Radiation-chemical removal of corrosion hydrogen from VVER first-loop coolant

Abstract

Room-temperature γ radiolysis of water solutions of ammonia in the presence of hydrogen peroxide is studied. It is found that in de-aerated solutions the yield of hydrogen peroxide decomposition is 3. 8-5.5 mol/100 eV depending on its initial concentration. In the absence of hydrogen peroxide, the yield of the decomposition of ammonia is 0.34-0.39 particles/100 eV; adding hydrogen peroxide to the solution increases the rate of decomposition of ammonia and saturation of the solution with hydrogen decreases it. The data obtained are used for mathematical simulation of the influence of hydrogen peroxide on the composition of the first-loop coolant of a hypothetical ship reactor facility with VVER where equipment corrodes with hydrogen being formed. It is shown that adding hydrogen peroxide to the coolant in molar concentration equal to that of corrosion hydrogen decreases the stationary concentration of hydrogen and ammonia to the level characteristic for the case where there is no equipment corrosion with hydrogen being formed in the loop.There have been cases where during the operation of ship reactor facilities with VVER the maximum admissible concentration of ammonia in the first-loop coolant was exceeded [1, 2] because the zirconium materials in the elements of the core undergo corrosion and a substantial amount of hydrogen is formed. Ammonia forms in the core as a result of radiation-chemical synthesis from dissolved nitrogen and corrosion hydrogen. One way to decrease the concentration of the latter and, correspondingly, ammonia in the first-loop water of VVER could be its radiation-chemical removal by introducing a water solution of hydrogen peroxide into the coolant. This method is attractive because new reagents are not introduced, since the hydrogen peroxide is a product of the radiolysis of water and is unavoidably present in the first-loop coolant of any light-water nuclear power reactor [3].Let us examine the equation of material balance for radiolysis of water solutions of ammonia in a closed single-phase system [4] for the specific case of the radiolysis of water coolant, initially containing dissolved ammonia, nitrogen, hydrogen, and hydrogen peroxide. For prolonged irradiation of water in a closed system, initially containing only dissolved ammonia, a stationary state is established with a stationary concentration of the products of radiolysis given by the relation [H 2 ] st = [H 2 O 2 ] st + 2[O 2 ] st + 3[N 2 ] st . If water initially containing dissolved ammonia and nitrogen is irradiated, then [H 2 ] st = [H 2 O 2 ] st + 2[O 2 ] st + 3[N 2 ] st -3[N 2 ] ini ,