Void reactivity and pin power calculation for a typical CANDU cell using CPs and a two-stratified coolant model

In a CANDU type reactor the void coefficient of the reactivity is positive. The experimental data are available only for fresh fuel at cold conditions. On the other hand, the reactivity effects induced by the coolant properties changing is often heavily taken into account. The safety analyses require an estimation of the calculation error. A comparison between models is a usual approach to obtain detailed information. In our paper a heterogeneous two-stratified coolant model is used. The coolant is treated as a two phase (liquid and vapour) medium, gravitationally separated. The results are compared with the classical (homogeneous) model. Eigenvalues are computed with the transport code CP_2D at four coolant states corresponding to the coolant densities of 0.80623 (the hot operating condition), 0.3, 0.1 and 0.001 g/cc for three burnup points of 0, 4000, and 13 000 MWd/TU. The results of CP_2D for classical model are compared with literature results of the transport code HELIOS. A detailed comparison of the cell parameters are performed between the homeogeneous and the two-stratified models.