Nuclear-Fueled Power Plants:Nuclear Fuel Cycle.Gasificationand enrichment- Most reactors need uranium enriched with235 The uranium concentrate is treated with hydrogen fluoride gas (氟化氢气体）andtheuraniumoxide（氧化铀）is converted touraniumhexafluorideUF,(六氟化铀),whichisawhitesolidthat sublimates(升华)toa vapor at a pressureof 1 atmosphere at56℃Enrichment can be achieved by gaseous diffusion(气体扩散)usingmembraneswithsmallpores（具有细小毛孔的膜）andtherateofdiffusionisafunction of pressureandtemperatureand is alsoafunction of the molecular diameter of the diffusing gas 235UFg has a slightly smaller diameter than 238UFg so that 235UF6diffuses fasterthan238UF Byforcing the gasesto pass manymembranes, almost anydegreeofenrichmentcanbeachieved
Nuclear-Fueled Power Plants: Nuclear Fuel Cycle • Gasification and enrichment – Most reactors need uranium enriched with 235U – The uranium concentrate is treated with hydrogen fluoride gas(氟 化氢气体) and the uranium oxide (氧化铀) is converted to uranium hexafluoride UF6 (六氟化铀), which is a white solid that sublimates (升华) to a vapor at a pressure of 1 atmosphere at 56 ◦C – Enrichment can be achieved by gaseous diffusion (气体扩散) using membranes with small pores (具有细小毛孔的膜) and the rate of diffusion is a function of pressure and temperature and is also a function of the molecular diameter of the diffusing gas – 235UF6 has a slightly smaller diameter than 238UF6 so that 235UF6 diffuses faster than 238UF6 – By forcing the gases to pass many membranes, almost any degree of enrichment can be achieved
Nuclear-Fueled Power Plants:Nuclear Fuel CycleGaseousDiffusionUraniumEnrichmentProcessNatural Uranium(0.711%U235)EnrichedUranium(≥1.0%U235)DepletedUranium(Tails)(<0.7%U235)LJ235U238PorousMembrane
Nuclear-Fueled Power Plants: Nuclear Fuel Cycle
Nuclear-Fueled Power Plants:Nuclear Fuel Cycle.Gasification and enrichment-Enrichment plants have been built that work on the principle of agaseouscentrifuge（气体离心机）Whentheuraniumgases are spunveryfast in acentrifuge, theheavier 238uF,spreads towardthe edges of the centrifuge while thelighter 235UF, concentrates toward the center-Theenrichmentdepends onthe rate of revolutions and thetimespent in the centrifuge-Gaseouscentrifugesareless energy-consumingthandiffusionplantsandrequirelowercapitalinvestment
Nuclear-Fueled Power Plants: Nuclear Fuel Cycle • Gasification and enrichment – Enrichment plants have been built that work on the principle of a gaseous centrifuge (气体离心机) – When the uranium gases are spun very fast in a centrifuge, the heavier 238UF6 spreads toward the edges of the centrifuge while the lighter 235UF6 concentrates toward the center – The enrichment depends on the rate of revolutions and the time spent in the centrifuge – Gaseous centrifuges are less energy-consuming than diffusion plants and require lower capital investment