In this thorium cycle very little plutonium is produced - 1000 to 10,000 times less than in conventional reactors. Thorium energy reserves appear to be practically ' inexhaustible. Rubbia has also simulated using lead as moderator. This involves working with neutrons of higher energy than in normal fast neutron reactors where the less agreeable liquid sodium is the moderator. Moreover, the constant reactivity opens up the prospect of energy gain increasing from about 60 to 100 or 120, with the assembly remaining sub-critical.
Fast neutrons open up interesting opportunities for the reprocessing of the irradiated rods.
This reprocessing will be limited to the separation of the fission products since all actinides become combustible, sidestepping the plutonium problem. Fission products can be recycled in the rods, the neutron flux transforming them into non-radioactive elements. However, unlike the fission of actinides, this transformation consumes neutrons and reduces energy production. To drive the assembly would require a 1 GeV cyclotron with an intensity of 10 mA or more - an entirely feasible prospect. The experiment at CERN, using a beam from the PS, shows that an energy of 800 MeV to 1 GeV is optimal.