JP2013054037A - Reactor control rod - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that hafnium as a neutron absorption member has a life longer than that of boron carbide, however, a conventional reactor control rod made of hafnium has a sheath made of stainless steel, and a risk of IASCC becomes high in accordance with irradiation in a long period.SOLUTION: A reactor control rod of the present invention includes: a blade 31; and a support member 1 which supports the blade, in which the blade 31 is constituted only of the blade in the shape formed by bending a flat plate constituted of zirconium-hafnium alloy which is a neutron absorption member.

Description

  The present invention relates to a nuclear reactor control rod having a neutron absorber and used for power control of a nuclear reactor.

The reactor control rod of the boiling water light water reactor moves up and down the gap formed by four adjacent fuel assemblies loaded in the core of the reactor pressure vessel. It is constructed by attaching two blades and has a cross-shaped cross section. The blade is composed of a hollow sheath and a neutron absorbing member built in the sheath. As the neutron absorbing member, there is a type using boron carbide (B4C), hafnium (Hf), or a combination thereof. Mainly, boron carbide is used as a powder, and hafnium is used as a plate or bar. Since hafnium is less susceptible to degradation by neutron irradiation than boron carbide, hafnium control rods have a longer life than boron carbide control rods.

The structure of a conventional hafnium control rod will be described with reference to FIGS. FIG. 10 is a partially exploded perspective view showing an outline of the hafnium control rod 100, and FIG. 11 is an enlarged cross-sectional view of the main part of the hafnium control rod blade 110 cut along a plane perpendicular to the major axis direction.

Four blades 110 are attached to the cross-shaped support member 101, and the support member 10
1 and the lower end of the blade 110 are connectors 102 connected to a control rod drive mechanism (not shown).
And a coupling socket 103 are attached. A handle 104 is attached to the upper ends of the support member 101 and the blade 110. The blade 110 includes a hollow sheath 111 and a hafnium plate 112 attached to the inside of the sheath 111, and the sheath 111 is provided with a plurality of cooling holes 113 for circulating a coolant in the sheath 111.

The structure of the blade 110 will be described in detail with reference to FIG. A hafnium plate 112 is attached to the inside of a sheath 111 formed in a substantially U-shaped cross section, and the hafnium plate 112 is fixed to the sheath 111 using a hafnium plate fixing member 114. The hafnium plate fixing member 114 penetrates the sheath 111 and the hafnium plate 112 and is attached by welding. Further, a coolant channel 115 is secured inside the sheath 111 so that the heat generated by the hafnium control rod 100 can be efficiently removed.

For such a control rod, when using a combination of hafnium and boron carbide as a neutron absorbing member, a cylindrical cladding tube is filled with a hafnium member and powdered boron carbide, and a plurality of cladding tubes are arranged inside the sheath. Place and use. In such a control rod, a hafnium member is disposed in a portion with a relatively high irradiation amount, and the remaining portion is filled with boron carbide. However, there is concern about swelling due to generation of tritium by the reaction of boron and neutrons. It was. On the other hand, for example, a neutron absorbing element for a reactor control rod described in Patent Document 1 is known.

On the other hand, the sheath of the control rod has no concern about swelling as described above.
Stainless steel with excellent stress corrosion cracking properties is used. However, since the hafnium control rod is used for a longer period of time than the boron carbide control rod, the neutron irradiation amount is high, and the irradiation embrittlement of the sheath portion made of stainless steel is more remarkable. Therefore, IASCC (irradiation-induced stress corrosion cracking) caused by a combination of irradiation embrittlement, residual stress in the welded part, thermal stress during operation, etc.
There is a problem that the possibility of occurrence of this is higher than that of a boron carbide control rod.

As an invention for solving such a problem, for example, a method for producing an austenitic stainless steel having a configuration described in Patent Document 2 is known.

JP-A-4-58193 JP 2005-290488 A

In addition to the above-mentioned issues, research and development for increasing the fuel density has been promoted in recent years for the purpose of improving power generation efficiency, and a transition from the current 9 × 9 fuel bundle to the 10 × 10 fuel bundle is expected. Issues are also attracting attention. That is, when the fuel bundle transition is realized,
The combustion density is increased, and the distance between the fuel rod and the control rod is shortened, so that the irradiation speed of the control rod is increased. Furthermore, extension of the span of regular inspections is also being studied to improve plant operating efficiency, and an increase in the amount of irradiation in one cycle is also expected.

The present invention has been made in view of the above-described problems, and realizes a nuclear reactor control rod further excellent in irradiation resistance and reliability in order to prevent the occurrence of IASCC even in a more severe irradiation environment than before. With the goal.

