JPS631559B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a solidified body of radioactive waste and a method for producing the same, and more specifically, the present invention relates to a solidified body of radioactive waste and a method for manufacturing the same, and more specifically, after mixing a titanium compound with a solidified ceramic body containing calcined radioactive waste (referred to as "calcined body") and powder of the calcined body, The present invention relates to a method of producing the solidified ceramic body by melting. The solidified material of the present invention can efficiently store radioactive waste, is chemically and mechanically stable, and is suitable for semi-permanently storing radioactive waste.
Although this solidified product may be stored as it is in a storage container, for example, the food may be irradiated with radiation by providing an appropriate container or container to control the radiation dose to prevent spoilage, insect damage, and damage during transportation and storage. It is useful for preventing germination, etc., and extending storage period. As the contribution of nuclear power generation to the electricity supply increases, the amount of highly concentrated radioactive waste fluid generated, especially from spent nuclear fuel reprocessing plants, tends to increase year by year. When storing these waste liquids in tanks, storage space is a problem not only in terms of safety and management, but also in terms of quantity and volume, so there is a strong need for the establishment of a solidified substance that is easy to store and a method for producing it. ing. In general, in solidified radioactive waste and its manufacturing technology, leakage of radioactive materials into the surrounding area is
It is necessary to convert waste into a minimum form, and the converted form must be chemically and mechanically stable and not cause environmental pollution even after long-term storage. In addition, since the amount of radioactive waste is expected to increase in the future, in order to store it efficiently, the ratio of the weight of waste to the total weight of waste and additives (hereinafter referred to as "contained rate"
) is desired to be as large as possible. The radioactive waste solidified body and its manufacturing method of the present invention were developed in response to such demands. Conventionally, it has been proposed to store radioactive waste as a calcined body. Processing temperature
The calcined body is manufactured at 400 to 650℃, and the nitrate component is completely removed.The calcined body made of oxides does not decompose the nitrate component, so it can maintain static stability for a long time. , it had the following drawbacks: In other words, the calcined body alone has poor sintering properties and is prone to scattering of some nuclides, has extremely poor leaching resistance because it is easily soluble in water, and has low thermal conductivity, so it is difficult to sinter radioactive elements. The heat generated by the decay of the container has poor radioactivity, and as a result, the temperature tends to rise during storage.Furthermore, this temperature rise tends to cause damage to the storage container, making it easy to collapse in terms of strength. Because of these shortcomings, it lacks stability in long-term storage, and is particularly unsafe in the face of unexpected natural disasters such as earthquakes and floods. In order to improve the resistance to leaching of radioactive substances into water, thermal stability and mechanical strength to a relatively large degree,
A possible solidified material is radioactive waste mixed with some additives and subjected to heat treatment. In this case, the greater the amount of additive, the lower the content of radioactive waste and the higher the safety, but the lower the efficiency in terms of storage. Therefore,
There has been a strong desire to select additives that can more efficiently pack radioactive waste at high density, and to develop solidified materials using such additives. Conventionally, a vitrified body is known as an example of such a solidified body. The vitrified material is a solidified material obtained by melting highly concentrated radioactive waste together with phosphoric acid or borosilicate glass, and then solidifying it into an ingot of a certain shape. According to this method, by considering the composition of the glass, the leachability of radioactive substances into water is small.
Although it is possible to obtain a vitrified body with relatively high mechanical strength, in order to obtain a vitrified body with a stable structure, the upper limit of the amount of calcined body powder added is 25 to 30% by weight. was. Therefore, a solidified body that has high thermal conductivity, has good heat dissipation properties, is resistant to the decay heat of radioactive materials, and can be filled and solidified with radioactive waste at a higher density, and a method for producing the same. development was desired. In addition, in the solidified body, molybdenum alone or
When phases such as Na ₂ O・MoO ₃ , K ₂ O・MoO ₃ , Cs ₂ O・MoO ₃ are present as constituent phases, these phases have extremely low leaching resistance to water, so they are less likely to elute radioactive substances. Furthermore, since these phases cause deterioration of the solidified product, it has been particularly desired to establish a solidified product in which these phases are not present and a method for producing the same. The object of the present invention is to use metal salts for radioactive waste to form a solidified ceramic material, which has a high content and can efficiently store radioactive waste, and which has a molybdenum phase or Na ₂ O.・
Because it does not contain phases such as McO ₃ , K ₂ O・MoO ₃ or Cs ₂ O・MoO ₃ , the leachability of radioactive substances into water is small, and it has excellent heat dissipation and heat resistance, as well as excellent mechanical strength. The purpose is to provide a solidified product.
