JP2505782B2 - Method for solidifying radioactive waste - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Industrial field of application) The present invention relates to a method for treating intermediate to low level radioactive waste generated from a radioactive material handling facility such as a nuclear power plant. The present invention relates to a method for solidifying plastic treatment of powder radioactive waste.

(Prior Art) Generally, concentrated waste liquid generated in a radioactive material handling facility such as a boiling water nuclear power plant or a nuclear fuel reprocessing plant is dried by a dryer such as a vertical thin film dryer, and is mainly treated with sodium sulfate or sodium nitrate. After being made into powder, cement,
It is solidified with a solidifying material such as asphalt or plastic.

As this solidification treatment method, a plastic solidification treatment method in which solidification treatment is performed with a solidifying material composed of a curable resin composition is a solidified body package that is lightweight and has excellent mechanical strength, volume reduction, and ability to trap radioactivity. It has been seen as promising recently because it can be obtained.

As this plastic solidifying material, a material using a thermosetting resin is widely used because it can be hardened at room temperature, but especially unsaturated polyester resin diluted with a polymerizable monomer such as styrene, solidifying A method of polymerizing and solidifying a solidifying material using an initiator and a solidification accelerator is generally adopted.

(Problems to be solved by the invention) However, when the radioactive waste liquid contains a reducing substance such as sodium nitrite, the reducing substance causes radicals generated by decomposition of the solidification initiator such as organic peroxide. Is consumed and loses its effectiveness as a solidification initiator, so that the hardening of the solidifying material is hindered and the hardness of the solidified package formed is low,
Therefore, there is a problem that the mechanical strength of the solidified package and the ability to trap radioactivity are reduced. In addition, solidified products made of unpolymerized unsaturated polyester resin are classified as dangerous substances under the Fire Service Law, and the problem that incompletely solidified solidified product packages put radioactive waste in a more dangerous state. there were.

For example, the concentrated waste liquid generated at a boiling water nuclear power plant has sodium sulfate (Na ₂ SO ₄ ) as its main component, but Ca, Si, F
Metal components such as e, Co, Ni, Cu, chlorine, nitrite, etc. are present in the waste liquid, and especially sodium nitrite is used as a rust preventive for equipment such as waste liquid tanks and concentrators. It is contained in a large amount and hinders the hardening of the solidified material.

According to the experiment of the present inventor, powder of sodium sulfate,
Sodium nitrite powder was mixed at a weight ratio of 59: 1, and 60% by weight of this powder was mixed with 40% by weight of thermosetting resin containing unsaturated polyester as a main component, and this thermosetting resin was mixed. On the other hand, 2.0% by weight of methyl ethyl ketone peroxide as a solidification initiator and cobalt naphthenate as a solidification accelerator.
When 0.5% by weight is added and mixed and then left to stand for 24 hours to be solidified, the formed solidified body is incompletely cured and the product is in a gel state. This is N in sodium nitrite (NaNO ₂ ).
This is because O ₂ reduces active radicals generated by the solidification initiator and the solidification accelerator, reduces the amount of effective active oxygen, and interferes with curing of the thermosetting resin. As described above, it was difficult to obtain a solidified product having good characteristics by plasticizing the radioactive waste containing a reducing substance such as sodium nitrite.

The present invention has been made to solve such a problem and improves the mechanical strength and stability without the curing of the solidifying material being hindered by the reducing substance such as sodium nitrite in the radioactive waste. It is an object of the present invention to provide a method for solidifying a radioactive waste capable of forming a solidified body.

[Structure of the Invention] (Means for Solving Problems) A method for solidifying radioactive waste according to the present invention is a method of mixing radioactive waste containing sodium nitrite generated in a nuclear facility with an unsaturated polyester resin. In the solidification treatment method for curing the mixture, the mixture is cured by allowing an alkaline substance in an amount such that the acid value of the unsaturated polyester resin is 0 to 5 to be present in the mixture.

The unsaturated polyester resin used in the present invention,
Those composed of unsaturated polyester and a polymerizable monomer such as styrene are suitable. Further, as the radioactive waste to be treated, powdery radioactive waste obtained by drying the radioactive waste liquid is suitable.

The unsaturated polyester used in the method of the present invention includes, for example, an esterified polycondensate of a dibasic acid and a glycol component, and examples of the dibasic acid component include maleic anhydride, fumaric acid, itaconic acid, and citracone. Α, β-unsaturated dibasic acids such as acid, mesaconic acid, chlorinated maleic acid, etc., and if necessary, phthalic anhydride, isophthalic acid, terephthalic acid, monochlorophthalic acid, dichlorophthalic acid, trichlorophthalic acid, Tetrachlorophthalic anhydride, tetrabromophthalic anhydride, endomethylenetetrahydrophthalic anhydride, hettic anhydride, hettic acid,
Saturated dibasic acids such as succinic acid, glutaric acid, adipic acid, pimelic acid and sebacic acid may be added. And as the glycol component, for example, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 2,3-butylene glycol, neobenthyl glycol, Hexylene glycol, octylene glycol, bisphenol A dioxyethyl ether adduct, bisphenol A dioxypropyl ether adduct, hydrogenated bisphenol A, ethylene oxide, propylene oxide, butylene oxide, and the like, and trimethylolpropane as necessary. , And polyhydric alcohols such as glycerin may be used in combination.

