NUMERICAL SIMULATION OF HEAT AND MOISTURE TRANSFER IN NUCLEAR WASTE REPOSITORY

Abstract

For the last three decades there has been serious efforts made worldwide to develop an efficient nuclear waste disposal technique. The problem of disposal of radioactive waste is not new but needs urgent attention due to its increasing volume worldwide. Only safe and successful solution of this problem would guarantee the long future of nuclear power. These highly radioactive materials must be protected so they won't harm people or the environment. The use of nuclear energy is increasing dramatically in the world, and hence the nuclear waste disposal and its short and long-term effects are of considerable importance. One of the options considered for nuclear waste disposal is underground nuclear waste facility. In this underground nuclear waste disposal system the waste filled canisters are placed in the rock surrounded by an engineered clay barrier and the whole system is buried in the geological formation, which serves as the natural or geological barrier. The knowledge about the heat and moisture transport through the clay barrier is critical in determining the performance of the disposal facility. Clay is an unsaturated porous material. The governing equations for heat and moisture transfer. through unsaturated porous media are coupled and nonlinear and hence they have to be solved using numerical solution technique. In this dissertation work previous research works in numerical methods for the solution of heat and moisture transfer phenomenon in nuclear waste repository has been discussed. Finite element formulation of the non-linear governing equations has been proposed in the present work for simulating heat and moisture transport through unsaturated clay material by using Galerkin's weighted residual method. A detailed computational procedure and flow chart has been established for the solution of the non-linear governing equations using Newton-Raphson technique. Computer code has been developed in FORTRAN language for numerical simulation. Numerical simulation results obtained for the temperature and moisture variations for .Dirichlet and heat flux boundary conditions which the clay barrier may be subjected to in real situation, are discussed. The comparisons of the results obtained from the present numerical simulation with the available experimental results shows that the present model can simulate the thermo-hydraulic behaviour of unsaturated porous media according to the physics underlying the problem..