Radiocarbon (14C) is one of the key radionuclides for the performance and safety assessment of a radioactive waste disposal, due to its high activity concentration in waste materials from the nuclear cycle and to its mobility. The measurement of the 14C content in spent ion exchange resins from nuclear reactors is important for the safety assessment of the disposal concept and for the choice of the appropriate treatment/disposal method. Ion exchange resins are commonly used in nuclear reactors as filters for the purification of process liquids or wastes streams and they retain molecules containing radioactive isotopes, among which is 14C. Their efficiency, both as filters and as waste containers, is strictly connected with the morphology. The preservation of spherical shape upon aging is one of the key parameters for their quality assessment and for the evaluation of the potential release of 14C during storage conditions. In this study, the change in IERs morphology during storage periods has been investigated in order to verify correlation with 14C release. Both brand new and aged specimens have been studied in order to assess the quality of the resins after 10 yr of storage and to contribute to the understanding of 14C release mechanisms.

An investigation and evaluation of the redox conditions around an underground rock cavern are important from the viewpoint of the safety assessment of the subsurface geological disposal of radioactive wastes. The in situ redox conditions around a cavern excavated in Neogene pyroclastic rocks were investigated. Rock samples were collected from a tunnel wall crossing the oxidation front, and the properties of pore water seeping into small holes drilled in the tunnel wall were determined. Chemical analysis of the rock samples revealed that pyrite-bearing rocks belowthe oxidation front were oxidized by the dissolved oxygen in the groundwater infiltrating from the surface. The water properties changed with increasing oxidation of the rocks. From the amount of oxygen-consuming components in the rocks, the migration rate of the oxidation front was estimated to be ~0.2 mm/y due to the flowrate of groundwater (0.1 m/y) containing oxygen.