*8.4.3. Mixed fuel*

Mixed fuel (with uranium-thorium raw materials) is rational to use in closed cycles with equilibrium between fission and raw materials.

This fuel is less dependent from neutron flux than pure thorium fuel. Together with it the fuel is more sensitive to the neutron losses. At 238U contents 75 % in campaign beginning, fission materials contents 1.16 % neutron losses 2.8% neutron flux less than 8\*1013 sm-2s-1 is possible effective work. The duration of the campaign can be 34000 hours.

Campaign with mixed fuel can supply simultaneous use of thorium and uranium fuel with burn-up corresponding to its natural contents with high and even full use of raw uranium [18].

Closed fuel cycles with uranium fuel after several cycles can have increased contents of 242Pu, which is feeble burning out and being absorber and filler decreasing of campaign effectiveness. The possible way of solving is plutonium isotope separation. In mixed fuel 242Pu accumulation will be less and its critical contents will be reached much later. The losses for it are also less.
