| Themes > Science > Chemistry > Nuclear Chemistry > Nuclear Reactions > Transmutation > Breeding and transmutation > Alternative policies |
Rather than specializing about one third of the PWR into MOX-PWR, it seems that replacing uniformly the traditional 3,5 % 235U enriched fuel elements by elements where about 2/3 of the fissile nuclei would be 235U and the remaining 1/3 239Pu and 241Pu would allow a stabilization of the Plutonium inventory. Minor actinides should be extracted at each reprocessing, since these cannot be incinerated in thermal reactors. The minor actinides could, then, be incinerated in fast or hybrid reactors as will be discussed below. For increased efficiency in reducing the Plutonium inventory it has, also, been proposed to substitute the 238U by non-fissile matrices such as tungsten , which have the same properties as uranium as far as the temperature behavior of the reactivity is concerned. However the reactivity would decrease rapidly with time, due to the rapid disappearance of the fissile nuclei. This decrease would require very frequent reprocessing or a high fuel enrichment in fissile species associated to an initially large quantity of consumable neutronic poisons. Another solution, proposed, among others, by C.Rubbia, is to replace the depleted Uranium by Thorium. Thorium has neutronic properties close to those of 238U. Incineration of plutonium would be associated to the production of 233U. This nucleus could, then, either be a substitute of 235U in standard PWR fuel, or be a part of a new fuel based on the mixture 232Th-233U. Such fuel could be reprocessed as many times as wanted in PWR reactors, at variance with the 238U-239Pu mixture. The main difficulty of such a scheme would be the fuel element fabrication: irradiation of 233U produces a significant amount of 232U (n, 2n) reactions, the decay of which is accompanied by an intense high energy gamma activity which would require large biological shielding for fuel fabrication. The whole reprocessing and conditioning process would have to be redesigned. |
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