JP2003146727A - Light weight mortal and solidifying method for radioactive waste using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide light weight mortal wherein satisfactory fluidity can be maintained for a long time and which is excellent in packing properties, low in specific gravity and excellent in strength and the like of the solidified material thereby and to provide a solidifying method for a radioactive waste by which a waste body can be made light in weight. SOLUTION: The light weight mortal is used, consisting of water-hardenable cement, light weight aggregate, a dispersing agent, a separation suppressing agent, a weight lightening promoter and water and characterized in that the light weight aggregate is formed by mixing an igneous rock calcined material and an obsidian calcined material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lightweight mortar and a method for solidifying radioactive waste using the same, and more specifically, it relates to a method for solidifying metal such as metal or concrete generated from a facility handling radioactive materials such as a nuclear power plant. The present invention relates to a lightweight mortar that is preferably used for filling and solidifying large-scale miscellaneous waste and a method for solidifying radioactive waste using the same.

[0002]

2. Description of the Related Art From nuclear facilities such as nuclear power plants, concentrated waste liquid is dried, pulverized, and then molded into pellets, solid pieces such as metal cutting pieces, filters, packings and concrete blocks. A lot of radioactive miscellaneous waste is generated. Such waste is cut and stored in an appropriate size so that it can be filled in, for example, a 200-liter drum, and then stored and solidified. As a method of this solidification treatment, a method is considered in which cement mortar is poured as a solidifying material into a drum containing waste, and the mixture is solidified by filling voids between the drum and waste or voids between wastes. The disposal of waste solidified in this way has started in some areas.

Further, it is expected that a large amount of large-scale waste will be generated at the time of dismantling the facilities of the nuclear power plant due to deterioration of the nuclear power plant, etc. A method of directly filling or storing in a large container of 1 m ³ or more, filling a solidifying material, and transporting to a disposal site for disposal is considered.

By the way, as for the cement-based solidifying material, a method of mixing water with cement to use it as a cement paste, a method of mixing sand (fine aggregate) and water with cement to form cement mortar, or cement In general, the method of mixing sand (fine aggregate), gravel (coarse aggregate), and water to form concrete is used in the civil engineering and construction industry. Among these, radioactive miscellaneous waste generated from nuclear facilities is generally solidified by filling cement mortar.

[0005]

However, in the case of the solidification treatment of large radioactive waste generated by the dismantling of a nuclear power plant or the like as described above, when conventional cement mortar is used as the solidifying material, Since the specific gravity is too large, the weight regulation may be exceeded, and it may be difficult to lift or transport the waste. Also, since it requires the use of a large amount of equipment or facilities,
There is concern that costs will increase.

Furthermore, when filling and solidifying heavy waste such as metal pieces and concrete lumps, the amount of waste to be stored in one disposal container is significantly limited due to the durability of the disposal container. Therefore, it is considered necessary to reduce the weight of the solidified waste. Such limitation of the amount of waste to be processed leads to an increase in the number of wastes, which not only increases the disposal cost, but also requires the expansion of the site area for storage and the addition of a management building. This is different from other countries
It is a serious problem in Japan, which is not endowed with a small land area, and reducing the number of waste will be an important issue in the future, as it could lead to the restructuring of the nuclear power business itself.

Therefore, the present inventors have paid attention to reducing the weight of the solidifying material in order to reduce the weight of the waste. Generally, in order to reduce the weight of cement mortar and concrete, a technique of using a lightweight aggregate or injecting bubbles to reduce the weight of a solidified body is used. Therefore, it is conceivable to apply such a technique to a solidifying material for waste, but in this case, regarding the mortar, the run-down time by the P funnel specified by the Japan Society of Civil Engineers is 16 to 5
High fluidity of about 0 seconds is required and 1.5
The solidified body is required to have a strength of about MPa or higher. Therefore, in the solidified material of waste, if the fluidity of the mortar using the lightweight aggregate is increased, the lightweight aggregate is floated and separated due to the difference in specific gravity from the waste, and a uniform solidified body is not obtained. Have difficulty. In addition, in the method of injecting bubbles,
The problem is that the strength of the solidified body is reduced.

The present invention has been made in order to solve the above technical problems, and can maintain good fluidity for a long time, has excellent filling properties, has a small specific gravity, and solidifies. It is an object of the present invention to provide a lightweight mortar having excellent body strength characteristics and the like.

