KR20000019838A - Method for improving performance of radioactive waste solid material - Google Patents

Abstract

PURPOSE: A method for improving a performance of a solidified radioactive waste is provided to reduce an initial hardening time by introducing an ultra threshold dioxide carbon(CO2) when hardening a radioactive waste matter with a cement. CONSTITUTION: In a method, a solidified radioactive waste of a low performance is enclosed again with a cement. A dioxide carbon is applied to a product in a reactive furnace under the condition of a predetermined temperature and a predetermined pressure. When the temperature and the pressure are forced at the product, the dioxide carbon has an ultra threshold state. A flow path is secured by the use of a vent pipe in order to shorten a reactive time of the ultra threshold dioxide carbon and for a uniform contact.

Description

Performance Improvement Method of Low Performance Radioactive Waste Solids Using Supercritical Carbon Dioxide.

The present invention is a method for improving the performance disposal capacity of low-performance radioactive waste solids among the medium and low level radioactive waste solids generated in a nuclear power plant to repackage using supercritical carbon dioxide and at the same time obtain excellent physical properties required for disposal. .

The present invention proposes a method of repackaging for improving the disposal stability of low-performance radioactive waste solids which do not have sufficient mechanical strength due to cracking or hardening during cement solidification among the medium and low level radioactive waste solids generated in nuclear power plants. The present invention relates to a device for manufacturing a product having superior leaching property that prevents leaching of radioactive material and mechanical strength superior to conventional cement by solidifying cement using supercritical carbon dioxide during repackaging.

Radioactive waste generated from nuclear power plants, etc., should not be leaked or dispersed during short-term control periods such as temporary storage and transportation to contaminate human life and the natural environment with radioactive materials. Therefore, wastes generated from nuclear power plants, etc., must be made and packaged in a stable form. In addition, even if the level of radioactive waste is generally low or low level packaging, it should be managed at the disposal site for 200 to 300 years. During this period, it prevents the leaching of radioactive material and prevents the migration of nuclides to the living area around the disposal site. It must be secured.

Methods of solidifying radioactive waste include cement solidification, asphalt solidification and vitrification. Among them, cement is the first material used in the nuclear industry for the solidification medium of various medium and low-level radioactive waste and packaging containers of solid wastes. Doing. Portland cement is mainly used as cement, but the mechanism of hardening reaction between cement and waste is not clear due to the complexity of water / cement chemical reaction and sensitivity to waste physicochemical composition.

Water-soluble waste forms a stable form because it chemically reacts with water, but it is not good if it contains a lot of substances that hinder the hardening.In particular, waste ion exchange resins swell when contacted with water. It is hard to infiltrate waste resin. Leachability varies greatly depending on the type and content of the waste, the type of cement, and the additives, especially the nuclides contained. Leaching rates of nuclides with high solubility of hydroxides such as cesium tend to be relatively high. In the case of boric acid concentrate, the curing is considerably delayed and in many cases the mechanical strength to be obtained as a solid is not reached.

In solidification of radioactive waste, swelling cracks are fatal to stability because they provide an outflow path for radionuclides. In addition, when the solidification contains a large amount of water due to the delay of the initial curing, the radionuclide transfer rate increases, which is not good for disposal stability. Due to the reaction between the cement and the mixture, the hardening process is not performed properly, and low-performance radioactive waste solidification drums often fail to secure the required stability in terms of disposal of radioactive waste.

The object of the present invention is to introduce supercritical carbon dioxide (CO ₂ ) in repackaging and solidifying low-performance radioactive waste with cement in order to compensate for the above-mentioned drawbacks, to shorten the initial curing time and to secure radioactive waste disposal stability by having excellent physical properties. It's there.

Carbon dioxide is present in the solid state at −78.5 ° C., 1 atm (14.696 psi), as a gas at 20 ° C., 1 atm, and in the liquid state at 50 atm (734.8 psi) and 20 ° C.

At 72 atm (1,058 psi) and above 31 ° C, it becomes a supercritical fluid, which continuously changes in density without condensation. Because it is fluid like gas but has the same density as liquid, it has the property of transporting the melt while simultaneously penetrating the solid material. The cement solidification process using supercritical carbon dioxide begins with the compression of carbon dioxide gas. After the cement repacking form is placed in the reaction chamber, the carbon dioxide gas is compressed until it reaches a supercritical state, heated to an appropriate temperature, and maintained for a predetermined time to accelerate the curing by removing water in the cement.

1 is a view showing the configuration of a low-performance radioactive waste repackaging apparatus according to the present invention.

Figure 2 is a view showing the structure of the low-performance radioactive waste repacking formwork.