Such solidified bodies are suitable for safe and semi-permanent storage of radioactive waste. The solidified material of the present invention has Na ₂ O 5 in terms of oxide.
~40 wt%, _{Fe2O3 5-20} wt%, _MoO3 5-15 wt%, _ZrO2 5-15 wt%, _CeO2 2-10 wt%,
Cs ₂ O2 ~ 10% by weight, BaO 1 ~ 5% by weight, SrO 1 ~ 5
% by weight, Rb ₂ O 0.2-2% by weight, Y ₂ O ₃ 0.2-2% by weight, NiO 0.2-2% by weight, rare earth oxides 5-20% by weight, Cr ₂ O ₃ 0.2-2% by weight, and other elemental oxides in the calcined body of radioactive waste,
It _is made by blending ₂₀ % by weight or more of _a titanium compound (as TiO ₂ ) and solidifying it by heat treatment of melting or sintering.
It is characterized by being a ceramic solidified body that does not contain MoO ₃ and Cs ₂ O・MoO ₃ as constituent layers.
(Other oxides contained in the calcined body include:
Tc ₂ O ₇ , RuO ₂ , Rh ₂ O ₃ , PdO, Ag ₂ O, CdO,
Examples include SnO, SeO ₂ , TeO ₂ and actinide element oxides. ) The calcined bodies of radioactive waste in the present invention include, for example, the remaining radioactive waste from which U and Pu are recovered after processing spent nuclear fuel, as well as the concentrated liquid of recycled waste liquid from a mixed bed desalter, and the waste from buildings. Various waste liquids containing radioactive materials such as concentrated waste liquid from floor drains and equipment drains, reactor purification systems, fuel pool systems, condensate systems, etc.
High concentration or medium-low concentration obtained by calcining various solid wastes such as used ion exchange resin and filter sludge generated from each drain system, and precipitated sludge generated by coagulation and sedimentation treatment of waste liquid. This invention can be used to treat a wide range of radioactive wastes. Furthermore, the titanium compound and aluminum compound used in the present invention can be prepared by TiO ₂ and Al ₂ O ₃ or by melting.
Any compound that converts into TiO ₂ and Al ₂ O ₃ may be used. Examples of titanium compounds that change to TiO ₂ when melted include titanium nitride (TiN), titanium carbide (TiC), and aluminum hydroxide (Al(OH) ₃ ).
etc. can be mentioned. Ceramic solidification manufactured by blending titanium compounds and aluminum compounds in a calcined body at 20% by weight or more (in terms of TiO ₂ ) and 25% by weight or more (in terms of Al ₂ O ₃ ) and by melting or sintering. The body is 1000℃
It is extremely stable even at the above high temperatures, and is extremely superior in terms of leaching resistance, thermal conductivity, and mechanical strength compared to a calcined body sintered alone.
Moreover, the content can be increased up to 75% by weight without sacrificing these excellent properties. The solidified body of the present invention is obtained by blending 20% by weight or more of a titanium compound (as ZrO ₂ ) and 5% by weight or more of an aluminum compound (as Al ₂ O ₃ ) into a calcined body of radioactive waste and solidifying it. , does not prevent further blending and solidification of other substances. That is, when 1 to 10% by weight (as NiO) of a nickel compound is blended, the mechanical strength of the solidified body can be further improved. The reason why the blending ratio is limited to 1 to 10% by weight is because if it exceeds 10% by weight, the leaching resistance of the solidified product deteriorates, and if it is blended at less than 1% by weight, no effect will be obtained. Nickel compounds include NiO or a compound that becomes NiO by melting or sintering, nickel acetate (C ₁₀ H ₁₄ NiO ₄ 4H ₂ O), nickel acetylacetonate (C ₁₀ H ₁₄ NiO ₄ ), nickel carbonate (NiCO ₃・
2Ni(OH) ₂・4H ₂ O) etc. can be used.