Another object of the present invention is to solidify radioactive waste by using the above-mentioned lightweight mortar, which has excellent filling properties and strength properties of the solidified product, and which can reduce the weight of the waste product. Is to provide a method.

[0010]

The lightweight mortar according to the present invention is a lightweight mortar comprising a hydraulic cement, a lightweight aggregate, a dispersant, a separation inhibitor, a weight reduction aid and water. Is characterized by being a mixture of an igneous fired product and an obsidian fired product. By blending such raw materials, it is possible to obtain a lightweight mortar which is excellent in fluidity and filling properties, has a small specific gravity, and is excellent in the strength characteristics of the solidified body and the like.

In the lightweight mortar, it is preferable that the particle diameter of the lightweight aggregate is 1.2 mm or less. In order to ensure a sufficient filling property even in a narrow void, it is preferable to use a lightweight aggregate having a particle size in the above range.

The hydraulic cement is preferably Portland cement or cement containing blast furnace slag or fly ash. Blast furnace slag contributes to improving the chemical stability of lightweight mortar and suppressing heat generation during solidification, and fly ash contributes to improving the fluidity and filling of lightweight mortar. .

Further, the separation inhibitor is preferably bentonite containing montmorillonite as a main component. The separation inhibitor is added to prevent the cement slurry from separating from the lightweight aggregate and to impart volume stability to the solidified body.

Furthermore, the weight saving aid is preferably sodium lauryl sulfate. The weight-reducing aid contributes to further lowering the specific gravity of the light mortar and reducing the blending amount of the lightweight aggregate due to the emulsifying action.

Further, the dispersant is preferably a naphthalene sulfonic acid type dispersant. The dispersant is for imparting good fluidity, and is preferably added also from the viewpoint of workability.

The light weight mortar contains 5 to 15% by weight of igneous calcinated lightweight aggregate, 10 to 30% by weight of obsidian calcinated lightweight aggregate, and 0. It is preferable that 5 to 2.0% by weight, a separation inhibitor of 5 to 15% by weight, and a weight saving aid of 0.01 to 0.05% by weight are contained. The composition of raw materials is suitable as a formulation for adjusting the lightweight mortar according to the present invention.

The specific gravity of the lightweight mortar is 1.00 g / c
It is preferable that m ³ or less and the compressive strength of the solidified mortar is 1.5 MPa or more. A lightweight mortar satisfying the specific gravity and the compressive strength of the solidified body can be suitably used for solidification treatment of waste as a mortar excellent in lightweightness and strength characteristics.

The method for solidifying radioactive waste according to the present invention is
It is characterized in that the above-mentioned lightweight mortar is filled and solidified. As described above, the lightweight mortar according to the present invention is excellent in fluidity, filling property, lightweight property and strength property of the solidified body. Therefore, by treating the radioactive waste with the waste mortar, It is possible to contribute to the reduction of weight and the reduction of the number of waste.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
The lightweight mortar according to the present invention comprises a hydraulic cement, a lightweight aggregate obtained by mixing an igneous calcination processed product and an obsidian calcination processed product, a dispersant, a separation inhibitor, a lightweighting aid and water. It has been compounded. With such a raw material composition, it is possible to obtain a lightweight mortar having high fluidity and filling properties, a small specific gravity, and excellent strength properties of the solidified body.

In the present invention, the lightweight aggregate is used by mixing a igneous rock baked product and an obsidian baked product. Especially for hydraulic cement, igneous rock firing processed products are 5
It is preferable to mix 15% by weight and the obsidian calcined product in the range of 10 to 30% by weight. By mixing and blending these two types of lightweight aggregates in the above proportions,
Compared with the case where each is added alone, the addition amount of the lightweight aggregate can be reduced, and the density of the mortar can be significantly reduced, and the target value of the density of the lightweight mortar is 1.0 g / cm ³ or less can be achieved.

When the igneous rock-fired lightweight aggregate alone is blended in an amount of more than 15% by weight, due to the water absorption of the aggregate,
A large amount of kneading water is required, which reduces the strength of the solidified body. In addition, due to the difference in specific gravity, a disadvantage occurs that the lightweight aggregate is easily floated and separated. On the other hand, the obsidian calcined lightweight aggregate has a hollow shape, and its water absorption is much lower than that of the igneous calcined lightweight aggregate. Therefore, if it exceeds 30% by weight, the viscosity of the mortar will increase. From the relationship
The aggregate floats above the solidified body and impairs the homogeneity of the solidified body.

