JPS60120299A - Method of solidifying radioactive 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 [Field of Application of the Invention] The present invention relates to a method for treating radioactive waste generated from nuclear power plants and the like, and particularly to an assimilation method suitable for pelleted radioactive waste.

[Background of the invention]

Various radioactive wastes are generated as a result of the operation of nuclear power plants, etc., but reducing the volume of these radioactive wastes and stably solidifying them in solidification containers such as drums is an effective way to secure storage space within the facility. It is not only important in terms of safety, but also indispensable for land storage and land disposal, which is one of the future final disposal laws.

For example, one method to reduce the volume of radioactive waste is to use recycled waste liquid (main component: sulfuric acid (IJ wam)), which is the main waste generated from boiling and barrel nuclear power plants, and waste ion exchange resin slurry. Attempts have been made to reduce the volume of the waste cap by a large amount by drying and powdering it using a dryer such as a centrifugal thin film dryer, and then pelletizing it using a granulator such as a briquerating machine. .

According to this method, compared to the method of directly solidifying waste liquid or slurry with cement (so-called Shichimen F solidification method), the cost is approximately 1/8
It has been confirmed that the volume can be reduced to

However, even with such a method that can significantly reduce the volume, there is a problem that a stable solidified body cannot be formed using a hydraulic filler such as cement. This is because cement is mixed with water and water is absorbed into the dry powder of the pellets, causing the pellets to swell and dissolve. For this reason, fillers that do not require the use of water, such as asphalt.

Attempts have been made to solidify the material using plastic. However, these assimilation methods have many drawbacks, such as the need for high temperature operations and the extremely expensive fillers themselves.

For these reasons, there is a need for a method of solidifying pellet-shaped radioactive debris using a filler (solidifying agent) that is easy to operate, inexpensive, and has excellent stability during long-term storage.

[Purpose of the invention]

The purpose of the present invention is to solidify radioactive waste with a hydraulic inorganic solidifying material such as cement, by dissolving the waste in place of water and hardening the solidifying material using a solution that does not cause swelling. Another object of the present invention is to provide a stable and inexpensive method for producing solidified radioactive waste.

[Summary of the invention]

The feature of the present invention is to cure radioactive waste, especially radioactive waste containing ion exchange resin, during the curing process of cement by curing hydraulic inorganic solidifying material such as cement with alkaline silicate solution a or alkaline hydroxide solution. The understanding of pellets,
Its purpose is to prevent swelling and stably solidify radioactive waste.

The present invention was accomplished through the following considerations and experiments. An example of this is Belento, the radioactive waste generated from the Boiling Mizuya Nuclear Power Plant (main components are sodium sulfate and ion exchange resin).
The case of solidifying with Class 0 blast furnace cement will be explained.

Cement is mixed with water to form a sol-like paste that is filled into the spaces between the pellets. At this time, the pellets absorb the water in the paste, and the sodium sulfate and ion exchange resin dissolve and swell, respectively, resulting in stable disposal. It was experimentally confirmed that solidified matter could not be obtained. In other words, the dissolved sodium sulfate diffuses onto the surface of the solidified body and induces the leaching of radioactive elements into the environment, and the swollen ion-exchanged fat easily causes cracks in the solidified VC waste body (1 moisture of the AT fat). The pressure is 100 to 300 Kg/crA, whereas the tensile strength of the hardened cement is lθ to 40 Kf/-). In particular, the occurrence of cracks is important because it may lead to solidified body destruction accidents.

The above problem when choosing cement as a solidification material is
To solve this problem, we considered t-curing the cement with a solution that is not absorbed by the pellets. Sodium sulfate IJ in various solutions
Figure 1 shows the change over time in the pellet absorption rate when pellets of 3QWHI, a powdery (average particle size: 50 μm) ion exchange resin containing 70 wt% of aluminum, were immersed. H snow 0 and C
! All solutions, except H80I, are prepared at a concentration close to saturation. In the case of actual radioactive waste pellet assimilation, cement particles are present in the solution in a considerable proportion (65 to 7.5 Wt).
The amount of free solution decreases as the cement hardens. Further, the hardening time of the cement is 3 to 5 hours. Therefore, although the experimental conditions can be said to be very severe compared to the actual case, it is still difficult to obtain a stable solidified body in a solution where the water absorption rate of the pellet exceeds Swt%° after 5 hours of immersion. Ta. It can be seen from FIG. 1 that a strong alkaline solution is preferable. In addition, even in a saturated N''g804 solution that should not dissolve sodium sulfate, it was found that most of the water was absorbed by the ion exchange resin, as it showed a water absorption rate of 10-wt% or more. This is thought to be due to the high concentration of hydroxyl groups preventing water from adsorbing to the resin.

