5:15 PM - 6:45 PM
[HCG20-P07] Gas migration model in the engineering barrier of the deep SNF (spent nuclear fuel) disposal site according to its geodynamic sequential evolution
Keywords:disposal site, engineering barrier, gas migration, nuclear power plant, radioactive nuclide, SNF
The quantitative understanding for the gas migration in the deep SNF (spent nuclear fuel) disposal site is very important to minimize the nuclide spreading in the multi-barriers because gases originated from the SNF disposal site are very mobile in the subsurface and may affect the migration of radioactive nuclides generated from the SNF. Thus, mechanisms of gas-nuclide migration in the barrier and their influences on the safety of the disposal site should be sufficiently investigated before the construction of the final SNF disposal site. However, researches related to the gas-nuclide coupled movement in the barrier of the disposal site have been very little both at home and abroad. In this study, the hydro-dynamic numerical model for the gas migration in the engineering barrier of the disposal site was developed and the mathematical gas migration simulations in the multi-barriers were performed at various conditions by considering the sequential evolution process of the disposal site.
For the numerical gas migration modeling, various migration scenarios of gas in porous medium were determined and four gas migration types including ① advection and diffusion of gas (or dissolved gas), ② visco-capillary two-phase flow, ③ dilatant two-phase flow, and ④ tensile fracture flow were considered for the gas migration modeling. Mathematical governing equations to simulate these gas flow scenarios in porous medium were established by using both the dynamic equilibrium equation and the momentum equilibrium equation. Finally, the gas migration models based on the advection/diffusion mechanism of dissolved gas phase and based on the non-reactive gaseous phase diffusion were applied for the gas migration scenarios in the multi-barrier of the disposal site. In the modeling, the hydrogen (the initial H2 concentration: 0.8 mol/m3) was assumed as the gas phase originated from the corroded Cu-canister and its migration in the engineering barrier of which boundary was the corroded Cu-canister and the natural barrier (bedrock) wall was mathematically simulated based on the different geodynamic evolution of the disposal site.
From the modeling results without considering the groundwater flow in the barrier, the front line of the dissolved H2 plume of which concentration reached to 50% of the initial concentration moved forward about 17 m from the buffer boundary after 100,000 years storage in the disposal site. By considering the groundwater flow in the barrier (including bedrock), the front line of 50% H2 concentration moved forward about 190 m after 100,000 years disposal time. For the simulation of gas migration on the fracture propagation scenario in the engineering barrier, the gas passed through fracture inside as the separate gas phase and its average velocity was very fast (it takes about 10 days to reach the gas pressure equilibrium in the fractures and the engineering gaps of the buffer barrier). These modeling results support that it is important to control safely the Cu-canister and the engineering barrier during the early stage of the disposal site because of the fast gas migration in the unsaturated engineering barrier.
* This research was supported by Particulate Matter Management Specialized Graduate Program through the Korea Environmental Industry & Technology Institute (KEITI) funded by the Ministry of Environment (MOE).
For the numerical gas migration modeling, various migration scenarios of gas in porous medium were determined and four gas migration types including ① advection and diffusion of gas (or dissolved gas), ② visco-capillary two-phase flow, ③ dilatant two-phase flow, and ④ tensile fracture flow were considered for the gas migration modeling. Mathematical governing equations to simulate these gas flow scenarios in porous medium were established by using both the dynamic equilibrium equation and the momentum equilibrium equation. Finally, the gas migration models based on the advection/diffusion mechanism of dissolved gas phase and based on the non-reactive gaseous phase diffusion were applied for the gas migration scenarios in the multi-barrier of the disposal site. In the modeling, the hydrogen (the initial H2 concentration: 0.8 mol/m3) was assumed as the gas phase originated from the corroded Cu-canister and its migration in the engineering barrier of which boundary was the corroded Cu-canister and the natural barrier (bedrock) wall was mathematically simulated based on the different geodynamic evolution of the disposal site.
From the modeling results without considering the groundwater flow in the barrier, the front line of the dissolved H2 plume of which concentration reached to 50% of the initial concentration moved forward about 17 m from the buffer boundary after 100,000 years storage in the disposal site. By considering the groundwater flow in the barrier (including bedrock), the front line of 50% H2 concentration moved forward about 190 m after 100,000 years disposal time. For the simulation of gas migration on the fracture propagation scenario in the engineering barrier, the gas passed through fracture inside as the separate gas phase and its average velocity was very fast (it takes about 10 days to reach the gas pressure equilibrium in the fractures and the engineering gaps of the buffer barrier). These modeling results support that it is important to control safely the Cu-canister and the engineering barrier during the early stage of the disposal site because of the fast gas migration in the unsaturated engineering barrier.
* This research was supported by Particulate Matter Management Specialized Graduate Program through the Korea Environmental Industry & Technology Institute (KEITI) funded by the Ministry of Environment (MOE).