KR100332981B1 - Simultaneously trapping method of volatile cesium and ruthenium compounds by using the mixture of fly ash and yttria - Google Patents

Abstract

PURPOSE: A method for collecting a simultaneously volatile cesium and ruthenium compound using a mixture of fly ash and yttria is provided to reduce a volume and a processing time of an exhaust processing apparatus by collecting simultaneously nuclear radiation materials such as cesium and ruthenium compound. CONSTITUTION: A thermal process for fly ash and yttria is performed under temperature of 1000 to 1200 degrees centigrade. The fly ash is mixed with yttria. The mixture of the fly ash and yttria is converted to a state of slip by using solution such as polyvinyl alcohol. The mixture is dipped into a sponge. A sintering process is performed under the temperature of 1150 to 1220 degrees centigrade in order to fabricate a ceramic foam filter. Volatile cesium and ruthenium compound are collected by using the ceramic foam filter.

Description

Simultaneously trapping method of volatile cesium and ruthenium compounds by using the mixture of fly ash and yttria}

An object of the present invention is to simultaneously collect radioactive cesium and ruthenium compounds using fly ash and yttria, which are by-products of coal-fired power plants.

The present invention relates to a technique for trapping cesium and ruthenium compounds, which are highly radioactive and toxic.

Cesium and ruthenium, which are radioactive materials, are generated during the volume reduction and solidification processes such as roasting of high-level radioactive wastes generated during the dry processing of nuclear or spent nuclear fuels or their wet reprocessing. Cesium leaks into cesium oxides that are radioactive under oxidizing conditions during the roasting, vitrification and dry treatment of spent fuel containing cesium. Ruthenium leaks into ruthenium oxides that are radioactive under oxidizing conditions during industrial catalysis, solidification of high-level waste containing ruthenium, and dry treatment of spent fuel. In addition, ruthenium is widely used as an oxidation catalyst due to its excellent reactivity, but it is known to exhibit chemically strong toxicity, and under oxidizing conditions, the melting point is oxidized to ruthenium tetraoxide, which is a sublimable substance of 25.4 ° C, and volatilized. When cesium and ruthenium, such semi-volatile materials, are present in the exhaust, they turn into aerosols upon cooling to produce deposits on the pipe walls of the exhaust treatment facility, resulting in partial blockage of pipes or high radiation fields resulting in performance of exhaust treatment equipment. And the safety of workers. Therefore, these volatile cesium and ruthenium should be collected, separated and stored as early as possible.

The methods for capturing volatile cesium and ruthenium are known as the physical cooling method using heat gradient pipe and the immobilization method to collect chemical and thermally stable materials. Development is required. In the case of cesium conventional immobilization method metakaolin _{(metakaoline) (Al 2 O 3} · 2SiO 2), bentonite _{(bentonite) (Al 2 O 3} · 4SiO 2 · 6H 2 O), fatigue fill light (pyrophyllite) (Al ₂ There is a technology of immobilizing cesium with cesium aluminosilicate, which has superior thermal stability than other cesium compounds by using O ₃ · 4 SiO ₂ · H ₂ O) as a cesium trapping material, but metakaolin (Al ₂ O ₃ 2SiO ₂ ), bentonite (Al ₂ O ₃ · 4SiO ₂ · 6H ₂ O), pyrophyllite (Al ₂ O ₃ · 4SiO ₂ · H ₂ O), etc., are expensive or require pretreatment, 1200-1400 ℃) is a situation in which there is a lot of problems in using the fixed cesium desorbed. Recently, the inventors have focused on the fact that coal ash having a Si / Al molar ratio of alumina (A1 ₂ O ₂ ) and silica (SiO ₂ ) of 2.1 is suitable for forming the most stable pollucite among cesium aluminosilicates. Cesium was reacted with alumina and silica in coal ash at high temperature to confirm that a thermally stable cesium aluminosilicate was formed ("Method for Capture of Radioactive Cesium Using Coal Ash", 1995-39590).

