Dissolver Off-gas Research Articles

Characteristics of iodine-bearing silver-impregnated alumina sorbents and their direct solidification via hot isostatic pressing.

Waste management for radioiodine is a key issue for the sustainable nuclear fuel cycle. The iodine adsorption behavior on a bed column of a silver-impregnated alumina sorbent (AgA) under conditions designed to match those of the Rokkasho reprocessing facility dissolver off-gas (DOG) system was investigated using different volatilized iodine concentrations. Cross-sectional observations of iodine-bearing AgA grains revealed that iodine was adsorbed as silver iodide and silver iodate, and gradually distributed from the surface to the inside of the AgA. The iodine distribution throughout the AgA beds allowed us to estimate the length of the mass-transfer zone. This suggests that the iodine load fraction in AgA (adsorbed iodine/total impregnated silver) will be averaged to 50% in the expected facility equipment design. This study also describes the waste form durability after disposal. To reproduce the average iodine loading in the waste form, 100%-loaded AgA grains were mixed with an equal amount of commercially available alumina reagents and consolidated through hot isostatic pressing at 175MPa and 1,325°C for 3h. The resultant 50%-loaded solid was used for the static leaching test over 4.5years, where the leached iodine was less than 0.2% under simple reducing conditions. This suggested that the HIPed solid of AgA from Rokkasho DOG showed preferable water resistance for after disposal safety.

Abatement of radioiodine in aqueous reprocessing off-gas.

The reprocessing used nuclear fuel (UNF) releases volatile fission and activation products, including 129I, into the off-gas of a processing plant. Mitigation of the release of vapor phase radionuclides is necessary for meeting regulatory requirements in the United States and other countries. In an aqueous reprocessing plant, volatile radioiodine could be present in several forms, depending on the chemistry of the process used. Inorganic iodine will be the predominate species in any shearing or voloxidation pretreatment off-gas and dissolver off-gas (DOG). Organic iodides such as CH3I, C4H9I, and C12H25I have been proposed to be generated during solvent extraction; thus, these species must be captured from the vessel off-gas (VOG). The abatement of inorganic and organic iodide species to meet United States regulatory requirements has been demonstrated in laboratory experiments using Ag-based solid sorbents. The data presented in this paper includes the effect of gas composition (e.g., the presence of water vapor and NO x ), iodine speciation (I2, CH3I, C4H9I, C12H25I), and sorbent bed parameters (e.g., temperature, sorbent age) on complete iodine capture on Ag-mordenite in an aqueous reprocessing plant.

Catalytic Effects of Silver in Iodine Reactors for Dissolved Used Nuclear Fuel

The dissolution of used nuclear fuel generates a variety of off-gasses including flammable hydrogen and other species that are a concern for environmental release. The H-Canyon facility at the Savannah River Site is currently dissolving aluminum-clad research reactor fuel from material test reactors and the High Flux Isotope Reactor (HFIR) using a mercury-catalyzed nitric acid flowsheet. Savannah River National Laboratory recently developed and deployed a Raman spectrometer to monitor the off-gas stream from the dissolution process. Results from these measurements indicated a lack of the expected hydrogen, nitrous oxide, and nitric oxide in the off-gas stream. It was proposed that the silver on the silver nitrate–coated berl saddles present in the reactors for iodine capture were acting as a catalytic hydrogen recombiner. Nitric oxide is readily oxidized to nitrogen dioxide under normal conditions, but it was unclear what happened to the nitrous oxide. A laboratory-scale iodine reactor was assembled and filled with silver nitrate–coated berl saddles to help ascertain the fate of nitrous oxide and hydrogen. Testing with this laboratory-scale reactor observed the recombination of hydrogen when a simulated dissolver off-gas was passed through the reactor containing silver nitrate–coated berl saddles at the approximate temperatures seen in H-Canyon. However, the nitrous oxide concentration was unchanged, suggesting a more complex process occurring within the off-gas stream before it reaches the iodine reactors at H-Canyon.

