Detailed Multi Canister Release Model of Radionuclides in High Level Radioactive Waste Repository Using Wavelet Galerkin Method

2002 ◽  
Author(s):  
Hesham R. Nasif ◽  
Atsushi Neyama
Keyword(s):  
Radioactive Waste ◽  
Galerkin Method ◽  
Near Field ◽  
Far Field ◽  
High Level Radioactive Waste ◽  
Compactly Supported ◽  
Wavelet Galerkin Method ◽  
Bentonite Buffer ◽  
Buffer Region ◽  
High Level

This work develops a model to calculate the radionuclides release from a repository for high level radioactive waste, taking into account multiple-canister interface. Once the overpack loses its integrity, the waste glass starts to dissolve by porewater in the bentonite buffer. Bentonite is expected to have hydraulic conductivity more than three orders of magnitude less than that of the surrounding rocks. The migrating nuclide from the buffer region is transported in the near field granite host rock, then releases to the far field of the repository. A mass concentration calculation in the far field of the repository is also included in the model. The model is diffusion-advection model. The model is solved using wavelet Galerkin method (WGM). The model is devised to be fast and compact due to the compactly supported property of the Daubechies’ wavelet. Since the scaling functions are compactly supported only a finite number of the connection coefficients are nonzero. The resultant matrix has block diagonal structure, which can be inverted easily. We tested our model for a try of canisters contains 200 canisters. The results show well agreements with the results obtained from the analytic solution with a proper selection of wavelet-dilation order pairs.

Integrated Multi Path Model to Calculate Radionuclide Release From a Repository Using Wavelet Galerkin Method

2002 ◽  
Author(s):  
Hesham R. Nasif ◽  
Atsushi Neyama
Keyword(s):  
Galerkin Method ◽  
Host Rock ◽  
Transport Model ◽  
Near Field ◽  
Nonlinear Partial Differential Equations ◽  
Path Model ◽  
Diffusion Type ◽  
Wavelet Galerkin Method ◽  
Buffer Material ◽  
High Level

This work represents a WIRS code developed using wavelet Galerkin method to solve radionuclide transport model in near field and far field of a repository for high-level radioactive waste. After overpack failure, radionuclides diffuse through the bentonite buffer material to the water bearing fracture around the repository transport horizontally through this geosphere then transport vertically through the major water conducting fault (MWCF) reach the biosphere. The radionuclides transport barriers considered in this model are engineered barrier system (EBS), geosphere, and MWCF. Hydraulic conductivity of the bentonite is more than three orders of magnitude smaller than that of the surrounding host rock, so the only transport mechanism through EBS is diffusion. In the host rock, the problem is of advection-diffusion type with highly varying parameters from one medium to other due to the variability in length, transmissivity and other transport-relevant properties of the transport paths. Daubechies’ wavelet is used as a basis function to solve the nonlinear partial differential equations arising from the model formulation of the radionuclides transport. Since the scaling functions are compactly supported, only a finite number of the connection coefficients are nonzero. The resultant matrix has a block diagonal structure, which can be inverted easily. We tested our WGM algorithm with several problems to verify the model. The solutions are very accurate with a proper selection of Daubechies’ order and dilation order. The solution is very accurate at the interfaces where the radionuclide concentration exhibits very steep gradients.

Sign in / Sign up

Export Citation Format

Share Document