Theoretical And Experimental Study On Base-isolated Nuclear Power Plant

Base isolation technique is able to standardize the seismic design ofnuclear power plants, shorten design and construction period, and improveeconomic benefits. Moreover, it provides nuclear power plants a largerseismic margin to protect structures and facilities from potential hugeearthquakes with larger intensities than fortification earthquakes. This studyreexamines the feasibility and effectiveness of the base-isolated concept ofnuclear power plants theoretically and experimentally. Major findings aresummarized as follows.1.Related theory of base-isolated nuclear power plants: Three simplifiedmodels are built, namely, rigid block model, flexible beam model andmass-spring model. Frequency analysis onthe rigid block model indicates thatthe vertical frequency of base-isolated nuclear power plant shall be larger than1.0Hz to avoid the dominated rocking mode, and the aspect ratio of nuclearpower plant shall not be too large. Time history analyses based on the flexiblebeam model further examines the possible and reasonable parameters used todesign the base-isolation layer. Also concluded is the additional dampingeffect to reduce the displacement response. Finally, a multi-degree-of-freedommass-spring model is employed to simulate the seismic responses of CPR1000reactor.The floor response spectrum of isolated structures and non-isolatedstructures are obtained, which demonstrate that the base-isolation technique isable to suppress the horizontal response of structures and facilities effectively,and the thick rubber bearing is able to suppress the vertical response offacilities.2.Design of base-isolation devices: The isolation devices includetraditional rubber bearings, thick-rubber bearings and oil dampers. They aredesigned based on the parameters selected from the concept models. Thedevices are examined physically following the seismic design code and relatedinspection standard. The test result shows that the design equations oftraditional rubber bearings are not suitable for the thick-rubber bearings.Modified equations are thus advanced based on P.B.Lindley theory to considerthe bulge of thick rubber layers, which were proven more accurate than thetraditional design equations. The oil damper is quite simple but equipped withan adjustable orifice. The damper works well without any malfunction duringthe strict inspection tests.3.Finite element modeling of base-isolated nuclear powerplant:Sophisticated finite element models are constructed to examine thedominated vibration modes and seismic responses. The time-history analysesare conducted using six representative earthquake ground motions.The resultsare used to calibrate the results obtained from the following shaking table tests.4. Shaking table tests:The seismic performance of base-isolated nuclear powerplants are finally examined through shaking table tests. Three models are built,i.e., the model using traditional isolators, the three-dimensionallybase-isolated model and the model without isolation. The seismic responsesare examined and compared in terms of acceleration response, displacementdeformation, and floor response spectra. It verifies that base-isolationtechnique is effective in protecting the facilities inside the nuclear building.