Capture and Sequestration of Radioactive Iodine
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Capture and Sequestration of Radioactive Iodine B.R. Westphal1, D..G. Cummings1, J.J. Giglio1, D.L. Wahlquist1, K.J. Bateman1, W.M. McCartin1, J.J. Park2, J.M. Shin2, and B.D. Begg3 1
Idaho National Laboratory, P.O. Box 1625, Idaho Falls, ID 83415 Korea Atomic Energy Research Institute, P.O. Box 105, Daejeon, Korea 305-600 3 ANSTO Inc., P.O. Box 2006, Idaho Fall, ID 83403 2
ABSTRACT Trapping experiments have been performed at the Idaho National Laboratory to assess the performance of AgX sorbent media in capturing volatile iodine during the oxidation of irradiated oxide fuel. The demonstration of iodine release and capture from the used fuel has been accomplished with laboratory-scale equipment in a hot cell environment. Iodine loadings as high as 6 ug/g media have been achieved via chemical adsorption with filter efficiencies in excess of 90%. In addition to iodine, significant quantities of tritium have also been collected on the AgX filter media. Filter media loaded with radioactive iodine has been sequestered in a tin matrix by hot isostatic pressing at 200oC. The placement and encapsulation of the sorbent media was examined by neutron radiography, thus confirming the sequestration of radioactive iodine. INTRODUCTION Considering the toxicity and mobility of radioactive iodine, its capture and sequestration is important following the processing of used oxide fuel. Whether the process flowsheet for used oxide fuel contains aqueous or pyrometallurgical methods, complete iodine release and capture can be achieved via an oxidative head-end step. The head-end step is based on prior research [1] and employs high temperatures (>1000oC) to promote the oxidation of UO2 to U3O8 via reaction with gaseous oxygen. During oxidation, the fuel experiences a 30% increase in lattice structure volume resulting in the separation of fuel from cladding and the removal of fission products, either by direct release from the fractured fuel structure or by volatilization of the resulting oxidation products [2]. The head-end step for the pyrometallurgical treatment of used oxide fuel is being developed by the Idaho National Laboratory (INL) in collaboration with the Korea Atomic Energy Research Institute (KAERI) through an International Nuclear Energy Research Initiative. The head-end step prepares the fuel for downstream processes by decladding the spent fuel, sizing the fuel particles, and removing volatile fission products [2-3]. For the pyrometallurgical treatment of used oxide fuel, the downstream processes include an electrolytic oxide reduction step followed by electrorefining. Trapping experiments are being performed at the INL to assess the performance of filter media during the oxidation of irradiated LWR oxide fuel. In addition to iodine, technetium and cesium are targeted for capture with an off-gas treatment system [4]. Each element is intended to be collected in distinct zones of the off-gas system and within that zone, on individual filters.
The filter medium for each zone has been specifically selected to
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