Use of heavy water in the control and safety rod loop of an RBMK channel-type uranium reactor

Abstract

We consider replacing ordinary water in the control and safety rod loop with D{sub 2}O, whose neutron absorption cross section is significantly lower. Using the WIMS-D4 program, we calculated the neutron physical constants of elements of the control and safety rod assembly with the coolant loop of the assembly filled with D{sub 2}O for different states of the core. Then using the program POLY (a version of the program STEPAN), we calculated the nuclear safety system characteristics of the RBMK-100 with the control and safety rod loop filled with D{sub 2}O compared with the standard situation. The composition of the polycell corresponds to the loading of actual RBMK-1000 reactors. When replacing light water by heavy water, the position of the control and safety rods were not altered; the volume distribution of fuel burnup for both cases was determined as a result of iteration calculations in the POLY program. The calculation results are presented. The analysis shows that the main goal of going to heavy water is certainly achieved. The effect of loss of water in the coolant loop of the control and safety rod assembly in the operational state changes from a large positive effect down to almost zero. Themore » efficiency of the RR manual regulating rods increases by 25% in the operational state, and by 70% in the shutdown state. The subcriticality changed especially significantly. Its increase by 3% along with the increase in the efficiency of the rods is determined to a large degree by the change in such reactivity effects as the density effect of the water and the reactor cooling effect. From Table 1 we see a significant increase in the reactivity upon loss of water from the fuel channels {rho}{sub LOC} (by 0.8{beta}), which is explained by the disappearance of the water columns in the control and safety rod assembly as absorbers upon going to heavy water. This also explains the increase in the efficiency of the control and safety rod assembly.« less