JPS6217688A - Spacer for fuel aggregate - 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 [Field of Application of the Invention] The present invention relates to a spacer for a fuel assembly that holds a fuel element of a nuclear reactor fuel assembly.

(Background of the Invention) In a fuel assembly used in a nuclear reactor, a spacer is interposed between the fuel elements to ensure a coolant flow path, and these fuel elements are connected to a leaf spring provided in the spacer. They are held in contact via a member.

In addition, the materials for the spacer include current boiling water reactors,
In pressurized wooden reactors, etc., Zircaloy, which is a zirconium-based alloy with a small thermal neutron absorption cross section, is used in consideration of neutron economy, and Inconel, which has high hardness, is used only for the leaf springs. . Incidentally, in recent years, problems such as legal problems have been pointed out in such a fuel element holding structure. In other words, when the fuel element is held in contact with a leaf spring made of Inconel or the like, electrochemical damage occurs between the leaf spring (Inconel) and the fuel element cladding tube (Zircaloy) at this contact area during reactor operation. As a result, an anode dissolution reaction (electrochemical corrosion mechanism) occurs at the spacer contact area of the fuel cladding, which increases the degree of corrosion at the spacer contact area of the fuel cladding. Ta. (“Development of High-Performance Fuel” by Michio Ichikawa 2
(Pages 35-36 of Nippon Hara Yoryoku Information Center Material Na8411245).

Furthermore, when such an anode reaction occurs, an oxide film is generated on the fuel element cladding tube, but when the burnup of the reactor fuel increases, heat is generated between this oxide film and the fuel element cladding tube. Due to the difference in expansion, the oxide film peels off, and localized abnormal corrosion progresses rapidly.

There was a risk that the integrity of the fuel cladding tube would be significantly impaired. Therefore, it is desired to solve these problems, and corrosion prevention means have been proposed in the past, for example, as shown in Japanese Patent Laid-Open No. 59-24289 and Japanese Patent Laid-Open No. 59-95494. All of these conventional means prevent local corrosion of the fuel element cladding tube by pasting dissimilar metals on the outer surface of the fuel element cladding tube to suppress the anode reaction of the fuel element cladding tube. Although it is true that corrosion prevention effects can be achieved, these conventional means complicate the manufacturing process of the fuel element cladding tube, which increases the manufacturing cost of the fuel element cladding tube, and also increases the production cost of the fuel element cladding tube. There was a risk that the strength of the fuel element cladding tube would change at certain points.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and its purpose is to prevent abnormal corrosion of the fuel element cladding tube at the contact area between the spacer component and the fuel element cladding tube during nuclear reactor operation. It is an object of the present invention to provide a spacer for a fuel assembly that prevents corrosion and further allows the corrosion prevention means to be easily formed without requiring a complicated manufacturing process.

[Summary of the invention]

In order to solve the above-mentioned technical problem, the present invention provides a spacer that holds a fuel element cladding tube constituting a fuel element assembly in contact with each other via a spacer component, in which the fuel element is attached to a surface portion of the spacer component. It is formed by forming a metal coating layer that is electrochemically more base than the cladding, and by forming such a metal coating layer on the surface of the spacer component, the standard electrode potential on the spacer component side can be increased. On the other hand, it is possible to lower the standard electrode potential on the fuel element cladding side, thereby suppressing the anode dissolution reaction of the fuel cladding. Therefore, the fuel element cladding tube has a corrosion protection function, and it is possible to prevent localized abnormal corrosion of the fuel cladding tube during operation of the nuclear reactor.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. This figure shows a plan view of a spacer for a fuel assembly in a nuclear reactor. Its basic structure is similar to that of conventional spacers of this type, and the spacer 1 has many parts inside an outer frame 1'. It is made up of grid members 2 arranged orthogonally, and a fuel element 3 is loaded in a plane space surrounded by the grid members 2.

Further, the fuel element 3 is connected to a leaf spring 4 provided on the spacer 1. The band protrusion 5 and the divider 6 hold the band in contact with each other.

7 is a leaf spring 4. This is an aluminum coating (hereinafter referred to as aluminum) formed by plating the surfaces of the band protrusion 5 and the divider 6. When the fuel element 3 is loaded onto the spacer 1, the aluminum coating (hereinafter referred to as aluminum) coats the cladding tube ( Zircaloy).

