Grant: NSERC/NRCan/AECL Generation IV Energy Technologies Program

The proposed study focuses on understanding the properties of supercritical water (SCW) containing solid corrosion or wear products, a detailed characterization of the particulates and their fluidic properties, and the development of high-pressure-temperature separation technologies for the removal of solids. While current CANDU designs have an indirect cycle, i.e., a separate primary heat transport system in contact with the fuel coupled (via steam generators) to the secondary side for steam production to drive turbines, the CANDU SCWR is likely to be a direct cycle plant, i.e., the same fluid that contacts the fuel will also drive the turbines. In a boiling water reactor (BWR), ionic impurities, precipitated solids, wear debris and radioactive corrosion products in heat transport systems are largely retained in the liquid phase of a two-phase vapor-water system. Those species are considered hazardous to system materials and heat transfer and radiation safety, and are controlled/removed by comprehensive chemistry control protocols. The proposed GEN IV SCWR maintains a single phase of SCW (instead of vapor and water phases) throughout the entire reactor circuit. SCW possesses a lower density, ranging from 0.1 to 0.7 g per cubic centimeter, and non-polar characteristics, thus presenting a chemistry paradigm different from liquid water currently used in nuclear power systems. If solids precipitated from SCW are not removed properly, they can transport, deposit and form fixed layers on the surface materials of a nuclear system. If they deposit on fuel cladding surfaces, this will affect the heat transfer and lead to fuel failures and increase radiation fields around the reactor circuit. It will be crucial that an SCWR has a purification system capable of removing impurities including ultrafine solids. The proposed project would address one of the technology gaps identified in the GEN IV program. It is also expected to find applications in other clean-energy areas such as SCW coal gasification and bio-fuel production.