Development of Thermal Swing Adsorption (TSA) Process for Complete Recovery of Iodine in Dissolver Off-gas

KEYWORDS: reprocessinglong-lived nuclidesiodine 129dissolver off-gasthermal swing adsorptionzeolitemordenite

Development of Thermal Swing Adsorption (TSA) Process for Complete Recovery of Iodine in Dissolver Off-gas

Development of Thermal Swing Adsorption (TSA) Process for Complete Recovery of Iodine in Dissolver Off-gas

Applicability of a Model Predicting Iodine-129 Profile in a Silver Nitrate Silica-Gel Column for Dissolver Off-Gas Treatment of Fuel Reprocessing

The applicability of a mathematical model predicting iodine-129 profile in a silver nitrate silica-gel (hereinafter referred to as Ag-S) column for radioactive iodine treatment was examined using actual off-gas from a dissolution step of a spent nuclear fuel reprocessing test rig, where PWR spent fuels with burnups up to 44,000 MWdt−1 were dissolved. The iodine-129 profile predicted by the model showed good agreement with the iodine profile obtained in the experiment. It was suggested that the model would be useful to predict iodine profiles in an Ag-S column operated at 423 K for the off-gas treatment of actual spent fuel dissolution. Also, the values of the parameters used in the prediction, i.e., the effective diffusion coefficient and the Langmuir coefficient, were supposed to be applicable within the volumetric NO2 concentration range lower than 1%.

Long-lived nuclide separation for advancing back-end fuel cycle process

An advanced PUREX process named PARC process having a partitioning function of long-lived nuclides has been developed for establishing the coming generation's fuel cycle technologies, which satisfy a sustainable energy security and global environmental protection. Key technologies applied in the process are: 1) removal of carbone-14 and iodine-129 with adsorption techniques in dissolver off-gas, 2) separation of neptunium and technetium by selective reduction of Np(Vl) by normal-butyraldehyde and the high acid scrubbing of technetium, 3) separation of americium from the raffinate of co-extraction step with adsorption technique, 4) solvent-washing with normal-butylamine compounds. The separation efficiency of long-lived nuclides in the process was measured in chemical flow sheet experiments using spent fuels burned up to 44,000 MWD/tU.

Investigations on the Partitioning of 129I from Silver-Impregnated Silica in Preparation for Future Transmutation

According to the current state of the art in reprocessing technology, the 129I contained in spent fuel elements can be completely transferred to the dissolver off-gas and efficiently adsorbed on AgNO3-impregnated silica (AC 6120). For future transmutation, the 129I should again be separated selectively and as completely as possible (>99%) from the AC 6120 adsorption matrix. Experimental studies show that a quantitative recovery of the iodine is possible by wet chemical and thermal processes. Extraction experiments using iodine-loaded AC 6120 with sodium sulfide solution provide recovery rates of 99 ± 1%. Reduction with hydrogen at 500°C, in which gaseous HI was liberated, provided recovery rates of >99%. After the separation of iodine, the reduced AC 6120 can be used again as an adsorbent for molecular iodine.

Thermochemical and Experimental Considerations of NOxComposition and Iodine Species in the Dissolution of Spent PWR-Fuel Specimens

Abstract The NOx composition and iodine species in the dissolution of spent fuels are discussed on the basis of thermochemical calculations and experimental results. The influence of N0x sparging on the expulsion of iodine is also discussed. The dissolution of a spent PWR-fuel specimen (–3g) in 30 ml of 3.5MHNO3 at 100°C is calculated to yield a concentration of 7×10−2atm of N02, which is 80% of the total NOX in the dissolver. This N02 fraction is much higher than experimental values of 15% or less that were reported for dissolver off-gas cooled near to room temperature. The high N02 fraction suppresses the formation of iodate (IO3 −) in the dissolution. The calculations predict that IO3 −) is not formed in 3.5 M HNO3 at 100°C at an NO2 pressure ≥3×10−2 atm (3kPa). Attempts to expel iodine from the fuel solution indicated that the main iodine species in the solution was colloidal iodine and not iodate (I03 −) which earlier workers postulated. The obtained experimental results are consistent with the therm...

疎水性銀添吸着剤によるヨウ素吸着

Hydrophobic adsorbents, which consist of porous styrene-divinylbenzene copolymer (SDB) impregnated with silver, were developed for the removal of iodine from the dissolver off-gas (DOG). The adsorption of iodine in a simulated off-gas including iodine, NOx and water vapor was examined by use of an adsorption column packed with the hydrophobic adsorbents.Silver impregnation methods using organic solutions were proposed. By use of dioxan and butylamine, which can swell the SDB easily, silver nitrate and metallic silver were uniformly distributed in the SDB particles.The breakthrough of iodine was not influenced by the presence of NOx and water vapor. For a macroporous SDB with the pore volume of 1.59ml/g-SDB and the average pore diameter of 500A, impregnated with metallic silver at silver content of 28wt%, a high adsorption capacity of 0.14g-I2/cm3-adsorbent was obtained, compared to that of a commercial adsorbent, AgNO3-impregnated silica gel. The impregnated silver was utilized about 91% for the iodine adsorption.

