The long-term evolution of cemented waste packages is governed by (bio)chemical reactions
between waste, cement, and barrier materials, and by transport processes inside the
waste package and through openings in the waste package hull. Inside a waste package,
gases can be generated by pH-dependent anoxic corrosion of metals and the degradation
of organic matter. The (bio)chemical reactions consume water and will not proceed
under dry conditions. The degradation of cementitious materials lowers the alkaline
pH of the pore water. The modeling of such a complex feedback system shows that the
internal structure of a waste package and the exchange of mass with the environment
(boundary conditions) are major factors that determine the importance of process couplings.
The (bio)chemical reactions are controlled by internal re-distribution of water predominantly
via vapor transport. Calculated gas generation rates were found to be affected by
dry-out processes inside the drum.