JPS59220690A - Method of processing radioactive liquid 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 (Industrial Field of Application) The present invention relates to a method for treating waste liquid (hereinafter referred to as waste liquid) generated from nuclear power plants or radioisotope facilities.

(Prior Art) Conventional methods for treating waste liquid include a coagulation-sedimentation method, an ion exchange method, and an evaporation concentration method.

(Re) The coagulation-precipitation method is a method in which a coagulant (aluminum salt, iron salt, etc.) is added to the waste liquid, and in the process of forming coagulated flocs such as hydroxide, radioactive substances are captured and co-precipitated. It is suitable for low-cost treatment of low-level radioactive waste fluid, but the decontamination coefficient (radioactivity concentration before treatment/radioactivity concentration after treatment) is low and it cannot be used for high-level radioactive waste fluid.

(2) The ion exchange method is a method in which the main radioactive substances in the waste liquid exist as cations and anions, and these are adsorbed and removed using a 4-one exchange resin. However, ion exchange resins are expensive and there are problems such as deterioration of the resin, so this method is limited to cases where it can be used repeatedly with low-level radioactive waste liquid. Furthermore, the treatment of this recycled waste liquid is also a big problem.

(3) The evaporation shallow reduction method is a method in which large pieces of water are evaporated and separated from the waste liquid, and the radioactive materials remain in the waste liquid. This method can separate ionic nuclides that are difficult to remove from water using methods (1) and (2) above, so the decontamination coefficient is
It is suitable for decontaminating high-level radioactive waste fluids compared to methods 1) and (2).

Currently, waste liquid generated at nuclear power plants, radioisotope handling facilities, etc. is mainly concentrated using method (3), mixed with cement or asphalt, solidified, and stored in drums.

Usually, in the evaporative concentration method, the waste liquid is heated in an evaporator to evaporate water, and the dissolved components are converted into a waste liquid with a large amount of dissolved components or into a powder form. The evaporated water is condensed to form condensate. This i4 thick waste liquid or powder contains non-volatile radioactive substances (
For example, 58Go.

Almost 100% of CO, Fa, Mn, etc.) is contained in this, and a decontamination coefficient of io' or more can be obtained. However, if the waste liquid contains volatile elements such as iodine
The waste liquid must be concentrated by evaporation.
This is to reduce the amount of iodine entrained in the evaporated water.

5I, +6DH-→5I-+1o; +5n2o...
(1) NaOH is usually used as the alkaline agent, but NaOH tilts the - side of the waste liquid to the alkaline side and contributes only to complete neutralization of dissolved components, and is used as an alkaline agent like water glass in the method of the present invention to be described later. S added to the action as
102 Various effects due to K! does not contribute in any way to
5102 cannot be expected to have the same effect.

On the other hand, an asphalt solidification method has been proposed as an assimilation treatment for the liquid. This method involves stirring and mixing asphalt heated to about 120-160C, evaporating the water in the waste liquid,
Since the dissolved components and radioactive substances are fixed in the asphalt, the reduction ratio (amount of radioactive liquid before treatment/amount of radioactive liquid after treatment) is larger than that of conventional cement solidification methods, and when crushed in water, The rate of penetration of radioactive substances can also be significantly reduced. However, since the moisture in the waste liquid is evaporated on the surface of the asphalt layer, the solidification rate of the waste liquid is slow, and the solidification speed is influenced by the degree of shrinkage of the waste liquid mentioned above.

In addition, after the asphalt is gradually removed from heat or allowed to cool and solidify, the trace amount of water remaining in the asphalt hydrates with the salts of dissolved components (such as Na2SO4) in the waste liquid, causing the asphalt to swell and then being immersed in water. There is a problem in that it increases the leaching of radioactive substances into the water.

(Object of the Invention) The object of the present invention is to provide a method for condensing radioactive waste liquid, which is devised to eliminate the drawbacks of the prior art as described above and to facilitate waste liquid treatment.

(Embodiment of the Invention) The gist of the present invention is to use water glass, boric acid, borate, phosphoric acid, ,
One or more substances selected from the group consisting of a primary phosphate tank and an aluminum salt are added to solidify the waste liquid by cassette solidification, thereby facilitating the treatment of the waste liquid.

