JPS60168100A - Method of treating radioactive waste resin - 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] [Field of Application of the Invention] The present invention relates to a method for processing waste resin (used radioactive ion exchange resin) generated from nuclear power plants, etc. The present invention relates to a method of reducing the amount of resin and processing it into a stable inorganic compound by maintaining the temperature inside the reaction vessel at a low temperature and improving the decomposition efficiency of waste resin.

[Background of the invention]

BACKGROUND OF THE INVENTION As nuclear power plants operate, waste fluids containing various radioactive substances are generated, and these waste fluids are often treated using ion exchange resins. The used radioactive waste resin (hereinafter referred to as waste resin) generated at this time is processed by nuclear power! 1. : It is considered to be an operational issue. For example, in boiling water nuclear power plants,
A considerable portion of the stock is occupied by waste resin.

Conventionally, this waste resin is mixed with a 1v/1-forming agent such as cement or asphalt, and converted into 1Ai in a drum can.
It is stored on-site. However, the amount of radioactive waste is increasing year by year, and it is difficult to preserve it.
Securing a single location and lack of security during storage are major issues. Furthermore, since anti-resin is an organic substance, it has the potential to decompose and rot if stored for a long period of time. For this reason, when assimilating waste resin, great attention has been paid to reducing its volume as much as possible (volume reduction) and converting it into a stable inorganic substance (mineralization).

Volume reduction and mineralization treatment methods for used ion-exchange fat control can be roughly divided into wet methods, typified by acid decomposition, and dry methods, typified by fluidized bed methods.

Here, a general waste resin decomposition system is shown in FIG. 1 using thermal decomposition as an example. The resin stored in the waste resin storage tank 1 is thermally decomposed in the decomposer 2, and the residue 5 is transferred to the solidification container 7 and solidified.
Radioactive secondary waste 4 and residue 5 have been solidified.

This 7-stem process uses a dry method, but the process is almost the same for the slag method.

Among the processing methods, the HEDL method (1-Janfor
dEngineer+ng Development
Laboratory method) and acid decomposition method (wet method) have the problem of corrosion of the container due to acid, but as shown in the publication, if waste resin is used in a dry method using a fluidized bed,
This problem is resolved.

However, when the dry method is used, there are the following problems.

(1) The scattering of residue and radioactive materials is only 1 large. In other words, in order to disperse and burn waste resin under vIL axis gas,
Residual residue and radioactive materials are entrained and scattered in the exhaust gas.

For this reason, the load on filters and the like for exhaust gas treatment increases.

(2) Since the combustion is performed at a temperature of 600 to 900C, the reaction vessel deteriorates as the 7411 is used for one year.

These problems occur because the temperature inside the reaction vessel is not maintained at a low temperature, and the waste AM llfτ
This is due to the heat generated during combustion.

In addition, in the conventional dry method, waste 4Ilt, which can be decomposed at low temperatures, is
The amount of fat + N is extremely low, and the processing capacity (processing efficiency) is poor.

[Purpose of the present invention] The purpose of the present invention is to suppress the deterioration of the reaction vessel at high temperatures by decomposing the radioactive resin at a low temperature, and furthermore, to suppress the deterioration of the reaction vessel at high temperatures, and also to prevent the decomposition of the radioactive resin from occurring during the decomposition. An object of the present invention is to provide a waste resin processing method that prevents the scattering of radioactive nuclear particles, reduces the load on exhaust gas processing filters and alkaline spools, and improves the processing capacity of waste resin. .

[The shield of invention, the main point]

The conventional feature of the present invention is that in a method for decomposing spent radioactive ion exchange resin (waste resin) generated in an atomic couplant by thermal decomposition, after separating the cracked gas generated in an inert atmosphere, , is a method for treating Pih 4D, I fat, in which this waste resin is thermally decomposed in an oxidizing atmosphere, and at the same time, the decomposition residue is separated by adding an endothermic agent.

Another feature of the present invention is that in the method for decomposing the waste 411.1 fat, the decomposition residue is separated by adding a substance that vaporizes below the decomposition temperature of the resin under the pressure inside the reaction vessel. This is a method of processing resin.

[Embodiments of the invention]

The basic principle of the present invention will be explained below.

Ion exchange resins generally have a base material of a copolymer of styrene and divinylbenzene + D, V, B), and add ion exchange groups to this, in the case of 4 cation exchangers and 1 resin, sulfonic acid groups, and anion exchange groups. In the case of an ion exchange resin, it is an aromatic organic polymer compound having a structure in which a quaternary ammonium group is bonded.The decomposition mechanism of such an ion exchange resin is shown by a reaction formula.

