Preliminary Assessment of Temperature Distributions Associated with a Radioactive Waste Vault

摘要

The temperature distributions of models which simulated radioactive waste vaults were determined, using a finite difference computer code to solve the transient heat conduction equation. Input parameters to the code included thermal properties for granitic rock and heat generation decay data for wastes that would be separated from CANDU fuel if it were recycled. Due to the preliminary nature of the study, only simple models were analyzed. A disc source was utilized to approximate a one-level repository. Various parmeters were investigated such as depth of disc, thermal properties of rock, and long-term effects. It was shown that, for a vault at 500 m depth with an initial areal heat flux of 31 W/m exp 2 , a maximum temperature increase of about 80 exp 0 C occurs at the vault level about 30 years after waste emplacement; maximum increases near the earth's surface occur after about 1000 years and are less than 1 exp 0 C. Modelling the vault by a number of vertical waste boreholes on one horizontal level, instead of by a disc, with the gross areal heat flux again 31 W/m exp 2 , did not cause serious local temperature increases as long as the initial heat generation rate of each container was less than about 750 W. It was also shown that, by using the vertical dimension available in granitic plutons and constructing either multiple-level vaults or very deep boreholes, initial areal heat fluxes greater than 31 W/m exp 2 can be utilized without exceeding the 80 exp 0 C maximum temperature increase anywhere in the vault. 14 figures, 8 tables.