Thermal Aspects of Using Thoria Fuel in SuperCritical Water-Cooled Nuclear Reactors

Abstract

SuperCritical Water-cooled Reactors (SCWRs) are one of six next-generation nuclear-reactor design options under consideration worldwide. These nuclear-reactor design options are included in the major international treaties such as: Generation IV International Forum (GIF) and INternational PROject on innovative nuclear reactors and fuels (INPRO). SCWR coolant is light water, which operates at supercritical pressures and temperatures. Typical SCWR coolant operating parameters are 25 MPa and 350–625°C. These SCWR operating conditions significantly increase the thermal efficiency of a SCW Nuclear Power Plant (NPP) (about 45 – 50%) compared to that of existing NPPs (30 – 35%). Also, SCWRs use significantly higher water parameters than existing water-cooled reactors, because of this they can support hydrogen co-generation. Previous thermal-design fuel-channel option studies for SCWRs have shown that the use of uranium dioxide (UO2) fuel at supercritical water conditions might be unacceptable as the fuel centerline temperature is close to or even exceeds the industry accepted limit of 1850°C. Alternative fuels with a higher thermal conductivity have to be considered. Thoria (ThO2) fuel is a suitable alternative to UO2 due to its higher thermal conductivity. Thoria fuel is beneficial because it complies with the Non-Proliferation Treaty and there are plenty of reserves worldwide. Therefore, ThO2 fuel and its suitability with SCWR use are considered in this paper.