Cation exchange resin and anion exchange J+64 in this formula
The molecular formula of 1't.1 fat was determined by elemental analysis and is different from the generally known molecular formula.

The decomposition process of the Hatake molecular base in this formula is an oxidation reaction mainly using oxygen and an exothermic reaction.
Up! There are many reasons for 1-. Meanwhile, the temperature inside the reaction vessel was set to 420. Experiments have been attempted to prevent the scattering of volatile radionuclides such as +37C3 by keeping the temperature below U, and it has been shown that the scattering of radioactive roots Φ can be suppressed by 4j(f
,It has been certified.

Therefore, by maintaining the temperature inside the reaction vessel at 420 U or less, it is possible to prevent radioactive nuclear particles from scattering, and the load on the exhaust gas treatment filter can be significantly reduced.

1. Since the temperature of the reactor can be maintained at a relatively low temperature of 420C, it not only becomes easier to select the material for the reaction vessel, but also prevents deterioration of the vessel due to long-term use.

Next, embodiments of the present invention will be described in detail with reference to the drawings.

The ion exchange resin includes a cation exchange resin that adsorbs cation elements and an anion exchange phase 1 that adsorbs anion elements.
There are two types of yuzu: fat and yuzu.

It has a copolymer gold polymer base with a crosslinked tl structure in which a sulfonic acid group (S(hH), which is an ion exchange group) is bonded, and has two three-dimensional structures, and has the following R structure. The molecular formula is I C10HlllOs S
) It is hailed by n.

On the other hand, anion exchange resins have quaternary ammonium groups, which are ion exchange groups, on the same polymer base as cation exchange resins.
It combines N& (JH) and has the following structural formula. Also, the molecular formula is I C211H26O
N) It is hailed by n.

Since the polymer base in the waste resin with such a molecular structure is composed of carbon and hydrogen, the ion exchange group is composed of sulfur or nitrogen. , 5 (generates and decomposes gases such as Jx and NOx. The decomposition region of the polymer substrate during this phase separation reaction is
This is an oxidation reaction that generates heat, causing an increase in the temperature inside the reaction vessel. The exotherm during this reaction is 16,10'
It is known that it is about kca+,/kg. In order to suppress the heat generation of this resin, there are two main ways of thinking:

(1) This heat of reaction is removed in an iroraka form.

(2) By delaying the reaction itself, rapid generation of reaction heat is suppressed.

Based on the concept of (2), the heat generation suppression method can easily slow down the reaction by reducing the number of air passages that supply the waste resin, and by lowering the oxygen concentration to reduce the white swell. be.

However, if this approach is selected, the amount of resin that can be decomposed in a certain period of time will be reduced as a result, so it cannot be said to be a percentage measure. Therefore, the inventors chose the idea of (]) and devised the following method as a specific method thereof.

(1) When decomposing waste resin, heat generation can be suppressed by adding an endothermic agent.

Based on the above results, the inventors found that in order to reduce the temperature inside the reactor during the decomposition process of waste resin, it is necessary to suppress the heat generated during the decomposition reaction, which is the main cause of temperature differences. I thought that if it was removed in some way, it would be a waste, so I pressed the heat of the waste resin.
A basic study was conducted regarding various properties at the time. Below, the experimental results for 1st leg are shown.

FIG. 2 shows the thermal decomposition characteristics of waste resin in an air atmosphere measured using a differential thermal balance. However, there is no evidence of a decrease in the positive phase due to the # release of water that occurs between 70 and 1 ioc. The solid line shows the thermal decomposition characteristics of the narrow ion exchange resin, and the dashed line curves that of the cation exchange resin. According to FIG. 2, in the anion exchange resin, the quaternary ammonium group, which is the ion exchange group to be separated, decomposes at 1:30 to 190C, and the polymer substrate decomposes at 350 to 420C. Regarding the decomposition of the polymer base, at 350-400C, the linear part is 410-500C.
The benzene di-part decomposes with C. Further, in the case of a cation exchange resin, after the sulfonic acid group, which is an ion exchange group, is decomposed at 200 to 300 C, the polymer base is decomposed in the same way as an anion exchange resin. These results are summarized in Table 1.

Table 1 Next, radioactive substances and decomposition residue when waste resin is thermally decomposed
The scattering behavior of the gas into the exhaust gas was investigated.

