Homogeneous radiolysis studies using 238Pu

Used nuclear fuel contains radiotoxic elements with lifetimes in the range of 100 000 years. Although possibilities for recycling of the fuel exist, a final storage for the ultimate high-level waste will be necessary. In Sweden, a deep geologic repository will be constructed, in which the used fuel will be protected from ground water contact by different barriers. However, considering the extensive time scale, scenarios of barrier failures and ground water intrusion are a necessary part of the safety assessment. In such a scenario, the possible release of radiotoxic elements into the environment will be governed by the solubility of the UO2 matrix, which may be altered by oxidative radiolysis products formed in the water. In this work, a method has been developed for the study of homogeneous α-radiolysis under final repository conditions, with the intention to determine the effect of dissolved bromide on the radiolytic yield of oxygen. To enable this study, a high activity 238Pu solution was stabilized at neutral pH, and a method for mass spectrometric measurement of oxygen gas at the ppm level was developed. Contrary to expectations, a qualitative evaluation of the measurement data indicated a consumption of oxygen in the radiolysis experiment. It was however concluded that the experimental procedure will require further improvements before any radiolytically produced, or consumed, oxygen could be quantified.