Formation of local, transient "acid spikes" in the fast neutron radiolysis of supercritical water (SCW) at 400 ℃: a potential source of corrosion in SCW-cooled reactors?

The use of supercritical water (SCW) in GEN IV reactors is a logical approach to the ongoing development of nuclear energy. A proper understanding of the radiation chemistry and reactivities of transients in a reactor core under SCW conditions is required to achieve optimal water chemistry control and safety. A Monte Carlo simulation study of the radiolysis of SCW at 400 ℃ by incident 2 MeV monoenergetic neutrons (taken as representative of a fast neutron flux in a reactor) was carried out as a function of water density over the range of ∼0.15-0.6 g/cm³. The in situ formation of H₃O⁺ by the generated recoil protons was shown to render the "native" track regions temporarily highly acidic (pH ∼ 1). This acidity, even local and transitory ("acid spikes"), raises the question of whether it may promote a corrosive environment under proposed SCW-cooled reactor operating conditions that would lead to progressive degradation of reactor components. (author)