JPS61189500A - Oxidative decomposition treatment method for radioactive waste - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to a method for oxidative decomposition treatment of radioactive waste, and more particularly, it relates to a method for oxidizing and decomposing radioactive waste, and more specifically, it relates to a method for oxidizing and decomposing radioactive waste, and more particularly, it relates to a method for oxidative decomposition treatment of radioactive waste, and more particularly, it relates to a method for oxidative decomposition treatment of radioactive waste, and more particularly, it relates to a method for oxidative decomposition treatment of radioactive waste, and more specifically, it relates to a method for oxidative decomposition treatment of radioactive waste, and more particularly, it relates to a method for oxidative decomposition treatment of radioactive waste, and more particularly, it relates to a method for oxidative decomposition treatment of radioactive waste, and more specifically, it relates to a method for oxidative decomposition treatment of radioactive waste, and more specifically, used ion exchange resin, PVC resin, rubber, This invention relates to a chemical decomposition method for reducing the volume of organic waste such as filter sludge.

[Prior art and its problems]

Nuclear power facilities such as nuclear power plants generate a variety of organic solid wastes as they operate, but at present no treatment method or final treatment method has been established for them. These wastes are packed into drums and stored within nuclear power facilities, but the problem of land shortage is becoming more serious as the amount of waste increases year by year.

Therefore, there is an urgent need to develop these volume reduction technologies. As methods for this volume reduction, combustion methods (incineration methods), thermal decomposition methods, oxidative decomposition methods, and the like have been proposed, but none of them has been definitive.

The combustion method has the characteristic of high processing speed, but because it generates dust, rilles, etc., the off-gas system becomes too complicated, maintenance becomes complicated, or volatile radioactive compounds are generated. There are drawbacks such as.

Furthermore, although the pyrolysis method does not generate radioactive volatiles, it has the disadvantage that it produces a large amount of carbonaceous residue and, like the combustion method, the flow system is complicated.

Furthermore, the acid decomposition method is a method of oxidative decomposition using sulfuric acid and nitric acid at about 260°C, but it has the following drawbacks.

In other words, the oxidizing agent decomposes and generates gases such as So, NOx, etc., the reactor requires the use of expensive materials such as tantalum, and the solidification of decomposition products requires a large amount of waste. It is necessary to add an alkali, and as a result, a large amount of salt is produced, which reduces the effectiveness of the volume reduction treatment by half.

A method that improves these drawbacks, that is, an effective volume reduction treatment method that requires less demanding equipment materials than the acid decomposition method and generates less exhaust gas than the combustion method, is to process organic matter under pressure and heat. A method of oxidative decomposition using oxygen gas has been proposed in
rocess) applied to radioactive organic waste. It has become clear that this method has the same oxidative decomposition effect on radioactive organic waste as it does on sludge, but considering the special nature of radioactive waste, it is difficult to reduce its volume. Even more advanced decomposition performance is required.

From this point of view, a method has been proposed in which metal ions such as Cu t 4 are coexisting as an oxidation catalyst in the above process (Japanese Patent Application Laid-Open No. 146899/1982). A higher decomposition rate can be obtained compared to the method of No. 56796. However, even with this method, a completely satisfactory decomposition rate cannot be obtained, and therefore, there is currently a need for an oxidative decomposition treatment method with an even higher decomposition rate.

[Purpose of the invention]

The present invention has been made in view of the problems of the prior art, and provides a very high decomposition rate in the oxidative decomposition treatment of radioactive waste, and also meets the requirements for equipment materials that are not compatible with the acid decomposition method. The purpose of the present invention is to provide an oxidative decomposition treatment method that is not as severe as the incineration method in terms of the amount of exhaust gas generated and is easy to maintain.

(Summary of the Invention) The present invention provides a method for oxidizing and decomposing organic waste into carbon dioxide and water by injecting oxygen-containing gas under heat and pressure into an aqueous liquid containing radioactive organic waste. This is an oxidation treatment method for radioactive organic waste, which is characterized by decomposition in the coexistence of radioactive organic waste and metal ions.

In carrying out the oxidative decomposition treatment method of the present invention, first, an aqueous liquid such as a slurry containing radioactive organic waste is prepared. Used ion exchange resin and filter slurry
Materials such as pipes are generally in the form of a slurry and can be used as is, but materials such as rubber and cloth are cut into pieces of a size that will not clog pipes, and an appropriate amount of water is added to form a slurry. I/・There is a need → 11- Mr. M is sorry, but from the point of view of stirring, speed of oxidation reaction, etc.
It is preferably 0% by weight or less.

The aqueous liquid prepared as described above is then sent to an oxidation reactor equipped with stirring means. Oxidation occurs at temperatures above 150°C.
Preferably, the temperature is maintained at 200-350°C and the oxygen partial pressure is 5-100 kir/cA, preferably 10-50
It is injected at a pressure of kg/ci and is stirred for several tens of minutes to several hours. The oxygen-containing gas may be air, pure oxygen, oxygen-enriched air, etc. The total pressure within the reactor must be greater than the saturated vapor pressure at that temperature.

In the present invention, hydrogen peroxide and metal ions are allowed to coexist in the oxidation reaction tank to promote oxidative decomposition. Metal ions include Fe", Fe3", Cu", Cu", Ni"・, C
o", Ce2+, Mn"", Pd", etc. are used.

Generally, these are added in the form of their water-soluble salts, and are used singly or in combination of two or more. Hydrogen peroxide is present in the aqueous liquid in an amount of 0.001 to 1 mol, preferably 0.005 to 1 mol.
At a concentration of 0.1 molar, metal ions range from 0.00001 to 0
．． It may be present in a concentration of 1 molar, preferably 0.0001 to 0.05 molar.

