Iodine chemistry in Falcon

The Falcon facility at Winfrith has been designed to study the transport of vapours and aerosols released from simulant and trace-irradiated UO2 fuel heated upto 2000 K. Fission product deposition can be studied in the presence and absence of control rod and boric acid aerosols along a pathway representing the upper plenum, primary circuit pipework and containment vessel of a light water reactor (including painted surfaces and an aqueous sump of defined initial pH). Various on-line and post-test analytical techniques can be used to provide information on the chemical species and physical forms of the gas-borne debris. A series of Falcon tests have provided evidence for chemical reactions within the primary circuit between iodine-based vapours and aerosols generated from bulk materials, and the formation of volatile, reactive iodine species within the containment. Ten times more iodine was detected on painted surfaces than equivalent unpainted walls, and approximately twenty times more iodine was found in the alkaline sump per unit surface area than on the 304 stainless steel floor. (author)