Hulls and hardware

Stainless steel hardware (including spacers, clips, springs, end plates, etc.) is removed in the first stage of reprocessing. The primary radionuclides in the hardware come from activation of stainless steel components (e. g., 54Mn, 55Fe, 60Co, and 63Ni). This stream makes up roughly 5 wt% of the fuel assem­bly. Cladding (sometimes referred to as hulls) refers to the metal tubes used to hold the fuel. At present, cladding compositions are typically >95% Zr with Sn and/or Nb alloying agents although stainless steels are sometimes used (e. g., in UK advanced gas-cooled reactor fuel). The primary radionu­clides in and on the cladding are activation products (e. g., 95Zr, 95Nb, 54Mn, 55Fe, 60Co, and 125Sb), tritium, and transuranics/fission products from alpha recoil at the fuel-cladding interface. Tests have shown that the transuranic contamination resides in the inner 7 pm of the cladding. As cladding makes up roughly 25% of the used nuclear fuel mass, it is the largest single fuel component after UO2.

Traditionally, hulls and hardware have been managed together. The most common approaches to managing these wastes are to wash and then (1) embed them in cement for disposal, (2) dispose directly, and (3) compact and dispose (IAEA, 1985). Compared to direct disposal, the compaction reduces disposal package volume by roughly a factor of four, while encap­sulation in cement increases the volume by roughly 100% (double the volume).

A number of alternative approaches have been studied for these wastes including: rolling compaction and cementation, embedding in graphite, compaction with malleable metals (e. g., Pb), compaction and encapsulation in low temperature metals, powder metallurgical encapsulation, glass encap­sulation, cryogenic crushing and encapsulation, oxidation and conversion to ceramic waste forms (e. g., zircon), oxidation and cementation, hot press­ing, melting to a Zr-Fe alloy zirconium separation using reactive gasses (Collins et al., 2011). Although these methods are not being currently imple­mented, many show promise for improved waste management compared to the reference technologies.

Добавить комментарий

Ваш e-mail не будет опубликован. Обязательные поля помечены *