In addition, at least one metal compound of calcium, strontium, and barium is added at 1 to 15
When incorporated in weight percent (as CaO, SrO, BaO), the leaching resistance of the solidified material can be further improved. The reason why the blending ratio is limited to 1 to 15% by weight is because if it exceeds 15% by weight, the leaching resistance of the solidified product deteriorates, and if it is blended at less than 1% by weight, no effect will be obtained. Compounds such as calcium can be used as long as they eventually become oxides. For example, strontium carbonate (SrCO ₃ ), strontium hydroxide (Sr(OH) _{2.8H 2} O), barium carbonate (BaCO ₃ ),
Barium acetate (C ₄ H ₆ O ₄ Ba), barium hydroxide (Ba(OH) _{2.8H 2} O), calcium carbonate (CaCO ₃ ), or calcium hydroxide (Ca
(OH) ₂ ) etc. Of course, compounds containing two or more of Zr, Ni, Ca, etc. can also be used. The solidified product of the present invention can be easily produced as follows. A predetermined amount of the above-mentioned zirconium compound is blended into the calcined body of radioactive waste, and if necessary, a predetermined amount of a nickel compound and/or a metal compound of at least one of Ca, Sr, and Ba is blended and thoroughly mixed. The method of mixing radioactive waste and metal compounds is not only the usual powder mixing, but also the method of forming a film on the surface of the metal compound powder to be mixed. For example, water is added to this powder and the mixture is kneaded to form a slurry, which is then granulated through a sieve and placed in a fluidized bed at, for example, 600°C.
Radioactive waste may be sprayed onto the surface of the particles at a temperature of This mixture is charged into a container, and approximately 1600
A solidified ceramic can be obtained by melting at ~2500°C and then solidifying into an ingot of a certain shape. If the metal compound to be mixed is titanium nitride (ZrN), titanium carbide (ZrC), etc., it will eventually change to an oxide (e.g. ZrO ₂ , NiO, CaO, etc.) in the solidified ceramic body by melting treatment. Therefore, it is necessary to perform melting in an oxidizing atmosphere such as air. The solidified body of the present invention can be produced by an existing sintering method, whether under normal pressure or pressurization, or by an existing melting method, whether by external heating or internal heating. By the solidified body of radioactive waste and the method for producing the solidified body of the present invention, the following effects can be obtained. (1) Calcined bodies of radioactive waste are generally made of metal oxides, for example, as shown in the simulated compositions in Tables 1 to 3, and are relatively poorly sintered and solidified by themselves. According to the invention, TiO ₂ and
Due to Al ₂ O ₃ , a dense and strong ceramic solidified body can be obtained. In particular, when a nickel compound is blended, a solidified product with even better mechanical strength can be obtained. (2) In the solidified body of the present invention, the calcined body is
It has a thermally stable phase along with ZrO ₂ , NiO, CaO, etc. As a result, radioactive waste can be safely stored for a long period of time. (3) The solidified product of the present invention is also excellent in leaching resistance, and in particular, when a metal compound such as Ca, Sr, Ba, etc. is blended and solidified, the leaching resistance becomes even more excellent. (4) The solidified body of the present invention can be filled with up to 70% by weight of calcined radioactive waste. In other words, the content rate is significantly improved compared to conventional vitrified materials, and as a result, radioactive waste can be packed in high density into storage containers (canisters), and the number of canisters can be reduced. can. (5) The solidified product may be stored as is in a storage container, but by controlling the radiation dose by, for example, providing an appropriate container or shield, food can be irradiated with radiation to prevent spoilage, insect damage, and damage during transportation and storage. Suitable for purposes such as preventing germination, extending storage period, etc. Next, examples and comparative examples of the present invention will be described. In addition, as the radioactive waste calcination bodies used in the examples and comparative examples, Nos. 1 to 3 were used to simulate the composition of the radioactive waste calcination bodies from which U and Pu were recovered after processing the spent nuclear fuel. Three types of powders having the compositions shown in the table were prepared (hereinafter referred to as "simulated calcined bodies").

[Table] Other actinide element oxides

[Table] Other actinide element oxides

[Table] Other actinide element oxides The mechanical strength, leaching rate, and thermal conductivity of the solidified bodies obtained in Examples and Comparative Examples were measured, and
Linear diffraction revealed molybdenum as a single element in the solidified material.
Examine whether phases of Na ₂ O, MoO ₃ , Cs ₂ O・MoO ₃ , K ₂ O・MoO ₃ are generated or not. Table 4 (1), Table 4 (2)
It was shown to. In addition, to measure the mechanical strength, a measurement test piece (3 x 3 x 30 mm square column) was prepared from the solidified body.
