Seismic Analysis Of The Radioactive Waste Geological Repository Structure

The kind of steel vessel containing radioactive materials must be treated according to the criterion of high level radioactive (HLW) waste geological repository. The earthquakes seriously threat the safety design for the HLW waste geological repository, in the long term of thousands or even ten thousands of years. During this period, the earthquake is one of the most important random events affecting the safety of HLW waste geological repository. Thus the seismic analysis of HLW waste geological repository structure is important.The two characteristics of HLW waste geological repository are (1) located deep underground and, (2) the capability of shielding radioactivity, which bring forward the two outstanding problems:(1) how to decide the deep design ground motion parameters, and (2) how to considering the complex shielding configurations.Firstly, the present status of underground seismic analysis are researched, and the change rules of the ground motion parameters in deep underground on the rock site are gained from the research results of analysis about lots of underground ground motion measuring data by seismologists. The key principle rules deciding the parameters of design ground motion for HLW geological repository were put forward by the author. Using the rules, the design ground motion of research structure can be directly obtained, or be indirectly gained according to the relations of parameters of design ground motion with the depth based on the ground earthquake records.The optimize seismic records were gained from above conditions. At last, the record of Loma Prieta is selected as the load curve of the structure in practical case study, which arises at 00:05 October 18 1989.Subsequently, the Mohr-Coulomb constitutive equation was decided to describe the behavior of the lightweight aggregate concrete and bentonite, which is based on the theory analysis of the elementary physical property of those materials. And the necessary parameters of the Mohr-Coulomb constitutive equation for those material were obtained with experiments. The parameters of the bentonite were tested with soil triaxial instrument and those of the lightweight aggregate concrete's with the rock triaxial instrument. The friction angle and cohesion yield stress of the lightweight aggregate concrete respectively 7.4°and 4.8 MPa, those parameters of bentonite are respectively 23.7°and 145.7kPa. Finally, the practical structure model were simplified to a reasonable model which can be analyzed by the ABAQUS software. The interactions between the rock body and concrete shielding layer, between the concrete shielding layer and bentonite layer, between the bentonite layer and steel vessel were considered in the numerical simulation model, and the displacement variation of the bentonite are researched under the earthquake load. The vibration characteristics of structure were studied on the condition of different constrain conditions for the steel vessel and different load types (accelerate, velocity and displacement). The results shows that the structure is most sensitively influenced by the velocity record, the response by the load of acceleration or displacement not so varified; and the boundary condition type of steel vessel also affects the structure response, which means that the relative positions of bentonite and other shielding layer were much influenced by the boundary conditions, which perhaps induce the destroy of concrete shell on the top of structure.The research results of this paper were useful for the seismic design of the HLW geological repository and the design of shielding layers.