Experimental Investigation of Liquid Tin Surface Property Safety Features for Potential Application as a Coolant in Direct Contact Liquid Metal Fast Reactors

The paper presents a description of an evolutionary innovative small modular fast reactor concept and predesign. The proposed predesign is based on the STAR (Secure Transportable Autonomous Reactor) concept. The use of a two fluid (gas/tin (Sn)) mixture for the reactor core cooling is the major modification. Currently, the reactor is considered to be working at one bar above the atmospheric pressure. The reactor core is cooled by liquid tin with inlet/outlet temperature of 793/1139K. The driving (pumping force) is provided by a bubble pump, where the pumping fluid is the gaseous nitrogen. The inlet/outlet temperature in the pump for liquid tin is 1130/793K while for gaseous nitrogen is 693/793K. The important thermal design characteristics are estimated and presented in the paper. The reactor provides electrical output by a MHD (magnetohydrodynamic) direct electricity generator up to 7.2 MWe without accounting for the losses. In addition, a Brayton cycle for additional electricity production could be considered. As the final design is considered to be of Gen-IV, there are included enhanced safety features such as passive core cooling and fast reliable shutdown. The high wetting of liquid tin while passing the MHD is of critical importance for direct electricity production as well as the chemical interaction with oxygen and surface tension modification. The paper presents the newly designed simple device, based on the Wilhelm plate surface tension measuring approach. The device is capable not only of measuring the surface tension evolution, but it also allows to estimate the kinetics of formation of stannic and hydrated oxides while liquid tin is exposed to atmospheric air.