Chong-Hun Jung

Preparation of Organic-Inorganic Composite Adsorbent Beads for Removal of Radionuclides and Heavy Metal Ions

Composite ion exchanger beads were prepared to remove the strontium and silver ions in acidic solution. Potassium titanate and nickelferrocyanate powder, which are acid resistant inorganic ion exchangers were synthesized and then mixed with polyacrylonitrile (PAN) binder to form a PAN-potassium titanate and a PAN-nickelferrocyanate composite ion exchanger beads. Spherical composite beads could be obtained by adjusting the viscosities of the composite dope in the range of 700–1000 cP. The composite beads porosities such as macropore volume and pore size were increased in proportion to the contents of PVP (polyvinylpyrrolidone) which was used as the porosity modifying chemical. The synthesized composite ion exchangers were evaluated on their adsorption characteristics for the Ag1 and Sr21 ion solutions of pH 2.

Adsorption of rhenium and rhodium in nitric acid solution by Amberlite XAD-4 impregnated with Aliquat 336

An Extractant Impregnated Resin (EIR) was prepared by impregnation of Aliquat 336 into Amberlite XAD-4 for tentative separation of rhenium from rhodium in nitric acid solution. An optimum loading ratio of the XAD-4 resin for Aliquat 336 was found to be about 0.4 (g Aliquat 336/g resin). The prepared EIR showed high preference for rhenium over rhodium and adsorption isotherms for rhenium were described well by Langmuir equation in both the single and multi-component systems. Maximum adsorption capacities obtained by modeling the isotherms of rhenium were 2.01 and 1.97 meq/g for the single and the multi-component systems, respectively. On the other hand, only little adsorption of rhodium ions was observed. The homogeneous model fitted the kinetic data quite well and the obtained effective diffusivities of rhenium and rhodium ions were on the order of 10-7 and 10-6 cm2 min-1, respectively.

Preparation of PAN-zeolite 4A Composite Ion Exchanger and its Uptake Behavior for Sr and Cs Ions in Acid Solution

A PAN-4A composite ion exchanger containing about 80% 4A powder was prepared to remove strontium and cesium ions from acidic solution. The SEM image of the fracture of composite bead showed that zeolite 4A powder was dispersed homogenously and the pores were well formed. The mean pore size of composite bead was 0.14 μm and its porosity was about 74%, which is much higher in comparison with the existing inorganic adsorbent beads. The acid and radiation stability tests showed that PAN-4A was stable against acid solution higher than pH 2 and radiation dose less than 1.89×108 rad, respectively. Ion exchange tests showed that the PAN-4A was selective for Sr ion. The distribution coefficients of PAN-4A for Sr and Cs ions at pH 2 were 2×104 mL/g and 280 mL/g, respectively. The ion exchange capacities (qs) of PAN-4A for Sr and Cs ions at pH 2, which are modeled by Dubinin-Polanyi equation, were 3.92 meq/g and 2.47 meq/g, respectively.

EVALUATION OF FERROCYANIDE ANION EXCHANGE RESINS REGARDING THE UPTAKE OF Cs + IONS AND THEIR REGENERATION

Ferrocyanide-anion exchange resin was prepared and the prepared ion exchange resins were tested on the ability to uptake ion. The prepared ion exchange resins were resin-KCoFC, resin-KNiFC, and resin-KCuFC. The three tested ion exchange resins showed ion exchange selectivity on the ion of the surrogate soil decontamination solution, and resin-KCoFC showed the best ion uptake capability among the tested ion exchange resins. The ion exchange behaviors were explained well by the modified Dubinin-Polanyi equation. A regeneration feasibility study of the spent ion exchange resins was also performed by the successive application of hydrogen peroxide and hydrazine. The desorption of the ion from the ion exchange resin satisfied the electroneutrality condition in the oxidation step; the desorption of the ion in the reduction step could also be reduced by adding the ion.

The Application of Visualization and Simulation in a Dismantling Process

The lack of as-built drawings and information for many old nuclear facilities impedes the planning for a decommissioning. Traditional manual walkthroughs subject workers to lengthy exposure to radiological and other hazards. And also there have been a delay in the dismantling schedules and that in an increase in the amount of waste, which have caused a heavy expenditure for the decommissioning cost. In order for a 3D model to represent the real dismantling operation environment, realistic dismantling activities and scenarios were modeled. We present a dismantling digital mock-up system that can show a dismantling process through an animation and enable us to evaluate the major parameters that can directly affect the cost in a static simulation as a preview to the dismantling activities on a hypothetical dismantling environment. We carried out a prototype 3D animation and a simulation system for dismantling the thermal column in Korean Research Reactor-1(KRR-1). The results show that the modeling of a realistic scenario makes it possible to demonstrate the adequacy of the design and can provide operators with a high fidelity under the real working conditions.

