A US nuclear reactor has switched from Regular to Premium fuel with Southern Nuclear inserting four Lead Test Assemblies (LTAs) into the Vogtle Unit 2 reactor in Waynesboro,关键字1 Georgia that contains uranium enriched above 5% – a US commercial first.
Nuclear fuel is one of those things that we tend to pretty much take for granted. You have a nuclear reactor, it needs fuel, you put fuel in. QED. The general assumption is that filling a reactor with uranium and plutonium is like shoveling coal into a boiler furnace – a straightforward operation that, in the case of nuclear, is just a bit more involved.
Let's leave aside how complex coal is (and, believe me, it is) and concentrate on nuclear fuel. In order for nuclear fission to occur, the nuclear ore not only needs to be refined, it needs to be enriched. That is, the natural percentage by weight of the uranium isotope 235 to 238 must be increased.
Natural uranium is only about 0.7% uranium-235 (U₂₃₅) and only a very few reactor designs can use this to any degree. The problem is that the balance that consists of uranium-238 (U₂₃₈) isn't fissionable. That is, the atoms won't split properly to produce energy, while those in U₂₃₅ do. Worse, in order for U₂₃₅ to produce a nuclear chain reaction, there has to be enough of it in a high enough concentration to sustain the reaction. In the case of most modern nuclear reactors, this concentration is about 3 to 5% U₂₃₅ to U₂₃₈, which is called Low-Enriched Uranium (LEU)