JPS58186099A - Method of solidifying 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 The present invention mainly relates to a method for reducing the amount of wastewater discharged from a pressurized water reactor containing boric acid or/and borates and radioactive substances.

In a pressurized water type light water reactor, which is one type of nuclear reactor, water containing boric acid, which easily absorbs neutrons, is used as primary cooling water, and the output of the reactor is controlled by increasing or decreasing the concentration of boric acid in this cooling water.

For this reason, the cooling water system of this reactor discharges wastewater containing boric acid and radioactive particles that are mixed into the cooling water during use, or neutralized wastewater. The radioactive solids in these wastewaters are separated from the water and solidified into blocks to withstand final disposal methods such as ocean dumping or underground burial, or intermediate storage and transportation during the process, so-called weight reduction treatment. It is necessary to Various methods have been disclosed as solidification methods for this purpose. For example, such a method is described in Japanese Patent Application Laid-Open No. 52-92100.
No., JP-A-52-104700, JP-A-54-340
No. 00, and Japanese Patent Publication No. 55-34397. Of these, the first three all have the property of solidifying themselves (hereinafter referred to as self-hardening), such as cement or thermosetting synthetic resin, by converting wastewater that has been concentrated to a certain extent or powder obtained by concentrating and drying wastewater. A method is used in which it is dispersed in an auxiliary agent and solidified. Therefore,
Since these conventional methods use a solidification aid, the weight increases at least by the amount of the solidification aid, and the amount of radioactive wastewater is insufficiently reduced. Furthermore, JP-A No. 55-34397 describes a method for pulverizing solidified matter in wastewater, but only a mechanical compression method is disclosed as a method for solidifying the obtained powder. However, the strength of the solidified product is insufficient to allow it to be stored for a certain period of time, and the powder obtained at that time does not have self-hardening properties and is not suitable for strength.
- still requires a self-hardening solidification aid.

Therefore, the purpose of this invention is to propose a method for solidifying wastewater into blocks that have sufficient compressive strength for disposal at sea without using boric acids and radioactive self-hardening solidification aids contained in wastewater. It is said that

This invention involves preparing wastewater containing boric acid or/and borates and radioactive substances to a pH of 7 or higher, and then adding at least one compound selected from the group consisting of compounds containing magnesium, calcium, and barium. After the reaction, the resulting slurry is prepared into a slurry containing 20 to 80% water on a wet basis, and this slurry is solidified.

The present invention will be described in detail below using calcium hydroxide as an example of the calcium compound.

First, raw wastewater containing boric acid is pH adjusted using concentrated caustic soda.
Adjust the value to 7 or higher (hereinafter this step will be referred to as the pH adjustment step).

Calcium hydroxide is added to the pH-adjusted solution so that the weight of calcium becomes about 0.5 times the weight ratio of boric acid in the solution (hereinafter, this step is referred to as the reaction step). In this reaction step, the boric acid groups present in the raw wastewater react with calcium hydroxide, and the liquid becomes a slurry. This slurry is adjusted to have a moisture content of 20 to 80% on a wet basis by means such as filtration and concentration, and the adjusted slurry is poured into a desired mold 24.

Leave to stand for a period of time or more (hereinafter this process will be referred to as the curing process).

This curing step allows the slurry to solidify into blocks of desired shape. The compressive strength of the solidified product taken out from the mold after completing the curing process is 150 kg/ct1 or more, and has sufficient strength to be dumped in the sea or buried in the upper reaches.

In the series of steps in the above example, all well-known alkaline substances such as sodium hydroxide, potassium hydroxide, and calcium hydroxide can be used alone or as a mixture, but sodium hydroxide It is most convenient to use concentrated aqueous solutions or solid substances. In addition, the temperature of the wastewater in this pH adjustment step can be from room temperature to 20°C (or below room temperature or above 120°C), but in particular cooling to below room temperature or heating to 120°C or higher is recommended. Not necessary.Also, the pH value after pH adjustment is preferably 7 or higher, but 9
-12 are particularly preferred.

