Question

You are Plant Manager at the Hokomokee Nuclear Power Station in Moustafa County, which has two 1000 MWe PWRs and are planning the fuel cycle for the next ten years. You are beginning negotiations with your fuel supplier, Verma Fuels, and must choose between the 3.3% enrichment fuel you have been using and a new 5% enrichment fuel.  

-Compare the environmental consequences of use of the two different fuels – i.e., consider which might generate more or less waste.

Answer 1

Thevenrichment of nuclear fuel is nothing but conversion of non acting fission isotopes of uranium into acting fission process isotopes. Uranium available in nature consists largely of two isotopes, U-235 and U-238. The production of energy in nuclear reactors is from the 'fission' or splitting of the U-235 atoms, a process which releases energy in the form of heat. U-235 is the main fissile isotope of uranium.

Natural uranium contains 0.7% of the U-235 isotope. The remaining 99.3% is mostly the U-238 isotope which does not contribute directly to the fission processing. Isotope separation is a physical process to concentrate one isotope relative to others. Most reactors are light water reactors and require uranium to be enriched from 0.7% to 3-5% U-235 in their fuel. This is normal low-enriched uranium (LEU). There is some interest in taking enrichment levels to about 7%, and even close to 20% for certain special power reactor fuels, as high-assay LEU (HALEU).

Uranium-235 and U-238 are chemically identical, but differ in their physical properties, notably their mass. The nucleus of the U-235 atom contains 92 protons and 143 neutrons, giving an atomic mass of 235 units. The U-238 nucleus also has 92 protons but has 146 neutrons – three more than U-235 – and therefore has a mass of 238 units.

The difference in mass between U-235 and U-238 allows the isotopes to be separated and makes it possible to increase or "enrich" the percentage of U-235. All present and historic enrichment processes, directly or indirectly, make use of this small mass difference.

Some reactors, for example the Canadian-designed Candu and the British Magnox reactors, use natural uranium as their fuel. (For comparison, uranium used for nuclear weapons would have to be enriched in plants specially designed to produce at least 90% U-235.)

Enrichment processes require uranium to be in a gaseous form at relatively low temperature, hence uranium oxide from the mine is converted to uranium hexafluoride in a preliminary process, at a separate conversion plant.

Hence the enriched fuel can yeild less losses in power generation, but needs more attention in containing the fuel to avoid any leak which may cause potential radiation issues. Large amount of water to be used in the process of enriching the fuel, this may not be considered as a environmental issue as this can be recirculated.

Therefore the enriched fuel has no additional environmental issues other than more stringent containment of enriched fuel.