It is preferable that the lightweight aggregate is blended in a ratio of igneous fired product: obsidian fired product = 1: 2 (weight ratio). With such a blending ratio, it is possible to obtain a solidified body that is lightweight and homogeneous and has excellent strength characteristics.

Further, the particle diameter of each of the lightweight aggregates is preferably 1.2 mm or less. Mortar, when used for solidification of waste, needs to be well filled in the small voids between wastes and has a particle size of 1.2.
If it exceeds mm, this filling property becomes insufficient.

The hydraulic cement used in the present invention is preferably Portland cement or cement containing blast furnace slag or fly ash. Specifically, Portland cement, blast furnace cement that is a mixture of Portland cement and blast furnace slag,
Fly ash cement obtained by mixing fly ash with Portland cement can be used.

As described above, the hydraulic cement preferably contains blast-furnace slag, but this has an excellent effect in that the chemical stability can be improved and the heat generation during solidification can be suppressed. This is because it is obtained. When mortar is used for filling and solidifying large-scale waste, a large amount of hydraulic cement to be filled is also required, the heat capacity at the time of solidification increases, and the temperature rises due to heat generation. In particular,
In the case of waste metal, cracks are likely to occur due to its thermal expansion. Therefore, by using the hydraulic cement mixed with the blast furnace slag, it is possible to suppress the amount of heat generated during solidification, which also has the effect of preventing the occurrence of cracks. The blending amount of blast furnace slag in this case is, from the viewpoint of the above effects, Portland cement: blast furnace slag =
It is preferable to mix in the range of 7: 3 to 2: 8 (weight ratio). Therefore, Class B blast furnace cement (Blast furnace slag content of 30 to 60%) and C defined by JIS standard
It is also possible to use a seed (60 to 70% by weight).

As the hydraulic cement, one containing fly ash can also be preferably used. However, since the fly ash itself has a spherical shape, it improves the fluidity of the mortar and the filling property thereof. This is because it contributes and is effective in filling a narrow space such as a narrow tube with mortar. In this case, the blending amount of fly ash is preferably in the range of Portland cement: fly ash = 9.5: 0.5 to 7: 3 (weight ratio) from the viewpoint of the above effects. Therefore,
Fly ash cement type A (fly ash 5-10% blended), type B (same 10) specified by JIS standard.
.About.20% blending) and C type (the same 20-30% blending) can also be used.

When the hydraulic cement and the lightweight aggregate as described above are mixed and kneaded, a dispersant is added. It is for imparting good fluidity, and a naphthalenesulfonic acid-based dispersant is particularly preferable. The amount of the dispersant added is preferably in the range of 0.5 to 2.0% by weight based on the hydraulic cement. 0.5% by weight
If it is less than the above, it is difficult to obtain good fluidity of the mortar slurry (P funnel flow time reference value: 50 seconds or less). On the other hand, if the addition amount exceeds 2% by weight, the effect corresponding to the addition amount cannot be obtained, leading to an increase in the cost of the mortar.

The separation inhibitor is added to prevent separation of the cement slurry from the lightweight aggregate and to impart volume stability of the solidified body, and bentonite containing montmorillonite as a main component is preferably used. To be The amount of the separation inhibitor added is preferably in the range of 5 to 15% by weight based on the hydraulic cement. When the addition amount is less than 5% by weight, a phenomenon of separation occurs between the lightweight aggregate and the cement slurry as the binder, and the lightweight aggregate floats above the solidified body. On the other hand, if the addition amount is 15
If it exceeds 5% by weight, the viscosity of the mortar increases extremely, and the strength of the solidified product decreases with an increase in kneading water.

Further, it is preferable to use sodium lauryl sulfate (C ₁₂ H ₂₅ .OSO ₃ Na) as the weight saving aid. Sodium lauryl sulfate is in the form of a white powder, and when kneading water is added, it becomes an emulsion and can further reduce the specific gravity of the lightweight mortar,
This addition can reduce the amount of the lightweight aggregate compounded. The amount of sodium lauryl sulfate added is preferably in the range of 0.01 to 0.05% by weight based on the hydraulic cement. The addition amount is 0.01% by weight
If it is less than the above range, the weight of the mortar cannot be sufficiently reduced. On the other hand, when the addition amount exceeds 0.05% by weight, the strength of the solidified body and the fluidity of the mortar are lowered with the increase of the kneading water.