Mechanical strength was measured by a three-point bending method (span length 20 mm, applied acceleration 0.5 cm/min). The leaching rate was measured according to the method of (JIS-R3502). Further, the thermal conductivity was measured at room temperature according to the laser flash method. Examples 1 to 11, Comparative Examples 1 to 10 Blends of the simulated calcined body and metal compound according to each of the Examples and Comparative Examples were adjusted at the blending ratios shown in Table 4 (1) and (2). Metal compound powder has an average particle size of 2μm
The following were used. 100 g of the prepared blend was filled into a carbon container, and a carbon electrode was inserted into the blend. 2000~2500 depending on arc discharge
After melting the blend at 0.degree. C., it was cooled to form a solid. The melting conditions and measurement results for the obtained solidified product are also shown in Table 4 (1) and (2).

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【table】

【table】

Claims (1)

[Claims] 1. 5 to 40% by weight of Na ₂ O in terms of oxide,
_{Fe2O3 5} ~20wt%, _MoO3 5~15wt%, _ZrO25
~15% by weight, CeO2 ₂ ~10% by weight, _Cs2O2 ~10% by weight, BaO1~5% by weight, SrO1~5% by weight,
Rb ₂ O 0.2-2% by weight, Y ₂ O ₃ 0.2-2% by weight,
NiO 0.2-2% by weight, rare earth oxides 5-20% by weight,
Adding 20% by weight or more of a titanium compound (as TiO ₂ ) and 5% by weight _or more of an aluminum compound (as Al 2 O ₃ ) to a calcined body of radioactive waste containing 0.2 to 2% by weight _of Cr ₂ O 3 , It is made by cooling and solidifying after melting, and contains elemental molybdenum, Na ₂ O・MoO ₃ ,
A ceramic solidified body of radioactive waste characterized by not containing K ₂ O・MoO ₃ and Cs ₂ O・MoO ₃ as a constituent layer. 2 Na ₂ O 5 to 40% by weight in terms of oxides,
_{Fe2O3 5} ~20wt%, _MoO3 5~15wt%, _ZrO25
~15% by weight, CeO2 ₂ ~10% by weight, _Cs2O2 ~10% by weight, BaO1~5% by weight, SrO1~5% by weight,
Rb ₂ O 0.2-2% by weight, Y ₂ O ₃ 0.2-2% by weight,
NiO 0.2-2% by weight, rare earth oxides 5-20% by weight,
A calcined body of radioactive waste containing 0.2 to 2% by weight of Cr ₂ O ₃ is combined with at least 20% by weight of a titanium compound (as TiO ₂ ), at least 5% by weight of an aluminum compound (as Al ₂ O ₃ ), and a nickel compound. It is made by blending 1 _to 10% by weight (as NiO) and solidifying it by cooling after melting _.
A ceramic solidified body of radioactive waste characterized by not containing K ₂ O・MoO ₃ and Cs ₂ O・MoO ₃ as a constituent layer. 3 Na ₂ O 5 to 40% by weight in terms of oxides,
_{Fe2O3 5} ~20wt%, _MoO3 5~15wt%, _ZrO25
~15% by weight, CeO2 ₂ ~10% by weight, _Cs2O2 ~10% by weight, BaO1~5% by weight, SrO1~5% by weight,
Rb ₂ O 0.2-2% by weight, Y ₂ O ₃ 0.2-2% by weight,
NiO 0.2-2% by weight, rare earth oxides 5-20% by weight,
A calcined body of radioactive waste containing 0.2 to 2% by weight of Cr ₂ O ₃ is combined with at least 20% by weight of a titanium compound (as TiO ₂ ), at least 5% by weight of an aluminum compound (as Al ₂ O ₃ ), and a calcium compound. 1 to 15% by weight of at least one of , strontium compound, and barium compound (as CaO, SrO, BaO)
It is made by blending, melting and then cooling to solidify, and it is composed of molybdenum alone, Na ₂ O・MoO ₃ , K ₂ O・MoO ₃ and
A ceramic solidified body of radioactive waste characterized by not containing Cs ₂ O/MoO ₃ as a constituent layer. 4 5 to 40% by weight of Na ₂ O in terms of oxides,
_{Fe2O3 5} ~20wt%, _MoO3 5~15wt%, _ZrO25
