JPS61112997A - Control rod for high-temperature gas cooling type 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 [Technical Field of the Invention] The present invention relates to a control rod used in a high-temperature gas-cooled nuclear reactor that controls a nuclear reactor by absorbing neutrons.

[Technical background of the invention]

In general, various types of control rods can be considered as control rods used in high-temperature gas-cooled nuclear reactors, but as shown in FIG. The wire lobe 2 is suspended, and by winding and unwinding the wire lobe 2, insertion and withdrawal are performed within the control rod guide tube 3 and the insertion hole 4. That is, in the case of this type of control rod, since flexibility is imparted to the control rod, there is an advantage that the degree of freedom of insertion is large against bending of the control rod guide tube 3 and positioning error of the insertion hole 4.

The control rod element 1, as shown in FIGS. 5 and 6,
The control rod element 1 is composed of a metal cladding tube 5 and a spider 7 welded to the inside of the upper end of the cladding tube 5, and the control rod element 1 is supported via the spider 7 by a spine 8 that penetrates through the center. In addition, a control rod element 1 is provided on the lower inner side of the cladding tube 5.
A spacer 9 is attached to prevent the vehicle from rolling. The metal cladding tube 5 is an inner cladding tube 1 having a double tube structure.
1, the outer cladding tube 10, the upper and lower ends of the double-wave cladding tubes 10 and 11 (two provided upper cap 12 and lower cap 1)
It is composed of 3. The upper cap 12 is welded to the outer cladding tube 10 so as to leave an appropriate gap 26 with respect to the inner cladding tube 11, and the lower cap 13 is integrally constructed with the inner cladding tube 11 and the outer cladding tube 10 by welding. It has become. Note that the reference numeral 25 in the figure is an exhaust hole.

[Problems with background technology]

In the conventional control rod having the above-mentioned configuration, during normal reactor operation, there is almost no change in the heat load applied to the cladding tube 5, so the temperature difference between the inner claddings tio and it is not so large. However, when the outer cladding tube 11 is rapidly inserted into a high-temperature reactor during a reactor scram or the like, the outer cladding tube 11 is rapidly heated by heat radiation from the insertion hole 4 and heat conduction via the coolant. This heat is transferred to the inner cladding tube 11 by thermal conduction through the gap 26 between the cladding tube 5 and the neutron absorbing material 6 over time, but during this time, a large temperature difference occurs between the inner and outer cladding tubes 11. This temperature difference causes a difference in elongation due to thermal expansion in both the longitudinal and radial directions of the cladding tubes 1.0 and 11. However, the elongation in the longitudinal direction is absorbed by the gap 26, but the elongation in the radial direction is absorbed by the lower gap 1.
3, the inner and outer cladding tubes 10 and 1.1 have an integral structure, so absorption is not possible. Therefore, the lower cap 1
Stress is generated due to stress concentration in the small curved part of the corner of 3. Furthermore, since the temperature in the lower part of the reactor core reaches as high as 900°C, there is a danger that plastic strain and creep strain will occur due to this stress in the lowest element of the control rod. Since rapid full insertion of control rods is frequently performed during the operation of a nuclear reactor, the plastic strain and creep strain combine to cause large fatigue damage and significantly shorten the life of the control rods.

[Purpose of the invention]

The present invention has been made in view of these points, and its purpose is to absorb the thermal expansion and the difference between the inner and outer cladding tubes, reduce the thermal stress that causes plastic strain and creep strain, and extend the life of the tube. The objective is to provide a control rod that can achieve

[Summary of the invention]

The control rod of the present invention has a double-tube structure cladding made of an inner cladding tube and an outer cladding tube, and houses an annular neutron absorber inside the cladding body to function as a control rod element, and has multiple control rod elements. In a control rod in which rod elements are connected in the longitudinal direction by a metal spine passing through the center thereof, the double wave cladding tube has a double pipe structure consisting of a helix, and the bottom part and the upper spider part of the double wave cladding tube are separated. It is characterized by its structure being separated.

Furthermore, the neutron absorber is characterized in that it is wrapped in metal foil such as molybdenum.

[Embodiments of the invention]

An embodiment of the control rod according to the present invention is shown in Figs. 1 to 3 below.
This will be explained using figures.

FIG. 1 shows a control rod element IA that constitutes a control rod according to the present invention.
FIG. 2 is a plan view of FIG. 1, and FIG. 3 is a longitudinal sectional view of FIG. 1. As is clear from each figure, this control rod element IA includes a metal helical cladding tube 14, an annular neutron absorber 6 enclosed by the helical cladding tube 14 with a certain gap, and It consists of spiders 15 and 16 welded to the inside of the upper part. The control rod element 1 is supported by a spine 8 passing through the center via a common spider 17. In addition, the cladding tube 14
A spacer 9 is attached to the lower inside of the control rod to prevent the control rod from rolling.