As described above, the preferred raw material composition of the lightweight mortar is 5 to 15% by weight of igneous rock-calcined lightweight aggregate and 10 to 10% of obsidian calcined lightweight aggregate with respect to hydraulic cement. 30% by weight, 0.5 to 2.0% by weight of dispersant, 5 to 15% by weight of separation inhibitor, 0.0 of a weight reduction aid.
1 to 0.05% by weight is contained.

The specific gravity of the lightweight mortar having the above raw material composition is as low as 1.00 g / cm ³ or less,
In addition, the solidified body obtained by curing the lightweight mortar has a characteristic that the compression strength is as high as 1.5 MPa or more. That is, it satisfies the physical properties of the solidified mortar required to be used as a filling and solidifying material for waste.

Therefore, the above-described lightweight mortar according to the present invention can be preferably used when solidifying radioactive waste. As the solidification process, first,
Based on hydraulic cement, a lightweight aggregate is blended with this, and after mixing, a separation inhibitor, a weight-reducing aid, a dispersant, and kneading water are added, and a lightweight mortar is obtained by kneading with a mixer or the like. . Then, the obtained lightweight mortar is directly filled in the radioactive waste or is filled in a disposal container in which the radioactive waste is stored in advance to be solidified. The solidified body (waste body) of this waste is transported to the disposal site for disposal.
Thus, by solidifying the radioactive waste by using the lightweight mortar according to the present invention, the weight of the waste can be significantly reduced as compared with the waste that has been fixed by the conventional general mortar. be able to. Furthermore, by using the above-mentioned lightweight mortar, even when filling and solidifying a large-scale metal waste, since there is little heat generation, cracks do not occur in the solidified body, and there are many narrow voids such as thin tubes. Even in the case of the waste containing, since the voids are sufficiently filled, it is possible to obtain a solidified body which is lightweight and homogeneous and has high strength.

[0033]

EXAMPLES The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited by the following examples. [Example 1] Portland cement was used as the hydraulic cement, and the particle size was 0.6 with respect to the hydraulic cement.
mm igneous rock calcination processed lightweight aggregate 6.7 wt% and obsidian calcination light weight aggregate 13.3 wt% 13.3 wt% mixed (mixing ratio 1: 2) is a lightweight aggregate As a naphthalenesulfonic acid-based dispersant 1% by weight, bentonite as a separation inhibitor 10% by weight, and sodium lauryl sulfate 0.03 as a weight-reducing aid.
A mortar was prepared by adding wt% and kneading with water. The P funnel flow time and the specific gravity of the obtained mortar were measured at 20 ° C. Further, various characteristics (breathing rate, volume change rate, compressive strength) and appearance of the solidified body obtained by curing each mortar for 28 days were evaluated at 20 ° C. The evaluation results are shown in Table 1. The target values shown in Table 1 are physical property values required for mortar used as a solidifying material for waste.

Example 2 A mortar was prepared and physical properties were evaluated in the same manner as in Example 1 except that blast furnace cement type B was used as the hydraulic cement.
The evaluation results are shown in Table 1. In addition, the change over time of the P funnel flow time of the mortar was measured by using Example 2 as a representative. The result is shown as a diagram in FIG. In FIG.
The vertical axis represents the P funnel flow time, and the horizontal axis represents the elapsed time after kneading.

Example 3 Fly ash cement was used as the hydraulic cement, and otherwise the mortar slurry was prepared in the same manner as in Example 1 and each physical property was evaluated. The evaluation results are shown in Table 1.

[Examples 4 to 9] As for the lightweight aggregate, the dispersant, the separation inhibitor, the weight reduction aid, and the mixing amount of the kneading water as shown in Examples 4 to 9 of Table 1, other than that, A mortar slurry was prepared and each physical property was evaluated in the same manner as in Example 2. The evaluation results are shown in Tables 1 and 2.

[0037]

[Table 1]

[0038]

[Table 2]

As shown in Tables 1 and 2, when Portland cement was used as the hydraulic cement (Example 1), the specific gravity of the mortar was 0.92 g / cm ³ , and the P funnel flow time showing the fluidity was 29. Second, the compression strength of the solidified body is 8
It was MPa, and all obtained results satisfying the target value. Further, it was confirmed that no bleeding was observed in the solidified product and that a good solidified product was obtained. Also, when blast furnace cement or fly ash cement is used as the hydraulic cement (Examples 2 and 3), the fluidity and solidified body properties are almost the same as when Portland cement is used (Example 1), It was recognized that all of them met the goals. Further, as shown in FIG. 1, it was confirmed that the lightweight mortar according to the present invention can maintain the initial fluidity for a long time of 2 hours or more.

