JPS59133345A - Neutron absorber - Google Patents

Abstract

PURPOSE:To obtain a neutron absorber made of a uniformly dispersed amorphous alloy which causes no transfer during use by mixing a specified percentage of Fe and/or Ni with a specified percentage of at least one among Sm, Gd, Er, Eu and Dy. CONSTITUTION:This invention relates to a neutron absorber for a water-cooled nuclear reactor, and the neutron absorber is made of an amorphous alloy represented by a formula TM100-aREa (where TM is Fe and/or Ni, RE is at least one among Sm, Gd, Er, Eu and Dy, and a is 40-70atomic%). A mixture 4 of said elements is put in a quartz vessel 1 and melted by heating to about 1,250 deg.C with a heater 2. The molten alloy is extruded from a nozzle and fed between rotating rolls 3 for rolling to form a neutron absorber 5 made of a ribbonlike amorphous alloy. The absorber 5 is filled into a tube and used.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to improvements in neutron absorbers.

[Technical background of the invention and its problems] It is well known that boron carbide (B4C) is particularly used as a conventional neutron absorbing material in water-cooled nuclear reactors. Since this boron carbide is a powder, it is normally filled in a closed container with a density of about 70-.

This airtight container is usually made of a long, thin stainless steel tube called a poison tube, into which boron carbide is filled. That is, as shown in Fig. 1, it is made of stainless steel and has a substantially cylindrical cross section, and its interior is filled and sealed with neutron absorbing powder made of boron carbide with an average particle size of 100 μm. There is. As described above, this neutron absorbing material (1B) is filled with a density of 70%, so there is little movement of powder within the cylinder, but in order to suppress this movement, the middle part inside the poison tube 0→ There are ball-shaped neutron-absorbing phase transfer preventers α in various places.
0 was fixed by deforming a part of the poison tube wall.

Since the boron carbide is a powder, the poison tube (14) must be completely sealed with the sealing body (11) at its end in order to prevent it from scattering.

However, when the enclosed neutron absorber (1B) is attached to the 'Id control rod and driven, it begins to move within the poison tube C1→ and is concentrated only near the upper part of the movement preventer (tQ). As shown in the figure, a space (drink) is likely to be formed, and in extreme cases, there is no absorber below the neutron absorber θ, and the neutron absorption ability in this area is lost, as shown in Figure 2. As shown by line A, the neutron absorption characteristics may become non-uniform, which is one of the causes of deterioration of the neutron control characteristics.

In addition, boron carbide, which is the above-mentioned neutron absorber QB), has a large neutron absorption cross section, so it is advantageous as an absorbing material, but (n, α) anti-boron carbide, which reacts with neutrons, causes a temperature increase due to the heat generated. The swelling caused by the generation of helium gas may cause undesired movement of the powder within the poison tube as described above, or may increase the internal pressure within the tube, leading to destruction of the tube in some cases.

Therefore, the disadvantage of the Voysen Nayup having the above-mentioned neutron absorbing material (9) is that its lifespan is short. In addition, since the poison tube is made up of a tube body, a neutron absorbing material, and a movement prevention body, the structure is complicated, and the powder must be filled into the tube body, and the movement prevention body must be crimped or other means. There is also the drawback that workability tends to deteriorate because it is necessary to insert and fix the device using a screw.

The present invention has been improved to eliminate the various drawbacks mentioned above.

[Object of the invention] The object of the invention is to prevent the neutron absorbing element from moving during use;
Moreover, it is an object of the present invention to provide a neutron absorbing material which is uniformly dispersed.

Another object of the present invention is to provide a neutron absorber having a simple structure.

Still another object of the present invention is to provide a neutron absorbing material that is lightweight.

Still another object of the present invention is to provide a neutron absorbing material that is easy to manufacture and has good workability.

Yet another object of the present invention is to provide a neutron absorber with a long lifetime.

[Summary of the Invention] The present invention is a neutron absorbing material characterized by being made of an amorphous alloy represented by TMloo-a RB'B or TMloo-a-bADb REa.

That is, in the present invention, a neutron absorbing material is formed of an amorphous alloy containing a metal having a large neutron absorption cross section. In other words, by making the component ratio of a metal with a large neutron absorption cross section, which cannot exist in a crystalline state, by making it amorphous, it becomes possible to add several times to several tens of times more, and since ribbon-shaped foil pieces can be obtained, it is lightweight. was achieved.