The metal helical cladding tube 14 has a double tube structure and is composed of an inner cladding tube 18, an outer cladding tube 19, and an upper cap 12 and a lower cap 20 and 21 disposed at the upper and lower ends of the double-corrugated cladding tube. ing.

The upper cap 12 is welded to the outer cladding tube 19 and the outer cladding tube spider 15.

The lower caps 20 and 21 are composed of a lower cap 20 for the outer cladding tube and a lower cap 21 for the inner cladding tube, and both have an appropriate gap 22 in the longitudinal direction.
It is constructed as a separate structure having an overlap part n in the radial direction.

The neutron absorber 6 rests on the bottom plate and is prevented from directly touching the lower caps 20 and 21. Furthermore, the neutron absorber is enclosed in a metal foil 27 made of molybdenum or the like to prevent it from touching the inner and outer cladding tubes 18 and 19.

The inner cladding tube spider 16 is welded to the upper inside of the inner cladding tube 18, and the outer cladding tube spider 15 is welded to the common spider 17 on the upper part of the inner cladding tube spider 16 through the upper cap 12 of the outer cladding tube 19.

Next, the operation of the present invention will be explained.

When the outer cladding tube 1 is rapidly fully inserted into the high-temperature reactor during a reactor scram, etc., the outer cladding tube 1
9 expands more in the longitudinal and radial directions than the inner cladding tube 18, creating a difference in thermal expansion between the inner and outer cladding tubes 18 and 19. However, the spiders 15, 16 and the lower cap 20
, 21, the inner and outer cladding tubes 18 are connected with a gap.
, 19 are completely separated, so that the inner and outer cladding tubes 18
, 19 are completely absorbed. In addition, the lower caps 20 and 21 of both corrugated cladding tubes are free ends and are not subject to any restraint against thermal expansion due to longitudinal temperature differences that occur within the same outer cladding tube 19 or inner cladding tube 18. Since there is no thermal stress, it can be absorbed and the generation of thermal stress can be prevented. Furthermore, since the inner and outer cladding tubes 18 and 19 are formed in a spiral shape made of metal, the coolant is absorbed into the cladding tube 18 and 19.
, 19 can be easily flowed into the inside of the pipe 18.
It is possible to reduce the temperature difference by 19 degrees. In addition, since the neutron absorbing material 6 is wrapped with a metal foil 27 made of molybdenum or the like, it is possible to prevent the absorbing material from falling into the core from the helical portion of the metal helical cladding tube due to deterioration of the absorbing material. It can prevent carbonization of itself.

As a result, the thermal stress generated in the cladding tube can be absorbed without placing a burden on each part of the control rod element, making it possible to reduce fatigue and creep damage caused by thermal stress, thereby extending the life of the control rod. Also.

It is also possible to prevent the neutron absorbing material from falling into the core from the helical part of the cladding tube.

〔Effect of the invention〕

Since the control rod of the present invention is constructed and operates in this manner, even if the thermal expansion and the difference between the inner and outer cladding tubes is absorbed, the heat that causes plastic strain and creep strain is absorbed. Stress can be reduced, and therefore the fatigue and creep damage applied to the cladding tube 141, which includes the inner and outer cladding tubes 18 and 19, can be reduced, and the life of the control rod can be extended. .

[Brief explanation of drawings]

1 to 3 show an embodiment of the control rod for a high-temperature gas-cooled nuclear reactor according to the present invention. FIG. 1 is a perspective view, FIG. 2 is a plan view of FIG. 1, and FIG. The longitudinal sectional view in Figure 1 and Figures 4 to 6 are for explaining the conventional control rod.
The figure is a longitudinal sectional view of a part of the gas-cooled nuclear reactor, FIG. 5 is a plan view of the control rod, and FIG. 6 is a longitudinal sectional view of the control rod. 1.IA...Control rod element 6...Neutron absorbing material 8...Spine 12...Upper cap 14...Spiral metal cladding tube 15...Outer cladding tube spider 16...Inside Spider for cladding tube 20... Lower cap for outer cladding tube 21... Lower cap for inner cladding tube... Bottom plate for neutron absorbing material 27... Metal foil for protecting neutron absorbing material (7317) Agent Patent attorney Rules Kensuke Chika (and 1 other person) Figure 1 Figure 2 Reverse Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] 1. A double-tube structure is formed from an inner cladding tube and an outer cladding tube, and an annular neutron absorber is housed inside the cladding to serve as a control rod element. In a control rod in which control rod elements are connected in the longitudinal direction by a metal spine passing through the center thereof, both the inner and outer cladding tubes have a double tube structure consisting of a helix, and the bottom and upper spider portions of both the cladding tubes are provided. A control rod for a high-temperature gas-cooled nuclear reactor, characterized in that the inner cladding tube and the outer cladding tube are separated into separate structures. 2. The control rod for a high-temperature gas-cooled nuclear reactor according to claim 1, wherein the annular neutron absorbing material is wrapped in a foil made of molybdenum or the like.