JPH0687672A - Boron carbide/carbon fiber composite sintered compact for wall material of nuclear fusion reactor - Google Patents

Abstract

PURPOSE:To obtain a wall material for a nuclear fusion reactor having remarkably improved heat conductivity and thermal shock resistance without losing the conventional characteristics by combining boron carbide with carbon fibers in a specified ratio and sintering them. CONSTITUTION:This composite sintered compact for the wall material of a nuclear fusion reactor consists of 90-50vol.% boron carbide and 10-50vol.% carbon fibers. In this composite sintered compact, the carbon fibers are preferably oriented so that the angle between the fibers and the direction of heat conduction is regulated to <=+ or -30 deg.. The aspect ratio of the carbon fibers is preferably >=100.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to the first reactor wall material used in plasma produced by hydrogen discharge at ultrahigh vacuum and high temperature, which is the center of a fusion reactor expected as an energy source to replace current nuclear power generation. Regarding

[0002]

2. Description of the Related Art At present, global environmental pollution associated with energy production has become a major social problem, and research and development of a fusion reactor using deuterium, which is a clean energy source, has been actively conducted. It is being appreciated.

At present, in Japan, research and development of nuclear fusion reactors are underway on a national scale. The tokamak type is a typical example of a nuclear fusion device, and its constituent elements span various fields including materials. The material used for the first wall must be a material that can withstand ultra-high temperature fast neutron irradiation, high-particle flux hydrogen plasma irradiation, and the like. In addition, there are various requirements, and materials satisfying these requirements have not yet been developed. However, it is being studied at various places because it is a key point for commercialization of fusion reactors. It is important to have a low atomic number as an item that must be provided in particular. That is, when a high heat load and a high particle load are applied from the high temperature plasma, the furnace wall material is mixed into the plasma as impurities through sputtering, evaporation, sublimation and the like. The amount of this contaminant has a great influence on the damage of the wall material of the fusion reactor and eventually on the performance. It has already been proven that lower atomic number materials are superior in order to reduce this as much as possible. In the present examination and research results, carbon, which is a relatively low atomic number and low induction activation material, is one of the promising candidates because it is less affected by activation by fast neutrons. In particular, the C / C composite, which is being improved in terms of thermal conductivity, thermal shock resistance, etc., is said to be several times superior to conventional carbon. As can be seen in JP-A-1-129188, a large number of documents including structures have been submitted. However, although the fusion reactor wall material has the above-mentioned advantages, it is very difficult to overcome the inherent drawbacks of the element that is easily damaged or eroded by chemical sputtering or neutron irradiation. In addition, beryllium, which has a lower atomic number than carbon, is also considered to be promising, as disclosed in JP-A-60-98385. However, because beryllium is toxic, it has not been actively investigated.

Fine ceramics such as silicon carbide have been studied because they have good high temperature characteristics, but problems to be solved including problems such as joining with a metal as a cooling device material for promoting heat dissipation. There are many. Therefore, the present inventors have focused on metallic boron having an atomic number smaller than that of carbon.

Metallic boron, which has a lower atomic number than that of carbon and serves as a wall material for a nuclear fusion reactor, has a property of compensating for the drawbacks of such a carbon material, has an effect of suppressing radiation loss due to plasma inclusion, and increases plasma temperature. make it easier. It is also known to have a larger thermal neutron absorption cross section than before,
It is used to control and shield reactors. However, metallic boron, including boron carbide, has low thermal conductivity and is vulnerable to thermal shock. Therefore, the inventors considered improving boron carbide as a fusion reactor wall material.

[0006]

For the above reasons, the inventors have selected boron carbide as the basic material for the fusion reactor wall material. However, as described above, boron carbide has low thermal conductivity and is weak against thermal shock. When the thermal conductivity is low, the heat dissipation is poor and there are various adverse effects, which is not preferable. In addition, the fusion reactor wall material is exposed to a wide temperature range from high temperature to room temperature, and thus must have high thermal shock resistance. Due to this major drawback, it is not a promising material despite its low atomic number. Therefore, taking advantage of the low atomic number,
A study was conducted to improve thermal conductivity and thermal shock resistance.

[0007]

The present invention has advantages and disadvantages when carbon and boron carbide, which are low atomic number materials, are used alone as a fusion reactor wall material. Therefore, by combining the two, studies were made to improve the defects and further improve the characteristics without impairing the advantages of each.

[0008]

The boron carbide / carbon fiber composite sintered body according to the present invention has several steps improved in thermal conductivity and thermal shock resistance as compared with a single boron carbide, and does not lose its conventional properties.
It exerts an excellent effect as a wall material for a fusion reactor that takes advantage of the low atomic number.

[0009]

