Gye-Nam Kim

WASHING-ELECTROKINETIC DECONTAMINATION FOR CONCRETE CONTAMINATED WITH COBALT AND CESIUM

A great volume of radioactive concrete is generated during the operation and the decommissioning of nuclear facilities. The washing-electrokinetic technology in this study, which combined an electrokinetic method and a washing method, was developed to decontaminate the concrete generated in nuclear facilities. The results of only an electrokinetic decontamination for the concrete showed that cobalt was removed to below 1% from the concrete due to its high pH. Therefore, the washingelectrokinetic technology was applied to lower the pH of the concrete. Namely, when the concrete was washed with 3 M of hydrochloric acid for 4 hours (0.17 day), the CaCO₃ in the concrete was decomposed into CO₂ and the pH of the concrete was reduced to 3.7, and the cobalt and cesium in the concrete were removed by up to 85.0% and 76.3% respectively. Next, when the washed concrete was decontaminated by the electrokinetic method with 0.01M of acetic acid in the 1L electrokinetic equipment for 14.83 days, the cobalt and the cesium in the concrete were both removed by up to 99.7% and 99.6% respectively. The removal efficiencies of the cobalt and cesium by 0.01M of acetic acid were increased more than those by 0.05M of acetic acid due to the increase of the concrete zeta potential. The total effluent volume generated from the washing-electrokinetic decontamination was 11.55L (7.2ml/g).

Vertical Electrokinetic-Flushing Remediation

Abstract An optimum reagent was selected to decontaminate the radioactive soil near nuclear facilities by using the developed vertical electrokinetic-flushing equipment, and the optimum remediation conditions were established to obtain a higher remediation efficiency and a minimum waste-solution volume. Namely, the acetic acid was selected as an optimum reagent due to its higher remediation efficiency. The average removal efficiency by a vertical electrokinetic-flushing remediation was 4.6% more than that by a vertical electrokinetic remediation. The optimum remediation conditions were suggested to be when the acetic concentration is 0.01 M, the injection rate of the reagent is 2.4 ml/g and the remediation period is 20 days for the vertical electrokinetic-flushing equipment of a 8.3 L volume. In these conditions, the removal efficiencies of Co2+ and Cs+ were 98.3% and 88.8%.

ESTIMATION OF THE BEHAVIORS OF SELENIUM IN THE NEAR FIELD OF REPOSITORY

The sorption of selenium ions onto iron and iron compounds as a disposal container material and its corrosion products, and onto bentonite as a buffer material, was studied to understand the behaviors of selenium in a waste repository. Selenite was sorbed onto commercial magnetite very well in solutions at around pH 9, but silicate hindered their sorption onto both magnetite and ferrite. Unlike commercial magnetite and ferrite, flesh synthesized magnetite, green rust and iron greatly decreased selenium concentration even in a silicate solution. These results might be due to the formation of precipitates, or the sorption of selenide or selenite onto an iron surface at below Eh= -0.2 V. Red-colored Se(cr) was observed on the surface of a reaction bottle containing iron powder added into a selenite solution. Silicate influences on the sorption onto magnetite and iron for selenide are the same as those for selenite. Even though bentonite adsorbed a slight amount of selenite, the sorption cannot be ignored in the waste repository since a very large quantity of bentonite is used.

A Study of Methods to Reduce Groundwater Contamination Around the Kimpo Landfill in Korea

Four different methods were studied to reduce the groundwater contamination around the Kimpo landfill in Korea by leakage of a leachate. The hydraulic parameters were measured for this study and then the groundwater flow and contaminant transport systems around the Kimpo landfill were simulated with MODFLOW and MT3D models. Both the method of establishing 5 sets of Radial Collector Well Laterals (RCWLs) within the landfill and a method utilizing the wells for dewatering condensed water brought about a 70% leachate elimination efficiency. Their construction costs were cheap, and the maximum concentrations of chloride and phenol in the leachate effluent were high. Meanwhile, a method establishing an interception wall to the 2nd layer at the circumference of the landfill and 22 sets of RCWLs within it brought about a 92% leachate elimination efficiency. Its construction cost was expensive, and the maximum concentrations of chloride and phenol in the leachate effluent were low. A method of establishing an interception wall to the 3rd layer and 40 sets of RCWLs brought about a 97% leachate elimination efficiency. Its construction cost was the most expensive, and the maximum concentrations of chloride and phenol were low. Conclusively, a method of establishing 22 sets of RCWLs was evaluated as the most stable and economical option to reduce groundwater contamination concentration below drinking water standard.