FIG. 3 is an example of changes in the scattering rate of radioactive substances when the thermal decomposition temperature is changed. In this figure, C and P are 11. %
The food products, F and P, are fission products. 6 shown by solid line
0 Co has a scattering rate of less than 1α-3 coefficient (detection limit) in all temperature ranges, 137CB shown by the broken line has a scattering rate of 10-3 or less at 4700C or less, and 0 at 470C or less.
．． It became 2L1y. In addition, the scattering rate of the residue is 60Co,
137cB and all temperatures 1) 10-3% within the range
The reason why 1370s, which was below 1370s, scatters at temperatures above 470C is that 187C adsorbed on the ion exchange group is oxidized by oxygen in the air and this occurs spontaneously.

To confirm this, we investigated the scattering rate of other radioactive substances, and as a result, as shown in Table 2, we confirmed that scattering begins above the melting point of each oxide.

The results shown in Table 2 and above show that if the waste resin is thermally decomposed at a temperature below 420C, the scattering of radioactive substances and decomposition residues into the exhaust gas can be suppressed. However, since the decomposition temperature of the benzene moiety in the Hatake molecular base is as high as 410-500C,
Radiation scattering cannot be suppressed. Therefore, prior to the present invention, the inventors succeeded in reducing the decomposition temperature to 300C or less by adding a catalyst to waste resin.

The following describes the thermal decomposition of cation exchange resin for this method.
This will be briefly explained as an example. The inventors selected iron as a catalyst and took advantage of the chemical properties of waste resin to adsorb and disperse iron as a cation into the waste resin, thereby lowering the thermal decomposition temperature of the resin. The weight was successfully reduced to 40t. The thermal decomposition characteristics at this time are shown by the solid line in FIG. Moreover, the broken line is the result when no catalyst was added.

By using this method, it has become possible to start the decomposition of waste resin at a temperature that does not cause scattering of radioactive materials, but in order to shorten the decomposition time of waste resin, the amount of air supplied must be If the temperature is increased, a rapid decomposition reaction occurs locally, and the reaction heat generated at that time causes the temperature inside the reaction vessel to run out of control. Figures 5 and 6 show the results of examining the temperature distribution inside the reaction vessel when waste resin adsorbed with iron as a catalyst was thermally decomposed by increasing the amount of air #L to a flow rate that caused temperature runaway. explain. FIG. 5 shows the experimental apparatus. Approximately 150 g of waste resin 9 on which iron has been adsorbed as a catalyst is filled into a stainless steel reaction vessel 8, and air 11 is uniformly distributed from the bottom via a dispersion plate 10. At the same time, the waste resin 9 is thermally decomposed in an electric furnace 12. A filter 13 was attached to the upper part of the reaction vessel in consideration of the scattering of radioactive materials due to heating. Additionally, in order to monitor the temperature distribution inside the reaction vessel, thermocouples were placed at three locations: the top, middle, and bottom. FIG. 6 shows the temperature distribution inside the reaction vessel during 8 hours of thermal decomposition using this apparatus. The temperature inside the reaction vessel was raised to 3500 ℃ using an upper thermocouple, and thereafter limited to ±50 CK. In this figure, the cicada indicates the temperature at the bottom of the reaction vessel, the temperature at the middle of the reactor indicates the temperature at the middle, and the dashed line indicates the temperature at the top. The lower and middle temperatures shown by the solid and broken lines in this figure are 600% at the culm for 2 to 4 hours.
It can be seen that the temperature rises to C. Therefore, in order to decompose waste resin using this method, it is necessary to supply a small amount of air to suppress the rapid decomposition reaction.
It was found that the length of I becomes longer and the amount of resin that can be processed becomes smaller.

Therefore, in order to lower the temperature inside the reaction vessel, the inventors focused on the endothermic reaction of water as one method of absorbing the reaction heat, and examined its practicality. This is an endothermic reaction called a water gas reaction, and the basic reaction is shown below.

C+H,0=CC1+H=-28,4kCal/mol
, -9(3)C+2H2(1=(,FO2+2)1t
18.5kC''/mol -(4)C(-)2+1
-Every 12==CO+1-1□0-1O1O""'/mo
l - (5) Also, in Figure 7, C-H at 1 atm.
An equilibrium diagram is shown. In this figure, at fi, 400tZ', the water container is approximately 1. /2, and the remaining 1/2 is carbon dioxide,
It can be seen that it changes to water and methane. Since this water decomposition reaction is an endothermic reaction shown in equations (3) to (5), it is effective in removing reaction heat.

When oxygen is supplied to waste resin, an exothermic reaction as shown in equation (6) occurs.

e+02=C(J, +97 kc21 ・(6)
This reaction causes a local temperature increase.

Therefore, when the reaction of formula (6) occurs, it is possible to remove this heat by intervening water and create a state in which neither heat generation nor endotherm occurs in terms of heat balance.

