Modification des caractéristiques radioactives des isotopes de l'uranium au cours de l'irradation

Uranium α- and γ-activity increases appreciably with U235 enrichment; this is due almost entirely to the 234 isotope.
Irradiation does not appreciably affect the uranium α-activity ; however, the U234 concentration could become relatively high if the fuel is recycled.
After reprocessing, the natural isotopes of uranium, separated from their daughter and fission products, have a low β-γ activity which will grow again at a rate which is faster for more highly enriched material irradiation causes the formation of U236, source of U237 ; the activity of the latter determines the cooling time of the fuel.
The α, β and γ activities and their variation are discussed as a basis for defining some reprocessing and refabrication conditions. Their effect on purity normes for uranium and on cycle economics has been especially considered.