JPH0646235B2 - Solidification material for radioactive waste - Google Patents

Description

TECHNICAL FIELD The present invention relates to a solidified material for radioactive waste, which is used for solidifying liquid or solid radioactive waste to safely handle, transfer, and dispose of it. is there.

[Conventional technology]

Radioactive wastes discharged from nuclear facilities, hospitals, and various research facilities are generally classified into high-level radioactive wastes and low-level radioactive wastes according to the source and concentration of radioactive substances. Of these, high-level radioactive waste is a concentrate containing fission products separated by reprocessing spent nuclear fuel, and low-level radioactive waste is mainly used for manufacturing and processing facilities such as conversion and enrichment of uranium fuel and nuclear power. It is generated from power plants, spent nuclear fuel reprocessing facilities, and radioactive isotope use facilities. Of these, the large amount of waste is low-level radioactive waste. Examples of the low-level radioactive waste include waste liquid concentrated in an evaporator, sludge and pellets, waste ion exchange resin and its melt, combustible solid and its incinerated ash, non-combustible solid and its melt, waste solvent. Etc. These radioactive wastes are generally stored, stored, or dumped in the ground or in the ocean after the volume is reduced, but the handling, transfer and disposal are safe and The radioactive waste is solidified so that it can be easily done. Cement, asphalt, plastics, ceramics, etc. are generally used as the radioactive waste solidifying material, and cement is widely used as the solidifying material for the low-level radioactive concentrated waste liquid. However, cement is inexpensive, easy to obtain and easy to handle, and does not require complicated equipment, but there is a problem that when the mixing ratio of radioactive waste liquid and cement increases, bleeding occurs and the solidified body is not homogeneously integrated. . Therefore, the amount of waste treated per unit weight of cement is relatively small and the curing time is long. Further, since the leaching of the radioactive material from the solidified body is relatively large and the material greatly shrinks during curing, it is necessary to reopen the drum after filling to fill the gap.

[Problems to be solved by the invention]

An object of the present invention is to eliminate the drawbacks of the conventional solidifying material and to provide a solidifying material capable of treating radioactive waste, particularly concentrated waste liquid, in a relatively large amount per unit weight. It is also an object of the present invention to provide an inorganic solidifying material for radioactive waste, which can be solidified easily and in a short time, is safe and easy to handle, does not significantly shrink during curing, and has little leaching of radioactive material from the solidified body. To aim.

[Means for solving problems]

The present invention was made based on the finding that, when gypsum, slag and an alkali stimulant are used in a specific ratio, and when a specific compound such as chloride is used in combination with these, the above object can be efficiently achieved. Of.

That is, the present invention is 20-70 parts by weight of gypsum, slag 20
Provided is a solidifying material for radioactive waste, which comprises ˜70 parts by weight and 5 to 40 parts by weight of an alkali stimulant.

Furthermore, the present invention also provides a solidified material for radioactive waste, characterized in that the solidified material contains a compound which is water-soluble per se and reacts with a water-soluble carbonate to form a water-insoluble carbonate. provide.

Gypsum used in the present invention is anhydrous calcium sulfate and calcium sulfate hydrate, dihydrate (natural gypsum or chemical gypsum by-produced in various chemical steps: CaSO ₄ 2H ₂ O), β-type hemihydrate ( The above natural gypsum and chemical gypsum were fired in batch or continuously in a kettle at around 130 ° C: βCaSO
₄ 1 / 2H ₂ O), α-type hemihydrate (the above-mentioned dihydrate is pressurized and baked in an autoclave etc .: αCaSO ₄ 1 / 2H ₂ O) and anhydrous salt (above dihydrate and hemihydrate) Examples include II, III and I-type CaSO ₄ ) obtained by calcining salt at a higher temperature. Of these, β type hemihydrate gypsum is used to solidify in a short time and to increase the amount of waste liquid treated per unit weight of the solidifying material, while solid waste such as sludge and incinerated ash is solidified. When increasing the strength, there is less kneading water and the volume of the cured product is β
It is preferable to use α-type hemihydrate gypsum, which is smaller than that of type hemihydrate gypsum.