Next, the operation of this embodiment will be explained.

During reactor operation, the leaf spring 4 degree band protrusion 5 of the spacer 1. Divider 6 is in the primary cooling water.

Since the surface aluminum 7 contacts the outer surface of the fuel element 3, a first-order electrochemical action occurs. That is, as is clear from Table 1 shown below, the standard electrode potential of aluminum 7 is higher than that of zirconium (fuel element 3).
Since the standard electrode potential of the cladding tube of the fuel element 3 is lower than the standard electrode potential of the cladding tube of the fuel element 3, the aluminum 7 cathodically polarizes the cladding tube of the fuel element 3 to the high potential side.
During this, a so-called local cell is formed which suppresses the anodic reaction of the fuel element cladding.

Table 1 Accordingly, during reactor operation, the 13 anode reaction in the cladding tube of the fuel element 3 is suppressed at the contact area with the spacer 1, and the so-called cathodic corrosion protection function (sacrificial anode method) is activated, and as a result, It is possible to prevent abnormal local corrosion from occurring in the fuel element cladding tube.

FIG. 2 shows the results of a corrosion protection test when the plate spring 4 of the spacer 1 was plated with aluminum 7, and the horizontal axis represents the thickness of the plating layer.

The vertical axis represents the ratio of the thickness of the oxide film of the fuel element cladding tube formed when plating is applied and when no plating is applied. As is clear from the figure, for example,
When plating is applied to a thickness of approximately 50 μm, the amount of corrosion (amount of oxide film formed) on the fuel element cladding tube is approximately 80% compared to when no plating is performed, and the thickness of the plating layer also decreases by approximately 80%. The results showed that as the amount of corrosion increases, the amount of corrosion decreases.
It has been demonstrated that applying a plating layer has an anticorrosion effect. In addition, when the plating layer becomes about 100 μm or more,
As shown in FIG. 2, the anticorrosion effect reaches a saturated state, so it is efficient to set the thickness of the plating layer within a range up to this saturated region.

In addition, in this example, Aluminum 7 is used for the plating layer, but aluminum is used as a coating material for nuclear fuel in material irradiation reactors, etc., and has a small thermal neutron absorption cross section, so it is not suitable from a neutron economic standpoint. There are no problems in use, and neutron irradiation characteristics comparable to conventional ones can be maintained. Furthermore, since aluminum is a softer metal than zirconium or zirconium alloy constituting the fuel element cladding, it is possible to reduce the occurrence of scratches on the fuel element cladding when the fuel element cladding comes into contact with a leaf spring or the like.

In this example, the leaf spring 4 of the spacer 1 is coated with aluminum; however, the present invention is not limited to this, and other metal materials that are electrochemically more base than the fuel element cladding tube may also be used. Similar effect.

Of course, it is effective.

〔Effect of the invention〕

As described above, according to the present invention, occurrence of abnormal corrosion of the fuel element cladding tube caused by contact between the fuel element cladding tube and the spacer component during reactor operation is prevented, and the integrity of the fuel element is maintained. It is possible to provide a spacer for a fuel assembly that can. Moreover, the structure of the spacer itself does not become complicated and can be manufactured easily.

[Brief explanation of drawings]

Fig. 1 is a partially omitted plan view of a spacer for a fuel assembly showing an embodiment of the present invention, and Fig. 2 shows the thickness of the plating layer of the spacer component and the fuel cladding tube when the same spacer is used. FIG. 2 is an explanatory diagram showing the relationship between the thickness of the oxide film generated in

Claims (1)

[Scope of Claims] 1. In a spacer that holds fuel element cladding tubes constituting a fuel element assembly in contact with each other via a spacer component, a surface portion of the spacer component has an electrochemical structure that is lower than that of the fuel element cladding tube. A spacer for a fuel assembly, characterized in that it is formed by forming a metal coating layer that is less base in nature. 2. In claim 1, the fuel element cladding tube is made of zirconium or zirconium alloy, and the metal coating layer of the spacer component is made of aluminum or aluminum alloy. Fuel assembly spacer.