JPH01176977A - Fuel rod and its manufacture - Google Patents

Abstract

PURPOSE:To suppress the sticking of a clad and to reduce corrosion by setting the intensity of magnetism on the surface of a coating pipe to <=4 gauss with respect to a nuclear fuel rod. CONSTITUTION:When the nuclear fuel rod is manufactured by filling pellets 3 formed by mixing uranium oxide with gadolinium in the cladding pipe 1 made of zirconium alloy, the amount of the gadolinium oxide in the pellets 3 is inspected in a high magnetic field. Then, the nuclear fuel rod is inserted into a solenoid coil and a current of tens of ampere is supplied from the right side of the coil and stopped several seconds later. Then a current which is about 80% of said current value is supplied from the right side of the coil and stopped several seconds later. Then, a current which is 60% of the 1st current value is supplied from the right side of the coil successively. Thus, the currents are supplied alternately from the right and left sides while being reduced in current value to set the intensity of the magnetism on the surface of the cladding pipe 1 to <=4 gauss. Consequently, the sticking of the clad of magnetite is suppressed and the corrosion is precluded in long-time use in furnace water.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a nuclear fuel rod in which a cladding tube is filled with pellets of uranium dioxide containing trinium (gadolinia) oxide, and a method for manufacturing the same.

(Prior Art) Nuclear power generation involves raising the temperature of water using the heat generated by the combustion of uranium dioxide, which generates high-temperature steam that rotates a steam turbine to generate electricity. Control rods are used to control reactions during reactor operation, and especially in the early stages, uranium dioxide pellets are mixed with gadolinia, which absorbs neutrons. Gadolinia is called pre-flammable, and loses its neutron absorption ability when it absorbs -carbon neutrons, so it is indispensable for reactivity control in the early stages of operation. Normally, a fuel assembly (1 fuel assembly) is made up of nuclear fuel rods that are partially or completely filled with pellets containing several percent of gadolinia mixed with uranium dioxide.
3 to 4 fuel rods are used per 63 fuel rods. As shown in FIG. 1, such a nuclear fuel rod includes a cladding tube l made of a zirconium alloy such as Zircaloy-2, a lower end plug 2b inserted into the lower opening of the cladding tube 1, and a lower end plug 2b inserted into the lower opening of the cladding tube 1. filled pellets 3 (at least in part consisting of a few percent of gadolinia mixed into uranium dioxide);
and an upper end plug 2a inserted into the upper opening of the cladding tube 1 via a spring 4.

By the way, structural materials loaded into a nuclear reactor are generally subjected to severe inspections. After manufacturing the nuclear fuel rod shown in FIG.
The pellet is passed through a magnetic field of several tens of thousands of Gauss called a magnetic field (Passlve Scaner) to examine the percentage of gadolinia mixed in the pellet. During these inspections, the gadolinia in the pellets filled in the nuclear fuel rods became magnetized, which caused the following problems.

In other words, hematite,
It is thought that floating substances such as magnetite are generated and adhere to the nuclear fuel rods, covering their surfaces. When these floating substances (referred to as cladding) adhere to the outer surface of the nuclear fuel rod, the thermal conductivity of the nuclear fuel rod is obstructed, and as a result, the temperature of the cladding tube that makes up the nuclear fuel rod increases and corrosion is promoted. . The magnetite that constitutes the suspended matter is magnetic iron oxide, so when the nuclear fuel rod is magnetized as described above, the magnetite becomes even more likely to adhere, and the corrosion of the cladding becomes noticeable. A problem arises.

(Problems to be Solved by the Invention) The present invention has been made to solve the above-mentioned conventional problems, and includes a nuclear fuel rod and a nuclear fuel rod that suppress the adhesion of crud and reduce corrosion when used in reactor water. This paper attempts to provide a manufacturing method for the same.

The first invention of the present application is a nuclear fuel rod in which a zirconium alloy cladding tube is filled with pellets containing a mixture of uranium oxide and gadolinium oxide, in which the strength of magnetization on the surface of the cladding tube is set to 4 Gauss or less. It is a nuclear fuel rod characterized by

The reason for limiting the strength of magnetization on the surface of the cladding tube is that if the magnetization exceeds 4 Gauss, the adhesion of cladding such as magnetite becomes noticeable during long-term use in the reactor water, which can lead to corrosion. This is because it becomes impossible to prevent.

The second invention of the present application is to inspect the amount of gadolinium oxide in the pellets in a high magnetic field in the production of a nuclear fuel rod in which a zirconium alloy cladding tube is filled with pellets containing a mixture of uranium oxide and gadolinium oxide. Thereafter, the method of manufacturing a nuclear fuel rod is characterized in that the strength of magnetization on the surface of the cladding tube is reduced to 4 Gauss or less by demagnetizing the cladding tube. .

