PNNL

Abstract

This paper presents some conceptual composite waste form ideas for radioiodine immobilization including halide metal (halmet) composites, polymer-halide-metal (polyhalmet) composites, and polymer-ceramic-metal (polycermet) composites. The encapsulant metal of choice for the pellets was Bi0 and a cold press and sinter approach was used for creating the pellets. The inclusion of a polymer (i.e., polyacrylonitrile or PAN) phase in these composite forms is based off the usage of this porous, passive polymer as a host matrix for active chemisorption-based getters for radioiodine gas capture. The target getters in this work included metals of Ag0, Bi0, and Cu0 embedded in PAN beads, which were loaded with iodine in static tests with elemental iodine through sublimation. Included in this paper are details of experiments where PAN removal from the iodine-loaded composite beads was evaluated to reduce the overall volume of the final waste requiring immobilization and to improve the thermal stability by removing the polymer phase. While these experiments demonstrate the concept of such an approach for iodine immobilization, more work is needed to fully understand the limitations of these concepts and further optimizations are needed before these approaches could be realized at larger scales.