In the present invention, gypsum with various particle sizes can be used, but it is preferable to use gypsum having a particle size of 50 μm or less because the solidification reaction can be accelerated and a large amount of waste can be treated.

As the slag used as the second component in the present invention, slag generated in various steps such as blast furnace slag, converter slag and electric furnace slag generated in the step of manufacturing steel from iron ore can be used. Of these slags, those having latent hydraulic properties by rapid cooling treatment such as water granulation can be used, but among them, those having a particularly small particle size are preferable.

Examples of the alkali stimulant used as the third component in the present invention include alkali compounds such as sodium hydroxide and calcium hydroxide, or generally commercially available ordinary Portland cement, early strength Portland cement, super early strength Portland cement, and moderate heat Portland cement. And cement such as sulfate resistant Portland cement. Of these, it is economical to use ordinary Portland cement because of its price.

The first solidified material for radioactive waste of the present invention is gypsum 20.
˜70 parts by weight (hereinafter abbreviated as “part”), preferably 2
0 to 50 parts, slag 20 to 70 parts, preferably 40 to 7
0 parts and 5-40 parts of an alkaline stimulant, preferably 5-3
Contains 0 parts.

The second solidified material for radioactive waste of the present invention comprises, in addition to the above composition, a compound which is water-soluble itself and reacts with a water-soluble carbonate to form a water-insoluble carbonate as a fourth component. contains. Examples of such a compound include one or more water-soluble inorganic salts selected from chlorides such as calcium, magnesium, barium, iron, copper and aluminum, sulfates and nitrates. Of these, calcium chloride and calcium nitrate are preferred in the present invention. It is preferable that these compounds are contained in the solidified material for radioactive waste in an amount equivalent to the amount of the water-soluble carbonate contained in the radioactive waste liquid to be treated or up to twice the equivalent amount thereof.

The first composition of the present invention is used as it is for radioactive waste liquid containing no carbonate, and for radioactive waste liquid containing carbonate, the pH of the liquid is lowered by adding an acid or the like to the radioactive waste liquid. It is possible to solidify the radioactive waste by adding the carbonate to carbon dioxide after releasing it into the atmosphere to remove it. That is, the presence of carbonate does not cure the first composition of the present invention. Even with conventional Portland cement, which is a conventional solidifying material, if carbonate is present in the radioactive waste liquid, it will instantly become a pseudo-condensation state (a state that it will seem as if it has hardened) during kneading and lose its fluidity. Difficult to use.

On the other hand, the second composition of the present invention is pretreated as a composition for treating low-level radioactive waste liquid containing a water-soluble carbonate such as sodium carbonate in radioactive waste. It can be preferably used without.

The first and second compositions of the present invention are not limited to solidifying liquid radioactive waste, and are also suitable as a solidifying material for solid radioactive waste.

〔The invention's effect〕

According to the present invention, radioactive waste, particularly concentrated waste liquid, can be treated in a relatively large amount per unit weight of the solidifying material. In addition, for radioactive waste, which can be solidified easily and in a short time, is safe and easy to handle, does not shrink significantly during curing, and is a stable solidified inorganic substance with little leaching of radioactive substances from the solidified body. A solidified material is provided.

Therefore, the solidified material for radioactive waste of the present invention can be suitably used for solidification treatment of various radioactive wastes.

Next, the present invention will be described with reference to examples.

〔Example〕

Example 1 The composition of the following simulated concentrated waste liquid similar to the low-level radioactive concentrated waste liquid discarded from the nuclear power plant was used, and various compositions shown in Table 1 were added thereto to examine the solidification property.

Composition of simulated concentrated waste liquid Na ₂ SO ₄ 20% Fe (OH) ₃ 0.6% Water 79.4% Experimental method Various compositions of simulated concentrated waste liquid shown in Table 1 for various amounts of waste liquid shown in Table 1 (1 kg) was added in 30 seconds and immediately stirred with a stirring bar having a diameter of 15 mm for 1 minute (100 rpm), and the obtained slurry was poured into a 4 × 4 × 4 cm ³ compressive strength mold and cured to give a test sample. . The curing time was determined from the exothermic peak of hemihydrate gypsum (JIS R9112).

