WAPPA modeling of post-emplacement performance of the AECL HLNW package

Environment Canada (EC) is anticipating, in the near future, a review of the EIS document released by AECL which addresses the performance of their HLNW disposal concept. This paper presents a summary of recently completed scoping calculations by the Subsurface Advisory Team (SAT) for EC using a waste package computer model to assess the likely performance of engineered barriers and potential releases from the waste package. A relatively sophisticated model was constructed with the waste package code, WAPPA. Included were corrosion of the metal container affected by radiation and heat, instant release (of I, Cs, Tc, Dissolved Inorganic Carbon (DIC)) and slow leaching (of Pu, Np, and U) of the waste fuel, transport of leachate through the breached container, buffer layer and into a damaged region of rock surrounding the package. Radioactive decay and buildup in the unleached fuel was considered but decay and buildup of transported elements was not. Results are reported for a titanium container with in-borehole emplacement geometry and in-room geometry