Nuclear waste forms composites

The design and evaluation of nuclear waste forms requires some understanding of the sources, volumes, compositions and activities of the various waste streams generated by the nuclear fuel cycle. There are three primary sources of radioactive waste in the United States (DOE 1997) the high-level waste (HEW) from the reprocessing of spent nuclear fuel, the spent nuclear fuel itself, and plutonium reclaimed by reprocessing or obtained by the dismantlement of nuclear weapons. 

Summary. Phosphate and silicate apatite offer a number of advantages as nuclear waste forms (1) a high capacity for the incorporation of actinide elements, as well as selected fission products such as °Sr (2) a reasonable chemical durability depending on the geochemical environment and (3) a propensity for rapid annealing of radiation damage for the phosphate compositions. Considerable work remains to be done, mainly systematic studies, under relevant repository conditions, of the effects of composition on chemical durability. 

Vance, E. R., Carter, M. L., Day, R. A., Begg, B. D., Hart, K. P. Jostsons, A. 1996b. Synroc and Synroc-glass composite waste forms for Hanford HLW immobilization. In Proceedings of the International Topical Meeting on Nuclear and Hazardous Waste Management SPECTRUM 96. American Nuclear Society, Inc. La Grange Park, 2027-2031. 

Boron is a highly significant element for nuclear engineering due to its capacity of neutron absorption. Therefore, boron compounds are crucial components in control rods, shielding and waste disposal or transport, but they can be also used in core catcher construction. So far, B4C, due to its highest boron content, is widely used in order to control fusion in nuclear reactors, typically as a composite in a steel matrix, or inserted into steel pipes. However, comparing to other borides, B4C is characterized by its poor chemical stability, and because of that, sometimes it is used as a substrate for other reactions with metals. It is also characterized by very poor corrosion resistance, since no protective oxides scale is formed. For instance, carbon is oxidized to COx(gas), while the only solid product of oxidation B2O3 melts at low temperature of 510°C. 

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