Separation Technology for Radioactive Iodine from Off-Gas Streams of Nuclear Facilities.

Abstract

Iodine separation technology using an inorganic adsorption material has been investigated in order to apply the technology to the off-gas treatment systems of nuclear facilities. Iodine removal efficiencies were checked by laboratory experiments using simulated off-gas streams of various conditions and the developed adsorbent, silver impregnated alumina (AgA). Laboratory test results demonstrated effective iodine removal with high decontamination factors (DF's) a t relatively high temperatures ( 2 100°C). Then the removal efficiency were confirmed using actual off-gas streams sampled from the dissolver off-gas treatment system of the Karlsruhe reprocessing plant. The D F ' s were over los with the AgA bed depth of lOcm and showed little change during the adsorption period, which indicated applicability of the iodine removal technology with AgA to nuclear fuel reprocessing plants. Iodine adsorption capacity and its release property were also investigated using simulated off-gas streams. The former had a value of -0.22g/g-AgA and this value could well predict the breakthrough property. The adsorbed iodine was judged stable during the storage of AgA saturated with iodine in air at temperatures below 500°C and in water a t -20°C after changing the adsorbed iodine form from AgIO, to AgI. Thus, the separation technology provided effective and stable iodine separation from the off-gas of nuclear facilities.

Capture of harmful radioactive contaminants from off-gas stream using porous solid sorbents for clean environment – A review

“…Caustic scrubbing may avoid this equipment pitfall with acceptable DFs, but the alkaline solutions tend to absorb CO 2 over time, decreasing the effectiveness of the method, and also may not effectively remove organic iodides [27]. Thus, high amounts of solvent must be used to combat this and retain an acceptable DF [12].…”

“…AgNO 3 reacted with elemental iodine to form the stable silver iodide/iodate. Fukasawa et al [12,45] developed a silver nitrate impregnated alumina sorbent (24% AgA). The capacity of sorbent was investigated for capture of iodine from a reprocessing plant using continuous column at a velocity of 20 cm s -1 at 423 K. They concluded that parameters (iodine concentration, gas flow rate) other than temperature had no effect on decontamination factor (DF's).…”

“…Only a small fraction of radionuclide emission takes place during nuclear plant operation, primarily from minor leakage from the fuel rods [11]. The majority of radionuclide emissions take places during the aqueous reprocessing of used nuclear fuel (UNF) as it is chopped and dissolved in boiling nitric acid for subsequent extraction steps (PUREX process) [12]. Major gaseous radionuclides released into the atmosphere through off-gas include 129 I, 14 C, 3 H and noble gases ( 85 Kr and multiple Xe isotopes).…”

Application of Silver Impregnated Iodine Adsorbent to Nuclear Facilities

“…6 indicate almost no iodine release for AgA after heating to 450C. As I 2 is known to adsorb as forms of insoluble AgI and soluble AgIO 3 and AgIO 3 changes to AgI by heating, AgA with heat treatment drastically reduces the iodine release to water (9) . Thus AgA is found to be also suitable for storage and disposal after use.…”

Activity of nanostructured C@ETS-10 sorbent for capture of volatile radioactive iodine from gas stream

“…In recent years, adsorption onto a porous adsorbent has been the primary choice for the removal of radioactive iodine gas due to its advantages that include reliability, simplicity and low operating costs [7]. Previously, several sorbents has been investigated to trap the iodine which includes activated carbon [8,9], silver-exchange zeolite [10], AgNO 3 -impregnated silica and alumina [11,12], silver-functionalized silica aerogels [13], silver-exchanged titania (ETS-10) [14], chalcogen-based aerogel [15][16][17][18], monolithic aerogels of polymeric organic framework [19], and metal organic frameworks [20][21][22][23][24].…”