REGAL model of gas and liquid migration from grout containing radioactive waste

A concern for hydrogen and flammable gas generation in the Hanford Site grout radioactive waste disposal facility led to the development of the REGAL model. This model predicts buildup of radiolytically formed gases in the grout region and their migration to air-filled regions surrounding the grout. The REGAL model is a three-dimensional finite difference code that couples models of gas diffusion, two-phase gas and liquid flow, liquid evaporation and condensation, and heat transfer. Final preliminary software quality assurance of the REGAL code has not been completed at this time; however, the current status of the model is adequate to demonstrate the liquid expulsion predictions described in this paper. A unique finding of this model was that an expulsion of liquid from the grout region could occur. This liquid is from the radioactive waste tanks and may contain soluble radioisotopes and chemicals, such as 137Cs and nitrates. This liquid expulsion is driven by displacement of gas bubbles formed within the grout microstructure. Liquid expulsion is very sensitive to the level of gas production, geometry and design of the grout region, and material properties of the grout