As a lightweight aggregate, calcinated igneous product: obsidian calcinated product = 1: 2 (weight ratio), and added 20% by weight in total to the hydraulic cement (Examples 1 to 1). It has been confirmed that the target performances can be obtained in all of Nos. 3, 6 to 9). When a total of 15% by weight of lightweight aggregate having the same composition is added (Example 4),
Alternatively, when a total of 45% by weight is added (Example 5),
Although the target performance was obtained, from the viewpoint of the specific gravity of the mortar and the compressive strength of the solidified body, the blending amount of the lightweight aggregate (calcined igneous rock product: calcined obsidian product = 1: 2) was a hydraulic cement. On the other hand, it can be said that it is preferably 15 to 45% by weight. Further, although the mortar specific gravity can be reduced by increasing the addition amount of the weight reduction aid,
From the viewpoint of the compressive strength of the solidified body, the addition amount of the weight saving aid is
It is preferably in the range of 0.01 to 0.05% by weight with respect to the hydraulic cement.

Bentonite, which is a separation inhibitor, is
When 5% by weight is added to hydraulic cement (Example 6), or when 15% by weight is added (Example 7)
In addition, although the target performance was obtained in all cases, the addition amount of the separation inhibitor was in the range of 5 to 15% by weight with respect to the hydraulic cement from the viewpoint of the fluidity of the mortar (flow time of the P funnel). It can be said that is preferable.

Further, from Examples 8 and 9, the compounding amount of the dispersant of naphthalenesulfonic acid, which is a dispersant, was 0.5 with respect to the hydraulic cement from the viewpoint of the fluidity of the mortar.
It can be said that it is preferably in the range of up to 2.0% by weight.

[Comparative Example 1] As the hydraulic cement, the same blast furnace cement as in Example 2 was used, and the lightweight aggregate was not blended. The naphthalenesulfonic acid-based dispersant 1.0 was added to the hydraulic cement. % And 35% by weight of water were added and kneaded to prepare a mortar. The physical properties of this mortar and its solidified product were evaluated in the same manner as in Example 2. The evaluation results are shown in Table 3. The target values shown in Table 3 are physical property values required for mortar used as a solidifying material for waste, as in Table 1.

[Comparative Examples 2 to 5] Light weight aggregates, dispersants, separation inhibitors, lightening aids and kneading water as shown in Comparative Examples 2 to 5 of Table 3 are used in all other amounts. A mortar slurry was prepared and each physical property was evaluated in the same manner as in Example 2. The evaluation results are shown in Table 3.

[0045]

[Table 3]

As shown in Table 3, when the lightweight aggregate is not blended (Comparative Example 1), the characteristics of the solidified body such as the fluidity of the mortar and the compressive strength of the solidified body are good, but the specific gravity of the mortar is 1 The value was 0.98 g / cm ³ , which was about twice the target value. Also,
When only 20% by weight of igneous rock fired product as a lightweight aggregate was mixed with hydraulic cement (Comparative Example 2), the mortar specific gravity exceeded the target value of 1.0 g / cm ³ ,
In order to improve fluidity, 100% by weight, that is,
The same amount of kneading water as the lightweight aggregate was required, resulting in residual breathing water. On the other hand, when 20% by weight of the obsidian calcined product is added as the lightweight aggregate to the hydraulic cement (Comparative Example 3), the mortar specific gravity can be set to the target value of 1.0 g / cm ³ or less. Although it was possible, the lightweight aggregate floated and separated, and it was difficult to integrate it as a solidified body.

When the separation inhibitor and the weight saving aid were not added (Comparative Example 4), the amount of kneading water for maintaining the fluidity could be reduced as compared with Example 2. Although it is possible, the mortar specific gravity cannot meet the target value,
Remaining breathing water was also seen, and roughening occurred on the upper surface of the solidified body. Moreover, when bentonite was added as a separation inhibitor and no weight saving aid was added (Comparative Example 5).
, The separation of the lightweight aggregate was suppressed and the solidified body characteristics were good, but the mortar specific gravity did not reach the target value. Therefore, as is apparent from Example 2, the addition of the weight-reducing aid (sodium lauryl sulfate) is effective in reducing the specific gravity of the mortar to the target value of 1 g / cm ³ or less without impairing the properties of the solidified body. I can say.

