Saturation of radiation damage in natural rock salt irradiated at moderate dose rate

Natural rock salt samples of the 800 m depth level from the Asse mine, Remlingen, Germany were gammairradiated at 100°C with spent fuel elements from the High Flux Reactor at Petten, The Netherlands. Dose rates in the experiments varied between 200 and 20 kGy/h in monthly cycles. Total doses of up to 1200 MGy were reached. After irradiation the radiation induced stored energy was studied as a function of total dose. It was found that, initially there is an approximately linear increase of stored energy with increasing total dose, but that stored energy values level of at higher doses until a saturation value of about 140 J/g is reached. The results of the stored energy measurements are shown here and compared with those obtained by others for irradiated pure and K-doped NaCl single crystals.