Behavior of iodine in the dissolution of spent nuclear fuels

Conference · Fri Aug 01 04:00:00 EDT 1997

OSTI ID:567215

Sakurai, Tsutomu; Komatsu, Kazunori; Takahashi, A ^[1]

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1. Japan Atomic Energy Research Institute, Ibaraki-ken (Japan)

The results of laboratory-scale experiments concerning the behavior of iodine in the dissolution of spent nuclear fuels, which were carried out at the Japan Atomic Energy Research Institute, are summarized. Based on previous and new experimental results, the difference in quantity of residual iodine in the fuel solution between laboratory-scale experiments and reprocessing plants is discussed, Iodine in spent fuels is converted to the following four states: (1) oxidation into I{sub 2} by nitric acid, (2) oxidation into I{sub 2} by nitrous acid generated in the dissolution, (3) formation of a colloid of insoluble iodides such as AgI and PdI{sub 2}, and (4) deposition on insoluble residue. Nitrous acid controls the amount of colloid formed. As a result, up to 10% of iodine in spent fuels is retained in the fuel solution, up to 3% is deposited on insoluble residue, and the balance volatilizes to the off-gas, Contrary to earlier belief, when the dissolution is carried out in 3 to 4 M HNO{sub 3} at 100{degrees}C, the main iodine species in a fuel solution is a colloid, not iodate, Immediately after its formation, the colloid is unstable and decomposes partially in the hot nitric acid solution through the following reaction: AgI(s) + 2HNO{sub 3}(aq) = {1/2}I{sub 2}(aq) + AgNO{sub 3}(aq) + NO{sub 2}(g) + H{sub 2}O(1). For high concentrations of gaseous iodine, I{sub 2}(g), and NO{sub 2}, this reaction is reversed towards formation of the colloid (AgI). Since these concentrations are high near the liquid surface of a plant-scale dissolver, there is a possibility that the colloid is formed there through this reversal, Simulations performed in laboratory-scale experiments demonstrated this reversal, This phenomenon can be one reason the quantity of residual iodine in spent fuels is higher in reprocessing plants than in laboratory-scale experiments. 17 refs., 5 figs., 3 tabs.

• Research Organization: Harvard Univ., Boston, MA (United States). Harvard Air Cleaning Lab.; USDOE Assistant Secretary for Environment, Safety, and Health, Washington, DC (United States). Office of Environmental Guidance; Nuclear Regulatory Commission, Washington, DC (United States). Office of Nuclear Regulatory Research; International Society of Nuclear Air Treatment Technologies, Inc., Batavia, OH (United States)
• OSTI ID: 567215
• Report Number(s): NUREG/CP--0153; CONF-960715--; ON: TI97008959
• Country of Publication: United States
• Language: English

Related Subjects

05 NUCLEAR FUELS
BENCH-SCALE EXPERIMENTS
COLLOIDS
DISSOLUTION
IODINE 129
PALLADIUM IODIDES
QUANTITATIVE CHEMICAL ANALYSIS
SILVER IODIDES
SPENT FUELS