JPH0782112B2 - Radioactive waste treatment container - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to a radioactive waste treatment container used for converting a radioactive waste into a final solidified form suitable for disposal such as underground burial or ocean dumping.

BACKGROUND OF THE INVENTION

The amount of various radioactive wastes emitted from various nuclear facilities such as nuclear power plants is increasing. Out of these radioactive wastes, medium and low level radioactive wastes are put into radioactive waste treatment containers such as drums and then solidified and sealed to form the final form suitable for underground burial or ocean dumping. I am making it. Various types of containers for treating such radioactive waste have been proposed in the past. For example, a mild steel drum or a steel fiber reinforced concrete molded in the shape of a container is impregnated with a polymerizable impregnating agent, and is polymerized and solidified, a radioactive waste treatment container (Japanese Patent Publication No. 56-12840), or the shape of the container. A radioactive waste treatment container (Japanese Patent Publication No. Sho 57-34518) obtained by partially impregnating a molded steel fiber reinforced concrete with a polymerizable impregnating agent and solidifying it, a metal container as an outer shell, and an inner surface of the metal container. There is proposed a multi-type container (Japanese Patent Laid-Open No. 59-85999) having a double structure of an outer shell and an inner shell, which is made of concrete reinforced with a reinforcing material and further reinforced with an impregnating agent. Is coming. Then, for example, fine radioactive waste such as powdery or granular incineration ash, other miscellaneous solids, etc. are filled in a radioactive waste treatment container together with a cement solidifying agent and solidified, and then, on this radioactive waste layer. After filling the cement paste and placing the inner lid, it is considered that the outer lid is placed on the radioactive waste treatment container, which is buried underground or dumped into the ocean. By the way, up to now, great efforts have been made to develop a container body for the treatment of radioactive waste, and some excellent ones have been proposed. However, the demand for safety is high, and the development of a safer radioactive waste treatment container is awaited. By the way, conventionally, for example, Portland cement has been usually used as the cement used for the construction of the radioactive waste treatment container. However, in the case where the radioactive waste treatment container is composed of ordinary Portland cement, damage may be recognized even after long-term storage.