As the degaussing means, for example, a method may be adopted in which a nuclear fuel rod that has been passed through a high magnetic field for testing the amount of gadolinia in the pellet is inserted into a solenoid coil and an exchange damping current is caused to flow therein. The specific exchange decay current supply operation is as follows:
Do it as follows. In other words, a current of several tens of amperes is passed from the right side of the solenoid coil into which the nuclear fuel rod is inserted.
Stop the current after a few seconds. Next, a current of about 80% of the previous current value is applied from the left side of the solenoid coil, and the current is stopped after a few seconds. Continuing, a current of 60% of the initial current value is applied from the right side of the coil. By passing current alternately between the left and right sides while gradually lowering the current value in this way, the strength of magnetization of the nuclear fuel rod can be reduced and approached to zero.

(Function) According to the first invention of the present application, by regulating the strength of magnetization on the surface of the cladding tube to a predetermined value or less, the adhesion of cladding such as magnetite is prevented during long-term use in reactor water. However, it is possible to obtain a nuclear fuel rod in which corrosion caused by the adhesion of the cladding is reduced.

Furthermore, according to the second invention method of the present application, after the amount of gadolinium oxide in the pellet is inspected in a high magnetic field by a simple operation, the strength of magnetization on the surface of the cladding tube is reduced to 4 Gauss or less by a simple operation. As a result, nuclear fuel rods with reduced corrosion can be manufactured.

(Example of the invention) Examples of the present invention will be described in detail below.

Example: It has the structure shown in Fig. 1 described above, and has an outer diameter of 12.5 ma+.
A short nuclear fuel rod with a length of approximately 40 cm was passed through a MAPS of 70,000 Gauss in order to determine the amount of gadolinia mixed in its pellet. When the magnetization strength on the surface of the cladding tube after passing through MAPS was measured, it was approximately IOO Gauss.

Next, the magnetized nuclear fuel rod was inserted and installed in the center of a solenoid coil with an inner diameter of about 20 mm and a length of 50 G.

Next, apply a current of 1 OA from the right side of the solenoid coil for 10 seconds, stop the current, and after 10 seconds, 8 OA from the left side.
A current of A was passed. Subsequently, 10 seconds after stopping the current, a current of 6 A was applied from the right side, then a current of 4 A was applied from the left side, then a current of 2 A was applied from the right side, and then a current of IA was applied from the right side. After passing current alternately between the left and right sides while gradually lowering the current value in this way, the nuclear fuel rod was removed from the solenoid coil and the strength of magnetization on the surface of the cladding tube was measured.
It was 2 Gauss.

Therefore, the nuclear fuel rod of this example and the short nuclear fuel rod with magnetization of 100 Gauss and not subjected to demagnetization treatment (comparative example)
Corrosion tests were conducted under the following conditions. first,
4000 cc of water and hematite ((Z-
Fe203) 50g, copper oxide (CuO) 5g
and 1 g of magnetite (Fe 304 ) powder were placed therein, and the nuclear fuel rods of Examples and Comparative Examples to be tested were inserted into the corrosion test layer connected to the steam generator via a valve. Next, the temperature of the steam generator was increased to 30
The temperature was maintained at 0°C and the steam was allowed to flow into the corrosion test tank, and the test tank was maintained at 500°C and 105 atm. 2
After 4 hours of testing, the condition of each nuclear fuel rod was examined. As a result, in the nuclear fuel rod of this example, no cladding mainly composed of hematite was observed.

On the other hand, in the nuclear fuel rod of the comparative example which was not subjected to demagnetization treatment, the cladding was adhered to the entire surface. Further, when the cladding was removed from the nuclear fuel rod of the comparative example to which the cladding was attached, it was confirmed that oxidation was accelerated compared to the nuclear fuel rod of the present example.

[Effects of the Invention] As detailed above, according to the present invention, it is possible to produce a nuclear fuel rod that suppresses the adhesion of crud and reduces corrosion during use in reactor water, and such a nuclear fuel rod by simple operations. I can provide a method.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing an intra-membrane nuclear fuel rod. DESCRIPTION OF SYMBOLS 1... Cladding tube, 2a... Upper end plug, 2b... Lower end plug, 3... Pellet, 4... Spring. Applicant's agent Patent attorney Takehiko Suzue Figure 1

Claims (2)

[Claims] (1) A nuclear fuel rod in which a zirconium alloy cladding tube is filled with pellets containing a mixture of uranium oxide and gadolinium oxide, characterized in that the strength of magnetization on the surface of the cladding tube is 4 Gauss or less. nuclear fuel rods. (2) In the manufacture of nuclear fuel rods in which pellets containing a mixture of uranium oxide and gadolinium oxide are filled into a zirconium alloy cladding tube, the amount of gadolinium oxide in the pellets is inspected in a high magnetic field and then demagnetized. A method for manufacturing a nuclear fuel rod, characterized in that the strength of magnetization on the surface of the cladding tube is 4 Gauss or less.