In addition, as a ruthenium immobilization material, carbonates such as calcium, strontium and barium or mixtures thereof, which are known to form a perovskite structure, are used as in the US patent 4092265. These are known to form mixed metal ruthenates which react with volatile ruthenium oxides to suppress the leakage of ruthenium oxides at 400 ° C. and 1000 ° C. or lower. Existing studies on the collection behavior of ruthenium oxide have been mainly carried out below 1000 ℃ to suppress the leakage of ruthenium oxide volatilized during the wet reprocessing and vitrification of high-level liquid waste. Recently, the inventors of the present invention conducted a study on the method of preventing ruthenium leakage using yttrium, sodium, lithium, potassium, rubidium oxide or compounds and mixtures thereof such that yttria reacts with volatile ruthenium oxide and thus yttrium ruthenate It forms a pyrochlore structure in the form of (Y ₂ Ru ₂ O ₇ ) and is very thermally stable up to 1400 ° C. The theoretical collection amount per gram of trapping material is 0.89g, which is higher than that of other trapping materials. It has been applied to confirm that it can be used as a trapping material ("How to remove ruthenium compound in industrial exhaust gas", 1997-l1957).

However, since the cesium and ruthenium collection method has to be carried out independently in an independent exhaust gas treatment unit process, the number of radioactive exhaust gas treatment unit processes in which cesium and ruthenium coexist is increased and the volume of the apparatus is inevitably increased. Therefore, the present invention can reduce the number of exhaust treatment unit processes by simultaneously collecting cesium and ruthenium contained in the exhaust, thereby simplifying the operation of the exhaust treatment and also reducing the volume of the exhaust treatment. The required space can be reduced and the amount of waste adsorbent generated can be reduced.

1 is a view of a coal ash and yttria composite ceramic foam filter sintered at 1200 ° C.

Fig. 2 shows the shape after capture of cesium and ruthenium at 1000 ° C. of coal ash and yttria ceramic foam filter.

Fig. 3 shows the results of X-ray diffraction analysis after capture of cesium and ruthenium at 1000 ° C of coal ash and yttria ceramic foam filter.

4 and 5 are schematic diagrams showing the number of pores per cm

6 is an electron microscope (SEM) photograph at 43 times the surface of a filter;

The method for preventing leakage of volatile cesium and ruthenium according to the present invention is first to prevent the formation of yttrium silicate ((Y ₂ Si ₂ O ₇ ) to react with yttria in SiO ₂ in coal ash. The SiO ₂ phase of the coal ash is heat-treated at 0.degree. C. to 1200.degree. C. to change from quartz to cristobalite. The overall configuration of the present invention is as follows.

Coal ash and yttria mixture heat-treated in the range of 1000-1200 ℃ are made of polyvinyl alcohol, etc., and then slip-impregnated and sintered at a temperature range of 1150 -1220 ℃, and the number of pores per cm is 15-40 (pore size 250-600㎛) ceramic foam filter (ceramic foam filter) is manufactured and passed through the volatile cesium and ruthenium compounds generated in the cesium and ruthenium containing process to collect them at the same time to prevent leakage and 1000-1200 Coal ash and yttria mixture heat-treated in the range of ℃ is made slip with a solution such as polyvinyl alcohol, and then supported on a carrier such as ceramic, metal, quartz, glass, and sintered at a temperature range of 1150 ~ 1220 ℃ to prepare a carrier. Passage of volatile cesium and ruthenium compounds from the cesium and ruthenium-containing process through the carrier to collect them at the same time to prevent leakage and in the 1000-1200 ℃ range The treated coal ash and yttria mixture were slipped with a solution such as polyvinyl alcohol, processed into beads and cylinders, and then packed into a 5-20 mesh size sintered at a temperature range of 1150-1220 ° C. Pass the volatile cesium and ruthenium compounds generated in the process of containing cerium and ruthenium through the adsorption column to simultaneously collect them to prevent leakage and simultaneously collect the volatile cesium and ruthenium compounds in the above three methods in the temperature range of 500-1200 ℃. It is comprised as a method of advancing.

Example 1

As an example of a manufacturing method in which a mixture of heat-treated coal ash and yttria is formed into a foam form, first, a binder is mixed in a weight ratio of 1% PVA and 1: 1 in a mixture of coal ash and yttria. The slip mixture was impregnated into a polyurethane sponge, then overnight at 90 ° C., and then sintered at 1200 ° C. for 3 hours. The manufactured coal ash and yttria overnight ceramic foam filter were manufactured with a porous structure having a number of pores per cm (pore size: about 280 μm) (FIG. 1).

Example 2

It is an example of a production method in which a mixture of heat-treated coal ash and yttria is supported by a ceramic carrier and molded. First, 0.5% of PVA is mixed at a weight ratio of 1: 1 with a mixture of coal ash and yttria. The honeycomb monolith was used as a carrier in this slipped mixture, followed by dipping, overnight drying at 90 ° C., and 5 hours of sintering at 1200 ° C. for honeycomb monolith. The filter of was prepared.

