Review of iodine behavior from nuclear fuel dissolution to environmental release

Abstract

During nuclear fuel reprocessing, radioiodine, can be released. The speciation of iodine drives its volatility, and partitioning processes are highly variable because they depend on facility operating conditions. Starting from iodine behavior in the fuel and progressing to its behavior in the environment, this review article describes the current understanding of iodine partitioning during aqueous fuel reprocessing. This review outlines knowledge gaps and describes the effects of state-of-the-art reprocessing techniques on iodine speciation and volatility. Whereas many review articles have described iodine behavior during specific reprocessing steps, this review provides a holistic overview of radioiodine, from the forms of iodine in different types of irradiated fuel to the forms of iodine released into the environment. The resultant behavior of radioiodine compared with stable iodine in the environment is also described.

Fig. 1. Schematic of process steps that are covered in this review. Fuel bundle disassembly is covered in Section 2, dissolution and off gas treatment in Section 3, solvent extraction in Section 4, and environment in Section 5.

Fig. 2. Block flow diagram for aqueous head-end processing. This figure was reprinted with permission. Copyright 2008 CRESP.

Fig. 3. Distribution of iodine (¹²⁹I) from dissolution of spent fuels in laboratory scale experiments. This figure was recreated from Sakurai et al. and was reprinted with permission.

Fig. 4. Traditional PUREX process.

Fig. 5. Basis of comparison flowsheet for UNF actinide recovery. This figure was recreated with permission from Arm.

Fig. 6. Outline of the movement of iodine in the environment. Figure was recreated from Whitehead and reprinted with permission. Copyright 1984 Elsevier.

Fig. 7. Diagram of the global iodine cycle at steady state that shows environmental compartment inventories in grams (g), transport pathways, and fluxes in grams per year (g per year). This figure was taken from ATSDR (2004).

Fig. 8. Variations of iodide (I⁻), iodate (IO₃⁻), non-ionic iodine, and total iodine concentrations in precipitation from Roskilde, Denmark from 2001–2006 for (a) ¹²⁷I and (b) ¹²⁹I. The error bars show a one standard deviation analytical uncertainty. Reprinted with permission from Hou et al. Copyright 2009 American Chemical Society.

Fig. 9. Air concentrations of (a) ¹²⁹I and (b) ¹²⁷I in various chemical forms at four sampling locations NNE from WAK in the dominant downwind direction, as measured between June and September 1987. This figure was modified with permission from Wershofen and Aumann. Copyright 1989 Elsevier.