Spent nuclear fuel elemental compositions

Once the radioactive fission products are isolated by one of the separation processes, the major problem in the nuclear chemical industry must be faced since radioactivity cannot be immediately destroyed (see Fig. 10-7c for curie level of fission-product isotopes versus elapsed time after removal from the neutron source). This source of radiation energy can be employed in the food-processing industries for sterilization and in the chemical industries for such processes as hydrogenation, chlorination, isomerization, and polymerization. Design of radiation facilities to economically employ spent reactor fuel elements, composite or individually isolated fission products such as cesium 137, is one of the problems facing the design engineer in the nuclear field. 

Hafnium-like boron is known to be a neutron absorber or neutron moderator element, and, therefore, composites of boron carbide, B4C, and hafnium diboride, HfB2, can be considered as nuclear materials. These boron compounds after sintering and °B/"B isotopic ratio adapting are found to be heterogeneous polyphone cermets useful for nuclear applications (Beauvy et al. 1999). Boron acid obtained from the °B enriched boron trifluoride also was used in nuclear reactors (Shalamberidze et al. 2005). Amorphous boron powders enriched both in °B and "B, boron carbide, and zirconium diboride (ZrB2) powders and pallets labeled with °B isotope And applications in nuclear engineering too. The °B enriched Fe-B and Ni-B alloys are useful for the production of casks for spent nuclear fuel transfer and storage. 

Due to its neutron-absorbing efficiency, boron carbide is attractive as a neutron absorber material, and is used both in powdered and solid forms to control the rate of fission in nuclear reactors (Figure 4.19b)[530j. B4C mixed with other materials, such as aluminum metal or polyethylene plastic, is applied to protect it against oxidation in the reactor environment. AI-B4C metal-matrix composite plates (e.g., Boral, Bortec) have wide applications as isolators in spent fuel element racks, in the inner sections of reactor shields as shutdown control rods and neutron curtains, as shutters for thermal columns, and as shipping containers. 

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