In the dry method, UF 6 is heated to a vapour and introduced into a two stage reaction vessel (eg, rotary kiln) where it is first mixed with steam to produce solid uranyl fluoride ( UO 2F 2) – this powder moves through the vessel to be reacted with H 2 (diluted in steam) which removes the fluoride and chemically reduces the uranium to a pure microcrystalline UO 2 product. Chemical conversion to and from UF 6 are distinct processes, but both involve the handling of aggressive fluorine compounds and plants may be set up to do both.Ĭonversion to UO 2 can be done using ‘dry’ or ‘wet’ processes. Most fabrication plants have their own facilities for effecting this chemical conversion (some do not, and acquire UO 2 from plants with excess conversion capacity). It needs to be converted to uranium dioxide ( UO 2) prior to pellet fabrication. Uranium arrives at a fuel manufacturing plant in one of two forms, uranium hexafluoride (UF 6) or uranium trioxide (UO 3), depending on whether it has been enriched or not. Producing the rigid metal framework for the fuel assembly – mainly from zirconium alloy and loading the fuel pellets into the fuel rods, sealing them and assembling the rods into the final fuel assembly structure.Producing high-density, accurately shaped ceramic UO 2 pellets.Producing pure uranium dioxide ( UO 2) from incoming UF 6 or UO 3.There are three main stages in the fabrication of the nuclear fuel structures used in LWRs and PHWRs: Nuclear fuel fabrication – process overview The industry is dominated by four companies serving international demand for light water reactors: Areva, Global Nuclear Fuel (GNF), TVEL and Westinghouse. The process for uranium-plutonium mixed oxide (MOX) fuel fabrication is essentially the same – notwithstanding some specific features associated with handling the plutonium component.įigure 1: The closed nuclear fuel cycle, showing primary and recycled materials flow The fabrication of fuel structures – called assemblies or bundles – is the last stage of the front end of the nuclear cycle shown in Figure 1, and represents less than 20% of the final cost of the fuel. Core monitoring giving detailed real-time information has enabled better fuel performance also. This is correlated with increased enrichment levels from about 3.25% to 5% and the use of advanced burnable absorber designs for PWR, using gadolinium.
Pressurised heavy water reactor (PHWR) fuel is usually unenriched natural uranium (0.7% U-235), although slightly-enriched uranium is also used.įuel assembly performance has improved since the 1970s to allow increased burn-up of fuel from 40 GWday/tU to more than 60 GWd/tU. For light water reactor (LWR) fuel, the uranium is enriched to various levels up to about 4.8% U-235. The standard fuel form comprises a column of ceramic pellets of uranium oxide, clad and sealed into zirconium alloy tubes.
Fuel structures need to maintain their shape and integrity over a period of several years within the reactor core, thereby preventing the leakage of fission products into the reactor coolant. The fission process releases large amounts of useful energy and for this reason the fissioning components – U-235 and/or Pu- 239 – must be held in a robust physical form capable of enduring high operating temperatures and an intense neutron radiation environment. Nuclear reactors are powered by fuel containing fissile material. The first modern metal fuel is due to be trialled in commercial reactors.
Batched into assemblies, the fuel rods form the majority of a reactor core's structure.Fuel fabrication is the last step in the process of turning uranium into nuclear fuel rods.
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