Researchers with the Fuel Cycles and Materials Laboratory within the Department of Nuclear Engineering at Texas A&M University are working on the development of a new approach to creating the fuel pellets that are used in nuclear power reactors. They are creating porous fuel pellets to replace the solid pellets that are now used to fuel reactors. The porous pellets promise to extend fuel life, get more power out of the same amount of fuel and possibly reduce the amount of waste generated by the fuel.
The new type of fuel pellets is being created with copper powder. The researchers are making pellets and testing them under different pressures and other conditions to see how they perform. Copper is being used because its properties are easier to translate into digital code for use in computer simulations of the new pellets.
Graduate student researcher Yesenia Salazar says "Our overall goal is that when we make this pellet, we take measurements for the porosity that it has. We're trying to be able to have pores that are more or less homogeneous, where they are not just in one section of the pellet. If we can get more or less homogenous pores, we test them at these different pressure and temperature levels to see how they would perform inside a reactor setting."
As conventional solid fuel pellets are burned in a nuclear reactor, the expulsion of gasses and fission products cause the pellets to swell. Over time, this expansion reduces the production of energy from the pellets. It also makes the removal of the fuel more difficult. The pores in the new fuel pellets delay the rate of expansion in the pellets as they are burned.
Salazar says "We believe that if you have even just a little bit of porosity introduced into these pellets, those gasses that are coming out and that swelling is happening will accumulate to make up for the space in those pores. It works very similarly to the way a kitchen sponge works, soaking up all the water it can before its pores are full, at which point it expels the water. We want to delay the expulsion as long as we can."
The researchers are hoping to reduce the swelling of fuel pellets by at least five percent. At this time it is uncertain exactly how long it will take for the gasses and fission products to fill the pores in the pellets and the cause the pellets to swell. Different reactors with different fuels will yield different expansion rates.
Salazar continues "Regardless, when we do take the fuel out it will be more dangerous than it was when we put it in. We want to be able to use this research to leave that fuel in longer, which will increase the efficiency and allow us to delay taking out this material because we are getting more out of it per ton."
Reactor fuel typically is replaced between sixteen and thirty-six months. The researchers are hoping that their new pellets will add at least an extra week. While that may not seem like much an improvement, it will still result in a significant extension of the amount of energy extracted from a ton of fuel.