A nuclear reactor control rod according to the present invention is a nuclear reactor control rod comprising a blade and a support member that supports the blade, and the blade bends a flat plate made of a zirconium-hafnium alloy that is a neutron absorbing member. It is comprised only by the blade of the shape formed in this way.

Further, a nuclear reactor control rod according to the present invention is a nuclear reactor control rod comprising a blade and a support member that supports the blade, wherein the blade is a neutron absorbing member zirconium-
A flat plate made of a hafnium alloy is only composed of a blade formed by providing a vertical hole.

ADVANTAGE OF THE INVENTION According to this invention, the nuclear reactor control rod excellent in irradiation resistance and reliability than before can be provided.

The principal part expanded horizontal sectional view of the reactor control rod by a 1st Example. The principal part expansion perspective view which shows the outline | summary of the structure | tissue arrangement | sequence of the sheath 2 of the reactor control rod by a 1st Example. Zirconium-niobium binary system phase diagram. The principal part expanded horizontal sectional view of the reactor control rod by a 2nd Example. The principal part expanded horizontal sectional view of the nuclear reactor control rod by another example of a 2nd Example. The principal part expanded horizontal sectional view of the nuclear reactor control rod by another example of a 2nd Example. The principal part expanded horizontal sectional view of the nuclear reactor control rod by another example of a 2nd Example. The principal part expanded horizontal sectional view of the nuclear reactor control rod by another example of a 2nd Example. (A) (b) The principal part expanded horizontal sectional view of the nuclear reactor control rod by another example of a 2nd Example. The partial exploded perspective view of the conventional nuclear reactor control rod. The principal part expanded horizontal sectional view of the conventional nuclear reactor control rod.

  Embodiments of the present invention will be described below with reference to the drawings.

[Example 1]
The configuration of the reactor control rod according to the first embodiment of the present invention will be described with reference to FIG. FIG. 1 is an enlarged cross-sectional view of a main part in which a nuclear reactor control rod according to the present embodiment is cut along a plane perpendicular to the major axis direction and a blade portion is enlarged.

A hollow sheath 2 using zirconium (Zr) or a zirconium alloy is attached to the cross-shaped support member 1. Inside the sheath 2 is attached a neutron absorbing member 3 configured by arranging a plurality of hafnium plates or hafnium rods. The neutron absorbing member fixing member 4 is welded and attached through the sheath 2 and the neutron absorbing member 3 to fix the neutron absorbing member 3 to the sheath 2. A primary coolant flows through the coolant channel 5 inside the sheath 2 during the operation of the nuclear reactor, and the primary coolant removes the heat of the blade 10.

Examples of the zirconium alloy used for the sheath 2 include tin (Sn), iron (Fe), chromium (
Zircaloy 2, Zircaloy 4 to which Cr) or the like is added, or an alloy having a composition similar to these is used. Zircaloy 2 and Zircaloy 4 are zirconium alloy standards established by the American Society for Testing and Materials (ASTM), respectively. The compositions of Zircaloy 2 and Zircaloy 4 are shown in Table 1.

Hereinafter, the operation of this embodiment will be described. Zirconium has a neutron absorption cross section of about 1/15 that of stainless steel, and is excellent in irradiation resistance. Zirconium and hafnium are both titanium group elements and are known to have similar physical properties other than the neutron absorption cross section. Therefore, a sheath 2 made of zirconium or a zirconium alloy and a neutron absorbing member 3
Is smaller than the thermal stress generated between the conventional stainless steel sheath and the hafnium plate. Therefore, it becomes more reliable than a conventional nuclear reactor control rod using a stainless steel sheath.

Zirconium has a hexagonal close-packed structure, but the texture can be controlled by processing and heat treatment in the same manner as titanium (Ti). By controlling the texture, the direction of the tissue arrangement can be controlled, and the generation of stress between the sheath 2 and other structures due to irradiation growth of the sheath 2 can be prevented. The reason will be described in detail with reference to FIG.

FIG. 2 is an enlarged perspective view of a main part showing an outline of the sheath 2 in which the tissue arrangement is controlled. For the sake of simplicity, the neutron absorbing member 3 and the neutron absorbing member fixing member 4 are omitted.

The crystal lattice 20 conceptually shows the tissue arrangement of the sheath 2 obtained by processing and heat treatment of the sheath 2. The tissue arrangement of the sheath 2 is controlled so that the c-axis 21 is in the thickness direction of the sheath 2 as indicated by the crystal lattice 20.

