Monte Carlo simulations of periodic pulsed reactor with moving geometry parts

Highlights: • In some periodic pulsed reactor, the reflector of the reactor core moves such that its state varies periodically from subcritical state to slightly prompt critical for producing periodic power pulses. • Current techniques of using the point kinetics approximations to simulate the dynamics in such a periodic pulse reactor are not very accurate when the reactor core is composed of zones with significantly different neutron lifetimes. • A Monte Carlo procedure is developed to simulate the geometrical movement of the reflector. • Two algorithms are proposed in modifying the neutron history tracks due to the movement of the reflector surfaces. • Numerical test cases have been developed to validate the developed Monte Carlo procedure. - Abstract: In a periodic pulsed reactor, the reactor state varies periodically from slightly subcritical to slightly prompt supercritical for producing periodic power pulses. Such periodic state change is accomplished by a periodic movement of specific reactor parts, such as control rods or reflector sections. The analysis of such reactor is difficult to perform with the current reactor physics computer programs. Based on past experience, the utilization of the point kinetics approximations gives considerable errors in predicting the magnitude and the shape of the power pulse if the reactor has significantly different neutron life times in different zones. To accurately simulate the dynamics of this type of reactor, a Monte Carlo procedure using the transfer function TRCL/TR of the MCNP/MCNPX computer programs is utilized to model the movable reactor parts. In this paper, two algorithms simulating the geometry part movements during a neutron history tracking have been developed. Several test cases have been developed to evaluate these procedures. The numerical test cases have shown that the developed algorithms can be utilized to simulate the reactor dynamics with movable geometry parts