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or, in terms of the fuel burn-up and the fuel loss,
R T (t) = R N (t) / (δ L)
where R N (t) is a time-dependent “neutronic transmutation factor” 4 . It should be noticed that the
toxicity reduction relative to the actinides to be burnt, which is of direct relevance for the assessment
of transmutation schemes, equals R T for all practical purposes because the toxicity of the fertile
component of the top-up fuel is negligible compared with that of the actinides to be burnt.
Figure 4 compares the neutronic transmutation factors for three systems: (a) an ALMR-type
critical TRU burner, (b) an ATW-type sub-critical TRU burner with a fast-neutron spectrum, and (c) a
minor actinide burner operating in the P&T cycle of a double strata fuel cycle. It can be seen that the
critical burner has a small “neutronic” advantage over the sub-critical burners, but the difference is not
significant compared with the goal for the total toxicity reduction by a factor of 100.
The general conclusions to be drawn from this discussion are that:
• Regarding the neutronic transmutation factor, no single transmutation system has a significant
advantage over other systems.
• Radiotoxicity reduction has to be achieved primarily by an actinide mass reduction which
implies the maximisation of fuel burn-up and the minimisation of reprocessing and fuel
fabrication losses.
The importance of advanced reprocessing and fuel technologies for P&T is thus confirmed.
Figure 4. Neutronic transmutation factors for transuranics and minor actinide burners
10
Neutronic transmutation factor
1
Critical TRU Burner
Subcritical TRU Burner
Subcritical MA Burner
0.1
1.E+2 1.E+3 1.E+4 1.E+5 1.E+6 1.E+7
Time after fuel reprocessing (a)
4 R N (t) is a characteristic of the core and is sometimes called “neutronic toxicity reduction”.
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