Poisoning of reactor Maria beryllium blocks in the period 1993-2000

The present work is a continuation of the REBUS-3 calculations of the poisoning of beryllium matrix of the Maria reactor by Li-6, and He-3 for the period 1974-1985. In the present work the decrease in H-3 density and the resulting increase of He-3 density have been determined during the July 1985 - June 1993 break in operation and then the following on-power and off-power period were simulated. The same geometrical model of calculation has been applied as for the first period, i.e. two-dimensional distribution of the parasitic isotopes, average for each beryllium block, has been obtained using REBUS-3 code with its microscopic library determined using WIMS-ANL code. Due to availability of the detailed operational records from the period considered, the exact operation and shutdown times could be applied together with detailed follow-up of actual reloading of fuel assemblies. In addition all the beryllium block movements have been followed. The boron control rods have been simulated by homogeneous admixture of control rod material the control rod containing beryllium blocks. (author)