ABRASIVE BLASTING TECHNOLOGY FOR DECONTAMINATION OF THE INNER SURFACE OF STEAM GENERATOR TUBES

The inner surfaces of bundled inconel tubes from steam generators in South Korean nuclear power plants are contaminated with cobalt and abrasive blasting equipment has been developed to efficiently remove the cobalt. The principal parameters related to the efficient removal using this equipment are the type of abrasive, the distance from the nozzle, and the blasting time. Preliminary tests were performed using oxidized inconel samples which enabled the simulation of cobalt removal from the radioactive inconel samples. The oxygen in the oxidized samples and the cobalt in the radioactive inconel were removed more effectively using the blasting distance, blasting time, and a silicon carbide abrasive. Using the developed abrasive blasting equipment, the optimum decontamination conditions for radioactive inconel samples were blasting for more than 6 minutes using silicon carbides under 5 atmospheric pressures.

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

Development of practical decontamination process for the removal of uranium from gravel

ABSTRACT In this study, a practical decontamination process was developed to remove uranium from gravel using a soil washing method. The effects of critical parameters including particle size, H2SO4 concentration, temperature, and reaction time on uranium removal were evaluated. The optimal condition for two-stage washing of gravel was found to be particle size of 1–2 mm, 1.0 M H2SO4, temperature of 60°C, and reaction time of 3 h, which satisfied the required uranium concentration for self-disposal. Furthermore, most of the extracted uranium was removed from the waste solution by precipitation, implying that the treated solution can be reused as washing solution. These results clearly demonstrated that our proposed process can be indeed a practical technique to decontaminate uranium-polluted gravel.

AN ANALYSIS OF THE EFFECT OF HYDRAULIC PARAMETERS ON RADIONUCLIDE MIGRATION IN AN UNSATURATED ZONE

A One-Dimensional Water Flow and Contaminant Transport in Unsaturated Zone (FTUNS) code has been developed in order to interpret radionuclide migration in an unsaturated zone. The pore-size distribution index (n) and the inverse of the air-entry value (α) for an unsaturated zone were measured by KS M ISO 11275 method. The hydraulic parameters of the unsaturated soil are investigated by using soil from around a nuclear facility in Korea. The effect of hydraulic parameters on radionuclide migration in an unsaturated zone has been analyzed. The higher the value of the n-factor, the more the cobalt concentration was condensed. The larger the value of α-factor, the faster the migration of cobalt was and the more aggregative the cobalt concentration was. Also, it was found that an effect on contaminant migration due to the pore-size distribution index (n) and the inverse of the air-entry value (α) was minute. Meanwhile, migrations of cobalt and cesium are in inverse proportion to the Freundich isotherm coefficient. That is to say, the migration velocity of cobalt was about 8.35 times that of cesium. It was conclusively demonstrated that the Freundich isotherm coefficient was the most important factor for contaminant migration.

Metal Surface Decontamination by the PFC Solution

PFC (perfluorocarbon) spray decontamination equipment was fabricated and its decontamination behavior was investigated. Europium oxide powder was mixed with the isotope solution which contains Co-60 and Cs-137. The different shape of metal specimens artificially contaminated with europium oxide powder was used as the surrogate contaminants. Before and after the application of the PFC spray decontamination method, the radioactivity of the metal specimens was measured by MCA. The decontamination factors were in the range from 9.6 to 62.4. The spent PFC solution was recycled by distillation. Before and after distillation, the turbidity of PFC solution was also measured. From the test results, it was found that more than 98% of the PFC solution could be recycled by a distillation.Copyright

TRIGA Soil Decontamination by Electrokinetic Method

The experiment for removing cesium and cobalt from the contaminated soil around the TRIGA reactor in Korea using the electrokinetic method were conducted. To increase removal efficiency by the electrokinetic method, a device to restrain the pH increase in the soil column was suggested. An acetate buffer solution (CH3 COONa+CH3 COOH) was injected into the soil column and acetic acid periodically was injected into the cathode reservoir to restrain any pH increase. Many 137 Cs and 60 Co were transferred by electromigration rather than electroomosis during the intial remediation period, and no precipitate was formed in the soil column. 25% of cesium radioactivity in the soil column was removed after 10 days, while 94% of cobalt radioactivity was removed. Furthermore, the remaining radioactive concentrations predicted by the developed numerical model were similar to those obtained by experiment.Copyright