3 is a three-dimensional view of the repackaging reaction chamber using supercritical carbon dioxide.

※ Explanation of number about main part of drawing

10: carbon dioxide feeder, 20: gas booster, 30: cooler

40: metering pump, 50: reaction chamber

60: Back Pressure Regulator

70: collecting device, 80: heating device

90: breathable pipe, 100: radioactive waste solidification drum

110: radioactive waste solidification drum in repackaging formwork

120: cement dough, 130: repacking formwork cement pipe

140: repackaging formwork, 150: reaction chamber

160: switchgear, 170: inlet pipe, 180: outlet pipe

The present invention uses carbon dioxide as the supercritical fluid. Supercritical state in carbon dioxide refers to a fluid state that has both liquid and gas characteristics at temperatures and pressures above the critical point (73.8 bar, 31.1 ° C). At this time, the fluid has the advantages of gas and liquid at the same time having a gas permeability and a high density of the liquid. When carbon dioxide enters the supercritical state, there is little surface tension. Therefore, it can penetrate into narrow, long pores, gaps, etc., which cannot be penetrated by liquids, and has a high density that cannot be obtained as a gas, so that the solubility of a specific substance is very high. Since it has the advantages of gas and liquid at the same time can be used as an excellent solvent that can accelerate the curing by removing the water from the cement dough. Complete carbonation of large structures takes centuries in the atmosphere. Cement hardens as moisture is discharged through the micropores, but slowly hardens because the micropores are blocked by carbon dioxide at the contact surface with the atmosphere. However, the use of supercritical carbon dioxide promotes hardening with good penetration and dissolving power. In the state of high temperature and high pressure, carbon dioxide first becomes a liquid state and then into a supercritical state. Supercritical carbon dioxide will first diffuse into the gas phase, then fill the micropores, dissolve and transport the material. In this process, supercritical carbon dioxide will grab water molecules and push them out of the cement to promote hardening and, consequently, to fill the micropores created by the water molecules, thereby almost eliminating permeability.

Carbon dioxide used in the present invention is most widely used as a supercritical fluid. The main reason is that the supercritical condition is near room temperature, so it is easy to handle and has high solubility in organic matter. The problem is that the pressure for maintaining the supercritical is more than 73.8 bar, but due to the development of current high pressure technology, high pressure equipment that maintains the pressure below 150 bar can be easily obtained with a little economic burden. In addition, carbon dioxide is nontoxic and non-flammable, and the consumption of carbon dioxide has an environmentally friendly advantage to prevent the effect of global warming.

A schematic of the device is shown in FIG. 1. Carbon dioxide is designed to enter two pressurization devices. Gas booster 20 capable of rapidly pressurizing carbon dioxide and metering pump 40 capable of precise pressurization and flow rate control. The cooler 30 before passing through the metering pump makes the carbon dioxide liquid and directs it to the metering pump. It is sent to the carbon dioxide reaction chamber (50) to increase the pressure by continuous pumping to reach the supercritical. The supercritical carbon dioxide is fitted with a breathable pipe 90 in the dodok formwork 140 to evenly act on the cement dough in the repackage formwork to form a flow path of supercritical carbon dioxide. Through this cement pipe, supercritical carbon dioxide contacts the resurfaced cement dough evenly and shortens the reaction time.

Additionally, a heating device 80 is attached to the side of the reaction chamber to control the temperature in the heating chamber. According to the size of the cement product, the mold is put into the reaction chamber for a predetermined time to cure the cement, and the carbon dioxide goes to the collecting device 70 through the back pressure stabilizer 60. Carbon dioxide can then be recovered and reused. In the present invention, when the carbon dioxide is used to promote the hardening of the cement, the pressure applied to the carbon dioxide is 73.8 bar to 180 bar and the temperature is 0 ° C. or higher and 70 ° C. or lower.

In order to improve the disposal capacity of low-performance radioactive wastes produced at nuclear power plants, the low-performance radioactive waste solidification drum repackaging body is manufactured by using supercritical carbon dioxide to secure radioactive waste disposal stability and mechanical strength required as radioactive waste solidification body. It improves performance such as leaching property.

Claims (3)

In the repackaging solidification process using cement as a method for improving the performance of low-performance radioactive waste generated in nuclear power plants, And applying carbon dioxide to the product in the reactor at a predetermined temperature and pressure. 2. The method of claim 1, wherein the application of temperature and pressure is such that the carbon dioxide is in a supercritical state. A method of securing a flow path using a breathable pipe on the wall for short reaction time and even contact of supercritical carbon dioxide in repackaging low-performance radioactive waste.