The compound to be added in the reaction step is preferably one containing magnesium, calcium, or barium. The anion group bonded to these elements in the additive may be any type, but may include OH group (including oxides as anhydrides of compounds having this group), chlorine ion, carbonate group, acidic carbonate group, and nitric acid group. , sulfate group, acidic sulfate group, phosphoric acid group, mono- or dihydrogen phosphate group, etc. are easily available.

These compounds can be added as an aqueous solution or powder to the liquid that has undergone the pH adjustment step, but it is preferable to add them as a powder or granular product with a low water content so as not to add the total amount of treated water. In addition, the amount of these compounds added is 02 to 1 mol of the above metals per mol of boric acid group in the liquid.
It is preferable that the amount is 0 mol. Moreover, these compounds may be added either singly or in a mixture of two or more, so as to satisfy the above-mentioned addition amount.

The temperature of the liquid at the time of addition is preferably 30 to 90°C, and it is usually good to add while stirring. In addition, the reaction with wastewater after addition of these compounds requires a temperature of 40 to 120°C and a temperature of 0.5°C.
Reaction times of 5 to 3 hours are preferred. Even if the temperature is outside the above temperature range and the time is longer than this time, there will be no particular effect on the curing reaction described below. Further, it is preferable to perform stirring during this reaction. As a result of the above reaction, the undissolved solid content in the slurry obtained has the above-mentioned self-hardening property in the presence of moisture. However, since the boric acid group content in the wastewater used as a raw material when applying the method of the present invention usually varies between 4 and 20% by weight, the concentration of undissolved solids in the slurry produced after the above reaction also increases. l]. Therefore, it is desirable to adjust the moisture content of the slurry before carrying out the next curing step and then inject it into the mold in order to effectively utilize the internal volume of the mold.

As a means for reducing the water content in the slurry, many known means such as centrifugation, filtration using a wire mesh or P cloth, evaporation, concentrated drying, etc. can be used. After reducing the water content, it is convenient for the slurry to have a water content of 20 to 80% by weight on a wet basis from both the fluidity of the slurry and the effective use of the internal volume of the mold. It varies depending on the type of compound, particle size distribution, etc.

By directly filling the slurry after adjusting the water content into a mold and leaving it to stand, the solid content in the slurry solidifies and a solidified block of the desired shape can be obtained.If the water content is less than 10%, a block with high strength cannot be obtained. In addition, as a result of dehydration by filtration as described above, if the water content becomes too low and the fluidity of the slurry becomes poor, add new water or P as appropriate.
By adding water, a slurry with good fluidity can be prepared within the above water content range, and the slurry can be filled into a mold. A convenient temperature for the curing step is between 10 and 50°C, e.g.
If left at a temperature of 0°C, it will reach a compressive strength of about 15 kg/7 in one day, and the strength will improve as the standing time is extended. In addition, when exposed to air and left in a heated state of 50° C., the compressive strength of 150 kg/i is reached in about 2 hours, and the time required for hardening can be shortened. When adjusting the water content of the slurry above,
It is also possible to use a cylindrical rotary dryer with or without an internal stirring blade or a band dryer that performs dehydration and drying on a wire mesh belt, but it is not always possible to dry to a moisture content of 20% or less. Not necessary.

The reason why the curing phenomenon occurs in the curing process of this invention is not yet clear. However, according to the present invention,
Thermosetting resins such as cement, epoxy resins, and unsaturated polyester resins, or polymerizable monomers that solidify through polymerization, which are always used in conventional methods, are not used as self-hardening solidification aids, but are contained in the raw wastewater. As shown in the Examples below, the solid content containing boric acid, borates, and other radioactive substances can be solidified into blocks. Therefore, according to the present invention, approximately 16,000 kg of cement or BOOkg is produced per ton of boric acid group in the conventional method.
Instead of using expensive synthetic resins, it is possible to obtain a block-shaped solidified product in the desired shape with sufficient compressive strength by adding 400 to 600 kg of the above-mentioned inexpensive compound, and the weight and volume of the solidified product can be reduced. At the same time, assimilation costs and transportation costs for solidified materials can be reduced.

