A general view on the radiolysis and hydrolysis of brine in the context of direct ultimate storage of spent nuclear fuel in salt domes

A study has been made investigating whether the radiolysis and hydrolysis of brine would cause problems for the ultimate storage in salt domes. The main radiolysis products are hydrogen, oxygen, chlorate and bromate. The latter will dissociate at high temperatures to oxygen and the respective halides. The G-values for hydrogen are between 0,45 (pure water) and 2.1 (concentrated chloride solution). For the sake of stoichiometry, the number of oxidized species will be the same as that of hydrogen. Most of the radiolysis gas is generated from brine bubbles in the salt. Additionally chloric acid will occur as a result of the hydrolysis of magnesium chloride solution (2.1 to 3 m) at higher temperatures. A pH-value of 3 to 4 is to be expected. An explosion-like recombination of hydrogen and oxygen will not occur under ultimate storage conditions. All fundamental thermochemical and radiochemical considerations may be transferred to the circumstances of the project 'Other waste management methods for spent nuclear fuel'. The main difference as compared with the circumstances taken as a basis in technical literature is the fact that the dose rate value will be smaller by a factor of 104 to 106, and the pH-value will be between 4 and 5. Therefore, only a few litres of radiolysis gas are to be expected during cask serviceable life. The requirements made on the cask material are exacting, because the corrosion medium is comparable to diluted chloric acid. No hydrogen generation due to cask corrosion is to be expected if the materials discussed in this report are used. (orig./HP)