Dimensionally adaptive neutron kinetics for multidimensional reactor safety transients - I: New features of RELAP5/PANBOX

A dimensionally adaptive, automatic switching algorithm has been developed for the RELAP5/PANBOX coupled thermal-hydraulics and neutron kinetics syste m to switch between three-dimensional (3-D), one-dimensional (1-D), and poi nt neutron kinetics models during a transient calculation. The 3-D, 1-D, an d point neutron kinetics models are del eloped and analyzed. The basis of t his development is the consistent and stable nodal expansion method. The 1- D and point neutron kinetics models are derived in a unified manner from th e 3-D model using the adiabatic approximation. The operator formation of pe rturbation/sensitivity theory is consistently used to determine the reactiv ity for the point-kinetics model. Furthermore, the new features of the coup led RELAP5/PANBOX code are described. This provides the basis underlying th e dimensionally adaptive algorithm.