Radiolytic yields in water reactor system and influence of dissolved hydrogen and nitrogen

Hydrogen or hydrogen peroxide formation and disappearance rates have been measured in cooling systems of swimming pool reactors as a function of the power level. The initial yield of the radiolytic decomposition of water is independent of the reactor power and equals the theoretical composite yield derivated from the separate contributions of gamma flux and fast neutrons. At a constant power level of the reactor, the molecular products are formed with a decreasing yield and reach a stationary concentration. This yield depends only on the difference between the stationary and the instantaneous values of their concentrations. A linear regression between the stationary value of the hydrogen concentration and the reactor power is also observed. The relation in the case of the OSIRIS reactor at a power level of 70 MWt is: (H2)sub(cm)3sub(.1)-1 = 0.16 Psub(MWt) + 2.5 (+ - 2). No appreciable conversion of dissolved nitrogen under ionizing radiation could be observed, confirming that nitric acid or ammonia formation takes place only in the existing gaseous phase. The non-detrimental effect of dissolved nitrogen was then demonstrated by varying the nitrogen concentration in the helium cover gas of the out-of-flux expansion vessel of a heavy water reactor. (author)