR SEISMIC ISOLATION SYSTEMS OF NUCLEAR POWER FACILITIES-BREAK TEST OF FULL SCALE LEAD RUBBER BEARINGS FOR NUCLEAR FACILITIES, PART 4 BREAK BOUNDARY CRITERIA OF REAL-SIZE ISOLATOR SPECIMENS-

摘要

A research program for seismically isolated Nuclear Power Plants (NPPs) has been conducted since 2008 as the newest Japanese national project, whose research results are summarized as the series papers on this conference. In this project a Lead Rubber Bearing (LRB) of 1600 mm in diameter with a large lead plug is newly designed to satisfy the current Japanese design requirements for seismic isolated NPPs, and a series of break tests is also conducted by using the real-size or closely real-size of LRB specimens to evaluate ultimate seismic performance of base-isolated NPPs beyond design earthquakes. Having no previous break test of large rubber bearing for nuclear facilities; e.g. of 1600 mm in diameter, the aim herein is to evaluate the breaking strength of the real-size LRBs to avoid the difficulties considering size effect. This paper presents twenty break test results of single-lead-plug typed and multi-lead-plug typed LRBs, mainly focused on two points: one is ultimate behaviours and the broken surfaces observed from each break test, and the other is break boundary criteria in the application for evaluating residual risk of base-isolated NPPs. It should be noted that the break capabilities of the real-size LRBs are well-evaluated as expected; i.e. the breaking shear strain and tensile stress exceed the commercial reference values of 400 in percentage and l.OMPa, respectively. A tentative break boundary criterion is also able to be conservatively evaluated for employing the risk analysis of base-isolated nuclear facilities.