The influence of water chemistry on the radiolysis of the primary coolant water in pressurized water reactors

In order to study the radiolysis of PWRs primary coolant we irradiated several water samples containing hydrogen and boric acid in an experimental reactor. It was found that water decomposition to oxygen and to hydrogen peroxide is a threshold phenomenon depending on the experimental parameters such as the characteristics of the radiation and the water chemistry. An increase in temperature reduces the extent of water decomposition in presence of hydrogen. On the other hand, an increase of the boric acid concentration causes a higher decomposition. The minimum amount of molecular hydrogen used to inhibit the decomposition in our experiments was 0.23 ppm. Experiments with iron(III) and zinc nitrate dissolved in water showed that, in our conditions, zinc nitrate does not have any influence on water decomposition whereas iron(III) nitrate causes a greater decomposition. An experiment at pH=7 (200°C) using ⁷LiOH also showed an important formation of oxidizing products.