Hybrid-transport point kinetics for initially-critical multiplying systems

•HTPK is a hybrid neutron kinetic model that combines transport with point kinetics.•The paper extends HTPK to deal with critical systems, including delayed emission.•Several results comparing performance of multi-collision, PK and HTPK are presented.•Some considerations on the mathematical model are included.

The paper presents an extension of the Hybrid Transport Point Kinetic (HTPK) model to initially-critical multiplying structures, i.e. in a source-free medium with transients starting from the equilibrium between neutron distribution and precursor concentrations. The mathematical model behind the HTPK methodology is derived from the detailed time-dependent balance equations and with reference to the limiting cases (i.e., point model and multi-collision models). Numerical simulations of transient systems demonstrate the interesting features of HTPK, which is shown to sensibly increase the accuracy of classical point kinetics models even at low truncation orders.