institutions and industry to manage or dispose of radioactive wastes. The most acute concern is the fate of high-level wastes generated in reprocessing plants or contained in spent fuel, but the management or disposal of the much larger bulk of intermediate- and low-level waste generated throughout the nuclear industry also raises public apprehension. Most experts are of the opinion that no technological obstacles stand in the way of safe management of any of these wastes,14 but governmental inaction, changes of program and emphasis, and the lack of approved facilities are not reassuring.

In the reprocessing and refabrication of fuel essential to making effective use of resources in advanced converters or breeders on either the thorium or the uranium fuel cycle, fissile material (either 233U or 239Pu) is separated from the spent fuel elements and is thus more readily subject to theft or illicit diversion than if it remained in the spent fuel elements. The appearance of pure plutonium or 233U in some stages of the fuel cycle presents the troubling possibility that weapons-usable material could be stolen by terrorists. Proposals have been advanced for reprocessing methods that avoid separation of plutonium in pure form. These schemes are given the generic name “coprocessing” when the plutonium is chemically mixed with its parent uranium throughout the cycle, and “Civex” when it is given the additional protection of retaining some highly radioactive fission products. Such processes are not now available and would require development.

A graver possibility than illicit diversion is that countries installing reprocessing plants would thereby have the means to build up arsenals of nuclear weapons in short order. This concern is particularly acute for breeder reactors, which have little or no value without reprocessing, and it was this consideration that persuaded the Carter administration to defer both commercial reprocessing and commitment to the fast breeder.

A possible advantage of the thorium-233U fuel cycle for fast breeders or advanced converters (it can be used in either) is that the 233U or 235U used to feed these reactors can be diluted with 238U in a 4:1 ratio (for 235U) or a 7:1 ratio (for 233U), making either undesirable as weapons material without physical isotope separation as well as chemical reprocessing. This is the “denatured” thorium cycle. The efficacy of denaturing is now the subject of extensive debate. It is being studied in the United States and will be studied further in the ongoing program of the International Nuclear Fuel Cycle Evaluation (INFCE).

In spite of the unsettled state of the reactor-safety issue following the Three Mile Island incident (which occurred late in the committee’s deliberations), the committee continued to regard proliferation and diversion as the most important—perhaps the overriding—issue in nuclear power. The degree to which the risks of national proliferation of nuclear



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