The effects of such tissue arrangement control will be described below. Zirconium having a hexagonal close-packed structure causes vacancies generated by irradiation to gather on a plane perpendicular to the c-axis 21 and grows by irradiation growth in a direction perpendicular to the c-axis 21. In the tissue arrangement shown in FIG. 2, elongation occurs in the direction 22 that is the vertical direction and the direction 23 that is the horizontal direction. Since the upper part of the sheath 2 is not restrained with respect to the direction 22 and the curved part side opposite to the support member 1 is not restrained against the extension with respect to the direction 23,
Can stretch freely. Therefore, as described above, generation of stress due to irradiation growth can be avoided.

Further, by using the sheath 2 made of zirconium or a zirconium alloy, it is possible to prevent the channel box from being subjected to shadow corrosion. Shadow corrosion is a phenomenon in which a surface facing a metal other than zirconium corrodes significantly in a structure using zirconium. It has been reported that shadow corrosion occurs in a channel box using zirconium on the surface facing the stainless steel sheath of a conventional nuclear reactor control rod. By using the sheath 2 made of zirconium or a zirconium alloy as in the present embodiment, the opposing surface of the channel box is also zirconium, so that shadow corrosion of the channel box can be prevented.

In addition, by adding a larger amount of iron to zirconium than to Zircaloy 2 and Zircaloy 4, it is possible to precipitate iron in the structure and strengthen the precipitation. It has been found from experiments that the density of precipitates is increased up to 0.5% by mass, and that the amount of iron added becomes larger when 0.5% by mass or more is added. Iron precipitates dissolve and become smaller as irradiation progresses, but the higher the density, the longer it takes for the precipitates to dissolve and the precipitation hardening can be maintained for a long time. The higher the density of the product, the better.

Furthermore, it is known that the corrosion resistance is improved by adding niobium (Nb) to zirconium. For example, a zirconium-2.5% niobium alloy is used for a pressure tube of a heavy water reactor. Furthermore, the above-described irradiation growth of hexagonal metal can be suppressed by adding niobium. Therefore, by adding niobium to the sheath, the corrosion resistance can be improved and the effect of suppressing irradiation growth can be obtained. Fig. 3 shows the binary phase diagram of zirconium-niobium (Binary Alloy Phase Diagrams Second edition, ASM Internation
al, edited by TBMassalski (1990)). Niobium dissolves in zirconium up to 0.6% by mass, as can be seen from the binary phase diagram shown in FIG.

In addition, about the addition of iron and niobium mentioned above, when only iron or only niobium is added, the respective effects are exerted, but when both iron and niobium are added, strengthening by precipitation of iron and corrosion resistance by niobium. Two effects of improvement can be obtained at the same time.

As described above, according to the reactor control rod of the present embodiment, the irradiation resistance of the reactor control rod is improved by adopting the sheath 2 made of zirconium or a zirconium alloy, and the sheath 2 and the neutron absorbing member 3 are used. It is possible to improve the reliability by preventing the generation of thermal stress between the two and the like, preventing the generation of thermal stress by controlling the tissue arrangement of the sheath 2, and preventing the shadow corrosion of the channel box.

[Example 2]
A reactor control rod according to a second embodiment of the present invention will be described with reference to FIG. FIG.
It is the principal part expanded horizontal sectional view which cut | disconnected the zirconium-hafnium blade 31 of the nuclear reactor control rod by a present Example by the plane perpendicular | vertical to a major axis direction. In addition, the same code | symbol is attached | subjected to the same structure as a 1st Example, and the overlapping description is abbreviate | omitted.

In this embodiment, the support member 1 is made of zirconium-hafnium alloy zirconium-
A hafnium blade 31 is attached. Zirconium-hafnium blade 31
Contains hafnium and functions as a neutron absorber.

Since the zirconium-hafnium blade 31 of this embodiment itself functions as a neutron absorber, there is no need to attach a neutron absorber to the inside, and no neutron absorber fixing member is required. Therefore, compared with the conventional nuclear power control rod, the number of welded parts can be reduced, and since no thermal stress is generated between the sheath and the neutron absorbing member, the reliability is improved. Furthermore, since hafnium has better corrosion resistance than zirconium, the corrosion resistance can be improved by adding hafnium to the zirconium alloy.

Further, hafnium has a hexagonal close-packed structure similar to titanium and zirconium, and the structure arrangement can be controlled in the same manner as zirconium. Therefore, the sheath using a zirconium-hafnium alloy is also described in the first embodiment. As described above, by controlling the tissue arrangement, it is possible to avoid the generation of stress due to irradiation growth.

