Kinetic Modeling for On-Line Advanced Plant Simulator

Abstract

A number of reactor kinetics models have been selected for evaluation and possible use in an on-line advanced PWR plant simulator which is currently under development at Oregon State University. The selected kinetics models include: the one-dimensional space- and time-dependent diffusion equation, modal expansion approximation methods, nodal approximation methods, and the regionwise point reactor kinetics (RWPRK) method. Evaluation of these models has been based on two major requirements: computational speed and accuracy. These requirements are pivotal to the development of the on-line advanced plant simulator which is expected to primarily solve a series of thermal hydraulics equations in a large number of computational nodes with a speed that is faster than the real time of the transient events. Solution of the one-dimensional space- and time-dependent diffusion equation requires a very lengthy and time consuming process to determine the spectrum averaged neutron cross sections at different reactor regions. The use of modal expansion approximation methods is impractical because of the difficulty in choosing proper shape and weighting functions. The primary difficulty which rules out the use of the nodal approximation method is determination of the coupling coefficients. However, if the rate of change of neutrons streaming into each nodal region is slow, the coupling coefficients can be set to zero and arrive at the regionwise point reactor kinetics equations. Performance of the RWPRK method in prediction of reactor axial power distributions during a variety of normal and abnormal operational transients is assessed. The transient events which have been chosen for this analysis are: a partial loss of flow; a control rod ejection event and unplanned increase and decrease in core coolant inlet temperature for PWR systems; and a pressure increase transient for BWR systems. For all of these transients, the reactor scram is intentionally delayed to make the changes in primary thermal hydraulics parameters with significant feedback effects more severe.