Russian physicists have discovered how to calculate the formation of nanocavities in nuclear fuel and other solid materials, according to the press service of the Moscow Institute of Physics and Technology (MIPT). Details were published by in Journal of Nuclear Materials.
“Our proposed method accelerates the calculation of the diffusion coefficient of nanopores in nuclear fuel by several tens of times. In the future, we plan to use it for other materials experiencing intense radiation damage in nuclear reactors,” said MIPT professor Vladimir Stegailov.
Nuclear fuel comprises uranium oxide powder, as well as various organic and inorganic additives, which is compressed into pellets weighing several grams. Pellet production is a complex process since the internal structure and chemical composition of the pellets changes with the decay of uranium atoms and the interaction of radiation with the cladding.
Understanding how these changes occur is important for several reasons. On the one hand, the safety of a nuclear reactor directly depends on how uranium pellets behave. On the other hand, how long the fissile substances will produce energy depends on the composition of the pellets.
The MIPT physicists were interested in how the decay of uranium atoms and other radioactive elements affects the formation of microscopic voids inside nuclear fuel, in which gaseous decay products often accumulate. These bubbles strongly affect the reaction rate and the mechanical properties of the nuclear fuel pellets. Scientists do not know exactly how these voids arise, since it is impossible to constantly monitor their formation. In addition, they grow very slowly, which is why it is impossible to observe them during short experiments.
Similar considerations, as noted by Stegailov and his colleagues, prevented physicists from calculating the process of forming these pores using computer models. Russian scientists have found a way to speed up these calculations. They noticed that these voids are similar in shape to polyhedra. Researchers also studied how their diffusion occurs - the "migration" of pores inside the crystal lattice of uranium oxide particles.
“Due to the fact that the diffusion of nanopores is very slow, the only real way to simulate their motion is to push them somehow. However, it is not obvious how to push a void. While working on the project, we proposed and justified a method in which the material surrounding the nanopore external force acts. In this case, the cavity begins to float like a bubble in water," explained Stegailov.
This allowed physicists to speed up the calculations tens of times and understand what principles govern the migration of these bubbles, their formation and growth.
Scientists hope that similar computer models of nuclear fuel and other materials used in the operation of nuclear power plants will help increase their safety and economic profitability.