JPS6196492A - Control rod 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] Industrial application field> This invention mainly relates to a control rod for a nuclear reactor that utilizes fast neutrons, and more specifically to a control rod with improved neutron absorption ability. .

<Prior art> In a nuclear reactor that utilizes neutrons, the a and II control rods used to control the reactor output generally consist of a plurality of control rod pins covered with a neutron absorbing material such as carbide pellets and sealed with a cladding tube. The book is organized as a whole.

In this specification, the term control rod is used to refer to a control rod system that is a combination of Hill and Illll rods having the above-described configuration.

A typical neutron absorbing material used in conventional control rods is boron carbide. Of the boron isotopes, boron-10 ("B") has a large ability to absorb thermal neutrons, and boron carbide Poison is often used in control rods of light water reactors, which are thermal neutron reactors, because its properties such as strength and chemical stability deteriorate in the Hatate temperature.

However, in fast neutron reactors, the absorption of boron-10 for fast neutrons is approximately 1/2 that for thermal neutrons.
．． In order to efficiently absorb fast neutrons and control the nuclear reactor, the concentration of boron-10 in boron carbide must be as high as possible (natural boron is B
/B is about 20%, but fast core control rods are often used that are more than 90% compressed (C), or it is necessary to increase the total load in the reactor. For example, The use of highly concentrated, high density boron carbide has been eliminated.

In addition, the ratio of boron-10 that actually absorbs neutrons and is used in a fast reactor is i
Throughout the lifespan of the dJ gO rod, approximately 10% of boron 10 is present, and the remainder is not used and is discarded.
;There is an i-state-C, and the situation is not much different from the situation in other countries.

(Problems to be Solved by the Invention) Therefore, the present invention increases the absorption capacity of a neutron absorbing material such as boron carbide, and thereby improves the control rod's IL+ controllability (1L). This was done to reduce the amount of boron carbide used or to use boron carbide with a low concentration of boron-10, thereby providing an economically superior nuclear reactor control rod.

<Means for Solving the Problems> The present inventors have discovered that the absorption capacity of fast neutrons by a neutron absorbing material can be increased by slowing down fast neutrons, and furthermore, in order to slow down fast neutrons, He discovered that metal hydrides could be effectively used in this process, and completed this invention. In other words, the nuclear reactor control rod according to the present invention is a control rod consisting of a plurality of control rod pins made by stacking and sealing a plurality of neutron absorbing material pellets inside a N tube and arranging them within a control rod outer frame. It is characterized by a neutron moderating layer containing metal hydride as the main component. .

<Examples> The present invention will be further described below with reference to examples shown in the drawings.

FIG. 1 shows a schematic horizontal cross-sectional view of a control rod 10 of the present invention, in which seven 1IIIJ pins 1 are arranged in an outer frame 2 of the control rod. Each control rod pin 1
The cladding tube 4 is constructed by loading pellets 3 made of a neutron absorbing material such as boron carbide into a cladding tube 4 made of Zircaloy or stainless steel, and both ends of the cladding tube 4 are fitted with plugs (
(not shown). The gap 5 of each cladding tube 4 serves as a coolant passage.

In the embodiment shown in FIG. 1, a neutron moderation layer 6 made of a plate-like zirconium hydride layer is provided on the inner peripheral surface of the control rod outer frame 2.

According to the control rod 1 having a curved structure, neutrons incident on this control rod pass through the control rod outer frame 2, are decelerated by the neutron moderation layer 6, and then travel through the cold tJ material in the gap 5. Transparent to m
It will be absorbed by the neutron absorbing material pellet 3 in the m-tube 4.

In addition, as shown in FIG. 1, a covering material layer 7 d3 made of stainless steel is provided on the inside and outside of the neutron moderation layer 6.
and 8 are preferably provided to protect the neutron moderation layer from direct exposure to the liquid metal coolant.

