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Management of Commercially Generated Radioactive Waste - U.S. ...

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6.123<br />

6.1.7.3 Status <strong>of</strong> Technical Development and R&D Needs<br />

Only the referenced use <strong>of</strong> transmutation - recycling, using commercial nuclear reactor<br />

fuels, to minimize the actinides contained in radioactive waste - is discussed here. Part <strong>of</strong><br />

the R&D associated with transmutation would be the continued investigation <strong>of</strong> other useful<br />

applications <strong>of</strong> the process. There are several other waste constituents that could be trans-<br />

muted.<br />

Present Status <strong>of</strong> Development<br />

Transmutation represents an advanced processing concept that would require R&D work be-<br />

fore incorporation into any system. There are still uncertainties associated with many <strong>of</strong> the<br />

subsystem details. Although the concept is technically feasible, it should be recognized<br />

that the required design bases have not been sufficiently refined to permit construction <strong>of</strong><br />

full-scale facilities. For some partition subsystems, laboratory experiments have been deve-<br />

loped to demonstrate technical feasibility only. Only preliminary material balance calcula-<br />

tions have been performed and, in most cases, no energy balances are available.<br />

A number <strong>of</strong> transmutation devices for converting various nuclides to other more desirable<br />

forms have been studied. Neutron irradiation can be carried out with nuclear explosive de-<br />

vices, fission reactors, or fusion reactors. Accelerators can provide charged particle beams<br />

<strong>of</strong> protons or heavier ions for producing neutrons for irradiating selected nuclides. For the<br />

actinides, the most practical transmutation occurs by irradiation by a fission reactor neu-<br />

tron source. The estimated actinide transmutation rate utilizing commercial light water re-<br />

actors is about 6 percent for each full-power year that the actinides are in the reactor<br />

(EPA/MITRE 1979).<br />

There are four principal methods for recycling actinides in light water reactors: (1)<br />

dispersing the actinides homogeneously throughout the entire fuel reload, (2) dispersing the<br />

actinides homogeneously in only the mixed-oxide fuel, (3) concentrating the recycled waste<br />

actinides in target rods within an otherwise ordinary fuel assembly, and (4) concentrating<br />

the recycled waste actinides in target rods that are then used to make up a target assembly.<br />

In the first two methods, the actinides include all <strong>of</strong> the plutonium generated in the reac-<br />

tor. In the second two methods, plutonium (an actinide) is excluded from the targets but is<br />

recycled in a mixed-oxide fuel. On the basis <strong>of</strong> preliminary qualitative evaluation, it would<br />

appear that the second recycle mode, homogeneous dispersal <strong>of</strong> the actinides in the mixed-<br />

oxide fuel, is preferred over the others (Wachter and Cr<strong>of</strong>f 1980).<br />

Technological Issues<br />

The effect <strong>of</strong> a transmutation recycle, as opposed to the uranium and plutonium recycle<br />

mode, on the various elements <strong>of</strong> a conventional fuel cycle depends largely on two factors--<br />

the transmutation rate in the reactors and the manner in which the transmutation reactors are<br />

decommissioned as the cycle is eventually terminated. Important technological issues are:

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