Final disposal of heat-generating radioactive wastes in rock salt: physico-chemical investigations on the nearfield

In the introduction the main effects of heat-generating radioactive wastes on the nearfield are discussed. It includes temperature fields as a function of time, resulting stresses and deformations in the rock salt, and effects of radiation such as formation of F-centres and colloidal sodium. For the mobilization of radionuclides from the nearfield via the aqueous pathway the quantitative assessment of container degradation is important. Corrosion studies on the basis of immersion experiments, electrochemical corrosion studies and longterm in situ corrosion experiments are described. Two types of container material are investigated: actively corroding material like unalloyed steels and passive layer forming materials like Ti- or Ni-base alloys. The assessment of the barrier function of the containers is based on the corrosion rates measured and the information available with respect to the local corrosion attack (pitting corrosion, crevice corrosion, stress corrosion cracking). The corrosion allowance concept on the basis of actively corroding unalloyed steels makes the design of containers (waste package) with a lifetime of ∼ 102 years a feasibility. (author)