JPS5810677A - Nuclear fuel assembly - 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 The present invention relates to a wire-type nuclear fuel assembly, and particularly to a nuclear fuel assembly suitable for use in a large fast breeder reactor or the like.

In order to prevent contact between the fuel element and the wrapper tube at the end of the fuel life, a nuclear fuel assembly has been proposed in which the wrapper tube is made of a material with larger swelling expansion than the cladding tube. This is an alternative to prevent this.

An object of the present invention is to provide a nuclear fuel assembly in which a nuclear fuel element is assembled in a trumpet tube, in which a hexagonal cross section of the trumpet tube is
The gap between the fuel elements located on the longest diagonal of the book can be widened by not wrapping a wire around some of the elements or by wrapping a small diameter wire, making it possible to extend the service life. The objective is to provide a fuel assembly with a

A wire-type nuclear fuel assembly for a fast breeder reactor has a structure in which a trumpet tube 2 covers fuel elements 1 arranged in an equilateral triangular lattice. Further, in order to prevent the fuel elements from coming into direct contact with each other due to the curvature of the fuel elements, a wire 3 is wound around each fuel element. The fuel element gap surrounded by the wrapper tube is designed to be sufficiently narrow to prevent flow vibrations of the fuel element caused by coolant flowing through the gap.

In general, as the tube and fuel element are subjected to neutron irradiation, the temperature of the wrapper tube is lower than that of the cladding tube, so a difference in swelling expansion between the wrapper tube and the cladding tube occurs, and the above gap disappears. go. When a bundle of fuel elements is tightly packed in the wrapper tube in this manner, unless the fuel elements are misaligned, a strong force will be applied to the fuel elements, potentially causing damage to the fuel elements. On the other hand, if misalignment occurs, the fuel elements may come into direct contact with each other without using wires, and the fuel elements may burn out.
To prevent damage and burnout of the fuel elements, limits are placed on the irradiation time of the assembly in the furnace.

The present invention achieves the above-mentioned by winding a small diameter wire or not winding a wire around a part of the fuel element located on the three longest diagonal lines of the hexagonal section of the trumpet tube when manufacturing the assembly. This delays the time it takes for damage and burnout to occur, making it possible to extend the irradiation period of the assembly in the furnace.

An embodiment of the present invention will be described below with reference to FIG. A small diameter wire is used for the fuel elements located at the corners of the trumpet tube 4, and the gap between the fuel elements located on the diagonal of the hexagonal cross section of the trumpet tube is widened.

As shown in FIG. 3, the inner wall 5 of the wrapper tube during manufacture deforms as shown in 6 at the end of its life due to thermal expansion, swelling expansion, and creep strain due to coolant pressure. Furthermore, since the temperature distribution generally reaches its maximum near the center of the assembly and decreases at the periphery, the amount of expansion of the fuel elements near the center is large. Therefore, in the conventional assembly, the gaps between the diagonally located fuel elements are
Disappear first. However, according to the present invention, it is possible to delay the time when the gap disappears, and as a result, there is an effect of extending the life of the fuel assembly. In addition, in the embodiment of the present invention, the fuel elements around which the small diameter wires are wound are located at the corners, so that when the diagonal gap disappears, contact between the fuel elements due to misalignment may occur. For example, the potential for contact of fuel elements located at corners is greater than in conventional assemblies. However, since the coolant temperature is low at the periphery of the assembly and the heat removal capacity is large, direct contact at the periphery of the assembly is less likely to result in fuel element burnout than at the center. .

According to the present invention, the fuel element bundle at the time of manufacture has a large gap on the diagonal line of the hexagonal section of the wrapper tube, so it is possible to delay the disappearance of the gap at the end of the life, and as a result, the nuclear fuel assembly can be used for a long time. The effect of change can be seen. Furthermore, according to the present invention, during manufacturing, only the gaps on the diagonal line can be made larger and the gaps on the other rows can be made smaller, so it is also possible to prevent fluid vibration of the fuel element.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the structure of a target product of the present invention, FIG. 2 is an embodiment diagram of the present invention, and FIG. 3 is a detailed explanatory diagram of the present invention. DESCRIPTION OF SYMBOLS 1...Fuel element, 2...Trumpet tube, 3...Wire, 4...Small diameter wire, 5...Inner surface during production of the wrapper tube, 6...First eye

Claims (1)

[Claims] 1. In a nuclear fuel assembly consisting of a fuel element built into a trumpet tube and a spacer wire wrapped around the fuel element, small diameter wires are attached to several of the fuel elements located on the longest diagonal line of the hexagonal cross section of the trumpet tube. A nuclear fuel assembly characterized by using wire or not wrapping wire.