Nuclear energy has gained crucial importance since it has a minor impact on climate change and greenhouse gas releases; additionally, the other energy sources are insufficient to reach the world's energy needs without nuclear energy. Another sign that the Generation IV International Forum (Kelly, Gen IV International Forum: A decade of progress through international cooperation, 2014) has pointed out is to utilize uranium resources to the maximum and recycle spent nuclear fuel through burn-up in the Generation IV reactor designs, one of which is the molten salt reactor (MSR). Therefore, the MSR can use the spent nuclear fuel as a fresh fuel when the actinides recycle. That reprocessing of spent fuel could be one of the opportunities to contribute to future nuclear energy goals.
This study aims to develop a modified pyroprocessing method to prepare molten salt fuels for MSR from spent oxide nuclear fuel that was burned in light water reactors (LWRs). The process diagram illustrated as (1) spent fuel treatment, (2) chopping and voloxidation of spent oxide fuel, (3) oxide reduction of spent fuel, and then depending on the fuel structure and composition for the MSR, it continues by one or two of the following; – electrorefining, – chlorination, and – fluorination. The subject of this study focused on oxide reduction in two categories: chemical reduction and electrochemical reduction. The system designs have been optimized in calcium salts since they have high calcium metal and calcium oxide solubility. The significant results indicated that both methods would substantially reduce the solid uranium dioxide pellet. The chemical reduction will reduce the total solid pellet at 850oC in the composition of 55.73mol%CaCl2-12.37mol%CaF2-26.58mol%Ca-5.32mol%UO2 over 12 hours. The total reduction in the electrochemical test is seen at 850oC during 12 hours with a salt composition of 79mol%CaCl2-17mol%CaF2-4mol%CaO.
These oxide reduction mechanisms are convenient ways to reprocess spent oxide fuel from LWRs to utilize in the MSR. Additionally, the reduced fuel is also applicable to using other next-generation reactors. The prospect of this research is the explicit comparison between chemical and electrochemical methods in calcium salts. / M.S. / Nuclear energy is a crucial energy production to meet the world’s future energy needs. The 6 (six) next-generation reactor design has been determined based on their sustainability, economic, and peaceful application for the world. One of those designs is molten salt reactors (MSRs) which have more attention due to their fuel choice. Most MSRs use the reprocessed fuel from current reactors or the fuel with the breeder blanket that creates more fuel while the reactor operates.
This study aims to provide a diagram showing the various steps involved in the preparation of molten salt fuel from spent oxide fuel, which is a mainly utilized form of fuel in current and previous operations. The flowsheet’s first step is the treatment of spent fuel that releases most of the decay heat. The second step is that spent fuel chopping and voloxidation, which meets the requirements of removing gas products and cladding material from used fuel. Afterward, the spent oxide fuel reduces into its metal form chemically or electrochemically in oxide reduction. Then, the molten salt fuel could be fabricated in n one or two more steps from reduced metals: electrorefining, chlorination, or fluorination. Chlorination and fluorination pass through the specific gas components to convert the metal forms into salt. Electrorefining could be applied to arrange the composition of the reduced metal, and this stage is strongly dependent on the MSR designs; it may get eliminated due to its unnecessity.
The oxide mechanisms mentioned above were examined under different design conditions to acquire a total reduction of the fuel pellet in calcium salts. The chemical reduction and electroreduction experiments have shown the reduced whole pellet at 850oC with two different salt mixtures. The design impacts of the reduction mechanism were discussed extensively between chemical and electrochemical reductions to identify the benefits and limitations.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/111990 |
| Date | 01 July 2022 |
| Creators | Karakaya, Nagihan |
| Contributors | Mechanical Engineering, Zhang, Jinsuo, Pierson, Mark A., Liu, Yang |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | en_US |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf, application/pdf |
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