Hydrogen peroxide and metal ion Me''' (
n is the valence) can be explained as follows.

Me” '″+Hzoz −* Me””)”+O
H−+−OH・・・・(1) or Me″′””+HzOz −Me”+HOz ・+
H”・・・(2) In these reactions, ・OH, which is a strong oxidizing agent, is generated by the reaction of (1) or (2) → (1), and strong oxidation occurs.Especially, ( 1) Formula using "Fe" is well known as Fenton's reagent. As described above, the reason why hydrogen peroxide and metal ions are allowed to coexist in the present invention is to perform strong oxidation by adding radicals (.011), which have a strong oxidizing effect, to the system.

Through the oxidative decomposition of the present invention, organic waste is mostly converted to carbon dioxide and water. The slurry containing undecomposed residue is then subjected to an evaporative concentration process. The evaporated water is condensed, recovered and reused, for example for the preparation of the aqueous slurry described above. The gases that do not condense are carbon dioxide and oxygen (nitrogen if air is used), and in some cases may contain trace amounts of radioactive materials.
It can be released into the atmosphere after being washed with water using a slurry soap bar.

The residue after evaporation concentration is separated into a supernatant liquid and a concentrated slurry by, for example, sedimentation separation, the former being used to prepare the above-mentioned aqueous slurry, and the latter being further concentrated and solidified. Processed according to.

According to the method of the present invention, radioactive organic waste can be oxidized and decomposed at a high decomposition rate, for example, as high as 97% in terms of total organic carbon (TOC) decomposition rate,
The amount of waste gas generated is small and maintenance is easy.
The advantage is that the demands on device materials are also low.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail with reference to Examples.

FIG. 1 shows a schematic diagram of the oxidative decomposition reactor used to evaluate the method according to the present invention. This device has a reaction tank l
There is a heating jacket 2 on the outside of the heating jacket 2, so that the heating is carried out from the outside. At this time, the temperature can be controlled by detecting the temperature with the thermocouple 3 and adjusting the voltage of the heating jacket with the temperature controller 4. The reaction tank 1 is configured to be supplied with oxygen gas A and nitrogen gas B at an appropriate ratio and pressurized with gas pressure. The pressure is read from the pressure gauge 5. The operating pressure (total pressure) shall exceed the saturated vapor pressure of water at a given temperature.

The oxidatively decomposed sample is made into a slurry, the top lid 6 is removed, and the sample is charged into the reaction tank 1. After this, the upper lid 6 is firmly attached, and oxidative decomposition is carried out at a predetermined temperature and pressure according to the above-described procedure. At this time, stirring is continued by the impeller 7.

Steam from the reaction tank 1 is condensed in a condenser 8, and uncondensed gas is released as exhaust gas C.

Example 1 A mixed ion exchange resin was subjected to oxidative decomposition using the oxidative decomposition reactor shown in FIG. Table 1 shows the conditions at this time.

Table 1 (Note) Conventional method 1: Follows the method described in JP-A No. 57-56796 Conventional method 2: Follows the method described in JP-A-58-146899 Under the conditions shown in Table 1, the temperature is Oxidative decomposition was performed by changing the

The results obtained are shown in FIG. The decomposition rate is the rate at which the total organic carbon (TOP) is turned into mineral, and is an index showing the effect of oxidative decomposition.

As is clear from Figure 2, HtO and catalysts (Cu and F
The decomposition of the present invention with the addition of e-ions is higher.

Similar high decomposition rates were obtained when Cu and Fe were used alone or in combination with other metal (Ni, Co, Mn, Ce, and Pd) ions for oxidative decomposition of the same sample.

Explosion 1 Using the apparatus shown in Figure 1, an oxidative decomposition experiment was conducted on pieces of vinyl chloride resin and rubber as examples of miscellaneous solid waste.

The conditions at this time and the obtained decomposition rates are summarized in Table 2.

Note that Conventional Methods 1 and 2 are similar to Example 1.

Table 2 clearly shows that the method of the invention gives a higher degradation rate than the conventional method. Similar results were obtained with other metal ions.

〔Effect of the invention〕

According to the present invention, when radioactive organic waste is decomposed by applying the Zimmerman process, highly efficient oxidative decomposition treatment has become possible by adding hydrogen peroxide and a metal ion catalyst.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an oxidative decomposition reactor for aliable waste. FIG. 2 is a graph showing the relationship between reaction temperature and decomposition rate. 1. Reaction tank, 2. Heating jacket, 3. Thermocouple, 4. Temperature controller, 5. Pressure gauge,
6. Upper lid, 7. Impeller, 8. Condenser, A. Oxygen gas, B. Nitrogen gas, C. Exhaust gas total: 10

Claims (1)

[Claims] 1) A method for oxidizing and decomposing organic waste into carbon dioxide and water by injecting an oxygen-containing gas under heat into an aqueous liquid containing radioactive organic waste, wherein hydrogen peroxide and metal A method for oxidative decomposition of radioactive organic waste, characterized by decomposition in the coexistence of ions. 2) The oxidative decomposition treatment method according to claim 1, wherein hydrogen peroxide is present in the aqueous liquid at a concentration of 0.001 to 1 mol. 3) An oxidative decomposition treatment method according to claim 1, characterized in that metal ions are present in a concentration of 0.00001 to 0.1 mol. 4) In the oxidative decomposition treatment method according to claim 1, the metal ion is Fe^2^+, Fe^3^+, C
u^+, Cu^2^+, Ni^2^+, Co^2^+,
An oxidative decomposition treatment method characterized by using one or more of Ce^2^+, Mn^2^+, and Pd^2^+.