(309f) Ultra-Microporous Materials for Efficient Removal of Krypton from Nuclear Reprocessing Facilities
Reprocessing of used nuclear fuel (UNF) is a prerequisite for any future expansion of civilian nuclear power. Major challenges during the reprocessing of nucler fuel is the release of volatile radio nuclides that must be captured and subsequently stored for an extended period of time before being released into atmosphere. While methods such as cryogenic distillation and fluorocarbon based absorption have been proposed and tested, solid state adsorbents in particular permanently porous Metal-Organic Frameworks (MOFs) are considered better alternatives in terms of cost and engineering control to capture these volatile radionuclide including 85Kr (t1/2 = 10.8 years). However, because of presence of more polarizable Xe during the reprocessing, adsorbent materials including MOFs are found to be more Xe- philic than Kr. To address this challenge, a two-bed breakthrough method is being developed herein which leads to enhanced Kr adsorption and separation of 85Kr during nuclear reprocessing. The extent of enhancement of Kr adsorption depends on the nature of adsorbing materials. Here, we evaluate the Kr adsorption capability of a series of hybrid ultra-microporous materials, namely SIFSIX-3-M (M= Zn, Cu, Ni, Co or Fe) for Kr adsorption and separation performance. The Fe-analogue in particular shows excellent Kr adsorption than the current benchmark materials: CC3, Ag-mordenite, NiMOF-74 and SBMOF-1, under simulated nuclear reprocessing off-gas conditions. The higher Kr adsorption and separation efficacy was attributed to the precise pore diameter of the Fe-analogue for such separation. All materials were systematically studied for gamma irradiation stability, which reveals that the metal center in these isostructural materials plays a crucial role in their irradiation stability. Zn and Ni analogues show phase change at 1KGy, while SIFSIX-3-Fe shows phase change at 3KGy. SIFSIX-3-Co structure was stable up to 10KGy before it undergoes phase change while SIFSIX-3-Cu was the most stable analogue. The phase change of all materials were interpreted using PXRD. These results attest the potential of these materials for Kr removal under the nuclear reprocessing conditions.