Now, assuming that equation (5) is in an equilibrium state in the water gas reaction, only equations (3) and (4) can be considered to be the endothermic reactions. In this case, a total of 46.9k for 3 mol of water
absorbs heat from cal. At 400C, water has a temperature of about 50
% decomposes, so it actually absorbs heat of 23.5 kcal. Therefore, in order to suppress heat generation, acid f, l 111
01, it is sufficient to supply approximately 12 n]ol of water.

In addition, the inventors have also developed a method of using the latent heat of vaporization of the liquid in the process of bundling the test H4.
I did this. Water, which is known to have a high latent heat, was selected as the liquid [7]. The latent heat of vaporization of water is 539.032
cal/g, so the theoretical amount to keep the inside of the reaction vessel below 420C is at most is, 6 for xg of resin treatment.
It is sufficient to supply xg of water.

Based on the above experiments and considerations, we decided to configure the system based on the following conditions.

(a) The decomposition equipment shall be a dry method in which air is supplied to thermally decompose waste resin.

(1)) In order to prevent residues and radioactive materials from scattering due to the flow rate of the supplied air, waste resin is decomposed under conditions close to static gas.

(C) The decomposition is carried out at 350C by adding water.
The temperature shall be maintained at ~420C.

Next, specific embodiments of the present invention will be explained in detail using drawings.
, reveal.

The embodiment shown in FIGS. 8 and 9 uses waste resin
The volume is reduced and mineralized by decomposition. Figure 8 (t) is a diagram of the system, and Figure 9 is a detailed diagram of the reaction vessel.

The waste resin is supplied in the form of slurry to the waste fat receiving tank 16 via the slurry transport pipe 15. This waste resin is
The decomposed core a1 contains corrosion products such as 60Co and Mn, and nuclear separation products such as Cs, Sr, and Ru at 10 μCi/g (dry oil phase), and is The ratio is 2 parts ion exchange resin, 1 part anion exchange resin, and 10 parts liquor fat. Transfer the waste resin in the waste resin receiving tank 6 to a predetermined square (20 kg in dry weight) adjustment tank 20, the cation catalyst storage tank 17, and the anion catalyst storage tank is;5. and Fec122r++ol i(
1 mol of 4Fe I CN ) aba is added and stirred by the stirring blade 36 for about 1 hour. Next, these waste resins are
It is centrifugally dehydrated by the dehydrator 21 and then passed through the valve 25.
It is supplied to the SUS reaction vessel 8 in the closed reaction device 34. The reaction vessel 8 has an internal volume of 100 mm and a diameter of 500 mm.

In addition, stirring blades 37 were attached to reduce the temperature distribution within the container and to prevent air flow paths from forming.

An electric heater 12 was used to heat the reaction vessel, and the temperature inside the reaction vessel was controlled to 350±5011''.

The waste resin 9 supplied to the reaction vessel 8 is then stored in an inert atmosphere without supplying oxygen, which is an oxidizing agent, to the outside.
It was heated to 350℃ with + air and thermally decomposed.

As a result, only the ion exchange groups in the waste resin 9 are decomposed, and sulfur compounds ISOx, H2S, etc.) and caustic compounds I
NOx, NHs, etc.) were generated in gaseous form over a distance of approximately 1.5 m'.

These exhaust gases are led to an exhaust gas treatment device via a valve 26, and are removed by an alkaline scrubber 30 with an aqueous sodium hydroxide solution led from a supply pipe 31 to form a sodium salt water bath solution (Nat 5 (J4 +
NaNOs, etc.) and is sent to the outside through the exhaust pipe 32. Since these aqueous solutions are non-radioactive, they can be treated in a non-radioactive chemical waste liquid treatment process within a nuclear power plant.

The waste liquid obtained in this example was dried, and the obtained solid Na2SO4 etc. had a radioactivity concentration of 10-'μCI/g.
The following results, and secondary waste such as Na2S (J, etc.) is non-h!
It can be treated as radioactive waste. alkaline scrubber 30
A certain amount of the exhaust gas after being treated is discharged to the outside air through the filter 33.

The waste resin (commercial molecule base only) whose ion-exchange groups have been decomposed in reaction vessel 8 for about one hour is then heated in a sweet, oxidizing atmosphere at the same temperature f35 (1') in the same vessel 8. At the same time as decomposition, water was added as an endothermic agent or as a vaporized substance. At this time, the waste AyJ in the reaction vessel 8
Air C, which is an oxidizing agent, was supplied to the oil 9 through a supply pipe 23 and a valve 24 from an air compressor or a cylinder. Air flow rate 1l-i, 0.2 cm/
At the same time as air, water in the form of steam or liquid was supplied via the supply pipe 22 and valve 24. The flow rate of water vapor was 2.7 ryn/s. Also, water in liquid state was supplied at 775 g/s+I,I.

