Fluoride Action Network

The Nuclear Fuel Cycle

Source: Tuumaenergia.blogspot.com | October 23rd, 2010
Industry type: Nuclear Industry

Note from Fluoride Action Network:
This article provides a clear explanation and graphic of “the series of industrial processes which involve the production of electricity from uranium in nuclear power reactors.” Here are some excerpts:


The uranium oxide product of a uranium mill is not directly usable as a fuel for a nuclear reactor and additional processing is required. Only 0.7% of natural uranium is ‘fissile’, or capable of undergoing fission, the process by which energy is produced in a nuclear reactor. The form, or isotope, of uranium which is fissile is the uranium-235 (U-235) isotope. The remainder is uranium-238 (U-238). For most kinds of reactor, the concentration of the fissile uranium-235 isotope needs to be increased – typically to between 3.5% and 5% U-235. This is done by a process known as enrichment, which requires the uranium to be in a gaseous form. The uranium oxide concentrate is therefore first converted to uranium hexafluoride, which is a gas at relatively low temperatures.

At a conversion facility, the uranium oxide is first refined to uranium dioxide, which can be used as the fuel for those types of reactors that do not require enriched uranium. Most is then converted into uranium hexafluoride, ready for the enrichment plant. The main hazard of this stage of the fuel cycle is the use of hydrogen fluoride. The uranium hexafluoride is then drained into 14-tonne cylinders where it solidifies. These strong metal containers are shipped to the enrichment plant.

The enrichment process separates gaseous uranium hexafluoride into two streams, one being enriched to the required level and known as low-enriched uranium; the other stream is progressively depleted in U-235 and is called ‘tails’, or simply depleted uranium.

There are two enrichment processes in large-scale commercial use, each of which uses uranium hexafluoride gas as feed: diffusion and centrifuge. These processes both use the physical properties of molecules, specifically the 1% mass difference between the two uranium isotopes, to separate them. The last diffusion enrichment plants are likely to be phased out by 2013.

The product of this stage of the nuclear fuel cycle is enriched uranium hexafluoride, which is reconverted to produce enriched uranium oxide. Up to this point the fuel material can be considered fungible (though enrichment levels vary), but fuel fabrication involves very specific design.

Enrichment is covered in detail in the page on Uranium Enrichment


The following figures may be regarded as typical for the annual operation of a 1000 MWe nuclear power reactor:b

Mining – 20,000 tonnes of 1% uranium ore

Milling – 230 tonnes of uranium oxide concentrate (which contains 195 tonnes of uranium)

Conversion – 288 tonnes uranium hexafluoride, UF6 (with 195 tU)

Enrichment – 35 tonnes enriched UF6 (containing 24 t enriched U) – balance is ‘tails’

Fuel fabrication – 27 tonnes UO2 (with 24 t enriched U)

Reactor operation – 8760 million kWh (8.76 TWh) of electricity at full output, hence 22.3 tonnes of natural U per TWh

Used fuel – 27 tonnes containing 240 kg transuranics (mainly plutonium), 23 t uranium (0.8% U-235), 1100kg fission products.