another question. consider the possibility of designing a fission reactor that will operate for decades or even centuries without refueling. limit the investigation to thermal reactors with reaction rates = 2200 m/s cross section. Consider 3 fissile/fertile combinations: 1) Fissile= U-233 Fertile= Th-232 2) Fissile= U-235 Fertile= U-234 3) Fissile= Pu-239 Fertile= U-238 show that the necessary condition for continuos steady state operation of this reactor is that the macroscopic absorption cross section for the fertile nuclides equals that for the fissile spesies. any hint how to approach this problem? where shall I start? then, i was asked to compute the ratio of natural abundances but the natural abundances of U-233 is 0, then what should I do?