JPS6022700A - Method of solidifying and treating 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] [Technical Field of the Invention] The present invention relates to a method for disposing of radioactive waste, and more particularly, the present invention relates to a method for disposing of radioactive waste, and more specifically, a solidified body made of glass or ceramics containing radioactive waste is surrounded by a metal coating. The present invention relates to a method of manufacturing a radioactive waste storage body.

[Technical background of the invention]

When disposing of radioactive waste generated from nuclear power plants and spent nuclear fuel reprocessing plants, the waste is solidified in a form that minimizes the dispersion of radioactive materials into the surrounding area, and the resulting storage medium is used as a chemical It must be physically and mechanically stable and not cause environmental pollution even during long-term storage.

From this point of view, vitrification is the mainstream solidification method conventionally used.

In this method, radioactive waste is melted together with a glass-forming material such as borosilicate glass or phosphate glass and solidified into a glass ingot of a certain shape.

The glass ingot thus solidified is usually stored in a metal container. Furthermore, many relatively small glass ingots are embedded in the metal. A so-called composite metal assimilation method has also been proposed.

However, the above-mentioned vitrification method and metal composite assimilation method have the following problems.

(b) Assuming that the metal sheath that houses or covers the vitrified material is damaged due to corrosion, etc., the solidified material inside will be in direct contact with the external environment, so it is difficult to ensure stable storage over a long period of time. In order to achieve this goal, it is required to minimize the rate of radioactive material leaching into the external environment (for example, water).

(b) Vitrified materials have the disadvantage that cracks are likely to occur during the production of the assimilated material, since there are restrictions on the composition of the glass, which is the basic material. In particular, since the metal cladding and the vitrified body have different coefficients of thermal expansion, when molten glass solidifies in the metal cladding, cooling is accelerated at the interface between the glass and metal, creating thermal stress in this area. As a result, cracks tend to form inside the surface of the solidified material. The crank produced in the solidified body will inhibit the dissipation of the radioactive decay heat generated inside the solidified body, and the resulting temperature increase may damage the mechanical and chemical stability inside the assimilated body. Additionally, cracks increase the surface area of the vitrified body, thereby increasing the leaching area when the glass assimilated body is in direct contact with the external environment.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned problems, and
The object of the present invention is to provide a method for manufacturing a solidified storage body that has even better resistance to leaching of radioactive substances and can be safely stored for a long period of time without cracking. Summary] In order to achieve the above object, the method for solidifying radioactive waste of the present invention involves manufacturing a solidified storage body in which an assimilate body made of glass or ceramics containing radioactive waste is further surrounded by a metal coating. The method is characterized in that an intermediate layer made of glass or ceramic nox containing no radioactive substance is provided between the solidified body and the metal coating.

[Detailed description of the invention]

Production of assimilates Radioactive waste to be treated in the present invention includes, for example, radioactive waste remaining after processing spent nuclear fuel and recovering U and Pu, as well as various types of waste such as recycled waste liquid and floor trains. It includes various solid wastes such as waste liquid, filtrate, tarsula, kuji, and settled sludge.

Further, examples of the solidified body containing radioactive waste used in the present invention include those formed by forming radioactive waste into a solidified body using glass, ceramics, or the like. For example, vitrified materials such as borosilicate glass and phosphoric acid glass that contain radioactive waste and are made through heat treatment processes such as melting or sintering, crystallized vitrified materials such as Diopside type, and Al2O5-8102 type glass. ,'rto
Ceramic assimilates such as z-based, MnO2-8iO2-based, and ZrO2-based are preferably used. The content of radioactive waste in the solidified body is suitably in the range of 10 to u%.

Formation of Intermediate Layer When surrounding the solidified body with a metal covering, an intermediate layer is formed between the solidified body and the metal covering. This intermediate layer is made of glass or ceramics that does not contain radioactive substances, such as borosilicate glass, phosphate glass, D
Crystallized glass such as iopside type, Al2O5, Z
rO2, Ti0a, A1205-8102 series, 5I
Ceramics such as C1S13N11 may be used.

In addition, to prevent cracks from forming in the solidified material,
It is preferable to appropriately select the thermal expansion coefficient of the intermediate layer. In other words, to reduce the thermal stress that occurs when a molten solidified body cools and solidifies in a metal coating (or when an already formed solidified body is surrounded by molten metal) and to prevent the occurrence of cracks. The average coefficient of thermal expansion of the intermediate layer in the temperature range from room temperature to the softening temperature of the solidified body is the average coefficient of thermal expansion of the solidified body in the temperature range, and the average coefficient of thermal expansion of the metal coating in the same temperature range. It is preferable that the value be between 1 and 2, and more preferably a value approximately in between.