Adsorptive Separation of Palladium from a Simulated Nuclear Waste Solution with Activated Carbon Fibers

Abstract Adsorptive separation of palladium from a nitric acid solution was performed by using a pitch‐based activated carbon fiber modified with NaOH (NaOH‐ACF). The NaOH‐ACF showed a markedly improved adsorption performance for the palladium ions as compared with the untreated ACF. It also showed a much higher preferential adsorption for the palladium ion over the rhodium and rhenium ions. The equilibrium capacity of the NaOH‐ACF for palladium was 1.25 meq · g−1. The breakthrough behavior obtained by using the bed packed with the NaOH‐ACF showed a complete separation of palladium from the coexisting ions of rhodium and rhenium. The spent bed was eluted effectively with nitric acid and a palladium nitrate with a purity of higher than 99% could be recovered.

PARTITIONING RATIO OF DEPLETED URANIUM DURING A MELT DECONTAMINATION BY ARC MELTING

In a study of the optimum operational condition for a melting decontamination, the effects of the basicity, slag type and slag composition on the distribution of depleted uranium were investigated for radioactively contaminated metallic wastes of iron-based metals such as stainless steel (SUS 304L) in a direct current graphite arc furnace. Most of the depleted uranium was easily moved into the slag from the radioactive metal waste. The partitioning ratio of the depleted uranium was influenced by the amount of added slag former and the slag basicity. The composition of the slag former used to capture contaminants such as depleted uranium during the melt decontamination process generally consists of silica (), calcium oxide (CaO) and aluminum oxide (). Furthermore, calcium fluoride (), magnesium oxide (MgO), and ferric oxide () were added to increase the slag fluidity and oxidative potential. The partitioning ratio of the depleted uranium was increased as the amount of slag former was increased. Up to 97% of the depleted uranium was captured between the ingot phase and the slag phase. The partitioning ratio of the uranium was considerably dependent on the basicity and composition of the slag. The optimum condition for the removal of the depleted uranium was a basicity level of about 1.5. The partitioning ratio of uranium was high, exceeding . The slag formers containing calcium fluoride () and a high amount of silica proved to be more effective for a melt decontamination of stainless steel wastes contaminated with depleted uranium.

Development and Performance Assessment of a Soil Washing Equipment for Soil Contaminated With Radionuclide

The purpose of this study is to develop a soil washing system and to define the most suitable experimental conditions for the individual elemental equipment in a soil washing system for decontaminating the radioactive soil from around a TRIGA (Training, Research, Isotope, General Atomic) reactor in Korea. Analysis results have shown that the main radionuclides were Cs137 and Co60 , the soil particle size ranges from 0.063 mm to 1.0 mm and the radioactive concentration was the strongest in a soil particle smaller than 0.063 mm as predicted. Meanwhile, an oxalic acid was found to be the most efficient chemical agent for washing, especially of cobalt. The scrubbing time of four hours was an optimum time to obtain a removal efficiency of more than 75% for 137 Cs and 60 Co. A mixing ratio of the soil weight to the volume of the oxalic acid solution, 1:10, was observed to be the best for a washing and it was estimated to be reasonable for 2 cycles of a scrubbing with 1.0M of oxalic acid to avoid a generation of an excessive waste-solution.Copyright

Evaluation of Foam Stability in Decontamination Foam Stabilized by Silica Nanoparticles with Nonionic Surfactant

The decontamination process was needed to remove the radionuclide in nuclear facilities under decommissioning. Among the decontamination techniques, the decontamination foam strongly decreases the amount of chemicals and the secondary wastes and, has wide application in nuclear facilities. The purpose of the present study is to investigate the effects of surfactants, silica nanoparticles (NPs) concentration, and pH for foam stability and oxide dissolution. The foam stability in acid pH has an effect on the concentration of nonionic surfactant, however, in neutral pH does not have concentration effect. The addition of 3 and 5 wt% silica NPs improves the foam stability by a factor of 3 and 5 at pH 2, compared to the foam stabilized with 1 % EM 100 surfactant only, indicating that the increase of silica NPs increased the foam stability. The oxide dissolution was evaluated for the decontamination foam containing 1 M HNO3 using the corroded specimens. The results of an iron dissolution test showed that increased foam stability enhanced the iron dissolution owing to an increase in the contact time between the chemical reagents and the corroded surface.

A Reductive Dissolution Study of Magnetite

Magnetite dissolution tests using a hydrazine base solution were performed at a temperature range of 90 to 150 °C. The dissolution rate of magnetite increased with [N2H4], time, and temperature. The optimum solution pH in the experimental range was 3. The addition of copper ion to the hydrazine base solution greatly increased the magnetite dissolution rate. This was explained by the complex formation between N2H4 and Cu ions, and the reducing power of the hydrazine-Cu complex to the ferric ions of magnetite. The reductive decontamination solution can be applied below 100 °C by the addition of copper ions. The chemical decontamination of a Type 304 stainless steel specimen using a hydrazine base reductive decontamination solution was also performed. The contact dose rate was greatly decreased by the repetitive application of NP and the hydrazine base solution.Copyright