~15% by weight, CeO2 ₂ ~10% by weight, _Cs2O2 ~10% by weight, BaO1~5% by weight, SrO1~5% by weight,
Rb ₂ O 0.2-2% by weight, Y ₂ O ₃ 0.2-2% by weight,
NiO 0.2-2% by weight, rare earth oxides 5-20% by weight,
A calcined body of radioactive waste containing 0.2 to 2% by weight of Cr ₂ O ₃ is combined with at least 20% by weight of a titanium compound (as TiO ₂ ), at least 5% by weight of an aluminum compound (as Al ₂ O ₃ ), and a nickel compound. 1 to 10% by weight (as NiO) and 1 to 15% by weight of at least one of a calcium compound, a strontium compound, and a barium compound (as CaO, SrO, BaO)
It is made by blending, melting and then cooling to solidify, and it is composed of molybdenum alone, Na ₂ O・MoO ₃ , K ₂ O・MoO ₃ and
A ceramic solidified body of radioactive waste characterized by not containing Cs ₂ O/MoO ₃ as a constituent layer. 5 Na ₂ O 5-40% by weight in terms of oxides,
_{Fe2O3 5} ~20wt%, _MoO3 5~15wt%, _ZrO25
~15% by weight, CeO2 ₂ ~10% by weight, _Cs2O2 ~10% by weight, BaO1~5% by weight, SrO1~5% by weight,
Rb ₂ O 0.2-2% by weight, Y ₂ O ₃ 0.2-2% by weight,
NiO 0.2-2% by weight, rare earth oxides 5-20% by weight,
Adding 20% by weight or more of a titanium compound (as TiO ₂ ) and 5% by weight or more of an aluminum compound (as Al 2 O ₃ ) to a calcined body of radioactive waste containing _0.2 to 2% by weight of _{Cr 2} O 3 , A method for producing a ceramic solidified body of radioactive waste, characterized by cooling after melting. 6 Combining 20% by weight or more of a titanium compound (as TiO ₂ ), 5% by weight or more of an aluminum compound (as Al ₂ O ₃ ), and 1 to 10% by weight of a nickel compound (as NiO) to the calcined body of radioactive waste. A method for producing a ceramic solidified body of radioactive waste according to claim 5, wherein the solidified ceramic body of radioactive waste is cooled after melting. 7 The calcined body of radioactive waste contains 20% by weight or more of a titanium compound (as TiO ₂ ), 5% by weight or more of an aluminum compound (as Al ₂ O ₃ ), and at least one of a calcium compound, a strontium compound, and a barium compound. 1-15% by weight (CaO,
A method for producing a ceramic solidified body of radioactive waste according to claim 5, which comprises blending SrO, BaO), melting and cooling. 8. In the calcined body of radioactive waste, 20% by weight or more of a titanium compound (as TiO ₂ ), 5% by weight or more of an aluminum compound (as Al ₂ O ₃ ), and 1 to 10% by weight of a nickel compound (as NiO), 1 to 15% by weight of at least one of a calcium compound, a strontium compound, and a barium compound (CaO,
(as SrO, CaO), melted and then cooled,
A method for producing a ceramic solidified body of radioactive waste according to claim 5. 9 5 to 40% by weight of Na ₂ O in terms of oxides,
_{Fe2O3 5} ~20wt%, _MoO3 5~15wt%, _ZrO25
~15% by weight, CeO2 ₂ ~10% by weight, _Cs2O2 ~10% by weight, BaO1~5% by weight, SrO1~5% by weight,
Rb ₂ O 0.2-2% by weight, Y ₂ O ₃ 0.2-2% by weight,
NiO 0.2-2% by weight, rare earth oxides 5-20% by weight,
Cr ₂ O ₃ 0.2-2% by weight and Tc ₂ O ₇ , RuO ₂ ,
_Rh2O3 , PdO, _Ag2O , CdO, _SnO , _SeO2 ,
TeO ₂ and at least one of actinide element oxides
The calcined body of radioactive waste containing seeds is blended with 20% by weight or more of a titanium compound (as TiO ₂ ), which is melted and then cooled to solidify.
A ceramic solidified body of radioactive waste characterized by not containing Na ₂ O.MoO ₃ , K ₂ O.MoO ₃ and Cs ₂ O.MoO ₃ as constituent layers.