JPH0631852B2 - Method for solidifying radioactive waste - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for solidifying radioactive waste generated from a nuclear power plant or the like, and in particular, an inorganic solidifying material containing water in a fluidized state is used as a solidifying filler. The present invention relates to a method for solidifying radioactive waste suitable for use.

[Prior Art] One of the forms of final disposal of radioactive waste generated from nuclear power plants is land storage and land disposal. For that purpose, the radioactive waste is solidified to solidify the radioactive waste. You need to create a body. Inorganic substances are suitable as materials for solidifying radioactive waste. Regarding the solidification method of radioactive waste using an inorganic material, there is a conventional method described in
The method described in JP-A-54-34000 or JP-A-57-197500 has been known. The former uses a cement-based solidifying material and the latter uses an alkali silicate-based solidifying material, both of which aim to stably fix radioactive waste.

[Problems to be Solved by the Invention] Although all the solidifying materials form a solidified body together with radioactive waste via a fluidized state, the conventional method does not pay attention to the characteristics of this fluidized state. No special consideration was given to the control of the solidified material in the state. The solidified body was created by mixing the solidified material component or the solidified material and the waste according to the mixing ratio of the solidified material component or the solidified material and the waste empirically obtained from the soundness of the solidified body after curing. . Therefore, since there was no idea to adjust or control the flow state of the solidified material immediately after mixing, there was a problem that cracks often occurred more than expected in the solidified material produced.

An object of the present invention is to provide a method for producing a sound radioactive waste solidified body in which cracks do not occur after solidification by a very simple means in order to solve the above problems.

[Means for Solving the Problems] The above object is achieved by adjusting the viscosity of the solidified material in a fluid state to 3000 cP or less.

[Operation] Strength is an important evaluation factor for radioactive waste solidification. The strength of the solidified body is greatly affected by the water content and the porosity. The effects of the water content and the porosity on the strength of the solidified body will be described.

Most inorganic solidifying materials contain water in the fluidized state.
This water may come from waste or the solidifying material itself, but it plays an important role of directly or indirectly accelerating the hardening reaction of the solidifying material. However, in general, in a fluid state, excess water is present in excess of the amount required for the curing reaction, and excess water remaining in the curing reaction weakens the bonding force between the solidifying materials after curing,
Alternatively, voids are formed in the solidified body to reduce the strength of the solidified body. It was found that when the relative strength of this solidified body (value under the optimum conditions) is 0.5 or less, it is not desirable as an equalized solidified body in which cracks occur. The relationship between the porosity of the solidified body and the strength of the solidified body is shown in FIG. 1 and Table 1. It can be seen that when the porosity of the solidified body is 30% or more, the relative strength of the solidified body becomes 0.5 or less and cracks occur in the solidified body. Therefore, in the past, many attempts have been made to reduce the addition amount or content of water to the solidifying material as much as possible.

However, conversely, it was found that the porosity increases even if the water content decreases. In this case, it was found that the solidified body porosity depends on the viscosity of the solidified material before curing. That is, when the viscosity of the solidifying material is high, the air taken in at the time of stirring (gas in contact with the solidifying material) is a solidified material (sol) in a fluid state before curing.
It becomes difficult to separate from, and the porosity in the solidified body after curing increases. FIG. 2 shows the relationship between the porosity of the solidified body and the viscosity of the solidified material sol (immediately after the formation of the sol). In order to reduce the porosity of the solidified body to 30% or less, the viscosity of the solidified material sol needs to be 3000 cP or less. Therefore, if the viscosity of the solidifying material is adjusted to 3000 cP or less, a sound solidified body without cracks can be prepared.

Actually, the viscosity of the solidified material in the fluidized state is a parameter that can be adjusted and controlled before curing rather than the porosity that can be measured only after curing, so the strength of the solidified material can be adjusted by a very simple means of adjusting the viscosity of the solidified material. It can prevent the deterioration.

The solidifying material used in the present invention is an inorganic solidifying material containing water in a fluidized state before hardening, such as various cements, alkali silicates, gypsum or substances based on these. The waste referred to in the present invention is a radioactive waste in the form of a solution or solid such as powder or pellets generated from a radioactive material handling facility such as a nuclear power plant. Also,
It can also be applied to general industrial waste that is not radioactive.

