Diamond Rheometer for the Measurement of High-Temperature Molten Salts

Small, modular nuclear reactors (SMRs) offer the promise of reliable, base-load energy that is not dependent on weather. Currently, around a dozen nations have programs to develop and deploy MSRs. Challenges to the deployment of MSRs are due primarily to the corrosive and dynamic molten salt. For safe operation of the reactor it is paramount to accurately monitorandcontrolthemoltensalt properties. Measuring viscosity and density data improve safety and lead to efficiency optimization for flow through fuel and coolant heat exchangers. The viscosity and density measurements must be high-throughput and require only a small amount of fluid. The measurements also need to be precise, and the instrument must withstand the extreme, corrosive temperature and radiation environment of the molten salt. Viscosity and density measurement using cantilever oscillators to serve these challenging needs are of interest. This project proposes a viscosity and density measurement probe made out of diamond for use in molten salt reactors. The technology is based on measurements of the resonant vibrational modes of a cantilever oscillator submerged in the molten salt. The position of the resonant modes allows for determination of the viscosity and density. The oscillator is made from diamond so that it can withstand the harsh conditions of the molten salt. Also, the diamond allows for the optical detection and readout of the oscillator vibrations using a reflecting laser interferometry. GLCT will synthesize the diamond and process it into the cantilever oscillators. Photolithography and structure masking will be done at Argonne National Laboratory (ANL) using the General User Program. Dry etching will be done at GLCT. Amplitude-frequency testing of the prototypes devices will be done at ANL. Success in the proposed effort will allow for the better monitoring of nuclear molten salt reactors, which will increase their safety, efficiency and commercial viability. Nuclear molten salt reactors overcome the primary hazard of traditional nuclear reactors; there is no meltdown risk with molten salt reactors. They are safer than traditional technology because they use molten salt as coolant rather than water, and because they operate at relatively low pressure near atmospheric. The waste from molten salt reactors is significantly less radioactive than traditional nuclear reactor technology. New, 100 megawatt thorium-MSRs are estimated to produce energy for $2,000 per watt compared to $2,300 per watt for coal and $4000 per watt for traditional nuclear.