Grades Enriched uranium

1 grades

1.1 reprocessed uranium (repu)
1.2 low-enriched uranium (leu)
1.3 highly enriched uranium (heu)

grades

uranium taken directly earth not suitable fuel nuclear reactors , requires additional processes make usable. uranium mined either underground or in open pit depending on depth in found. after uranium ore mined, must go through milling process extract uranium ore. accomplished combination of chemical processes end product being concentrated uranium oxide, known yellowcake , contains 60% uranium whereas ore typically contains less 1% uranium , little 0.1% uranium (henderson 2000). after milling process complete, uranium must next undergo process of conversion, either uranium dioxide, can used fuel types of reactors not require enriched uranium, or uranium hexafluoride, can enriched produce fuel majority of types of reactors . naturally-occurring uranium made of mixture of u-235 , u-238. u-235 fissile meaning split neutrons while remainder u-238, in nature, more 99% of extracted ore u-238. nuclear reactors require enriched uranium, uranium higher concentrations of u-235 ranging between 3.5% , 4.5%. there 2 commercial enrichment processes: gaseous diffusion , gas centrifugation. both enrichment processes involve use of uranium hexafluoride , produce enriched uranium oxide.

a drum of yellowcake (a mixture of uranium precipitates)


reprocessed uranium (repu)

reprocessed uranium (repu) product of nuclear fuel cycles involving nuclear reprocessing of spent fuel. repu recovered light water reactor (lwr) spent fuel typically contains more u-235 natural uranium, , therefore used fuel reactors customarily use natural uranium fuel, such candu reactors. contains undesirable isotope uranium-236, undergoes neutron capture, wasting neutrons (and requiring higher u-235 enrichment) , creating neptunium-237, 1 of more mobile , troublesome radionuclides in deep geological repository disposal of nuclear waste.

low-enriched uranium (leu)

low-enriched uranium (leu) has lower 20% concentration of u; instance, in commercial light water reactors (lwr), prevalent power reactors in world, uranium enriched 3 5% u. fresh leu used in research reactors enriched 12% 19.75% u-235, latter concentration being used replace heu fuels when converting leu.

highly enriched uranium (heu)

a billet of highly enriched uranium metal

highly enriched uranium (heu) has 20% or higher concentration of u. fissile uranium in nuclear weapon primaries contains 85% or more of u known weapons-grade, though theoretically implosion design, minimum of 20% sufficient (called weapon(s)-usable) although require hundreds of kilograms of material , not practical design ; lower enrichment hypothetically possible, enrichment percentage decreases critical mass unmoderated fast neutrons rapidly increases, example, infinite mass of 5.4% u being required. criticality experiments, enrichment of uranium on 97% has been accomplished.

the first uranium bomb, little boy, dropped united states on hiroshima in 1945, used 64 kilograms of 80% enriched uranium. wrapping weapon s fissile core in neutron reflector (which standard on nuclear explosives) can dramatically reduce critical mass. because core surrounded neutron reflector, @ explosion comprised 2.5 critical masses. neutron reflectors, compressing fissile core via implosion, fusion boosting, , tamping , slows expansion of fissioning core inertia, allow nuclear weapon designs use less 1 bare-sphere critical mass @ normal density. presence of of u isotope inhibits runaway nuclear chain reaction responsible weapon s power. critical mass 85% highly enriched uranium 50 kilograms (110 lb), @ normal density sphere 17 centimetres (6.7 in) in diameter.

later nuclear weapons use plutonium-239 in primary stage, jacket or tamper secondary stage, compressed primary nuclear explosion uses heu enrichment between 40% , 80% along fusion fuel lithium deuteride. secondary of large nuclear weapon, higher critical mass of less-enriched uranium can advantage allows core @ explosion time contain larger amount of fuel. u not fissile still fissionable fusion neutrons.

heu used in fast neutron reactors, cores require 20% or more of fissile material, in naval reactors, contains @ least 50% u, typically not exceed 90%. fermi-1 commercial fast reactor prototype used heu 26.5% u. significant quantities of heu used in production of medical isotopes, example molybdenum-99 technetium-99m generators.