When the solidified block obtained by this invention is subjected to final disposal such as burial in the ground or dumping in the sea, in order to reduce the elution of radioactive elements contained in the block into the ground or seawater, The outer periphery of this block is closely surrounded by concrete or a synthetic resin jacket, or the inside of the obtained block is impregnated with uncured unsaturated polyester resin of low viscosity, polymerizable monomer, etc.
It may be desirable to apply known means such as subsequently carrying out a polymerization reaction to reduce the water permeability of the book. In the case of the former method of tightly enclosing the drum, for example, the inner surface of the drum except for the small hole for the slurry inlet is coated with concrete or a cured product of unsaturated polyester resin, and the slurry is poured into the hollow part inside the inner-coated drum. A simple method is to fill and harden the slurry, and after hardening, close and seal the slurry inlet with concrete or unsaturated polyester resin. In addition, in the case of the latter impregnation polymerization method, the block obtained by the present invention is left indoors at room temperature for about a month, and after drying and removing free water near the surface of the block, the pressure is once lowered to below normal pressure. The block is degassed under pressure, and then immersed in the unsaturated polyester resin or polymerizable monomer containing a polymerization catalyst to impregnate the inside of the block with the resin or monomer, and then heated at room temperature to 50℃. It is preferable to polymerize and cure at a temperature of °C. Desirable polymerizable monomers include styrene monomers and methacrylic acid esters.

In addition, in this invention, the chemical structures of boric acid and borates contained in raw wastewater and wastewater being treated are based on the history of these boric acids and borates before they are discharged as wastewater with water or the concentration at the time of discharge. Although the details are unknown as it varies depending on the temperature, etc., it is thought that it usually contains many boric acids and their derivatives with different chemical structures. Taking these circumstances into consideration, boric acid and borate in the present invention refer to boric acid compounds having the following chemical formula, either singly or as a mixture.

XMmO-yB, 0o(OH)k-Z(H2O) In this formula, X is an integer from 0 to 3. y is an integer from 1 to 5. 2 is an integer from 0 to 10. n is an integer of 0 to 15; M is a monovalent or divalent metal atom; 0 is an oxygen atom; B is a boron atom; H is a hydrogen atom;

In addition, in this invention, when the R water is filtered after the reaction as described above, it usually contains almost no radioactive substances, and the P water can often be discharged after neutralization. but,
If the fresh water still contains radioactive substances, the P water alone or together with the raw waste water can be concentrated by a known method and the method of this invention can be applied again. .

Example l Simulated wastewater 101 containing 1.3 kg of orthoboric acid! When 400g of solid caustic soda is added and dissolved, the pH value becomes 91. 650 gr of calcium hydroxide powder was added to this solution and reacted at 60° C. for 1 hour with stirring. Immediately after the reaction, the mixture was vacuum filtered using a Buchner funnel. The moisture content of the obtained cake was 30% on a wet basis (the same applies hereinafter), and the cake weight was approximately 2.7 kl? It is. In this example, the fluidity of the cake is poor with this cake moisture content, so 700g of fresh water is added in a separate container to increase the moisture content to approximately 44%. is 4
The mixture was injected into three series of molds of 0 in x 40 mi + x 16'O and allowed to initially harden for 1 day. Thereafter, this initially cured product was taken out of the mold and placed in a glass container at 20℃ for 2 hours.
Curing was allowed to proceed for 7 days.

When the unconfined compressive strength was measured on the 28th, the average s 5
It showed a value of 0 kg/d.

For comparison, in order to solidify the simulated wastewater 101 by the method disclosed in JP-A-52-92100, it is necessary to add about 1.5 kg of slaked lime, about 5 kg of Portland cement, and about 1.5 kg of water glass. and boric acid 1.3
It is clear that both the weight and volume of the solidified material (kg) are small in the case of the present invention.

Example 2 An experiment similar to Example 1 was carried out, and if the suction after the suction f was continued for a long time, the cake would become dry.

Fresh water was added to the cake dried to a moisture content of 3% to form a slurry with a moisture content of 50%.The subsequent operations were carried out in the same manner as in Example 1, and the resulting solidified product had an average uniaxial compressive strength of 570K.
g/cII.