[Reference Example] A mortar slurry was prepared in the same manner as in Example 2 except that a polycarboxylic acid type water reducing agent was added in place of the naphthalenesulfonic acid type dispersant in Example 2 above. Was prepared and each physical property was evaluated. The evaluation results are shown in Table 3. In this case, good results were obtained regarding the solidified body properties such as the compressive strength of the solidified body, but the P funnel flow-down time of the mortar was as long as 62 seconds, and the fluidity was lower than the target.

[0049]

According to the present invention, as compared with the conventional mortar for solidifying waste, the specific gravity is about half and light,
In addition, it is possible to obtain a lightweight mortar that maintains good fluidity for a long time and is excellent in filling properties, strength properties of the solidified body, and the like.
Therefore, according to the method for solidifying radioactive waste according to the present invention, the weight of the waste can be reduced by using the above-mentioned lightweight mortar, so that the number of wastes can be reduced and the efficiency of the waste treatment can be improved. Can contribute.

[Brief description of drawings]

FIG. 1 is a diagram showing a change with time in fluidity of a lightweight mortar of Example 2.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C04B 24/22 C04B 24/22 A G21F 9/30 515 G21F 9/30 515F // C04B 103: 40 C04B 103 : 40 103: 44 103: 44 (72) Inventor Kazuaki Matsuo 1 Minamito, Ogakie-cho, Kariya city, Aichi Toshiba Ceramics Co., Ltd. Kariya Plant (72) Inventor Hisenori Umemura 1-nanfu, Ogakie-cho, Kariya city, Aichi prefecture Toshiba Ceramics Co., Ltd. Kariya Plant (72) Inventor Tatsuaki Sato 2-1, Ukishimacho, Kawasaki-ku, Kawasaki-shi, Kanagawa Stock Company Toshiba Hamakawasaki Plant (72) Inventor Naomi Toyohara Ukishima, Kawasaki-shi, Kanagawa Town No.2-1 Stock Company Toshiba Hamakawasaki Factory (72) Inventor Masaaki Kaneko No.2-1 Ukishimacho, Kawasaki-ku, Kawasaki-shi, Kanagawa Stock Company Shibahama Kawasaki Factory (72) Inventor Kaji Natsui 8 Shinsita-cho, Isogo-ku, Yokohama-shi, Kanagawa Kanagawa Prefecture, Yokohama Office (72) Inventor Kuniaki Shinbori 66-2, Horikawa-cho, Kawasaki-shi, Kanagawa Prefecture Toshiba Engineering Ring F Co., Ltd. F-term (reference) 4G012 PA06 PA07 PA27 PB22 PC03 PC08

Claims (9)

[Claims] 1. A lightweight mortar comprising hydraulic cement, lightweight aggregate, dispersant, separation inhibitor, lightweighting aid, and water, wherein the lightweight aggregate is an igneous calcinated product and an obsidian calcined product. A lightweight mortar characterized by being mixed with a product. 2. The lightweight mortar according to claim 1, wherein the particle diameter of the lightweight aggregate is 1.2 mm or less. 3. The lightweight mortar according to claim 1 or 2, wherein the hydraulic cement is Portland cement or cement containing blast furnace slag or fly ash. 4. The lightweight mortar according to any one of claims 1 to 3, wherein the separation inhibitor is bentonite containing montmorillonite as a main component. 5. The lightweight mortar according to claim 1, wherein the weight saving aid is sodium lauryl sulfate. 6. The method according to claim 1, wherein the dispersant is a naphthalene sulfonic acid-based dispersant.
Lightweight mortar described in any of the above. 7. The lightweight mortar contains 5 to 15% by weight of igneous calcinated lightweight aggregate, 10 to 30% by weight of obsidian calcinated lightweight aggregate, and 0. 5 to 2.0% by weight, the separation inhibitor 5 to 15% by weight,
The lightweight mortar according to any one of claims 1 to 6, wherein the lightweighting aid is contained in an amount of 0.01 to 0.05% by weight. 8. The specific gravity of the lightweight mortar is 1.00 g /
cm ³ or less and, lightweight mortar according to claim 1, the compressive strength of the solidified bodies of said light amount mortar, characterized in that at least 1.5MPa to claim 7. 9. A method of solidifying radioactive waste, which comprises filling and solidifying the lightweight mortar according to any one of claims 1 to 8.