Reduced order models in reactor kinetics: A comparison between point kinetics and multipoint kinetics

Due to the heavy computational burden of full reactor kinetics modeling, reduced-order models are usually employed to simulate transients. Among those, point and multipoint kinetics have small computation time and provide satisfying results for many applications. We implemented point and multipoint kinetics (Avery's and Kobayashi's models) in the APOLLO3 code. Then these models are applied to study two simple transients, one in a coupled fast-thermal configuration, the other in a fast reactor. As at present we focus on the neutronic response only (neutron and precursor populations), the study is limited to step-change transients with no thermal feedback. This work permits to better delineate the potential of these methods and opens interesting perspectives. As an example, multipoint kinetics allows accounting for very fast shape transients that, depending on the coupling of the system, may result in global population changes occurring before the conventional prompt jump and altering significantly its quantitative value.