DISCLOSURE OF THE INVENTION

The present inventor, as a result of pursuing the cause of the damage,
The damage to this container is due to the presence of sulfate in the radioactive waste or in the disposal atmosphere, and this sulfate reacts with the calcium hydroxide present in the cement layer of the container to react with Ca (OH ) ₂ + Na ₂ SO ₄ + H ₂ O → CaSO ₄ · 2H ₂ O + NaOH Gypsum is produced, and this gypsum contains 3C in the cement layer of the container.
aO · Al ₂ O ₃ and _{4CaO · Al 2 O 3 · 13H} 2 O and reacts as follows _{CaSO 4 · 2H 2 O + 4CaO} · Al 2 O 3 · 13H 2 O → 3CaO · Al 2 O 3 · 3CaSO 4・ 31-32H ₂ O Ettringite 3CaO ・ Al ₂ O ₃・ 3CaSO ₄・ 31-32H ₂ O is generated, and a large expansion pressure is generated during the generation of this ettringite, which damages the radioactive waste treatment container ( It was determined that peeling occurred from expansive cracks). The present invention has been achieved based on the results of such research, and an object of the present invention is to provide a radioactive waste treatment container that is highly resistant to damage such as cracking and peeling and has high safety. That is. The above-mentioned object of the present invention is (3Al ₂ O ₃ + 1.5SiO ₂ ) / (CaO-SO
_A radioactive waste treatment container constituted by using cement having a molar ratio of ₃ ) of 1 or more. The cement constituent layer of this container has a Ca (OH) ₂ peak observed by an X-ray diffractometer. Achieved by a radioactive waste treatment container characterized by the absence. Meanwhile, as the cement used in the present invention, for example, _{3CaO · 3Al 2 O 3 · CaSO} 4, CaO · Al 2 O 3, 12CaO · 7Al 2 O 3 such as CaO / Al ₂ O ₃ (molar ratio) is less than 3 Portland cement, a mixed cement with a first raw material that can make a calcium sulphoaluminate compound or a clinker or cement mainly composed of a calcium aluminate compound into 3 to 20% by weight in terms of calcium sulphoaluminate compound or calcium aluminate compound. 3 silicates (3CaO ・ SiO ₂ ) or 2 silicates (2CaO ・
A _second raw material that can make clinker or cement mainly composed of SiO ₂ ) 3 to 20% by weight in terms of calcium silicate compound and gypsum such as anhydrous gypsum and gypsum.
The third raw material that can be 6 to 40% by weight in terms of SO ₄ , the fourth raw material that can be 20 to 88% by weight of blast furnace water slag, and 0.1% oxycarboxylic acids such as sodium citrate and malic acid.
Mixed with a fifth raw material, which can be up to 1.5 wt% (3Al ₂ O ₃
Some have a + 1.5SiO ₂ ) / (CaO-SO ₃ ) molar ratio of 1 or more. As the X-ray diffractometer for measuring the peak of Ca (OH) ₂ , the Rotaflex series manufactured by Rigaku Denki Co., Ltd. can be used. And, when the cement of such a composition is used as a material for a radioactive waste treatment container, damage such as cracking or peeling hardly occurs in this container, and a highly safe radioactive waste treatment container rich in durability It consists of a calcium sulphoaluminate compound 3CaO ・ 3Al ₂ O ₃・ CaSO ₄ as the main component,
An example of using Portland cement and blast furnace slag slag will be described below from the viewpoint of hydration reaction. As shown in the following formula, the calcium sulfaluminate compound reacts with calcium hydroxide and gypsum during hydration to form an ethrin guide. 3CaO ・ 3Al ₂ O ₃・ CaSO ₄ ＋ 8CaSO ₄ ＋ 6Ca (OH) ₂ ＋ 9OH ₂ O → 3 (3CaO ・ Al ₂ O ₃・ 3CaSO ₄・ 32H ₂ O) Anhydrous gypsum or dihydrate gypsum is consumed for this reaction. To be done. On the other hand, as calcium hydroxide, calcium hydroxide generated by the hydration reaction of Portland cement is supplied. Portland cement, which is a common stimulant, produces calcium hydroxide to raise the pH of cement, elute silica and alumina in slag, and react with them to react with calcium silicate hydrate (CaO-SiO ₂ -H ₂ O-based), calcium aluminate hydrate (CaO-Al ₂ O ₃ -H ₂ O-based), and further reacts with gypsum and calcium sulphoaluminate hydrate (CaO
-Al ₂ O ₃ -CaSO ₄ -H ₂ O system) is promoted. However, in the present invention, since calcium hydroxide generated from Portland cement is consumed for hydration of calcium sulfaluminate clinker, the amount of Portland cement is 3 to 3 as compared with general slag cement.
As high as 20%. In order to prevent damage such as cracking and peeling, and to provide a highly durable radioactive waste treatment container, calcium hydroxide produced from Portland cement, which is a slag stimulant, is used as another stimulant. It is important that the sulfaluminate clinker is completely consumed and calcium hydroxide does not exist in the system. In other words, 3 lime silicate (3CaO
・ SiO ₂ ) and calcium hydrate formed by hydration of dicalcium silicate (2CaO ・ SiO ₂ ) react with calcium sulphoaluminate (3CaO ・ 3Al ₂ O ₃ -CaSO ₄ ), gypsum (CaSO ₄ ). Then, a composition that produces an ethrin guide may be used. The hydration reaction of calcium sulfaluminate clinker is faster than that of Portland cement. Therefore, oxycarboxylic acids are added to delay the hydration reaction of calcium sulfaluminate clinker,
It is preferable that the hydration timings of both are substantially the same, and that calcium hydroxide generated from Portland cement stimulates the slag, and then the surplus is consumed for hydration of the calcium sulfaluminate clinker. Examples of oxycarboxylic acids for this purpose include sodium citrate, malic acid, tartaric acid, sodium tartrate and the like. Calcium hydroxide produced in the hydration process of the cement is finally C-S-Hgel (3CaO · 2SiO 2 · 3H 2 O equivalent) and d [pi] n guide _{(3CaO · Al 2 O 3 ·} 3CaSO 4 · 32H 2 O Must be fixed as). C-S-Hgel has CaO / SiO ₂ (molar ratio) = 1.5, and ethrin guide has CaO / Al ₂ O ₃ (molar ratio) = 3, and part of the lime component of cement forms gypsum. Because it is a thing,
When (3Al ₂ O ₃ + 1.5SiO ₂ ) / (CaO-SO ₃ ) ≧ 1, free calcium hydroxide does not exist in the system stoichiometrically. Therefore, in order to obtain a radioactive waste treatment container that is highly durable and is resistant to damage such as cracking and peeling from the beginning, it is necessary to use (3Al ₂ O ₃
A cement having a molar ratio of + 1.5SiO ₂ ) / (CaO-SO ₃ ) of 1 or more should be used. And, when cement such as calcium hydroxide is substantially not used in the cement layer constituting such a container, the surface hardness of this radioactive waste treatment container is large,
For example, there is no surface weakening phenomenon, which is said to be a drawback of slag-based cement, and calcium sulfoaluminate clinker and Portland cement itself exert hydraulic properties, and since the slag shows hydration activity from the beginning, the cement is It exhibits early strength, large long-term strength extension, non-shrinkage, small dry shrinkage, high durability, and safe as a radioactive waste disposal. In addition, as the Portland cement, ordinary moderate heat Portland cement can be used, but the effect of stimulating the slag having latent hydraulicity is that the amount of tricalcium silicate (3CaO · SiO ₂ ) is large, the reactivity is high, and the strength is high. Super early strength Portland cement is more effective. In addition, white portland cement whose main compound is tricalcium silicate (3CaO · SiO ₂ ) can be used, and mixed cement such as blast furnace cement and fly ash cement can also be used. In addition to calcium sulfaluminate, CaO, Al ₂
It is also possible to use a calcium aluminate compound such as O ₃ , 12CaO · 7Al ₂ O ₃ or an alumina cement containing them as a main component. Calcium aluminate compound (mCaO ・ nAl ₂ O ₃ ) or calcium sulfaluminate compound (mCaO ・ nAl ₂ O ₃・ Ca
SO ₄ ) consumes calcium hydroxide in the hydration reaction when CaO / Al ₂ O ₃ <3 (molar ratio), so CaO / Al
₂ O ₃ is preferably smaller than 3 (molar ratio).

