JPS636493A - Channel box for nuclear reactor - 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 Industrial Application] The present invention relates to a channel box for a nuclear reactor.

[Conventional technology]

What is the performance of the fuel assembly loaded into the reactor core?

One of the most important elements for the smooth and safe operation of a nuclear reactor, the channel box, which is located at the outermost part of the fuel assembly and covers the fuel band, is the coolant for the fuel assembly. It plays an important role in ensuring the strength of the fuel assembly, maintaining the insertability of adjacent control rods, etc. Conventional channel boxes use zirconium-based alloys due to their strength, corrosion resistance, thermal neutron absorption properties, etc.
Mechanical deformation (
Creep deformation) is known to occur. In other words, during reactor operation, coolant flows under high pressure in the channels, and at this time, mechanical deformation force is continuously applied to the channel box walls due to the pressure difference inside and outside the channel box. It turns out. This pressure is approximately 1 kg/C higher inside the channel box than outside.
Since the channel box is about 1.5 m in height, it expands and deforms outward, and the deformation is further amplified by the thermal effect and neutron irradiation effect caused by long-term operation.The channel box that expands outward interferes with the adjacent control rod and is controlled. There was a risk that the insertion of the rod into the reactor core would be deteriorated and the proper and safe operation control of the reactor would be hindered.Also, due to the deformation of the channel box,
The coolant flowing inside the channel box tends to leak from the gap created between the lower end of the channel box and the lower tie plate, and there is a risk that the cooling effect on the fuel bundle will not be sufficiently exerted.

In order to solve such problems, for example,
As disclosed in Japanese Patent Application Laid-open No. 10516, each side of the channel box is bent inward in advance during manufacture to cancel out the outward deformation during use and the initial inward deformation; As disclosed in Japanese Patent Application No. 27320, conventional methods include reversing the vertical relationship of the channel box midway through its life, thereby uniformly distributing the amount of deformation in the axial direction and prolonging the life of the channel box. More suggested.

[Problem that the invention seeks to solve]

However, if the channel box is previously deformed inward during manufacturing as in the prior art disclosed in JP-A-55-10516, the channel box interferes with the fuel bundle when assembling the fuel assembly, resulting in poor manufacturing. Moreover, when the channel box is used with the positional relationship reversed, as in the prior art disclosed in Japanese Patent Application Laid-Open No. 55-27320, the outer deformation itself still occurs. However, all of the above-mentioned conventional techniques have a problem that should be improved in that as the period of use of the channel box is extended, the outward creep deformation continues to progress and eventually reaches the permissible limit.

The present invention has been made in view of the above problems, and
The purpose is to provide a channel box for a nuclear reactor that can prevent creep deformation of the channel box and maintain its functional integrity even after long-term use.

[Means for solving problems]

The above purpose is to make the plate material constituting the channel box for a nuclear reactor have different neutron irradiation growth characteristics in the thickness direction, and also to make the neutron irradiation growth characteristics different in the circumferential irradiation growth amount on the outer surface side of the channel box. This is achieved by setting the growth amount in the circumferential direction smaller than that on the inner surface side.

[Effect]

As mentioned above, the channel box undergoes creep deformation toward the outside due to the pressure difference between the inside and outside of the channel box during its period of use. The pressure difference inside and outside the channel box, which is the main cause of this creep deformation, and the high temperature and fast neutron flux, which are the acceleration factors, are unavoidable during nuclear reactor operation, so the distortion due to creep is basically unavoidable. The strain caused by this creep can be expressed by the following formula. This will be explained based on a schematic diagram of a modified channel box in FIG. channel box 1
is displaced outward by δ due to its use in a nuclear reactor. Here, assuming that one side of the channel box bends with a -like radius of curvature r, the central angle θ of the fan shape where one side of the channel box is an arc is θ = 12o / where the length of one side of the channel box is Qo. It is represented by r.

Furthermore, there is a relationship between this equation and the amount of deformation δ of the channel box as shown in the following equation.

δ= r (1-cos(-))2rθ2/8 However, α
Approximate formula when % is small Formula % Also, if the thickness of the channel box 1 is t, the circumferential strain difference Δε on the inner and outer surfaces of the channel box is Δε= t
/r. Therefore, the relationship between the circumferential strain difference Δε between the inner and outer surfaces and the amount of deformation δ is expressed by the following equation.

Δε=8tδ/Qo" On the other hand, the zirconium-based alloy that makes up the channel box has a neutron irradiation growth characteristic that causes it to deform when exposed to fast neutrons even when no stress is applied.Using this irradiation characteristic, it is possible to It is possible to create a strain difference between the front and back surfaces by neutron irradiation.In other words, one side of the plate (A
If a plate with a relatively small amount of irradiation growth is used on the side (referred to as the B side) and a plate with a larger amount of irradiation growth than the A side is used on the back side (referred to as the B side) and irradiated with fast neutrons, the B side of the plate will be convex. A deflection deformation occurs as follows.

