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The volume of salt in the fertile area is that for which the mass of 233 U to be added at equilibrium
is zero.
Equilibrium was achieved for several ratios of salt volume in fertile zone to salt volume in fissile
zone. For reasons of precision, we took a time pitch of 10 efpd
4.3 The thorium support
In the fertile zone the 233 U balance is positive: More 233 U comes out of the blanket than goes in. If
we increase the blanket volume, we increase the quantity of 233 U produced and at any given moment,
the 233 U contribution of the blankets will compensate the 233 U consumption by the fissile core. The
core will generate its own uranium. To determine the volume of the blankets needed, we varied the
ratio between the fertile salt volume and the fissile salt volume between 1.5 and 2.5.
For each of these ratios, we give (Table 2) the consumption of 233 U, the masses in the reactor at
equilibrium, the increase in core size (volume and radius) necessary, and the proportion of power
given off in the fissile zone.
These calculations show the feasibility of the concept. This configuration is particularly
interesting because:
• It does away with the uranium enrichment phase.
• It requires no extraction of 236 U.
• It offers a very small transuranium elements inventory.
• It reduces consumption of heavy nuclei to 100 kg of 232 Th per TWhe, thus reducing mining
waste accordingly.
• It considerably reduces the masses of depleted and reprocessed uranium.
4.4 The thorium-uranium support
It is also possible to add uranium (i.e. depleted U in stock) to the thorium support. We thus
increase the quantity of transuranium elements at equilibrium, while remaining within a reasonable
range. But we then burn 238 U and make 232 Th savings. We significantly reduce the fissile nuclei
enrichment of the uranium in the core, thus making the reactor non-proliferating.
As a counterpart, we will have to increase the production of 233 U and thus the volume of the
blankets.
We thus varied the proportion of 238 U added to the load from 0 to 100% for 2 volumes of fertile
salts: 2 times the fissile volume and 2.5 times the fissile volume.
Figure 4 shows the mass of 233 U consumed (or produced) versus the percentage of uranium 238
in the fertile material added;
The more uranium is placed in the support, the more 233 U must be added and the more the volume
of the blanket must be increased. Between 0 and 50 % 238 U the 233 U input is small enough to be
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