JP2655908B2 - Method for producing nuclear fuel pellet containing gatolinium oxide having large crystal grain size - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing gadolinium oxide-containing uranium dioxide nuclear fuel pellets having a large crystal grain size.

[Conventional technology and its problems]

Conventionally, as a nuclear fuel, a uranium dioxide sintered pellet filled in a cladding tube made of Zircaloy or the like has been used as a nuclear fuel element.

However, recently, gadolinium oxide-containing uranium dioxide sintered pellets filled in a cladding tube of radiocaloy or the like have begun to be used as nuclear fuel elements. Since the nuclear fuel element filled with the gadolinium oxide-containing uranium dioxide sintered pellet contains gadolinium having a neutron absorbing ability, the nuclear fuel element itself is a burnable poison rod (hereinafter referred to as a BP rod). ) Plays the role of suppressing core reactivity. This is to increase the availability of current nuclear plants,
Increasing the uranium enrichment and controlling the excess reactivity in the early life of the core and maintaining the moderator temperature coefficient on the negative side are necessary to increase the number of BP rods. Instead, the problem can be solved by using a nuclear fuel element filled with sintered pellets of gadolinium oxide-containing uranium dioxide, thereby greatly improving the economics of nuclear power generation using a nuclear reactor.

The above uranium dioxide sintered pellet containing gadolinium oxide is prepared by mixing 3 to 15% by weight of gadolinium oxide with ordinary uranium dioxide powder, adding a lubricant thereto, mixing the mixture, and forming a green compact. It is manufactured by sintering in a reducing atmosphere at 11800 ° C.

When nuclear fission is performed, the nuclear fuel element obtained by filling gadolinium oxide-containing uranium dioxide sintered pellets in a cladding tube such as zircaloy is a fission product gas (hereinafter referred to as FP gas) such as xenon or krypton. ) Occurs, and when such FP gas is generated inside the cladding tube, a high gas pressure is generated, and there is a problem that the cladding tube may be damaged.

Therefore, as one of the means for suppressing the release of FP gas generated from nuclear fuel pellets, in the case of pellets made of uranium dioxide alone, crystal grains grow during sintering of the green compact, and the FP gas holding capacity is increased. Has been proposed for imparting gallium oxide to sintered compact pellets, but the present situation has not been solved for uranium oxide nuclear fuel pellets containing gadolinium oxide.

[Means for solving the problem]

Therefore, the present inventors conducted research to develop a method for producing gadolinium oxide-containing uranium oxide nuclear fuel pellets having a large crystal grain size having FP gas holding capacity, and found that uranium dioxide powder containing gadolinium oxide powder was Furthermore, it has been found that by adding 1000 to 5000 ppm of an aluminum compound in terms of aluminum, uranium oxide nuclear fuel pellets containing gadolinium oxide with large crystal grains can be produced.

The present invention has been made on the basis of such findings, and it has been found that gadolinium oxide powder having an average particle size of 8 to 10 μm: ~ 5000ppm (0.1 ~ 0.5
% By weight), mixed, and press-molded the mixed powder to produce a green compact. Then, the green compact was sintered to obtain a gadolinium oxide-containing uranium dioxide nuclear fuel pellet having a large crystal grain size. It is characterized by the manufacturing method.

The aluminum compound is one or more of aluminum oxide, aluminum hydroxide, and an aluminum salt of a fatty acid. Examples of the aluminum salt of the fatty acid include aluminum stearate, aluminum oleate, and aluminum palmitate. But not limited thereto.

Zinc stearate was generally used as a lubricant to produce a green compact of UO ₂ powder containing Gd ₂ O ₃ powder, but the aluminum salt of the above fatty acid functions as a lubricant during green compact molding. Therefore, it can be used as a substitute for the zinc stearate, and can be added together with zinc stearate to reduce the amount of zinc stearate added.

In the present invention, uranium dioxide containing Gd ₂ O ₃ was mainly described, but a mixed oxide of uranium and plutonium was used for MO.
It will be theoretically recognized by those skilled in the art that a similar effect is obtained for a nuclear fuel obtained by adding Gd ₂ O ₃ powder to what is called X.

〔Example〕

Next, the present invention will be specifically described based on embodiments.

Average particle size: 0.97 μm UO ₂ powder, average particle size: 5.00 μm Gd ₂ O ₃ powder, average particle size: 0.50 μm Al ₂ O ₃ powder were prepared. Each of the mixed powders obtained by blending and mixing to have the composition shown in Comparative Example 1 was filled in a mold, and press-molded at a pressure of 3 ton / cm ² to obtain a diameter of 10 mm × high. A compact having a thickness of 15 mm was produced.

These green compacts were sintered in a hydrogen stream at a temperature of 1750 ° C. for 5 hours to produce Ud ₂ pellets containing Gd ₂ O ₃ .

The resulting Gd ₂ O ₃ containing UO ₂ measures the average crystal grain size and sintering density of the pellets, showed results of these measurements are given in Table 1.

〔The invention's effect〕

From the results of the above examples, it can be seen that U containing Gd ₂ O ₃ in the present invention.
By adding an aluminum compound to O ₂ powder in an amount of 1000 to 5000 ppm (0.1 to 0.5% by weight) in terms of aluminum, the crystal grain size of the uranium dioxide pellet containing Gd ₂ O ₃ can be easily increased. However, as can be seen from Comparative Example 1, even if the content exceeds 0.5% by weight (5000 ppm), the average crystal grain size does not increase any more, but rather decreases.

In this example, aluminum oxide was used for the addition of aluminum. However, the addition of aluminum is not limited to aluminum oxide. In addition, aluminum hydroxide, aluminum salts of fatty acids (for example, aluminum stearate, palmitic acid) Aluminum and aluminum oleate).

Claims (1)

(57) [Claims] 1. A method of producing a gadolinium oxide-containing nuclear fuel by blending a predetermined amount of gadolinium oxide with uranium oxide, mixing, molding and sintering, wherein the aluminum compound is converted to aluminum in an amount of 1,000 to 1,000.
A method for producing nuclear fuel pellets containing gadolinium oxide having a large crystal grain size, wherein 5000 ppm (0.1 to 0.5% by weight) is added.