Therefore, if the plate material constituting the channel box used in the present invention is one in which the amount of circumferential irradiation growth on the outer surface of the channel box is small and the amount of circumferential irradiation growth on the inner surface side is large, neutrons during reactor operation The irradiation causes the channel box to bend inward. If the strain difference Δεcr due to the difference in irradiation growth characteristics and the strain difference ΔE due to the creep deformation described above are made equal, the strain differences acting in opposite directions cancel each other out, and the total strain difference between the inner and outer surfaces that occurs during use of the channel box Δεtot can be set to zero, that is, the total deformation amount δtot can be set to zero as shown in the following equation.

δtot o=Δεtot::Δε−Δεcr=0In order to make the neutron irradiation growth characteristics different on the inner and outer surfaces of the plate material, the simplest method is to join two types of plate materials with different characteristics. However, the most preferable material is a zirconium-based alloy, which has excellent corrosion resistance, strength, neutron absorption properties, etc., and has a sufficient track record in nuclear reactors.Using this material, the neutron irradiation growth characteristics of the inner and outer surfaces of the channel box can be varied. is desirable. When a zirconium-based alloy is used, the neutron irradiation growth characteristics can be varied as follows.

In other words, the basic mechanism of irradiation growth of zirconium-based alloys is that, due to the accumulation of lattice defects caused by neutron irradiation, the hexagonal zirconium crystal shrinks in the C-axis direction (the central axis direction of the crystal) and shrinks in the a-axis direction ( (direction perpendicular to C-axis)
By spreading to.

Therefore, the neutron irradiation growth characteristics of zirconium-based alloys are C
It is controlled by the direction of the texture of the axis. By taking this characteristic into consideration and changing the crystal orientation of the texture on the inner and outer surfaces of the channel box, it is possible to obtain a channel box plate material with different irradiation growth on the inner and outer surfaces of the channel box. As a method of varying the neutron irradiation growth characteristics of such a zirconium-based alloy, there is a method of changing the heat treatment process of the zirconium-based alloy. For example, when a zirconium-based alloy is annealed, the amount of irradiation growth of the annealed material is smaller than that of the processed material before annealing. Therefore, by changing the annealing conditions on the inner and outer surfaces of the channel box,
The outer surface of the zirconium plate material for the channel box is annealed in the final manufacturing process.

Even if the degree of processing before annealing remains on the inner surface side, it is possible to obtain a channel box plate material with different neutron irradiation growth on the inner and outer surfaces of the channel box.

〔Example〕

An embodiment of the present invention will be described based on FIGS. 1 to 3.

FIG. 1(a) is a cutaway cross-sectional view of a channel box that is an embodiment of the present invention, and FIG. 1(b) is a schematic diagram of the texture showing an enlarged view of section A in FIG. 1(a). be. Figure 1(a)
As shown in the figure, the plate material constituting the channel box 1 consists of an outer layer 2 and an inner layer 3, which are divided into two layers approximately at the center of the plate thickness. The outer layer 2 and the inner layer 3 are each formed of a zirconium-based alloy having a different texture, and are joined at their interfaces by metal bonding. Looking at the texture of the outer M2, as shown in Figure 1(b), the C-axes of the crystals are relatively uniformly oriented in all directions, but the C-axes of the inner layer 3 are aligned in the thickness direction. It has become a collective organization like this. Such a channel box is manufactured through the steps shown in FIG. That is, as shown in (If) in Fig. 2, the member that becomes M3 in the channel box is melted, then hot-forged, hot-rolled, and annealed to a certain degree, and then cold-worked into a heavily worked ring. Add rolling. When a heavily worked ring is cold rolled, most of the crystal C axes are oriented in the thickness direction. On the other hand, the outer M2 of the channel box is melted, hot forged, and hot rolled as shown in FIG. 2 (I).

After annealing, it is formed without adding a strongly worked ring by cold rolling as described above, and the orientation of the crystal C axis is relatively uniform and random. After the plate elements of the inner and outer layers of the channel box are manufactured in the manufacturing steps (1) and (n), each plate element is joined by welding and hot rolled as shown in FIG. 2(m). By doing so, a single plate for the channel box is formed. After this, it is cold rolled according to the normal channel box manufacturing process.

After annealing and polishing, the material is shaped so that the hard cold rolled surface faces inside, and a channel box is formed through annealing and finishing steps. Note that a special heat treatment step may be added between forming and annealing to improve corrosion resistance.

In addition, in the portion that will become the outer layer 2, the C-axis is slightly oriented in the thickness direction in the latter half of the process, but the deviation is much smaller than in the portion that will become the inner layer 3.