Furthermore, the present invention facilitates solidification by preventing water adsorption during asphalt solidification, the aqueous phase of dissolved component salts, and the resolubilization of dissolved components by the silicic acid gel inhabited by the above-mentioned tAM assimilation. Even when acid salt vitrification is performed, the gist is to facilitate the solidification with the silicic acid gel.

Specific example 1 The waste liquid contains lt=volatile radioactive material (58C□, “Co
In addition to 59 volatile radioactive materials such as FCAN and FCAN, the waste liquid contains boron-18 (H3BO3) or borates (for example, N
a H2B 05 etc.) is the Na of the water glass below.
If the boric acid content is less than CB/Na molar ratio = 1 or more, it can be left as is, but if the boric acid content is less than CB/Na
(i) If so, add boric acid to the waste liquid.

The waste liquid is concentrated by heating at 100 to 160 C while adding water glass and, if necessary, boric acid or a boric acid salt to the waste liquid. When heating and condensing, either reduced pressure or normal pressure may be used. Water glass is dehydrated and silicic acid gel (n5io2・Xb20
J is generated.

Na2O・n5i02・mH2O-+ n5i02-x
H20+yH20+zNaOH where m:= x 10y +2 Water glass is JIS standard sodium silicate No. 1-5 (Na20
-nsio2·mH2O).

In this method, silicic acid gel (n5io2・XH2O)
It is preferable to use product No. 3, which produces quickly. This is because the larger the SiO2/Na2O molar ratio, the faster the gelation rate. (N a 20/5i for No. 6 product
02 molar ratio -=-5.15].

The amount of water glass added is 5102% of the amount of solids in the waste liquid.
Add 1 to 15% protein.

Dissolved components and radioactive substances in the waste liquid precipitate as solids as they are concentrated. The silicic acid gel acts as a binder on the surface of this homogeneous material to firmly adhere the solid materials to each other and form a pellet. (If the solid matter in the shrunk waste liquid reaches 1 wt% or more, the solid matter becomes pellets.9 The 131 metals contained in the waste liquid become concentrated in the form of Na and NaIO3 due to the alkali action of water glass. It remains as a dissolved component on the liquid side, and eventually precipitates as a solid substance, which is subjected to the action of the silicic acid gel.

Furthermore, in addition to the above-mentioned dehydration reaction, water glass undergoes a complex reaction with boric acid or boric acid salts to rapidly gel.

This reaction machine is a bit messy and not obvious, but
It is known that boron 412 ions bind to polymerized silicic acid gels.

Note that gelation of water glass is extremely slow if only six liquids of boric acid or borate salts are added to water glass.

Furthermore, by heating and concentrating the waste liquid, residual moisture can be removed.
As the amount decreases, when the temperature of the solid reaches 1000 or higher, the crystallization water of the pre-silicic gel (n5io2.XH2O) is lost and becomes anhydrous silicic acid gel (n5lo2).

In the process in which the waste liquid is heated and S-condensed as described above, the dissolved components and radioactive substances in the waste liquid are precipitated according to their solubility, and eventually a granular solid substance is produced.

The granular solids are immediately stirred and mixed with asphalt heated to 120-160C8 degrees, fixed in the asphalt, filled into drums, and gradually removed from heat or allowed to cool, and the asphalt solidifies inside the can.

The granular solids generated above easily adhere to the hydrophobic asphalt due to the layered action of the silicic acid gel that covers the surface, and also adsorbs moisture in the fine particles remaining in the asphalt, allowing the solids to absorb moisture. It does not allow penetration and has the effect of preventing dissolved components of solids from eluting from the inside to the surface. The mixing weight ratio of granular solids and asphalt varies depending on the dissolved components in the waste liquid.
The ratio is approximately 0 to 60:40 (weight % ratio).

In addition, boric acid (Ha2804・1oH2
0) and silica sand (mainly s iO2) to add 900 to 1
After melting at 300C, a glass-like solidified product can be obtained by gradually removing heat or allowing it to cool.

The above granular solids are warmed by silicic acid gel, so boric acid,
When mixed with silica sand and then subjected to Ma, it has the effect of binding to borosilicate gas.

