Calculation of the radiation transport in rock salt using Monte Carlo methods

To improve the final concept for a high-level radioactive waste (HAW) disposal in geological salt formations, plans have been developed in Germany for a full scale testing of an underground repository. As a main part of this so-called HAW project, the testwise emplacement of 30 vitrified highly radioactive canisters was planned in test galleries at the 800 m level of the Asse salt mine near Braunschweig, Germany. An attempt should be made to correlate the changes induced to the salt with the amount of energy deposited there. This paper provides absorbed dose rate and photon fluence rate distributions in rock salt around these highly radioactive canisters, containing the radionuclides Cs-137 and Sr-90, and around a single canister containing radioactive material of a lower activity level (INHAW experiment). The data given were calculated using a Monte Carlo method simulating photon transport in complex geometries of differently composed materials. The aim of these calculations was to enable determination of the dose absorbed in any arbitrary sample of salt 1 m around the canisters to be further examined in the future with sufficient reliability for safety considerations. The geometry of the test arrangement, the materials involved, the calculational method and selected results are shown.