Figure 2 shows that boron carbide pellets have +5 ("3(n・α)
)"This is a graph showing the results of investigating the rate of absorption reaction in the radial direction toward the pellet 1 (2). In the curve ■) in the figure, the absorption reaction rate is slightly larger on the outer surface of Belene 1 than on the center, but when the neutron moderation layer 6 is provided () (curve (≧) in Figure 2) (the same boron carbide It can be seen that most of the absorption reactions in the pellets occur in the area close to the outer surface of the pellets, and the absorption reactions in the center of the pellets decrease, resulting in the so-called skin effect in light water reactors.

If the reaction rate distribution is as shown by curve ① in Figure 2, the degree of condensation of boron 10'a of boron carbide in the center of the pellet can be lowered, or even the boron carbide in the center of the pellet can be removed to form a hollow hole. , it becomes possible to reduce the amount of boron carbide in the pellet as a whole.

In addition to the above-mentioned zirconium hydride, metal hydrides used as the neutral I moderator 6 in this invention include yttrium, titanium, and nickel.

Metal hydrides such as lanthanum, cerium, hafnium, etc.
Alternatively, hydrides of binary or multi-component alloys of these metals can also be used. Furthermore, any substance that has a metal hydride compound as a main component and has a neutron moderation effect can be used as the neutron moderation layer in the present invention even if it is not a metal hydride alone.

Compounds containing hydrogen (for example, light water 1-1□O) have been widely used as the best neutron moderator in the field of nuclear reactors.

The reason for using metal hydride as a moderator in this invention is that it contains a large amount of hydrogen and has characteristics such as chemical stability at high temperatures, so it can withstand coexistence with neutron absorbers such as boron carbide. In addition, it has few scratches, the manufacturing method is sufficiently accurate, and it is relatively lightweight.

Further, in the illustrated embodiment, the neutron moderating layer is installed in an annular manner on the inner surface of the control rod outer frame 2, but it is also possible to install it at other locations within the control rod. For example, in the case of J shown in FIG. Shiyoi. Alternatively, as shown in FIG. 4, a neutron moderating layer 26 covered with a coating layer 27 may be provided between the neutron absorbing material pellets 3 stacked in the mm tube 4 of the control rod pin 1. You can also do it.

<Effects of the Invention> As explained above, according to the present invention, (1) a neutron moderation layer containing metal hydride as a main component is provided in the control rod, and fast neutrons are decelerated in the control rod; By increasing the absorption capacity of the neutron absorbing material and improving the control performance of the n1lJ rod, it is possible to save the amount of expensive neutron absorbing material used and reduce the cost of It is also possible to increase the economic efficiency.

[Brief explanation of drawings]

Fig. 1 is a schematic horizontal cross-sectional view showing an embodiment of the nuclear reactor 111 control rod of the present invention, and Fig. 2 shows the radial reaction of pellets with and without a neutron moderation layer. Fig. 3 and Fig. 4 are longitudinal cross-sectional views of the a, II tau rod pins in the pond implementation 1f1 of the present invention. 1... control rod pin, 2... - Control rod outer frame, 3...
Neutron absorbing material pellet, 4... Cladding tube, 5... Gap, 6.16.26... Neutron moderation layer, 7.8, 17゜27... Covering material layer, 10... Control rod . 1h revision applicant: Power Reactor and Nuclear Fuel Development Corporation Representative Yuki Omata Yumen
Araki Tomonosuke 笥 I Zubue 2 [ri Figure 3 Figure 40

Claims (1)

[Scope of Claims] 1. A control rod is constructed by arranging a plurality of control rod pins in a control rod outer frame, which are made by stacking and sealing a plurality of neutron absorbing material pellets in a cladding tube. A nuclear reactor control rod characterized by having a neutron moderation layer mainly composed of a chemical compound. 2. The metal in the metal hydride is zirconium,
A nuclear reactor control rod according to claim 1, which is yttrium, titanium, nickel, lanthanum, cerium, hafnium or lithium, or a binary or multi-component alloy of these metals. 3. The reactor control rod according to claim 1, wherein the neutron moderating layer is disposed on the inner surface of the control rod outer frame, on the surface of the neutron absorbing material pellets, or between stacked pellets.