The leaching amount of radioactive substances in the solidified body was replaced by a leaching test of sodium ion from a sodium compound, which has a very high solubility and is easily eluted, and the test was carried out for 30 days in a 25 ° C 100% RH constant temperature and humidity chamber. The test sample was immersed in 1 of deionized water, and 8 days later, the sodium ion in the solution was measured by an atomic absorption method, and the amount of leaching was determined from the following formula.

The change in the volume of the solidified body was determined by measuring the change in the length of the test sample with a dial gauge after curing for 30 days in a thermo-hygrostat at 25 ° C. and 100% RH. The cement hardening time is J
It is obtained according to ISR-5201.

The results are summarized in Table-1. In addition, in the table, BSA of * slag is 4000 cm ² / g, BSA of other slag is 65
It is 00 cm ² / g. Further, breathing occurred in Comparative Example No. 2.

From the results of Table 1, it can be seen that the present invention provides an excellent solidified material for radioactive waste. Further, it is understood that fine granules of granulated blast furnace slag used as slag are preferable. In the compositions shown in Table 1, slaked lime was used in place of ordinary Portland cement, which is an alkali stimulant, but good results were obtained.

Example 2 Instead of the simulated concentrated waste liquid used in Example 1, a simulated concentrated waste liquid of a reprocessing plant having the following composition was used in the same manner as in Example 1 to give a fourth composition to the first composition of the present invention. The performance of the solidified material for radioactive waste to which the component calcium chloride was added as shown in Table 2 was examined.

Table 2 shows the collectively composition _{NaNO 3 21.64% NaNO 2 5.94%} Na 2 CO 3 11.82% Water 60.60% The results of the simulated concentrated liquid waste. In Comparative Examples 3 and 4 of the present invention in the table, sulfuric acid was used to adjust the pH of the waste liquid to the acidic side to generate carbon dioxide gas from the simulated concentrated waste liquid and release it into the atmosphere, and then solidified by adding a solidifying agent. .

The first aspect of the present invention in which calcium chloride is removed from the present invention No. 5
The composition (1) does not cure, and the ordinary Portland cement shown in Comparative Example 1 has a drawback that it instantly pseudo-sets. However, as is clear from Table-2, Comparative Example No. 3
As in the present invention No. 4 or the like, acid such as sulfuric acid is added to the simulated concentrated waste liquid in advance to adjust the pH of the liquid to the acidic side to generate carbon dioxide gas from the carbonate (Na ₂ CO ₃ ) in the liquid. It is understood that according to the present invention Nos. 5 to 7, solidification can be easily carried out without performing a pretreatment for removing. Also, it can be seen that the performance of the solidified body thereby is not inferior to that of the solidified body obtained by pretreatment.

In addition, as shown in Comparative Example No. 2, in the solidifying material in which calcium chloride was added to ordinary Portland cement, the present invention No. 4 was used.
An effect equivalent to that of ~ 7 was not obtained.

Further, in the compositions Nos. 5 to 7 shown in Table 2, ferric chloride or calcium nitrate was used instead of calcium chloride, but good results were obtained in all cases.

The compressive strengths of the solidified bodies of the compositions of the present invention shown in Examples 1 and 2 were 150 kg / cm ² or more.
This satisfies the regulation value (“The uniaxial compressive strength of solidified radioactive waste is 150 kg / cm ² or more”) stated in Notification No. 7 of the Science and Technology Agency on November 1, 1980. To do.

Claims (2)

[Claims] 1. Gypsum 20-70 parts by weight, slag 20-70
A solidified material for radioactive waste, which comprises 5 parts by weight and 5 to 40 parts by weight of an alkali stimulant. 2. Gypsum 20-70 parts by weight, slag 20-70
100 parts by weight of a solidifying material containing 5 parts by weight and 5 to 40 parts by weight of an alkali stimulant, and a compound which itself is water-soluble and reacts with a water-soluble carbonate to form a water-insoluble carbonate. A solidified material for radioactive waste, which is characterized in that