Coolant radiolysis near the saturation temperature in a VVER core

This paper presents calculations of coolant radiolysis in the process of hydrogen transfer from the liquid phase into vapor–gas bubbles near the coolant saturation temperature. It is established that hydrogen concentration in the liquid phase continues to decrease until the hydrogen flow into bubbles equalizes with hydrogen generation by radiolysis, with the hydrogen concentration jump leading to a drastic change in the entirety of time dependencies of the component concentrations. It has been demonstrated that local oxygen concentration may increase more than 1000 times relative to the maximum allowed value, while an increase in the concentration of hydrogen peroxide is slightly greater than an order of magnitude. The significant local increase in the concentration of oxidizing radiolysis products – O₂ and H₂O₂ – in the coolant appears to be the main reason for corrosion of VVER fuel element claddings observed near the 12th spacer grid with the increasing reactor power.