is nearly proportional to the core power density. As a result of water radiolysis, liquid-vapor phase equilibrium and recirculation, the reactor recirculation water contains oxygen and hydrogen peroxide in the concentration range from 100 to 300 ppb, and about 10 ppb (less than stoichiometric ratio of 8 to 1) of dissolved hydrogen.

It is known that the dose rates decrease as the distance from the core increases, and the fast neutron fluxes decrease faster than the gamma fluxes. At out-of-core regions, the total dose rate could be ≈0.1–1% of the core dose rate. The production of radiolytic species is not important in the peripheral regions, but the levels of radiation are still high enough to initiate the “recombination” of dissolved O2 and excess H2 in the coolant (see Section 6.4).

The overall simplified general expression for the radiation-induced water decomposition can be written as:


which is not chemically balanced.

Although the detailed mechanism of water radiolysis is complex, a simple scheme has been well established to explain the observed effects.(2,3) The primary process is to produce H and OH radicals,


Many of these radicals react with each other in regions of high local concentration to form molecular products, H2 and H2O2, or reform water according to the reactions:




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