The completely supplied air and water were dispersed by a perforated plate 10 made of SUS and flowed through the waste resin 9 at a uniform speed. In addition, a stirrer 37 was installed inside the reaction vessel 8 for the purpose of further dispersing air and water and uniformizing the temperature inside the furnace.

At about 8:00+t+1, as a result of continuing thermal decomposition of water while adding (As) in an oxidizing atmosphere, the diurnal molecule substrate was also completely decomposed, leaving only a stable residue.At this time, 1:, l-12( I
CO2, CO, JJ2, etc. are generated, and among these exhaust gases, H2o is condensed in a condenser 39 via a valve 38, and is received in the &M water tank for reuse. After passing through the filter 40, other exhaust gases are combusted in a flare stack or the like, if necessary, and C()2, )]2
0 Exhausted as gas. The radioactivity -Pi1· captured in the exhaust gas and the filter 40 was measured, and both were below the detection limit.

Further, it was confirmed that only 1 g or less of residue (detection limit) was captured in the filter 40, and the filter load was reduced.

FIG. 10 shows the temperature distribution inside the reaction vessel in this example. In this figure, the solid line indicates the temperature Ki when air and steam are supplied.
i, and the broken line shows the temperature distribution when only air is supplied.

The hatched area in the figure shows the temperature range measured by three thermocouples placed in the second part, middle part, and bottom part. From this figure, even in an oxidizing atmosphere, the suction inside the reaction vessel 8 is suppressed to 420C or less, and the YAA
I found that I was able to maintain my level.

As shown above, when waste resin is thermally decomposed, water vapor or liquid jf,
By supplying water at α, it is possible to prevent temperature runaway due to heat generation during waste resin decomposition and maintain the temperature around 50C.As a result, it is possible to reduce the amount of resin that can be produced by This not only made it possible to increase the lifespan of the reaction vessel, but also to prevent radioactive substances such as +37CIl from scattering into the exhaust gas.

In this example, water was used as the endothermic agent, liquid, or vaporized substance, but it is also possible to use other substances.

〔Effect of the invention〕

When waste resin is decomposed by thermal decomposition or incineration, by adding an endothermic agent or a vaporized substance together with an oxidizing agent, it is possible to suppress temperature runaway in the reaction vessel and improve waste resin treatment efficiency. It is possible to suppress the scattering of radioactive substances η into the exhaust gas, and further to minimize the deterioration due to temperature associated with long-term use of the reaction vessel.

[Brief explanation of drawings]

Figure 1 is a system diagram showing an example of a general waste resin pyrolysis system, Figure 2 is a diagram showing the thermal decomposition characteristics of waste resin in an air atmosphere, and Figure 3 is the temperature of the scattering rate of radioactive substances. Figure 4 is a diagram showing the thermal decomposition characteristics of a cation exchange resin with iron adsorbed as an ion. Figure 5 is a cross-sectional diagram showing the measurement of temperature distribution in the reaction vessel. Figure 6 is a diagram showing the temperature distribution inside the reaction vessel during pyrolysis, Figure 7 is a diagram showing the C-H20 equilibrium of water gas reaction at 1 atm, and Figures 8 to 10 are diagrams showing the temperature distribution in the reaction vessel during pyrolysis. Figure 8 is a system diagram of the system, Figure 9 is a detailed diagram of the reaction vessel, and Figure 10 is a diagram showing an example.
The figure is a diagram showing the temperature distribution inside the reaction vessel. ■... Waste resin tank, 2... Pyrolysis device, 3...
Absorption tower, 4...Second layer/waste, 5...Residue, 6...
- Solidifying agent tank, 7... Assimilation device, 38... Pulp, 39... Capacitor, No. /1. D 20th, JL degree (0c) 3rd /θQ 300! ; θθ 7θ0 De plate (°C) Figure 4 Temperature, reception (te) Figure 5 Figure 6 Time (h) Seventh slow wave (°C) Continued from page 1 [Co., Ltd.] Inventor Yoshiyuki Aoyama Moriyama-cho 1st Institute, Hitachi City

Claims (1)

[Claims] 1. In the method of thermally decomposing or decomposing the used radioactive ion exchange resin generated in the atomic couplant, after separating the decomposed gas generated in an inert atmosphere, this A method for processing radioactive waste resin, which is characterized by thermally decomposing the waste resin in an oxidizing atmosphere and at the same time separating the decomposed gas by adding an endothermic agent.