It has also been found that it can conveniently be formed into a neutron absorbing material that is foil-like and has excellent mechanical properties. In order to confirm the above, the neutron absorbing element city 18 no. 8 m, Gd, B r, Bu *
5 to 30% of f6 earth elements such as Dy as the second component (
Atomic ratio) (2nd 1st component iron (Fe) s Nickel (
An amorphous alloy was made by mixing N1) or iron-nickel elements. This amorphous metal is formed into a uniform ribbon shape with a width of about 10 (lsu+JjJ) of about 20 to 80 μm, and the above-mentioned rare earth elements, which are neutron absorbing elements, are also uniformly dispersed to obtain a neutron absorbing material. It will be done.

Note that if the amount of the rare earth element added is less than 40% in terms of atomic ratio, neutron absorption ability cannot be expected. z, so it is uneconomical. Moreover, if it exceeds 70%, it is difficult with current technology to obtain an amorphous thin plate with excellent mechanical properties and in which the rare earth element is uniformly dispersed.

The rare earth elements am, Gd, Er, Eu, D
y is an element that has a high neutron absorption ability with a deviation of 1/1, and the upper limit of the amount added is the maximum value that can exist as an amorphous state, and the lower limit is the minimum value.

In addition, as additional components (AD), an amorphous alloy neutron absorbing material is formed by adding approximately 10% or less of B, 20% or less of Cr, and 10% or less of at least one of Rh, Re, Ir, Ag, and Au. You can. In this case, it is necessary to monitor so that the total of these gradually added components does not exceed about 40%.

C" is added to improve corrosion resistance, and Rh.

Re, Ir, Ag, and Au are added because they are elements with high neutron absorption ability. The upper limit of each is the maximum amount that can be added in a stable amorphous state.

In all of the above, the neutron absorption capacity is uniform throughout, the weight is reduced by forming a foil-like ribbon, and there is no undesirable movement of the neutron-absorbing element, or the neutron-absorbing element is simply made into an amorphous alloy. It has been confirmed that manufacturing is easy because the elements can be dispersed and arranged.0Also, when the neutron-absorbing element is made amorphous, it can be contained in an amount several tens of times larger than when it is crystalline, as mentioned above. There are limits to this, but
Furthermore, by adding other elements to increase the ability, it has the characteristic that it can be dispersed in an incomparably large amount.

[Embodiments of the invention] Next, an example will be described.

Example 1 Samarium (am
) in an atomic ratio of 40%, 40% nickel (Nl), and <20% iron (Fe), and heated the mixture to 1250°C in a quartz container (1) as shown in Figure 1. 2)
Melt by heating. This molten alloy is extruded from a nozzle (5) with a diameter of 0.4 atm under a pressure of 0.2 atm, and is inserted between rotating rolling rollers (81) with a diameter of 200 M and rapidly cooled at a high speed of 200 Qrpm. , thickness 40
A ribbon-shaped amorphous alloy neutron absorbing material (5) of 0 μm was formed. This is because samarium has a large neutron absorption cross section and is uniformly dispersed in the neutron absorbing material, so it is used in control rods of nuclear reactors. It is characterized by its ability to absorb neutrons efficiently and has a long lifespan because there is no undesirable movement during reactions with neutrons. Further, as a result of forming a ribbon having the same length as the poison tube shown in FIG. 1 and measuring its neutron absorption capacity, it was confirmed that the ribbon had an extremely uniform absorption capacity as shown in curve 1VB of FIG. 2.

Example 2 Boro y (B) 10%, chromium (Cr) 15 in atomic ratio
%, dysprosium (Dy) 3% sThe remainder is iron (F
As e), amorphous alloying was performed in the same manner as in the second example to form an amorphous alloyed neutron absorbing material. In this case, due to the action of chromium, it has good corrosion resistance and stability and is able to absorb neutrons.

Example 3 Boron (B) 5%, chromium (Cr) 10%, in atomic ratio
Europium (Eu) 10%, rhenium (Re)
) 596m Nickel (Nl) 20%, remaining iron (P'
The alloy consisting of e) was made into an amorphous alloy as described above to produce a neutron absorbing material made of an amorphous alloy. In this case as well, the same effect as above was obtained.

Next, Table M1 shows the neutron absorption cross sections of amorphous alloys of various compositions, including the above examples, in comparison with conventional B4C and Hf, which has been considered for use in recent years.

As is clear from the results in Table 1, although the neutron absorption ability of Bie itself may be inferior in some cases, it can be said that it is practically effective as it can obtain a uniform absorption ability as shown in FIG. 2 above.