As described above, according to the present invention, by adjusting the viscosity of the solidifying material before curing, it is possible to prepare a sound radioactive waste solidified body in which cracks do not occur after curing by a very simple means.

[Embodiment] An embodiment of the present invention will be described below with reference to FIGS.

Example 1 An example of the present invention shown in FIG. 3 is a waste pellet obtained by dry-pulverizing concentrated waste liquid (main component Na ₂ SO ₄ ) generated from a nuclear reactor as radioactive waste and then pelletizing it. 60% by weight of sodium silicate (Na ₂
This is an example in which a solution of O · nSiO ₂ , n = 0.5 to 4) is further selected, and calcium silicate (CaSiO ₃ ) is selected as a hardening agent, and the solution is solidified in a 200-drum can used for solidification of radioactive waste.

As shown in FIG. 3, first, about 260 kg of radioactive waste pellets 7 containing Na ₂ SO ₄ as a main component is filled in a metal cage 6 provided in a 200 drum can 5. Next, the 60 wt% aqueous sodium silicate solution, the calcium silicate and the cement contained in the tanks 1, 2 and 3, respectively, of 150 kg, 60 kg and 30 kg are homogeneously mixed in the mixing and stirring tank 4. At this time, from the relationship between the torque obtained in advance from the torque of the stirrer in the stirring tank and the viscosity of the solidifying material mixture, make sure that the solidifying material viscosity does not exceed 3000 cP. Then, the solidifying material is caused to flow into the 200 drums to fill the spaces between the pellets and between the pellets and the drums. After filling, in order to remove air bubbles remaining in the solidified material, vacuum deaeration is performed at about 50 torr, and the material is left to cure at room temperature. Curing is completed in about 2 hours.

Example 2 FIG. 4 shows an example in which sodium silicate powder was used instead of the sodium silicate solution. In this case,
In order to facilitate homogeneous stirring of the powder and water, the powders of sodium silicate, calcium silicate and cement contained in the tanks 8, 2 and 3 are mixed in advance in the premixing tank 10 to homogeneity. deep. This is mixing tank 4
In (1), the mixture is homogeneously kneaded with water from the tank 9, and the viscosity is confirmed by the same method as in the above-mentioned example. Or 30 if necessary
Adjust to less than 00cP. Then, the radioactive waste pellets 7 are made to flow into the 200 drums 5 filled in the inner cage 6 in advance. Deaeration and curing are performed in the same manner as in the above embodiment.

The radioactive waste solidified body as shown in FIG. 5 can be obtained by the methods shown in the above two examples. The solidified body thus produced had no crack and had sufficient strength.

According to Example 1 and Example 2, an inorganic substance containing sodium silicate as a main component is used as the solidifying material, and the viscosity of the solidifying material in a fluid state can be confirmed or adjusted by a simple means such as torque measurement of a stirrer. This makes it possible to prepare a high-strength solidified body of radioactive waste pellets that does not crack after curing.

In the above two examples, the pellets are described as almond-shaped in the drawings, but the pellet shape is essentially irrelevant, such as a sphere, an elliptic sphere, a cylinder, a cube, and a rectangular parallelepiped.
The present invention can be applied in any form.

Further, in the above embodiment, the inner basket 6 is used so that the radioactive waste pellets do not come into contact with the inner wall of the drum can 5.
It is also possible to solidify the waste pellets by placing a fibrous material such as glass fiber, asbestos, carbon fiber, metal fiber, or polymer-impregnated cement inside the drum.

In the case of solidifying the radioactive waste pellets, the radioactive waste pellets may be filled in the drum can by mixing the radioactive waste pellets and the solidifying material instead of filling the drum can in advance. The effect of can be produced.
In this case, it is desirable to check the viscosity in the final mixed state.

