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Figure II.12 Flow sheet of pyrochemical partitioning of TRUs from HLW (CRIEPI)
1.2.3 Condensed actinide-burner cycle: double-strata concept
The Japan Atomic Energy Research Institute (JAERI) has proposed a P&T scheme based on a
double-strata concept in which MAs from the familiar fuel cycle pass to an “actinide burner cycle” for
total fission [50]. Here, concentrations of actinides are kept high in nitride fuels to be reprocessed
pyrochemically. Nitrides have excellent properties, allowing (a) low fuel temperatures that reduce
release of fission gas, and (b) a thinner cladding with consequently harder neutron spectrum than with
oxide. Moreover, actinide mononitrides, unlike the metals, are expected to be mutually soluble.
The outline of the burner cycle is shown in Figure II.13:
• actinide salts from the first stratum are converted to mononitride microspheres by sol-gel
techniques. A very high yield is expected.
• irradiated nitride fuel is reprocessed by a molten-salt electrorefining technique [51],
basically the same as for metal fuels. The highly-enriched 15 N, necessary to minimise
production of 14 C, is easily recovered and recycled.
• recovered metallic actinides are converted to nitride by direct reaction between liquid
cadmium alloys and nitrogen [52].
In a recently devised alternative to this last step, called LINEX (Lithium Nitrate Extraction of
Actinides), actinide nitrides are produced in a single step by addition of Li 3 N to the molten salt [53]. It
is obtained by direct reaction of Li metal with the 15 N evolved on dissolution of fuel in molten salt. Thus
recycling of 15 N is also facilitated.
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