The mixing weight ratio of boric acid and silica sand is B, 'Si in one carving.
Although it varies depending on O2, solids: porcelain sand: silica sand = 25
~60:20~50:30~6 degrees (wt% ratio). It is known that this vitrified material has a much lower rate of leaching of radioactive substances into water than the above-mentioned asphalt solidified material, and has an extremely high total biomass because it is not easily attacked by chemicals.

Specific Example 2 In the same manner as in Specific Example 1, water glass was added to the waste liquid, and then the waste liquid was heated at a temperature of 100 to 160 l:'. The amount of water glass added and the asphalt solidification operation are the same. The differences from specific example 1 are as follows.

(1) If the boric acid content of the 1N8 solution is low, use phosphoric acid (H3P04) or primary phosphate (
For example, adding rqaH2po4) or an aluminum salt. The amount added is Na/
P○4 molar ratio = 1 to 2 or Na/A, 1 molar ratio = 1 to
It is 2.

Add phosphorus (H6PO4) or primary phosphate (Na
In the presence of aluminum salt (A12o4'-) or aluminum salt (A12o4'-), water glass rapidly gels due to a complex reaction with phosphoric acid or aluminum salt in addition to the dehydration reaction caused by heating g-condensation. It is much faster than simply heating and concentrating. This reaction mechanism is extremely complex and not clear, or the polymerized silicon 1
It is known that phosphoric acid or aluminum ions bind to the step cells.

When the solid obtained by evaporation concentration is vitrified, it depends on the amount of p (as p o ) or Al (as A12035) in the solid, or the solid: P (P2O).

) Borax (as B206) = aluminum e-oxide (as A12035) = 20-4o:s.

A glass-like solidified product can be obtained by mixing at a ratio of about 70:6 to 10:1 to 201 tons, melting at 1000 to 1500 C, and gradually removing heat or allowing it to cool.

The solid matter covered with the silicic acid gel film exists in a form combined with phosphate ions or aluminum ions, so phosphorus,
It has the effect of bonding with phosphate glass through mixed wave melting with borax and aluminum oxide.

It is known that this vitrified material has a much lower leaching rate of radioactive substances in water than the above-mentioned asphalt solidified material, and has extremely high detoxification properties.

The results of experiments conducted by the method of the present invention based on Specific Examples 1 and 2 are shown in Table 1 as Examples 1 and 2.

As is clear from Table 1, high decontamination coefficients and volume reduction ratios can be obtained according to the method of the present invention.

Furthermore, the infant pot of the present invention, which is superior to the conventional method, is as described in H6 below.

■ Dissolved components and radioactive substances in the waste liquid rapidly turn into pellets filled with silicate gel, and the water in the waste liquid is easily evaporated.

■ Since the pelletized assimilate is crushed by silicic acid gel, it will not be rebathed even if it comes into contact with unevaporated water.

■ The pelletized solidified material contains almost no moisture or water of crystallization, and is easily converted into asphalt. Due to the LI layer, the asphalt solidification processing speed is high.

■ Since silicic acid gel is a non-swelling R1-electrogel, it does not swell even when it absorbs the reduced amount of water in the asphalt, and does not create gaps with the asphalt.

Therefore, radioactive substances are released (this increases safety).

■ Even waste liquid containing 131 kg can be efficiently steamed (the steamer can be reduced).

■ Since the solidified material contains boron, it efficiently absorbs the neutrons generated during decay, so it can improve safety such as measures against radiation exposure.

(2) The pelletized solidified material of (2) above has the same composition as borosilicate glass, so it is easy to vitrify and is not easily attacked by chemicals.

■ The pelletized solidified material described in Example 2 has the same composition as phosphate glass, so it is easy to assimilate into glass.
Moreover, it becomes less susceptible to attack by chemicals.

As described above, the present invention is an industrially advantageous method with various advantages.

To my representative 1) Akira Sub-agent Ryo Hagi Hara -

Claims (1)

[Claims] One or more substances selected from the group consisting of boric acid, borates, phosphoric acid, primary phosphates, and aluminum salts and water glass are added to the waste liquid while heating and condensing the waste liquid containing radioactive substances. A method for treating waste liquid, characterized by adding it to a liquid and concentrating and solidifying it.