In FIG. 4, the neutron absorbing blade 31 is illustrated as having a U-shape by bending a plate material. However, as shown in FIGS. In addition, a simple shape / structure can be obtained in which one or more vertical holes 32 are provided in a thick plate material. Moreover, you may provide a cooling hole as needed.

In addition, as shown in FIG. 8, it is also possible to attach a flat plate-shaped zirconium-hafnium alloy to the support member 1 to obtain the neutron absorption blade 41. It is not necessary to process the zirconium-hafnium alloy, and the shape can be made simpler than that of the neutron absorbing blade 31 shown in FIG.

Further, FIG. 9A and FIG. 9B show a modified example in which the attachment property of the flat plate-shaped neutron absorption blade to the support member is improved. In FIG. 9A, a neutron absorption blade 41a in which one end of a flat plate is formed into a concave shape is used, and the support member 1 is fitted and attached to this concave shape portion. In FIG. 9B, a support member 1a having a recess in the attachment portion of the neutron absorption blade 41 is used, and the neutron absorption blade is fitted and attached to this recess. The support member 1 and the neutron absorbing blade 41 shown in FIG. 8 are attached by welding or the like, but according to the modification shown in FIGS. 9A and 9B, the support member 1 and the blade 41 are attached. As a result of the engagement, it is possible to attach with bolts or the like instead of welding, and to avoid load concentration on the welded portion.

In this embodiment, the zirconium-hafnium alloy applied to the zirconium-hafnium blade can be more easily manufactured than adding hafnium to the zirconium simple substance to make an alloy. The reason will be described below.

Zirconium and hafnium are contained in zirconium ores (zircon and baderite), respectively. However, zirconium and hafnium have similar physical properties and are difficult to separate. Therefore, in order to obtain zirconium and hafnium, it is necessary to perform a special separation step for separating zirconium and hafnium after removing impurities other than hafnium from the zirconium ore. However, impurities other than hafnium can be removed by general electrolytic refining. Therefore, a zirconium-hafnium alloy can be obtained by electrolytic refining zirconium ore to remove elements other than zirconium and hafnium, and adding a desired alloy element. Further, hafnium concentration may be performed to increase the abundance ratio of hafnium. Thus, the zirconium-hafnium alloy can be manufactured more easily and at a lower cost than the simple substance of zirconium and hafnium.

As described above, according to the reactor control rod employing the zirconium-hafnium blade 31 according to the present embodiment, the same effect as the first embodiment can be obtained, and the reactor control rod can have a simple structure. In addition, it can be produced more easily and at a lower cost than in the past.

Although the embodiments of the present invention have been described with reference to the drawings, the present invention is not limited to the above-described embodiments, and the first and second embodiments are combined without departing from the spirit of the invention. Various modifications can be made. For example, the neutron absorbing member 3 and the neutron absorbing member fixing member 4 are attached to the neutron absorbing blade 31 shown in the second embodiment, niobium is added as shown in the first embodiment, or the first embodiment The blade according to the second embodiment and the blade according to the second embodiment may be used in combination. Those skilled in the art can make various modifications and changes in specific embodiments without departing from the technical idea and scope of the present invention.

1, 1a Support member 2 Sheath 3 Neutron absorbing member 4 Neutron absorbing member fixing member 5 Coolant flow path 10 Blade 20 Crystal lattice 21 c-axis 22, 23 Direction 31, 41, 41a, 42b Zirconium-hafnium blade 32 Vertical hole 100 Hafnium control Rod 101 Support member 102 Connector 103 Coupling socket 104 Handle 110 Blade 111 Sheath 112 Hafnium plate 113 Cooling hole 114 Hafnium plate fixing member 115 Coolant flow path

Claims (4)

A blade,
A nuclear reactor control rod comprising a support member for supporting the blade,
The nuclear reactor control rod, wherein the blade is constituted only by a blade having a shape formed by bending a flat plate made of a zirconium-hafnium alloy which is a neutron absorbing member. A blade,
A nuclear reactor control rod comprising a support member for supporting the blade,
The reactor control rod according to claim 1, wherein the blade is composed of only a blade formed by providing a vertical hole in a flat plate made of a zirconium-hafnium alloy which is a neutron absorbing member. The nuclear reactor control rod according to claim 1 or 2, wherein the blade or the sheath contains niobium, and the niobium is 0.6 mass% or less. The nuclear reactor control rod according to any one of claims 1 to 3, wherein the blade or the sheath contains iron, and the iron is 0.5 mass% or less.

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