10.82. Although spent LWR fuel is not reprocessed in the United States to recover the plutonium contained therein, extensive reprocessing is car­ried out in Europe. Also, the possibility exists that there may be a desire to make use of the energy available from plutonium recovered from dis­mantled nuclear weapons. Therefore, we will briefly examine a few of the design considerations in using some plutonium dioxide in LWRs.

10.83. Plutonium formed in present LWRs from slightly enriched ura­nium is fissioned in place during the latter part of the operating cycle. Therefore, one should anticipate no major problems in adding some plu­tonium to a fresh fuel batch. However, since fabrication costs would be high if the addition would be made uniformly to all rods, most plans call for using mixed uranium—plutonium oxide in selected rods. The large fission cross section of the fissile plutonium isotopes could result in power peaking in such rods. The neutron absorption in plutonium could also affect the reactivity worth of control rods as well as reactivity temperature coef­ficients. Therefore, we see that the use of plutonium to replace some of the uranium-235 in fresh fuel can affect the core safety characteristics and must be accounted for in the design. The use of recycled plutonium was extensively studied during the 1970s and significant literature developed [17]. Currently, recycled plutonium is being used routinely in French PWR fuels [24].