Evolution of the core physics concept for the Canadian supercritical water reactor

The supercritical water cooled reactor (SCWR) is one of the advanced reactor concepts chosen by the GEN-IV International Forum (GIF) for research and development efforts. The GIF aims to develop advanced reactor concepts that achieve enhanced safety, clean energy, sustainability, economics and non-proliferation. Canada's contribution to this effort is the Canadian SCWR, a heavy water moderated, pressure tube supercritical light water cooled reactor. The lattice and core physics concepts are key aspects of the development of the Canadian SCWR concept. Lattice and core physics optimizations are used to obtain target values for reactivity coefficients (appropriate for enhanced safety), exit burnups and fissile utilization (that enable efficient and economic fuel use), and fuel cycles (that minimize the desirability of spent fuel for proliferative use). These metrics must also be balanced with operational constraints such as maximum allowable fuel cladding temperature and fuel element power rating. The balance among various performance metrics requires an iterative process in the development of the lattice and core physics concepts. Recent developments in the SCWR lattice and core concepts, primarily the introduction of a large central flow tube filled with coolant combined with a two-ring fuel assembly, have enabled significant improvements compared to earlier concepts. These improvements include a reduction in coolant void reactivity (CVR) by more than 10 mk, and an almost 40% increase in fuel exit burnup, which is achieved via balanced power distribution between the fuel pins in the fuel assembly. These improvements translate directly to improvements in enhanced safety (via CVR reduction) and improved sustainability and economics (via the increase in exit burnup for the same average enrichment fuel as earlier concepts). In this paper the evolution of the physics concept is reviewed, and the present lattice and core physics concepts are presented.