PNNL

Abstract

Separation of volatile radionuclides particularly, 85Kr from the off-gas streams of a used nuclear fuel reprocessing facility has been a topic of significant research.1-4 The current technology uses energy intensive cryogenic distillation, which is expensive. Another downside of this technology is the accumulation of ozone due to radiolysis of oxygen. Therefore alternate materials/technologies are needed for separation of Xe/Kr from process off-gases at room temperature or colder temperature. In this regard, Pacific Northwest National Laboratory is exploring a new class of materials called metal organic frameworks and porous organic cage like materials for separation of Xe and Kr at near room temperature. Our laboratory results demonstrate the removal Xe and Kr with high adsorption capacity and selectivity compared to benchmark materials such as Zeolites and activated carbons. The extraordinary selectivity towards Xe/Kr at low concentration indicates the perfect match between the pore size and the kinetic diameter of the gas molecule. Though significant work has been performed to identify the best adsorbent material for room temperature separation but very limited attention has been focused on separating the noble gases at low temperature. The advantages of separating lower temperature include, higher adsorption capacity, reduced foot print of the separation unit, and more volume of gas can be processed compared to room temperature based separation.