Two-group sparse-grid nodal neutron balance equation of the BIPR-8 computer program

The transition from finite-difference diffusion equations for solving problems of neutron transport in VVER to the nodal sparse-grid neutron balance equations used in the BIPR-8 computer program is examined. The solution error is decreased by using trial functions to describe the neutron field inside cells in addition to the condition of continuity of the neutron flux and current on the common boundaries between the cells. The corresponding nodal equations for solving the problems of three-dimensional neutron kinetics in the BIPR-8KN program are presented.