Vitrification of Radioactive Iodine-129 Generated from Pyro-processing

Abstract

Iodine-129 (129I) is a long-lived (t1/2=1.57ⅹ107 y) product of 235U fission. 129I is highly mobile and can thus easily pollute the environment. Currently, 129I from the off-gas treatment system of pyro-processing is adsorbed on AgX zeolite as AgI, which decomposes at a relatively low temperature of ~558 °C. Two processes to fabricate iodine waste forms were suggested in this thesis. First is to encapsulate waste inside the low-melting-temperature (Tm) borosilicate glass with wastes; the other is to design a low-temperature sintering process that exploits the viscous flow of commercial glass frits. Low-temperature vitrification is expected to decrease the volatilization of AgI components. 129I wastes were successfully immobilized inside the glass matrix through both melting and viscous sintering processes. Dissolution of iodine from chemical durability test of the melt-quenched glass was almost zero.