【Example】

FIG. 1 is a sectional view showing one embodiment of a radioactive waste treatment container according to the present invention. In the figure, A is a main body of a radioactive waste treatment container, and the main body A of this treatment container is a drum can 1 made of, for example, copper and integrally provided with a polymer-impregnated concrete layer 2. B is a polymer-impregnated concrete lid used as an inner lid of the processing container body A. Then, as the cement constituting the polymer-impregnated concrete layer 2 and the cover B of the container body A, as a calcium sulfoaluminate _{clinker, 3CaO · 3Al 2 O 3 ·} Ca
10% by weight of clinker containing 60% SO ₄ , 16% free lime, 1% free gypsum and 21% dicalcium silicate, and 3CaO.
_{SiO 2 60%, 2CaO · SiO} 2 24%, and 20% by weight of ordinary Portland cement clinker containing _{3CaO · Al 2 O 3 12%} ,
15% by weight of hard gypsum mainly composed of anhydrous gypsum and 55% by weight of blast furnace water slag slag were mixed, crushed to a Blaine value of 4000 cm ² / g, and then 0.3% by weight of sodium citrate was mixed to obtain I used one. In addition, (3Al ₂ O ₃ + 1.5SiO ₂ ) / (CaO-S of this cement
O ₃ ) was 1.3 (molar ratio). Then, the filling rate (volume ratio) of various metals (miscellaneous solids) such as pipes, wires, angles, valves, and motors 13
The same cement paste (solidifying material) as described above was filled into 1 m ³ of the container A housed in the inside and solidified.

【Characteristic】

For the purpose of comparison with the case where cement having substantially no calcium hydroxide is used as the cement constituting the container used in the above-mentioned examples, ordinary Portland cement (comparative example 1) and blast furnace type C cement (comparative example 2) are used. Since the durability test was carried out as compared with the case where the temperature was high, the results are shown in Table 1, Table 2 and Table 3-1.
And shown in Table 3-2. According to this, it can be seen that the product according to the present invention has high durability and therefore the safety of the radioactive waste treatment container is high.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing an embodiment of a radioactive waste treatment container according to the present invention. A ... Main body of radioactive waste treatment container, B ... Lid, 1 ... Drum can, 2 ... Polymer impregnated concrete layer.

Front page continuation (72) Inventor Ikuo Uchida 2-1-1 Tsukimi-cho, Kumagaya-shi, Saitama Chichibu Cement Co., Ltd. Related Products Division (56) Reference JP-A-60-171498 (JP, A) Sho 62-293199 (JP, A) Japanese Patent Publication 6-75120 (JP, B2)

Claims (1)

[Claims] 1. A radioactive waste treatment container comprising a cement having a molar ratio of (3Al ₂ O ₃ + 1.5SiO ₂ ) / (CaO-SO ₃ ) of 1 or more. The radioactive waste treatment container is characterized in that the cement constituent layer of No. 1 does not show a peak of Ca (OH) ₂ by an X-ray diffractometer.