Modelling the Release of Radionuclides from the Spent Fuel and their Transport in the Near Field: a Coupled Approach
- PDF / 484,670 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 109 Downloads / 227 Views
0RGHOOLQJWKH5HOHDVHRI5DGLRQXFOLGHVIURPWKH6SHQW)XHODQGWKHLU7UDQVSRUWLQWKH 1HDU)LHOG D&RXSOHG$SSURDFK Juan Merino1, Esther Cera1, Jordi Bruno1 and Aurora Martínez-Esparza2 1 Enviros Spain Pg. de Rubí 29-31, 08197 Valldoreix (Spain) 2 Enresa C/ Emilio Vargas 7, 28043 Madrid (Spain) $%675$&7 In this work we have developed a model for the release of radionuclides from the spent fuel coupled with their transport through the near field. A compartmental approach has been used, as this methodology is well suited to model integrated systems. Several processes have been taken into account: oxidative dissolution of the spent fuel matrix, radioactive decay and chains, diffusive and advective transport, retardation by sorption and secondary phase precipitation. Results illustrate the complex evolution of the radionuclide concentrations in the gap and the near field. Hence, the main conclusion from this study is the requirement to model this coupled system using a compartmental integrated approach. ,1752'8&7,21 In recent years Enresa, the Spanish Radioactive Waste Management Agency, has been developing a variety of research and development activities to support its Performance Assessment exercises. One of the key points to be studied is the stability of the spent fuel under repository conditions, and a conceptual and mathematical model has been developed in the past [1], [2] to address this issue. In this work we propose to model the release of radionuclides from the spent fuel coupled with their transport through the near field. The objective of this modelling exercise is to give a wider perspective to matrix alteration modelling by incorporating the near field into a coupled model. In this way we can assess the significance of the different radionuclides not only in terms of their release from the matrix, but also in terms of their transport properties. 02'(/'(6&5,37,21 The system to be modelled has been derived from the repository layout given in the Spanish performance assessment Enresa 2000 [3]. It includes the whole canister (including 4 fuel elements with filling material), bentonite as buffer material and granite as the host rock (see Figure 1). It is assumed that the canister fails 1000 years after closure of the repository. Water from the saturated bentonite gets in contact with the spent fuel and an oxidative dissolution process begins which leads to the release of the radionuclides to the gap water and their transport through the engineered barriers.
1
Container with SF
Bentonite
EDZ
Granite
0.725 m
0.2 m
1.2 m
0.475 m
Diffusive flux Advective flux
)LJXUH. Model of the system studied: canister with spent fuel, bentonite layers, EDZ and granite layers. The compartment tool AMBER [4] has been used to solve the system. The different processes taken into account are: • Oxidative dissolution of the matrix • Congruent dissolution of radionuclides embedded in the matrix • Decay chains in all the compartments • Radionuclide retention by adsorption (Kd) in the bentonite and granite • Second
Data Loading...