【Example】

Example 1 Commercially available boron carbide powder (average particle size: 1.5 μm) as a base material, carbon fiber (pan-based thermal conductivity 120 w / m · k 8.0 μm φ × 1.0 mm) and carbon powder (as an additive) A composite sintered body was produced using an average particle size of 2.5 μm. That is, a predetermined amount of each of the base material boron carbide and the additive is mixed and hot-pressed at 2050 ° C.
Sintered with. For comparison, a sintered body of boron carbide alone was simultaneously sintered. The surface deposits of this sintered body were removed by a grinder for cleaning and then subjected to a test. FIG. 1 shows a simulated view of the sectional structure of the sintered body. (A) shows the case where the fibers are oriented in one direction, (b) shows the case where the fibers are not oriented, and (c) shows the case where the powder is added. Using this test piece, the thermal conductivity was first examined. In the case of carbon fiber,
In the case of the unidirectionally oriented one shown in (a), the thermal conductivity was measured for two types of the oriented fiber (parallel (P) direction and right angle (V) direction). FIG. 2 shows the measurement results of the thermal conductivity of the composite sintered body including the addition of carbon powder. The thermal conductivity in the direction parallel to the orientation of the (a) oriented sample is remarkably improved. At 5 vol%, the effect is small, but when added at 10 vol% or more, it is noticeable. The thermal conductivities of the other samples and the oriented fibers in the vertical direction are almost the same as the thermal conductivities of the single boron carbide and do not contribute to the improvement. Figure 3
Of the sample containing 30 vol% of the carbon fiber of (a) shown in FIG.
It is the result of measuring the thermal conductivity by changing the angle of the fiber. As is apparent from the figure, the thermal conductivity is improved up to the fiber angle of 30 °, but if it is more than 30 °, the effect disappears due to the influence of the interface between the base material and the additive or the increase of pores. Therefore, in order to improve the thermal conductivity of boron carbide, the angle between the oriented carbon fiber and the heat conduction direction is ± 30
It is suitable to arrange so that it becomes less than or equal to °. Similar to FIG. 3, FIG. 4 shows the results of measuring the thermal conductivity by changing the aspect ratio using a sample containing 30 vol% carbon fiber.
There is little increase in thermal conductivity up to an aspect ratio of 50, but 1
When it is over 00, the increase is large. From this result, an aspect ratio of 100 or more is suitable for increasing the thermal conductivity. In addition, although the measurement result of the bread-based carbon fiber is shown in this example, there is another pitch-based carbon fiber having good thermal conductivity. A similar experiment was conducted on pitch-based carbon fibers (thermal conductivity 250 w / m · k), and similar results were obtained for the aspect ratio, but the thermal conductivity was about twice as excellent. From this, it is better to use the pitch-based carbon fiber having high thermal conductivity. Further, in this example, the commercially available carbon fiber having a diameter of 8 μm was used. However, in the case of 5 μm or less and 30 μm or more, the strength, the thermal conductivity, etc. do not exceed the values of this example. There wasn't. Therefore, considering the workability and economy, the fiber diameter is 8
~ 15 μm is good.

Example 2 A bending test was conducted on a carbon fiber-added sample which was effective in improving the thermal conductivity of boron carbide in Example 1. The result is shown in FIG. The decrease is small up to the sample containing 50 vol% of carbon fiber added. However, when it is added in an amount of 60 vol% or more, the bending strength is remarkably reduced. FIG. 6 shows the results of measurement of fracture toughness K ₁ c.
Similar to thermal conductivity, 5 vol% is less effective, but 10
Above vol%, the effect of carbon fiber addition appears and increases. However, if it is added in an amount of 60 vol% or more, it will decrease. The decrease in fracture toughness value and bending strength is not preferable because it is related to the fracture of structural materials including the wall material of the fusion reactor. From this, the amount of carbon fiber added for improving the thermal conductivity of boron carbide is 10 to 50 vol%.

Example 3 The thermal shock resistance of the sample (a) of FIG. 1 having good thermal conductivity and mechanical properties in Examples 1 and 2 was examined. For comparison, thermal shock resistance was also measured for boron carbide alone. FIG. 7 shows the results of a bending test after holding at a predetermined temperature for 30 minutes and quenching in water at 20 ° C. 250 ° C for single boron carbide
The quenching caused cracks and the bending strength dropped at once. Compared with this, the boron carbide / carbon fiber composite sintered body is 5
The temperature begins to drop from 00 ° C., and when it is rapidly cooled from 700 ° C., it is almost the same as when the single boron carbide is rapidly cooled from 250 ° C. Moreover, the bending strength does not decrease at once, but gradually progresses. By adding carbon fiber, the crack initiation temperature can be shifted to the high temperature side, and the progress of cracking can be delayed. In this way, the thermal shock resistance of boron carbide was significantly improved by adding carbon fiber.

[0012]

EFFECTS OF THE INVENTION The boron carbide / carbon fiber composite sintered body as a fusion reactor wall material of the present invention has a significantly improved thermal conductivity, and can improve thermal shock resistance and mitigate the progress of cracking. .

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a test piece manufactured to confirm the effect of the present invention.

FIG. 2 is a characteristic diagram in which the thermal conductivity was measured for the sample of FIG. 1 while changing the addition amount.

FIG. 3 is a characteristic diagram in which the thermal conductivity is measured by changing the orientation angle of carbon fibers.

FIG. 4 is a characteristic diagram in which the thermal conductivity is measured by changing the aspect of carbon fiber.

FIG. 5 is a characteristic diagram in which bending strength is measured by changing the amount of carbon fiber added.

FIG. 6 is a characteristic diagram in which fracture toughness was measured by changing the amount of carbon fiber added.

FIG. 7 is a characteristic diagram in which the thermal shock resistance of the boron carbide / carbon fiber composite sintered body of the present invention is measured.

[Explanation of symbols]

P ... A sample in which the carbon fiber of the present invention is oriented parallel to heat conduction, V
... a sample in which carbon fibers are vertically oriented for heat conduction, b ... a non-oriented sample of carbon fibers, c ... a sample in which carbon powder is added.

Claims (3)

[Claims] 1. Boron carbide 90 to 50 vol% / carbon fiber 1
A composite sintered body for a fusion reactor wall, comprising 0 to 50 vol%. 2. In a composite sintered body of boron carbide / carbon fiber, an angle formed by the carbon fiber and a heat conduction direction is ±.
A boron carbide / carbon fiber composite sintered body for a fusion reactor wall material, characterized by being oriented so as to have an angle of 30 ° or less. 3. The boron carbide / carbon fiber composite sintered body for a fusion reactor wall material according to claim 1, wherein the carbon fiber to be composited has an aspect ratio of 100 or more.