Kiyomi Funabashi

Decomposition of ion exchange resins by pyrolysis

Pyrolysis of spent ion exchange resins is one of the most effective methods for reducing radioactive waste volume and for making the final waste form more stable. Fundamental experiments were perfo...

Investigation of silver-impregnated alumina for removal of radioactive methyl iodide

The removal efficiency of methyl iodide for silver-impregnated alumina from gaseous waste has been experimentally evaluated as a function of atmospheric relative humidity. A new adsorbent has been developed for the iodine filter installed in the off-gas treatment system of a radioactive waste tank vent. To improve its removal efficiency under a highly humid atmosphere, the optimum average pore size of alumina was determined to be {approximately}60 nm, and the most effective chemical form of the impregnated silver was identified as silver nitrate. Holding capability of the impregnated silver was also improved by developing a double-pore-structure alumina.

Removal of radioactive cobalt ion in high temperature water using titanium oxide

Abstract The adsorption of Co 2+ on titanium oxide (TiO 2 ) has been experimentally evaluated as a function of temperatures in the range 20–280°C. The selectivity experiments showed that corrosion products such as Co 2+ , Ni 2+ and Mn 2+ in reactor water are preferentially adsorbed at high temperatures. The data suggest that there are two reaction mechanisms, i.e. an ion exchange reaction at low temperatures, and chemical adsorption with the formation of insoluble cobalt meta-titanate (CoTiO 3 ) on the TiO 2 surface at high temperatures.

Effect of Metallic Impurities on Oxidation Reaction of Ion Exchange Resin, (I)

Dry oxidation of spent ion exchange resin is one of the most effective methods to reduce radioactive waste volume and also to make the final waste form more stable. Thermo-gravimetric measurements were performed using cation exchange resins with or without Fe in either an ionized or unionized form to clarify the effect of metallic impurities on the resin oxidation. The presence of an ionized Fe resulted in a considerable increase in the reaction rate constant, indicating that the Fe functioned as a catalyst. On the other hand, the unionized Fe showed no catalytic activity. Measurement of EPMA revealed that the ionized Fe was distributed uniformly throughout the resin particles, while the unionized one was distributed only on the surface of the resin particle. Catalytic activity increased with ionized Fe concentration up to 0.5 mmol-Fe/g-dry resin, above which the activity tended to decrease. The X-ray diffraction study attributed this to Fe coagulation in the resin particle. Kinetic models for solid-gas r...

Using Titanium Oxide for Cobalt Removal from High-Temperature Water

Improvement of the reactor water cleanup system is one of the most effective methods for radiation reduction in boiling water reactor plants. This necessitates development of a heat-resistant adsorbent for direct use to remove cobalt under reactor conditions (285/sup 0/C, 70 kg/cm/sup 2/). We have developed a suitable adsorbent by impregnating granular sponge titanium with titanium oxide. Adsorption of Co/sup 2 +/ on titanium oxide was evaluated as a function of temperature. Selectivity experiments showed that corrosion products, such as Co/sup 2 +/, Ni/sup 2 +/, and Cu/sup 2 +/, were preferentially adsorbed at high temperatures. The data suggested that chemical adsorption occurred with the formation of insoluble cobalt metatitanate on the TiO/sub 2/ surface. In-plant tests, carried out to evaluate the performance using actual reactor water, verified the applicability of the new adsorbent to the hightemperature reactor water cleanup system.

Application of Carboxylic Acid Cation Exchange Resin to Water Purification in Nuclear Power Plants

Weakly acidic carboxylic resin, with no sulfur atoms, was selected as an alternative to sulfonic cation exchange resin for water treatment in nuclear power plants. Pyrolysis experiments showed that no corrosive SOx gas was produced by the former, and its residual ratio was one-third that of the latter conventional resin. Spent resin treatment then becomes relatively simple for the new resin. Subsequently, filtration characteristics were examined by use of simulated condensate water, assuming that the resin was applied to a filter demineralizer. The resin lifetime was ∼1.5 times that of the conventional one, suggesting that the amount of spent resin generated from a filter demineralizer could be reduced to about two-thirds. Therefore, the carboxylic resin showed favorable features for both water purification and spent resin treatment.

Reuse System for Powdered Ion-Exchange Resins

A reuse system has been developed for powdered ion-exchange resins generated from nuclear power plants in order to reduce their waste volume. The system consists of: 1. crud removal from resins; 2. decomposition of flocks (flocculated resins); 3. resin separation into cation and anion types; 4. regeneration of each type. The most important points in this system are items 2 and 3, because generally resins flocculate too tightly to separate easily. By combined usage of a strong electrolyte (15 wt% NaOH solution) and a dual-basket-type centrifuge, spent powdered resins can be separated with an efficiency of 95% and regenerated for another use. The waste volume can be reduced to one-half after four reuse cycles, with a decrease in the ion-exchange capacity of only 5%.

Properties of a radioactive waste pellet package using cement-glass

This paper reports on radioactive waste slurry generated from nuclear power plants which is dried and compressed into pellets. These pellets are dropped in a polymer-impregnated concrete (PIC) barrier and solidified with cement-glass, which is a mixture of sodium silicate and cement. The mechanical strength of the PIC barrier is about three times higher than that of ordinary portland cement because of added steel fibers. The leaching ration form the package is experimentally studied using {sup 14}C, {sup 60}Ci, {sup 85}Sr, {sup 99}Tc, {sup 125}I, and {sup 134}Cs. Because of the low porosity of the PIC barrier, the leaching rate is controlled and increases in proportion to immersion time. The maximum leaching ratio from a 200-l package is estimated to be 0.004/yr.

Filtration of crud by powdered ion exchange resin.

The filtration mechanism of powdered ion exchange resin, which is used in BWR power plants, was studied through filtration experiments of two type resins. A filtration model was proposed to calculate the increase in pressure drop of a powdered resin layer by crud filtration.According to observations of the sectional appearance of the powdered resin layer, crud was adsorbed in it, and this amount decreased exponentially with increased depth. This meant that filtration in powdered resin could be evaluated by a conventional model for deep bed filtration. But this model includes no consideration of contraction of the powdered resin layer, because it was developed for a deep bed without contraction.Therefore, the effect of contraction was measured by basic compaction experiments, and a new model was proposed to evaluate this effect by modification of the conventional one. The new model provided calculation results which agreed within 5% of the experimental ones.

Effect of metallic impurities on oxidation reaction of ion exchange resin. (II) Comparison of catalytic activity between six metals.:Comparison of Catalytic Activity between Six Metals

The catalytic effect of six metallic impurities on the oxidation reaction of cation exchange resin was investigated. The impurities, which were originally adsorbed onto the resin by an ion exchange method, combined with S present in the functional sulfonic acid group during heat-treatment in a nitrogen atmosphere to give the metal sulfides. The sulfides were subsequently oxidized to metal oxides. In the case of Pd2+, Cu2+, Fe2+ and Fe3+ impurities, their sulfides were easily converted into oxides, which catalyzed the resin oxidation. Their catalytic activities depended on the heat of formation of the catalyst oxides ΔH‘0; the lower was ΔH’0, the more active the catalyst was. However, Co2+ and Ni2+ impurities had relatively low catalytic activities. This was because Co and Ni sulfides slowly changed into oxides, and the main chemical compositions of the impurities were not oxides but sulfides, which had no catalytic effect on the resin oxidation.