[Effects of the Invention] As is clear from the above, the neutron absorbing material of the present invention is made of an amorphous alloy that can sufficiently alloy elements with a large neutron absorption cross section, thereby taking advantage of its amorphous characteristics to increase its neutron absorption ability. We were able to obtain a neutron absorbing material with high That is, it was only possible to add a metal with a large neutron absorption cross section, which is difficult to form into an alloy, to a mixing ratio that was considered impossible to form in a crystalline material by making it amorphous. Furthermore, the above neutron absorbing material has a 20 to 80
It is micrometer thick, foil-like, has strong mechanical strength, and has good workability and can be molded into any shape. Furthermore, since the above-mentioned neutron-absorbing elements are uniformly dispersed in the amorphous alloy, the neutron-absorbing ability is uniform, and the desired characteristics can be maintained over a long period of time without being transferred due to reactions with neutrons. Longer life is now possible.

Furthermore, since it is in the form of an extremely thin foil of 20 to 80 μm, it has the characteristic that it can be used as a neutron absorbing material in terms of weight, which is significantly different from that of poison tubes and the like.

The above-mentioned neutron absorbing material of the present invention can be used in the following manner to obtain suitable results.

First, it can be used as a neutron absorber in control rods.

This case is extremely advantageous in various respects.

When the neutron absorbing material of the present invention is used in place of the conventional boron carbide-containing poison tube, the structure is completely changed and extremely simplified, eliminating the need for poison tubes, blades, etc., and requiring only one support frame. In addition, the ability of the neutron absorbing material can be adjusted by laminating the neutron absorbing materials according to the requirements. This can be done by taking advantage of the fact that the neutron absorbing material is extremely thin in the form of a foil. Furthermore, if it is desired to partially change the ability, this can be easily done by partially summerizing the laminated layers of the neutron absorbing material. Even if they are stacked in this way, there is no risk of the control rod becoming larger because it is lightweight.

In addition, the lighter control rod is easier to drive, the small movement mechanism is simplified, and a speed limiter can be omitted. The operating temperature in this case is about 280°C, and the crystallization temperature of the neutron absorbing material is about 400°C or higher, so
There is no limit to the undesirable decrease in the effectiveness of neutron-absorbing elements.

It can also be used as a clinical neutron absorber. In other words, by taking advantage of the fact that the above-mentioned neutron absorbing material is in the form of foil, has excellent mechanical strength, and is extremely easy to process, for example, the neutron absorbing material can be
It is made of a wide material with a width of 0 to 400 m, and a hole is formed in a part using a press, etc., and when neutrons are irradiated to a diseased area through this hole, it is used to protect other parts from the neutrons. Possible 0 That is, for example, when neutrons are used to irradiate an affected area for cancer treatment. In this case, neutrons are irradiated only to the affected area to exterminate cancer cells, but neutrons can be used as a shield to prevent normal tissues other than cancer cells from receiving neutron irradiation. . In this case, since the neutron absorbing material is thin, it can be held closely to the irradiated area, so that it can efficiently protect areas other than the affected area.

Note that it is possible to make a neutron and r-ray shielding body using a combination of an r-ray shielding material containing lead and the above-mentioned neutron absorbing material of the present invention. In this case as well, it is extremely effective to utilize the flexibility of amorphous materials.

Spent fuel from current nuclear reactors is highly radioactive and is stored in a water tank in a spent fuel rack for several years, waiting for its radioactivity to reduce before it can be treated as waste or recovered for reuse. At that time, they are stored in a water tank in the form of fuel assemblies, and boron-containing aluminum is inserted between the assemblies as a partition to absorb the neutrons that fly out and prevent nuclear reactions from occurring. I have to. If the amorphous neutron absorbing material of the present invention containing an element with a large neutron absorption cross section is used as a partition between the aggregates, the distance between the aggregates can be shortened. This contributes economically to expanding the capacity of spent fuel racks for storing spent fuel as demand for nuclear power generation increases.

[Brief explanation of the drawing]

Fig. 1 is a side view showing the inside of a poison tube, which is a conventional neutron absorbing material, with a part cut away, Fig. 2 is a characteristic diagram of its neutron absorption capacity, and Fig. 3 is a production of the neutron absorbing material according to the present invention. FIG. 2 is a side view showing a part of the device. Representative Patent Attorney Noriyuki Chika (one person) Figure 1
Figure 2 Figure 8 Inside the Tokyo Shibaura Electric Co., Ltd. Research Center, 1 Komukai Toshiba-cho, Saiwai-ku, Kawasaki City

Claims (1)

[Claims] 1) A neutron absorbing material comprising an amorphous alloy represented by TMloo-a REa. 2) A neutron absorption absorber characterized by being made of an amorphous alloy represented by TMloo-a-bADb RBa.