JPH03220496A - Control rod of nuclear reactor - Google Patents

Abstract

PURPOSE:To intend improvement of economy and life extention of nuclear functions by diminishing weight of an expensive hafnium and by increasing its surface area. CONSTITUTION:The control rod in this invention constitutes a nuclear reactor core, consists of a cross blade 1 and controls nuclear reactor output. This blade 1 is formed by a plurality of blades made of hafnium thin plates forming a cross plate by engaging one end of each blade with a tie rod of a central part, and by providing gaps through which reactor water can freely flow, between the thin plates. By this fin constitution, using amount of an expensive hafnium can be decreased, and the control rod can be a less weighed and less expensive one. Also, by improvement of blade shape to a fin structure, surface area of the hafnium increases relatively and therefore a neutron absorption power of the control rod is much enhanced. Furthermore, by the gaps provided between the hafnium thin plates, coolant flowing through the gaps removes gamma heat generation of the hafnium thin plates.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a reactor control rod used in a boiling water nuclear reactor, and particularly to a reactor control rod suitable for extending the life of nuclear performance. .

[Prior Art] A reactor control rod used in a conventional boiling water reactor has a cross-sectional cross-section in the center, as shown in the overall perspective view in Fig. 3 and the cross-sectional view in Fig. 4. A sheath 5 extending in the longitudinal direction and having a U-shaped cross section is fixed to each lug 4 of the long tie rod 3, and is composed of four blades in which neutron absorption rods 6 are arranged inside the sheath. The neutron absorption rod 6 has a structure in which boron carbide powder, which is a neutron absorption material, is filled inside a long and thin cladding tube. When boron carbide is irradiated with neutrons, it generates helium gas through a (n, α) reaction, which increases the pressure inside the boron carbide cladding tube, causing damage to the neutron absorption rod 6 and shortening the life of the reactor control rod. Become. Therefore, as a control rod with a long lifespan,
For example, a nuclear reactor control rod using hafnium in the blade of the control rod as described in Japanese Unexamined Patent Publication No. 59-17192 has been proposed.

[Problems to be Solved by the Invention] In the prior art example described above, a thick plate of hafnium is used as the blade, but there are problems in that hafnium is heavy and very expensive. Also, hafnium is (n
, γ) Because it is a reactive neutron absorption rod, there was a problem that the hafnium itself became hot due to γ rays.

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, reduce the amount of hafnium used, and provide a nuclear reactor control rod that is inexpensive and has a long life.

[Means for Solving the Problems] The structure of the reactor control rod of the present invention for solving the above problems is a reactor control rod consisting of a cross-shaped blade for configuring the reactor core and controlling the reactor output. In the rod, one end of the blade is fitted with a tie rod in the center, forming a cross-shaped plate made of multiple blades made of thin hafnium plates.

A gap is provided between each thin plate to allow reactor water to flow freely.

[Function] A blade with a fin structure composed of a plurality of hafnium thin plates reduces the amount of expensive hafnium used, thereby achieving lighter weight and lower cost of the reactor control rod. Furthermore, by improving the shape of the blade to have a fin structure, the surface area of hafnium increases relatively, which increases the neutron absorption capacity of the reactor control rod. Further, due to the gaps provided between the hafnium thin plates, the coolant flowing through the gaps has the effect of removing the heat generated by the hafnium thin plates.

[Example 1] An example according to the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 is an overall perspective view of a nuclear reactor control rod according to the present invention, and FIG. 2 is a cross-sectional view of the same. In FIG. 2, 2 is a thin plate of hafnium, which is fitted into the tie rod piece 4 of the tie rod 3. The blade 1 is composed of three hafnium thin plates in each month of the tie rod, and gaps are formed between each hafnium thin plate for the flow of the coolant.

Therefore, in the control rod of this embodiment, the amount of hafnium used can be reduced to about 172, and the weight of hafnium can be reduced to about 80 kg per control rod, compared to the case where one thick hafnium plate is used as the plate. . Even when the hafnium weight of this example is approximately 80 kg, the control rod has a life approximately three times longer than that of a conventional boron carbide control rod.

In addition, since there is a coolant between the hafnium thin plates, neutrons that are not absorbed by the hafnium thin plates on both sides are decelerated by the coolant and absorbed by the central hafnium thin plate, which reduces the neutron absorption capacity of the control rod. It will be further improved. The coolant flowing through the gaps between the hafnium thin plates acts to remove the 7 heat generated by the (n, γ) reaction of hafnium, and has the effect of preventing thermal deformation of the hafnium thin plates due to the 7 heat generation.

In the control rod of this example, hafnium is used as the neutron absorbing material, so nuclides with a large neutron absorption cross section are generated in a chain manner, resulting in a longer nuclear life than conventional boron carbide, which allows control rods to be controlled using hafnium. It can extend the service life of the rod.

The thickness and number of hafnium thin plates attached to the blades of the control rods can be appropriately selected depending on the control capability such as power distribution required of the control rods installed in the reactor.

Furthermore, the control rod of this embodiment is relatively easy to manufacture, and is effective in reducing manufacturing costs, assembly costs, labor costs, etc. compared to the conventional example.

[Effects of the Invention] According to the present invention, the weight of expensive hafnium can be reduced,
Since the surface area of hafnium can be increased, it is possible to provide a nuclear reactor control rod that is highly economical and has a longer nuclear life than conventional reactor control rods using boron carbide.

Furthermore, since the number of processing steps is smaller than in the conventional example, manufacturing costs can be reduced.

[Brief explanation of drawings]

FIG. 1 is an overall perspective view of a nuclear reactor control rod according to an embodiment of the present invention, FIG. 2 is a cross-sectional view of the same, and FIG. 3 is a cross-sectional view of the same. FIG. 4, which is an overall perspective view of a conventional nuclear reactor control rod, is a cross-sectional view of the same as above. <Explanation of symbols>

Claims (1)

[Claims] 1. In a reactor control rod consisting of a cross-shaped blade that constitutes the reactor core and controls the reactor output, one end of the blade is fitted with a tie rod in the center to form a cross-shaped plate. A nuclear reactor control rod characterized in that a plurality of blades are made of hafnium thin plates and gaps are provided between each thin plate to allow reactor water to freely flow.