If the thickness of the intermediate layer is too thin, its function as a barrier to prevent radioactive substances in the solidified material from leaching to the outside world will be reduced, while if it is too thick, the weight of waste relative to the total amount of the composite solidified storage material will be reduced. A range of 0.02 m to ioorm is suitable since the ratio (ie, content) decreases.

The method for forming the intermediate layer includes (a) forming the intermediate layer in advance on the inner surface of a metal covering (for example, a metal container) surrounding the solidified glass or ceramic body by a melt coating method, a flame spray method, etc.; A method in which a glass or ceramic melt containing radioactive waste is then injected and solidified; (b) the already formed assimilate is charged into a metal container and then solidified with the metal container; A method of injecting and solidifying a molten glass or ceramic material that is a material for the interlayer between the body and the body, (c) flame spray method, plasma spray method, CVD method, PV
The intermediate layer is coated on the surface of the solidified material that has already been formed using the D method, vacuum evaporation method, or directly immersed in the melt of the intermediate layer material, and then this is coated with the metal by a conventional method. Methods such as surrounding with a covering can be used.

[Embodiments of the invention]

Example/ The drawing shows a longitudinal cross-sectional view of a composite assimilation storage body obtained in this example. First, simulate radioactive waste with the composition shown in Table 1 below and borosilicate glass with the composition shown in Table 2 below are mixed into 3=7
A molten material containing a weight ratio of 100 ml was poured into a carbon mold having an inner diameter z and a height Oy, and was slowly cooled and solidified.

/ (canister) is prepared, and the glass melt for the intermediate layer having the composition shown in Table 3 below is first poured into the bottom of the canister, and then slowly cooled and assimilated. After forming an intermediate layer, the glass assimilate was removed from the carbon mold and placed in a canister 7. Furthermore, the glass melt for the intermediate layer is injected into the gap between the inner surface of the canister and the vitrified body and the top opening in the same manner as described above, and is slowly cooled and solidified between the canister and the vitrified body. An intermediate layer λ is formed between SU
A top cover made of S was placed on top and sealed by welding to obtain a composite solidified body.

In addition, a vitrified body (diameter, u mm, height tOvx) containing the simulated radioactive waste created in this example,
This solidified body was further coated with an intermediate layer having the composition shown in Table 3 above (the thickness of the intermediate layer was λjam), and the leaching rate of radioactive substances in the solidified body with respect to water was measured.
After each sample was immersed in 0100O for 2 hours, the Mo ions in the solution were quantified.

For those without covering the intermediate layer, the leaching rate is 2. j
X 1O-5F/crn2” day, intermediate 1
The leaching rate of the fljiL method is below the detection limit / × 10 9
It was less than 7 cm''-day.

Example λ The weight ratio of the simulated radioactive waste having the composition shown in Table 1 above and the ceramic 7x forming material having the composition shown in Table 1 below is 3.
The mixing ratio was adjusted to near, and this was sintered to obtain solidified ceramic particles having diameters in order of 7.

Next, CVD is applied to the surface of the obtained ceramic solidified particles.
method (1ooo℃, 81H3C1, H2, CHII, A
A SIC film with a thickness of 3 μm was formed using a gas atmosphere).
Cu plating was applied.

Next, this is 5U with an inner diameter Jjl+l+ and a height/10mm.
Insert the S30≠ canis into the tar, and add C into it.
A molten u-30% Zn alloy was injected and solidified to obtain a metal composite solidified body.

〔Effect of the invention〕

The composite solidified storage body obtained by the present invention has an intermediate layer that does not contain radioactive materials between the solidified body containing radioactive waste and the metal coating surrounding it, so it has even higher leakage resistance. You can improve your performance.

Moreover, since cracks can be effectively prevented from forming in the assimilated product, it is possible to prevent a decrease in the dissipation of radioactive decay heat generated inside the solidified product and an increase in the leaching area due to the cracks.

[Brief explanation of the drawing]

The drawing is a longitudinal sectional view of a composite solidified storage body according to an embodiment of the present invention. C. Canisuku, B. Intermediate layer, 3. Solidified body containing radioactive waste, ≠. Lid. Applicant's agent Kiyoshi Inomata

Claims (1)

[Scope of Claims] l When producing a solidified storage body in which a solidified body made of glass or ceramics containing radioactive waste is further surrounded by a metal coating, radioactive substances may be present between the solidified body and the metal coating. 1. A method for solidifying radioactive waste, comprising providing an intermediate layer made of glass or ceramics that does not contain radioactive waste. The average coefficient of thermal expansion of the intermediate layer in the temperature range from room temperature to the softening temperature of the solidified body is the average coefficient of thermal expansion of the solidified body in the temperature range, and the average coefficient of thermal expansion of the metal coating in the same temperature range. is a value between
Method 0 according to claim 1