Yields of water radiolysis products from proton irradiated water

The yields of aqueous radiolysis products under the high temperature and pressure regimes relevant to Light Water Reactors are important parameters in the use of chemical models to simulate reactor circuits, as high temperature corrosion requires the oxidising products of water radiolysis in order to sustain the process. The main species of interest are the oxidising radical, OH·, and the molecular product H2O2. The yields of these species from radiolysis of water at temperatures below 100degC have been extensively measured. However these measurements have proved difficult at elevated temperatures and pressures because of the requirements to contain the water safely at high temperature and pressure and yet permit entry of a radiation beam. A major source of radiation in the core of the reactor primary circuit is the neutron flux. However, when neutrons interact with water molecules the dominant process for energy loss is with protons by elastic scattering and the formation of energetic recoil protons which then interact further with the surrounding water molecules by electrostatic interaction. Therefore the neutron radiolysis of water can be well simulated by using protons as the incident radiation. Protons are conveniently produced using a Van de Graaff accelerator and in this work the Harwell Tandem accelerator has been used to produce protons with energies up to 12 MeV. (J.P.N.)