Although it was found in the preliminary disaster test that a saturated strong alkaline solution was not absorbed by waste pellets containing ion-exchange resin, we next investigated to what extent the concentration could be tolerated. Figure 2 shows the dependence of pellet water absorption on solution concentration. Alkaline silicate solution is 20 wts or more, alkaline hydroxide solution is a
It has been found that it is desirable to use it at a concentration of o wt1 or higher.

Furthermore, it was investigated whether the cement would harden with these solutions and develop a desired strength. ao for class 0 blast furnace cement
Figure 3 shows the compressive strength of a sample cured by adding water and 40 wt% of the above solution at a ratio of wt (t).Compared to the case of water, the strength decrease was 10 to 20 cm, and the sample was thoroughly disposed of. It was found that it can be used for solidifying materials.

Based on the above considerations and experimental results, radioactive waste containing ion exchange resin can be stably solidified by curing cement with an alkali Ti solution of 20 Wt or more or an alkaline hydroxide solution of more than 30 Wt. Can be done.

[Embodiments of the invention]

An embodiment of the present invention will be explained below with reference to FIG. In this Example 7Ili, radioactive waste pellets of sodium sulfate containing ion exchange resin AOWT are solidified in a 200 ton drum with Class 0 blast furnace cement and 4 owt sodium silicate solution.

The radioactive waste pellets 4 are placed in the inner basket 6 in advance.
Put about 300 kg into c200t drum 5. In this, C. blast furnace cement 1 and 40 wt% silicic acid) IJ
After kneading the Kumu solution 2 homogeneously in the mixer 3,
The pellets are filled to fill the gap between the drum 5 and the pellets 4 for about 15 minutes.

After filling, if left at room temperature, it will harden in several hours, and a solidified product as shown in FIG. 5 can be obtained. Moreover, the solidified product obtained in this manner is stable and solid, with no cracks caused by water absorption and swelling of the pellets.

According to this embodiment, a stable solidified body of radioactive waste pellets can be provided by heating C Taneshima reactor cement' with a sodium silicate solution.

Although class 0 blast furnace cement was used in the above example, similar effects can be obtained by using other cements (Portland cement, fly ash cement, etc.) or gypsum.

In the above embodiment, the shape of the waste is pellets, but the same effect can be obtained even if the pellets are in powder form. However, it must be homogeneously mixed with the assimilate in a mixer or drum.

In the above example, the waste generated from BWR is Na2
Although SO4 was used as the waste material as the main component, the same effect can be obtained even if the main component is sodium borate (NazBaOt) generated from PWR or other various waste materials.

Although a silicic acid solution was used in the above example, the same effect can be obtained by using other alkaline silicate solutions or alkaline hydroxide solutions.

〔Effect of the invention〕

According to the present invention, since it is possible to prevent water absorption #3 of radioactive waste containing ion exchange resin, it is possible to prevent cracking and destruction of the radioactive waste solidified body.

In addition, to harden cement, simply use an alkali silicate or alkali hydroxide bath solution in place of the water.
The conventional system can be used as is, which has the effect of improving economic efficiency.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the water absorption rate of pellets in various bath liquids;
Figure 2 is a diagram showing the relationship between dissolved tL concentration and pellet water absorption rate;
Figure 3 is a diagram showing the strength of a cement hardened product hardened with water and 6 liquids, Figure 4 is a schematic diagram showing the pellet assimilation method according to the present Mi example, and Figure 5 is a diagram showing the pellets made in this example. This is a cross-sectional view of the solidified material. 1... Type 0 blast furnace cement, 2... 4 Qwt% sodium silicate worm solution, 3... Mixer, 4... Radioactive waste pellets, 5... 200t drum can, 6... Inner basket, 7... Mento cured product in Cfji blast furnace. Agent Patent attorney Akio Takahashi ￥ II2] 3'jL4g1 (JL) ￥20 Meltability (wt2',) Kaya 30 Light A time (direct) Kyou 4 (!1

Claims (1)

[Claims] 1. A method for solidifying radioactive waste with a hydraulic inorganic solidifying material, characterized in that the inorganic solidifying material is hardened using a solution that does not dissolve or swell the radioactive waste instead of water. A method of solidifying radioactive waste. 2. The method for solidifying radioactive waste as set forth in claim 1, wherein the prehydraulic inorganic solidifying material is % seed cement and gypsum. 3. The method for solidifying radioactive waste according to claim 1, wherein the solution that does not dissolve or swell the radioactive waste is an alkaline silicate solution or an alkaline hydroxide solution. 4. A patent claim characterized in that the radioactive waste is radioactive waste such as a and m waste liquids, ion exchange resins, filter sludge, etc. generated from BWRs and PWRs, which have been turned into dry powder or pellets. Range 1st to 3rd
Methods for assimilating radioactive waste as described in Section. 5. The method for solidifying radioactive waste according to claims 1 to 3, which is effective for radioactive waste pellets that sometimes contain an ion exchange resin among the radioactive wastes.