Extraction Of Noble Metals In A Molten Salt Reactor By Helium Bubbling

The world population keeps growing and along with that the energy consumption. However, the fossil fuels we were used to have plenty of are now depleting. New ways for energy production need to be found. These new ways of energy production need to be environmental friendly, but also efficient. One of the options is nuclear energy. In this research one nuclear reactor type is emphasized. This type of reactor is the Molten Salt Reactor. This reactor uses a liquid salt fuel which is also used as cooling fluid. The advantages of an MSR are the reduced life time of the fission products and the very safe design. This reactor type is very suitable for the thorium fuel cycle. Some of the fission products from this thorium fuel cycle need to be extracted from the fuel salt. For example, xenon is formed, which is a neutron poison and needs to be extracted. This is done through an online reprocessing step, called the helium bubbling process. Helium bubbling uses the insolubility of certain fission products in the salt to extract them. It is already used for the extraction of noble gasses from the fuel salt, but it is possible to also use it for the extraction of noble metals.
These noble metals can attach to the surfaces of important reactor components. To prevent this, it is desired to remove the noble metals as well. The goal of this research is to see which parameters influence the helium bubbling process and if these parameters can be optimized to increase the extraction of noble metals from the fuel salt. The set-up used simulates the bypass of the helium bubbling process in an MSR. It consists of a loop with a venturi tube as bubble generator, a column with a Hallimond tube on top as bubble extractor and a pump to get the liquid flowing through the loop. The used liquid is a mixture of water and glycerol, which have a kinematic viscosity similar to the salt. The particles are molybdenum, as this is one of the real fission products. Finally, the used gas is air, as the density of the gas has very little influence on the process. The bubble size was studied to determine the influence of the liquid and gas flow rate on the bubble size. Also, the efficiency at different gas flow rates was studied to try and find a relationship between this parameter and the efficiency of the process. The results show that the liquid flow rate has the most influence on the bubble size while the influence of the gas flow rate on the bubble size is not very high. The optimal gas flow rate found in this study is 25 sccm/min.

Extraction of noble metals in a molten salt reactor by helium bubbling

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