Simulation of the Migration of ³H and ¹⁴C Radionuclides on the 2nd Phase Facility at the Wolsong LILW Disposal Center

Numerical model was developed that simulates radionuclide (³H and ¹⁴C) transport modeling at the 2^nd phase facility at the Wolsong LILW Disposal Center. Four scenarios were simulated with different assumptions about the integrity of the components of the barrier system. For the design case, the multi-barrier system was shown to be effective in diverting infiltration water around the vaults containing radioactive waste. Nevertheless, the volatile radionuclide ¹⁴C migrates outside the containment system and through the unsaturated zone, driven by gas diffusion. ³H is largely contained within the vaults where it decays, with small amounts being flushed out in the liquid state. Various scenarios were examined in which the integrity of the cover barrier system or that of the concrete were compromised. In the absence of any engineered barriers, ³H is washed out to the water table within the first 20 years. The release of ¹⁴C by gas diffusion is suppressed if percolation fluxes through the facility are high after a cover failure. However, the high fluxes lead to advective transport of ¹⁴C dissolved in the liquid state. The concrete container is an effective barrier, with approximately the same effectiveness as the cover