Change in the stationary oxygen concentration in RBMK-1000 reactor water accompanying variation of the oxygen concentration in the feed water

Abstract

UDC 541.15 The neutral water regime with oxygen dosing at a nuclear power plant with a RBMK-1000 reactor has been under discussion now for a long time [1, 2]. A central point of this discussion is estimation of the a priori possible increase in the oxygen concentration in reactor water accompanying the addition of a small, measured quantity of oxygen into the feed water. In [2-4] an attempt was made to solve this problem empirically by examining the oxygen balance in the first loop of the reactor. Although the radiation-chemical process was mentioned as a source of oxygen in reactor water, nothing was said about the mechanisms of the process. At the same time, in our opinion, the problem can be solved by applying the general laws of the radiation chemistry of water to the formation of the products of radiolysis of water in RBMK-1000. From the standpoint of the radiation chemistry of water, an estimate of the change in the stationary concentration of oxygen formed by radiolysis of water accompanying a change in the initial concentration of oxygen can be formulated as follows. Let the reactor feed water contain the regulated concentration of oxygen [O2]feed R. When such water is fed into the multiple forced circulation loop (MFCL), it is mixed with the circulation water, and its concentration at the entrance into the core becomes equal to [O2]iniR. In accordance with this concentration, on passage through the core a stationary hydrogen concentration [H2]st R and oxygen concentration [O2]st R is established in the coolant. If the oxygen concentration in the feed water is increased up to [O2]feea s, then the oxygen concentration in the water at the entrance into the core (we denote it by [O2]iniS ) and the stationary concentration of hydrogen and oxygen in the coolant after passage through the core (we denote them by [H2]st s and [O2]st s) will change. The problem is to determine the extent to which or by how many times the stationary oxgyen concentration in the reactor water will change when its concentration in the feed water fluctuates. To solve this problem we employ the experimental data on the mechanisms leading to the establishment of a stationary concentration of the products of radiolysis of water solutions of oxygen, data on single measurements of the parameters of the water-chemical regime of RBMK reactors and other boiling-water reactors, and the fundamental laws of the radiation chemistry of water. It is known that the stationary concentration of hydrogen, oxgyen, and hydrogen peroxide during -t-radiolysis of water is proportional to the initial concentration of oxygen dissolved in the water prior to irradiation: