Fuel and Core Physics Considerations for a Pressure Tube Supercritical Water Cooled Reactor

Abstract

<p>The supercritical water cooled reactor (SCWR) is a Generation IV reactor concept that features light water coolant in a supercritical state. Canada is developing a pressure tube variant of the supercritical water reactor as an evolution of the CANDU reactor. The main advantages of the pressure tube SCWR are an improved thermal efficiency over current reactors, enhanced safety through passive safety features, and plant simplifications. The objective of this thesis was to investigate current fuel and core designs for the Canadian SCWR concept.</p> <p>Simulations of 2-D lattice cells for fuel assemblies containing 43 and 54 fuel elements were performed using the neutron transport code WIMS-AECL. Safety parameters and fuel burnup performance were investigated here. Three dimensional full core simulations were performed using the diffusion code RFSP. These studies examined batch fueling, cycle length, radial and axial power profiles, linear element ratings, and reduction of axial power peaking through graded enrichment along the fuel channel. Finally, a study of reactivity transients was performed using the FUELPIN heat transfer/point kinetics code.</p> <p>The main results of the studies show that the coolant density change that occurs as water passes through the pseudocritical point strongly affects fuel performance. It is concluded that the 54 element assembly design is acceptable in terms of coolant void reactivity performance with lattice pitch smaller than 26 cm. To meet the burnup target, a fuel enrichment of about 5% is required. From the RFSP studies, this level of fuel enrichment will provide an operating period of 370 days between refueling. Relatively high axial power peaking is observed at the beginning of cycle conditions. A main finding is that the proposed reactor power level of 2540 MWth produces unacceptably high linear element ratings. This is confirmed using the FUELPIN code. A reduction in linear element rating is suggested for consideration.</p>