Example 3 Next, as another example of the present invention, in the case of solidifying radioactive waste liquid (main component Na ₂ SO ₄ ) in a state of being generated from a nuclear power plant into 200 drums, not radioactive waste pellets This will be described with reference to FIG. In this case, in order to secure the strength of the solidified body and the volume reduction of the waste, the radioactive waste liquid stored in the tank 12 is dehydrated by the dryer 13, converted into powder of the radioactive waste, and put in the tank 14. As a method for drying the radioactive waste liquid, a centrifugal thin film drying method, a spray drying method, a fluidized bed drying method, a drum drying method, a freeze drying method, a crystallization method and the like are known, but any method may be adopted. .

In this way, after the radioactive waste liquid is pretreated, the sodium silicate aqueous solution, the hardening material, the cement, and the radioactive waste powder are fed to the mixing and stirring tank 4 from the respective tanks 1, 2, 3 and 14 to homogenize them. To mix. At this time, the viscosity of the mixed substance is checked, and the viscosity is adjusted if necessary. Then, it is flowed into and filled in 200 drums to remove residual bubbles in the solidified material.

As described above, according to the present embodiment, it is possible to prepare a homogeneous solidified body of radioactive waste as shown in FIG. 7, which has sufficient strength without cracks.

In Example 3, the water in the radioactive liquid waste is removed by the dryer 13 to be converted into powder. However, even if the water content is not completely removed, the water content in the mixed liquid is kept in an appropriate range. It is sufficient to adjust the water content of.

In each of the above-mentioned Examples (Examples 1, 2, and 3), the case of solidifying radioactive waste (waste pellets or waste liquid) containing sodium sulfate as a main component generated from a boiling water reactor has been described. The waste component is not essential, but for radioactive waste mainly containing boric acid generated from a pressurized water reactor, or used ion-exchange resin, and waste generated from a reprocessing facility for spent nuclear fuel. However, the same effects can be obtained by implementing the present invention.

In each of the above examples, calcium silicate was used as the hardening agent for sodium silicate, but the same effect can be obtained by using a substance that hardens sodium silicate such as an inorganic phosphate compound. The same effect can be obtained by using an inorganic solidifying material such as cement or gypsum other than sodium silicate. In the case of cement and gypsum, water acts as a hardener. Further, although the viscosity of the solidified material in the fluidized state was measured from the torque of the stirrer in the above-mentioned examples, the same effect can be obtained by applying any other viscosity measuring method.

Further, in the above embodiment, the air bubbles in the solidified material after filling are removed by vacuum deaeration, but the same effect can be obtained by shaking or heating the drum can after filling the solidified material.

[Effects of the Invention] According to the present invention, it is possible to create a sound radioactive waste solidified body that does not cause cracks by using an inorganic solidified material by a simple means of checking the viscosity of a solidified material in a fluidized state. .

[Brief description of drawings]

1 and 2 are diagrams showing the relationship between the characteristics of the basic solidifying material and the solidified body that led to the invention, FIG. 3, FIG. 4 and FIG. The figure which shows an Example, 5th
FIG. 7 and FIG. 7 are views showing a cross section of a solidified radioactive waste produced according to an embodiment of the present invention. 1 …… Sodium silicate solution tank 2 …… Hardening material tank 3 …… Cement tank 4 …… Mixing and stirring tank 5 …… Drum can 6 …… Cage made of wire mesh 7 …… Radioactive waste pellets 8 …… Silicic acid Sodium powder tank 9 ... Water tank, 10 ... Powder premixing tank 12 ... Radioactive waste liquid tank 13 ... Dryer 14 ... Radioactive waste powder tank

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical display location G21F 9/36 511 F 7381-2G (72) Inventor Yoshihiro Ozawa 1168 Moriyama-cho, Hitachi-shi, Ibaraki Shares Incorporated in the Institute for Energy Research, Hiritsu Seisakusho Co., Ltd. (56) Reference JP-A-58-20767

Claims (2)

[Claims] 1. A method for solidifying radioactive waste with an inorganic solidifying material, characterized in that the viscosity of the solidifying material before or after addition to the radioactive waste is adjusted to 3000 cP or less. Method. 2. A method for solidifying radioactive waste with an inorganic solidifying material, wherein the solidifying material in a fluid state has a viscosity of 3000 c.
A method for solidifying radioactive waste, which is adjusted to P or less and poured into a container filled with radioactive waste pellets.