Eventos Anais de eventos
COBEM 2023
27th International Congress of Mechanical Engineering
The transition of Research Reactor fuels from Dispersions to Monolithic
Submission Author:
Daniel de Souza Gomes , SP , Brazil
Co-Authors:
Daniel de Souza Gomes
Presenter: Daniel de Souza Gomes
doi://10.26678/ABCM.COBEM2023.COB2023-0423
Abstract
Nuclear research reactors work as a neutron source for research and do not produce electricity or heat energy. However, the reactor core must employ a fluid coolant to maintain operational safety limits. Until 1978, the concept of a compact core with dispersion plates using a highly 235U-enriched to produce a higher neutron flux was very common. Over the years, the dispersions of fission materials in the aluminum matrix practically became the standard. Currently, there are 222 research reactors in operation spread over 53 countries, and under construction are 24 units in 17 countries. In Brazil, we used four reactors for irradiation, spectrometry, neutron radiography, and radiopharmaceuticals production. Only one is under a conceptual design for multipurpose tasks. All units have used dispersion fuels, with a low enrichment below 20% of 235U. These units operate with a thermal neutron flux of 1×109 n/cm2 to 4.3 ×1012 n/cm2, using light water as a coolant, sometimes graphite as the moderator, and beryllium as the reflector. During irradiation, the dispersions have showed a series of transformations that can change the mechanical properties of the fuel. These phenomena can vary depending on the chemical composition producing densification, fuel swelling, chemical interaction, fission products, hardening of the materials, and cladding corrosion. Dispersion plates create an amorphous material phase interface, a type of metallic glass. Many reactors still work with U3O8-Al, UZrX and U3Si2-Al, and UMo-Al, with variable uranium densities. However, in the last decade, a few dispersions, such as uranium silicide U3Si2-Al have presented a series of failures formed on the interaction layer between the fuel meat and aluminum matrix. In this region, they were undesirable chemical compounds resulting from the reactions offering a dependency on time, temperature, fission rate, and fission density. Today, exists a trend for monolithic fuels, eliminating Al-matrix such as U-10Mo, with higher uranium density than dispersions, achieving double uranium densities of around 15.5 gU/cm3.
Keywords
Aluminium Dispesion, Monolithic Fuel, U3O8-Al, U3Si2-Al, U-10Mo