Example 3 500 gr of solid caustic soda was used instead of 400 gr of solid caustic soda in Example 1, and 790 gr of barium hydroxide powder was used instead of 650 gr of calcium hydroxide powder.
The reaction and filtration were carried out in the same manner as in Example 2 except that gr was used. The moisture content of the cake obtained by long-term suction was probably 5%, and fresh water was added to this to create a slurry with a moisture content of 30%. After curing, the axial compressive strength was measured in the same manner as in Example 2. The average was 6+okg/c++l.

Example 4 An initially cured cloth was prepared in the same manner as in Example 1. After being left in the room air at room temperature for 28 days to proceed with curing, it was placed in a glass airtight container under a vacuum of 10its of mercury for 30 minutes.
After degassing for seconds, methyl ethyl ketone, hydroperoxide, and cobalt naphthenate were added as a polymerization catalyst and a polymerization accelerator in a sealed container under vacuum at 10% and 0.02%, respectively.
After injecting 5% methyl methacrylate monomer, the vacuum was broken to impregnate the cured product with methyl methacrylate monomer.

This impregnated cured product was left at 60° C. for 24 hours to advance polymerization of methyl methacrylate. Thereafter, the axial compressive strength was measured and showed a value of 610 kg/cd.

Example 5 1.56 kg of sodium tetraborate and 3.0 cesium chloride
Solid caustic soda 1'00g in simulated wastewater 107 containing gr.
Example 1 by adding r and 700g of calcium hydroxide powder
Six initial cured products were produced in the same manner as in Example 4. Three of these were cured for 100 days in a glass container and used as test specimens, and the other three were cured at room temperature for 28 days as in Example 4. Then, methyl methacrylate was impregnated and polymerized, followed by curing for 70 days.The unconfined compressive strength measured after that was 5.
The amount is 20 kg/cI/l, whereas the amount obtained by impregnating and polymerizing this monomer is 600 kl? /d. In addition, three cylindrical test pieces each having an outer diameter of 45 mm and a height of 44 mm prepared in the same manner as above were immersed in 700 ml of water at 20° C. for 100 days to conduct a cesium elution test into the water. The amount of cesium eluted was analyzed by atomic absorption spectroscopy, and the results showed that in the case of the same monomer without impregnation polymerization, the average was 481 V in 100 days, whereas in the case of the same monomer in the case of impregnation polymerization, the average was 4~4. Ta.

Patent Applicant Toyo Engineering Co., Ltd. Bergogne Clairère Niss A Procedural Amendment April 4, 1980 Commissioner of the Patent Office 1, Indication of Case 1982 Patent Application No. 68717 2
, Title of the invention: Radioactive wastewater solidification treatment method 3. Relationship with the person making the amendment: Applicant: Toyo Engineering Co., Ltd. (and one other person) 4. Agent address: No. 16 Kowa, 1-9-20 Akasaka, Minato-ku, Tokyo. Building 8th floor 5, Date of amendment order Voluntary amendment 6, Detailed description of the invention column 7 of the specification subject to amendment Contents of amendment (1) Page 3, line 4 of the specification, "solidified content" changed to "solid content" Minute”
I am corrected.

(2) On page 3, line 8 of the specification, "fixed" is corrected to "temporarily for a limited period of time."

(3) On page 4 of the specification, lines 1 and 2, ``obtained slurry'' is corrected to ``1 solid content produced''.

(4) Page 6, line 9 of the specification, “addition” to “increase”
I am corrected.

(5) Page 15 of the specification, lines 12 to 14, [and polymerization accelerator... 1.0% each] is 1, and 1 mouthful of methyl ethyl ketone oxide is 1.0
and naphthenic acid salt as a polymerization accelerator.''

524-

Claims (1)

[Claims] A method for treating wastewater containing boric acid or/and a borate and a radioactive substance, in which at least one compound selected from the group consisting of compounds containing magnesium, calcium, and barium is added to the wastewater after adjusting the pH to 7 or more to cause a reaction. After that, the produced solid content has a moisture content of 20 to 8
1. A method for solidifying radioactive wastewater, comprising preparing a slurry containing 0% radioactive wastewater and solidifying this slurry.