Therefore, according to the channel box having such a structure, the crystals of the zirconium-based alloy, which is the material of the channel box, shrink in the C-axis direction by neutron irradiation, as described in detail in the "effect" section of the invention, and the a Since it has an irradiation growth characteristic that spreads in the axial direction, the amount of irradiation growth in the circumferential direction of the channel box is larger for the inner layer 3, in which the C axis is more biased in the thickness direction, than for the outer layer 2. As a result, a difference in irradiation growth occurs between the inner and outer layers of the channel box 1, and a force is generated that tends to bend and deform the channel box inward. As a result, as shown in Figure 3 (Figure 3 shows the relationship between the amount of deformation of the channel box and the time spent in the reactor in this example), the channel box was deflected inward (inside and out) due to this irradiation growth. The difference in strain between the layers) cancels out the outward deformation of the channel box due to creep deformation, making it possible to substantially suppress the deformation of the channel box. In particular, according to the above embodiment, the amount of deformation due to neutron irradiation growth can be adjusted by controlling the difference in the degree of inclination of the C-axis between the inner and outer layers. The amount of deformation can also be adjusted arbitrarily.

FIG. 4 shows the main manufacturing process of a channel box in another embodiment of the present invention, and FIG. 5 shows a channel box annealing furnace used in this manufacturing process. The part indicated by (1) in Fig. 4 is a conventionally known manufacturing process for forming a channel box using a zirconium-based alloy, and this example is the part shown in Fig. 4 (1). The channel box formed in the manufacturing process is further shown in Figure 4 (
As shown in II), recrystallization is performed by annealing only the outer surface, leaving a processed layer on the inner surface of the channel box. As shown in FIG. 5, such a channel box is manufactured by setting a pre-formed channel box 1 in an annealing furnace 4 during the final manufacturing process, and passing a coolant through the inside of the channel box 1 to cool the inner surface. It can be manufactured by annealing the outer surface.

However, in the channel box manufactured in this way, since the outer surface of the channel box is annealed in the final manufacturing process, the amount of neutron irradiation growth is relatively small (that is, the crystal C axis is in a random state due to annealing). On the other hand, the inner surface of the channel box retains the degree of cold rolling, so the amount of neutron irradiation growth is relatively large. Therefore, due to neutron irradiation growth during reactor operation, the channel box plate material tends to deform inward to counteract the creep deformation6.Therefore, in this example as well, the annealing temperature during final annealing or the cooling of the inner surface of the channel box Since the irradiation growth characteristics of the inner and outer surfaces of the channel box can be controlled arbitrarily depending on the conditions, creep deformation of the channel box can be suppressed to substantially zero.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide a channel box that can prevent creep deformation of the channel box and maintain its functional soundness even after long-term use in a nuclear reactor. Furthermore, by achieving the above effects, it is possible to realize a high burnup fuel assembly that can be used for a long period of time in a reactor, and secondary effects of reducing fuel cycle costs and radioactive waste can also be achieved.

[Brief explanation of the drawing]

FIG. 1(a) is a partially cutaway sectional perspective view showing a first embodiment of the present invention, FIG. 1(b) is an enlarged sectional view of section A in FIG. 1(a), and FIG. An explanatory diagram showing the manufacturing process of the channel box of the above embodiment, FIG. 3 is a characteristic diagram showing the relationship between the amount of deformation of the channel box of the above embodiment and the residence time in the furnace,
FIG. 4 is an explanatory diagram showing the manufacturing process of the channel box in the second embodiment of the present invention, FIG. 5 is a schematic diagram showing the final annealing process of the channel box manufacturing process in the second embodiment, and FIG. is a schematic diagram showing creep deformation of a channel box. 1 - Channel box, 2... Outer layer, 3... Inner layer, 4 Potato 1 Diagram 2nd item (1) (9 - 2) 2 Thatch 4 Mouth

Claims (1)

[Scope of Claims] 1. The plate material constituting the channel box for a nuclear reactor is made to have different neutron irradiation growth characteristics in the thickness direction, and the neutron irradiation growth characteristic of the plate material is different in the circumferential direction on the outer surface side of the channel box. A channel box for a nuclear reactor, characterized in that the amount of irradiation growth is set smaller than the amount of irradiation growth in the circumferential direction on the inner surface side of the channel box. 2. The channel box for a nuclear reactor according to claim 1, wherein the plate material constituting the channel box has a layer structure of at least two or more layers having different neutron irradiation growth characteristics. 3. The channel box for a nuclear reactor according to claim 1 or 2, wherein the plate material constituting the channel box is made of a zirconium-based alloy. 4. The channel box for a nuclear reactor according to claim 3, wherein the plate material constituting the channel box has different crystal orientations of texture on the inner and outer surfaces of the channel box. 5. In claim 3, the plate material constituting the channel box is an atom formed by annealing only the plate material on the outer layer side in the final manufacturing process of the channel box, and leaving the processed layer before annealing on the plate material on the inner layer side. Channel box for furnace.