Example 3

The mixture of heat-treated coal ash and yttria is thoroughly mixed, and then 5% of PVA is mixed in a 4: 1 weight ratio. The mixture was processed into a 15-mesh bead, an overnight drying at 90 ° C., and a sintering process at 1200 ° C. for 1 hour to prepare a bead-shaped filter.

Example 4

As an example of volatile cesium and ruthenium collection method, a mixture of cesium nitrate (CsNO ₃ ) and ruthenium metal (Ru) as a source of volatile cesium and ruthenium is mixed in a heat-treated coal ash and yttria mixture, which is then heated in an air atmosphere in the range of 700 ° C to 1250 ° C. X-ray diffraction analysis of the material obtained by heating to room temperature after heating for 1 hour showed the formation of pollucite (CsAlSi ₂ O ₆ ) and yttrium ruthenate (Y ₂ Ru ₂ O ₇ ) to simultaneously form cesium and ruthenium. It was confirmed that it was collected.

Example 5

As an example of volatile cesium and ruthenium collection method, a volatile cesium and ruthenium compound was passed through a ceramic foam filter prepared from a heat-treated coal ash and yttria mixture at 1000 ° C. (FIG. 2) pullulite (CsAlSi ₂ O ₆ ) and yttrium lute. Nate (Y ₂ Ru ₂ O ₇ ) was formed to confirm that the cesium and ruthenium is simultaneously collected (Fig. 3).

Example 6

Adsorption column containing volatile cesium and ruthenium oxides was maintained in the air atmosphere while the adsorption tower filled with a filter processed into a bead, cylinder, etc. of 8-16 mesh size using heat-treated coal ash and yttria. As a result of X-ray diffraction analysis of the filter obtained by passing through, it was confirmed that cesium and ruthenium were simultaneously collected by forming pullulite (CsAlSi ₂ O ₆ ) and yttrium ruthenate (Y ₂ Ru ₂ O ₇ ).

The present invention is not limited to the above embodiments and other applications will be possible by those skilled in the art. As described above, the present invention can be used as an immobilization material of gaseous cesium and ruthenium having a high radiological risk by using heat-treated coal ash and yttria, and it is possible to simultaneously collect cesium and ruthenium, thereby reducing the exhaust gas treatment unit process number. Not only can it be reduced and simple to operate, but also the volume of the device can be reduced and the amount of waste adsorbent can be reduced.

Claims (4)

Coal ash and yttria mixture heat-treated in the range of 1000 ~ 1200 ℃ are made of slip such as polyvinyl alcohol, and then impregnated in sponge and sintered at 1150-1220 ℃ temperature range. The number of pores per 1cm is 15 ~ 40 (pore size) 250-600㎛) ceramic foam filter (ceramic foam filter) is manufactured, and the volatile cesium and ruthenium compounds generated in the cesium and ruthenium containing process is passed through this filter to collect them simultaneously to prevent leakage Simultaneous Collection of Volatile Cesium and Ruthenium Compounds Using Yttria Mixture. Coal ash and yttria mixture heat-treated in the range of 1000 ~ 1200 ℃ made of polyvinyl alcohol, such as slip and then supported on a carrier such as ceramic, metal, quartz, glass and sintered at a temperature range of 1150 ~ 1220 ℃ to prepare a carrier And then collecting volatile cesium and ruthenium compounds using a coal ash and yttria mixture, which pass through the volatile cesium and ruthenium compounds generated in the cesium and ruthenium-containing process to prevent them from leaking. . Coal ash and yttria mixtures heat-treated in the range of 1000 ~ 1200 ℃ are made of polyvinyl alcohol, etc., and then slip-shaped and processed into beads or cylinders, and then sintered at a temperature range of 1150 ~ 1220 ℃. After filling the adsorption column, the adsorption column passes through the volatile cesium and ruthenium compounds generated in the cesium and ruthenium-containing process, and simultaneously collects them to prevent leakage. How to collect. The method according to any one of claims 1 to 3, Simultaneous collection of volatile cesium and ruthenium compounds using a coal ash and yttria mixture, characterized in that the simultaneous collection process of volatile cesium and ruthenium compounds in the temperature range of 500 ~ 1200 ℃.