Physico-Chemical Characterization of Particle Fallout from a Damaged Nuclear Reactor — Consequences for Remediation Procedures

Abstract

The Chernobyl accident was exceptional in the sense that there was a disruption of the different confining barriers and fusion of the core with mechanical and thermal disintegration of the fuel and of the reactor structures. As a consequence of the thermal stress undergone by the fuel, particles of various sizes were emitted. Once in the atmosphere, various physico-chemical reactions may have occurred between UO₂ particles (partially vitrified) and vapours from the reactor (H₂O, CO, CO₂, fission products, air). These reactions which occurred at relatively high temperature were able to alter the chemical speciation of the radionuclides and to incorporate some of the volatile fission products into the UO₂ particles. This ended up in reducing their availability to the environment. Caesium, for example, so far considered as being present in the environment as a very soluble cationic form, can react with fuel UO₂ and form uranates which are relatively insoluble. This was probably the case in the plume of the reactor at Chernobyl.