Two-Step Procedure for the Iodine Removal from Nuclear Fuel Solutions

In order to minimize the consumption of iodine filters in a nuclear fuel reprocessing plant without increasing the radiological exposure of the environment, it is desirable to route the {sup 129}I almost quantitatively into the dissolver off-gas. To achieve this, an additional step for the complete removal of the iodine from the nuclear fuel solution after dissolution is proposed. The distribution of the iodine residues in the fuel solution between nitric acid and TBP, MIBK, toluene and dodecane is also measured. (orig.).

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Behavior of iodine-131 in dissolution of irradiated uranium dioxide.

A hundred milligram of UO2 was irradiated In JRR-4 (burn up 0.017%) and dissolved In boiling 3 M-HNO3 (20 ml) to study the behavior of fission-product iodine (131I, − 1 ng) During the dissolution, 80–90% of the iodine volatilized together with 133Xe. Zeolite 13X (–4g) trapped completely the iodine in the dissolver off-gas Blowing a NO2 flow through the solution was effective for expulsion of the remaining iodine and finally 90–95% of the initial iodine was removed from the solution with the aid of addition of KIO3. The Iodine species in the solution includes I2, I−, IO3 − (IO4 −), organic iodides and other unknown species The expulsion operations caused the unknown species to increase In relative abundance. This tendency was also noticed for iodine of higher concentration in 3 M-HNO3.

A Study of Mineral Zeolite as a Nitrogen Oxides Adsorbent for Dissolver Off-Gas Treatment

In the nuclear fuel reprocessing plant, dissolver off-gas (DOG) is supposed to include nitrogen oxides (NOX) during the operation. An adsorption process by mineral zeolite has been studied for DOG treatment that follows a dehydration and iodine removal process. According to the results, the characteristics of the mineral zeolite hydrogenated by 1 N HCl are very favorable for this purpose. As for the actual operation, a small fraction of iodine is supposed to penetrate the I2 removal process to the NOX adsorption process. No degradation has been observed for the NOX adsorption of mineral zeolite by the presence of I2.

Application of Zeolites to Remove Iodine from Dissolver Off-Gas, (III) Adsorption of Methyl Iodide (CH3I) on Zeolite 13X

Click to increase image sizeClick to decrease image sizeKEYWORDS: Iodinesilver-free zeolitemethyl iodidenitrogen dioxidezeolite 13Xdissolver off-gasiodine 131adsorption

Application of Zeolites to Remove Iodine from Dissolver Off-Gas, (II) Thermal Stability of Iodine Adsorbed on 13X, 5A, and Silver-exchanged Zeolites

KEYWORDS: iodine removal processiodine 1315A zeolite13X zeolitesilver zeolitesnitrogen oxidesdissolver off-gasthermal stability

Application of Zeolites to Remove Iodine from Dissolver Off-Gas, (I)

KEYWORDS: iodine removal processiodine 131zeolite 5Anitrogen oxidesdissolver off-gasWahlgren and Meinke's experimentstemperature dependence

Application of zeolites to remove iodine from dissolver off-gas, (III). Adsorption of methyl iodide (CH3I) on zeolite 13X.

Click to increase image sizeClick to decrease image sizeKEYWORDS: Iodinesilver-free zeolitemethyl iodidenitrogen dioxidezeolite 13Xdissolver off-gasiodine 131adsorption

Application of zeolites to remove iodine from dissolver off-gas. (II). Thermal stability of iodine adsorbed on 13X, 5A, and silver-exchanged zeolites.

Click to increase image sizeClick to decrease image sizeKEYWORDS: iodine removal processiodine 1315A zeolite13X zeolitesilver zeolitesnitrogen oxidesdissolver off-gasthermal stability

Application of zeolites to remove iodine from dissolver off-gas, (I). Follow-up of Wahlgren and Meinke's experiments.

Click to increase image sizeClick to decrease image sizeKEYWORDS: iodine removal processiodine 131zeolite 5Anitrogen oxidesdissolver off-gasWahlgren and Meinke's experimentstemperature dependence