The polymerizable monomer used in the method of the present invention includes, for example, styrene, α-methylstyrene, vinyltoluene, aromatic compounds having an ethylenic double bond such as paramethylstyrene, methyl methacrylate, and fatty acid such as acrylic oligomer. Examples include group compounds. The amount of the polymerizable monomer used is preferably in the range of 20 to 80% by weight based on the total amount of the unsaturated polyester and the polymerizable monomer.

Further, if necessary, a plasticizer or a polymerization inhibitor may be added to the above unsaturated polyester resin. Examples of the plasticizer include phthalic acid esters such as dibutyl phthalate and dibutyl maleate, and phosphoric acid esters. Examples of the polymerization inhibitor include hydroquinone, benzoquinone, t-butylcatechol and the like.

And in order to polymerize and solidify the unsaturated polyester resin, for example, a method using a ketone peroxide as a solidification initiator, an organic metal salt as a solidification accelerator, benzoyl peroxide as a solidification initiator, dimethylaniline or diethyl as a solidification accelerator. A method using aniline, benzoyl peroxide as a solidification initiator, t-
A high temperature curing method using butyl perbenzoate or the like is used.

Furthermore, examples of the alkaline substance used in the method of the present invention include hydroxides or oxide powders of Na, K, Mg, Ca and the like, or solutions. This alkaline substance may be mixed in the radioactive waste in advance, or an alkaline substance may be added when the unsaturated polyester resin and the radioactive waste are mixed, and an alkaline substance may be added to the solidification accelerator. You may add. The amount of this alkaline substance added is such that the acid value of the unsaturated polyester resin (neutralizes carboxyl groups contained in 1 g of a curable resin composition such as an unsaturated polyester resin obtained by diluting an unsaturated polyester with a polymerizable monomer). The amount of potassium hydroxide required for the above is 0-5, preferably 0-2.

(Operation) In the method for solidifying radioactive waste according to the present invention, the radioactive waste is mixed with an alkaline substance and an unsaturated polyester resin and cured to reduce a reducing substance such as sodium nitrite in the radioactive waste. As a result, the hardening of the solidified material proceeds without losing the effect of the solidification initiator, so that a completely solidified package of hardening is formed.

Therefore, by using the method of the present invention, radioactive waste containing a reducing substance such as sodium nitrite can be solidified as a solidified package having improved mechanical strength and stability.

(Examples) Examples of the present invention will be described below.

Examples 1 to 7 76 g of maleic anhydride, 170 g of phthalic anhydride and 182 g of propylene glycol were reacted at 200 ° C. and 8 hours later, an unsaturated polyester having an acid value of 40 was obtained. After cooling the unsaturated polyester, a polymerization inhibitor and 600 g of a styrene monomer were added to produce an unsaturated polyester resin having an acid value of 16. Then, 40% by weight of unsaturated polyester resin and 59% by weight of sodium sulfate and 1% by weight of sodium nitrite as a simulated radioactive waste are mixed, and the mixture is mixed with methyl ethyl ketone peroxide as a solidification initiator. 2% by weight, and 1% by weight of cobalt naphthenate as a solidification accelerator to the unsaturated polyester resin were added and mixed. To this mixture were added the alkaline substances in the amounts shown in the following table, mixed, and then cured. The gelation time and surface hardness of the solidified body formed at this time are shown in the following table (Examples 1 to 7). As a comparative example, the simulated radioactive waste was solidified in the same manner as in Examples 1 to 7 except that the alkaline substance was not added. However, the mixture of the simulated radioactive waste and the solidifying material was left to stand overnight. Even though it did not gel, it remained liquid (Comparative Example 1). As still another comparative example, a simulated radioactive waste was prepared in the same manner as in Examples 1 to 7 except that alkaline substances were mixed in the amounts shown in the following table and the acid value of the unsaturated polyester resin exceeded 5. Was solidified. The gelation time and surface hardness of the solidified body formed at this time are shown in the following table (Comparative Example 2,
3). The mixing amount of the alkaline substance in the table is shown by weight% with respect to the resin.

As can be seen from the results in the above table, in the method of the present invention, the radioactive waste is mixed with the unsaturated polyester resin and the alkaline substance in a blending amount such that the resin acid value is preferably 0 to 5, and then cured. As a result, even if a reducing substance such as sodium nitrite is contained in the radioactive waste, the curing of the solidification material proceeds without losing the effect of the solidification initiator, so that a completely solidified pair package is formed. Therefore, the radioactive waste can be solidified as a solidified package having improved mechanical strength and stability.

[Effects of the Invention] As described above, when the method for solidifying radioactive waste according to the present invention is used, the reducing material such as sodium nitrite in the radioactive waste does not interfere with the hardening of the solidifying material. It is possible to treat radioactive waste as a solidified package having improved mechanical strength and stability.

Claims (3)

(57) [Claims] 1. A radioactive waste containing sodium nitrite generated at a nuclear facility is mixed with an unsaturated polyester resin,
In the solidification method of curing this mixture, the mixture is cured by allowing the mixture to contain an alkaline substance in an amount such that the acid value of the unsaturated polyester resin is 0 to 5. Solidification treatment method. 2. The method for solidifying radioactive waste according to claim 1, wherein the unsaturated polyester resin comprises an unsaturated polyester and a polymerizable monomer. 3. The radioactive waste according to claim 1 or 2, wherein the radioactive waste is a powdered radioactive waste obtained by subjecting a radioactive waste liquid to a dry treatment to be powdered. Solidification treatment method.