JPS6144144B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the 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 (B ₄ C) is particularly used as a conventional neutron absorbing material in water-cooled nuclear reactors. Since this boron carbide is a powder, it is stored in a sealed container for approximately 70 minutes.
% density is usually maintained. This airtight container consists of an elongated tube made of stainless steel, usually called a poison tube, into which boron carbide is filled. In other words, as shown in Figure 1, it is made of stainless steel and has an almost cylindrical cross section, and inside it is made of stainless steel with an average grain size of approximately
A neutron absorbing material powder 13 made of 100μ boron carbide is filled and sealed. As described above, this neutron absorbing material 13 is filled with a density of about 70%, so there is little movement of powder within the cylinder.
In order to suppress this movement, the above poison tube 1
Ball-shaped neutron absorbing material movement preventers 10 are fixed at various locations in the intermediate portion of the poison tube 4 by deforming a portion of the poison tube wall. Since the boron carbide is a powder, it is necessary to completely seal the ends of the poison tube 14 with the sealing body 11 in order to prevent it from scattering. However, when the sealed neutron absorber 13 is attached to a control rod and driven, it begins to move within the poison tube 14 and the movement preventer 1
As shown in the figure, a space 12 is likely to be formed, and in an extreme case, there is no absorber below the neutron absorber 13, and the neutron absorption capacity in this area decreases. As a result, the neutron absorption characteristics may become non-uniform as shown in curve A in Figure 2, which is one of the causes of deterioration of the neutron control characteristics. In addition, boron carbide, which is the neutron absorber 13, has a large neutron absorption cross section and is therefore advantageous as an absorber, but it reacts with neutrons (n,
α) Reaction, 5B10 + 0n ¹ = 3Li ⁷ + 2He ⁴ , is an exothermic reaction, and boron carbide may cause undesired movement of the powder in the swollen poison tube due to the temperature rise due to the heat generation and the generation of helium gas, as described above. In some cases, the tube may be destroyed by increasing the internal pressure inside the tube.
Therefore, the poison tube having the above-mentioned neutron absorbing material 13 has the disadvantage that its lifespan is short.
Furthermore, 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] An object of the present invention is to provide a neutron absorbing material in which a neutron absorbing element does not move during use and 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] TM _100-ab AD _b RE _a TM is at least one of Fe and Ni RE is at least one of Sm, Gd, Er, Eu, and Dy AD is A B 0-10 atomic% b Cr 0- 20 atomic% C At least one of Rh, Re, In, Ag, Au 0 to 10 atomic% of the above a),
The neutron absorbing material is characterized by being made of at least one amorphous alloy selected from the groups b) and c), in which a represents 40 to 70 atomic % and b represents 0 to 40 atomic %. 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, into an amorphous state, it becomes possible to add several times to several tens of times more, and ribbon-shaped foil pieces can be obtained. We were able to achieve weight reduction. 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. To confirm the above, rare earth elements such as Sm, Gd, Er, Eu, and Dy, which are elements with large neutron absorption cross sections, are used as the second component, and 40 to 70% (atomic ratio) of the first component is iron (Fe). ), Nickel (Ni)
Alternatively, an amorphous alloy was made by mixing iron-nickel elements. This amorphous alloy is about 100mm wide and about 20~80mm thick.
A neutron absorbing material is obtained which is formed into a uniform ribbon shape with a diameter of μm and in which the above-mentioned rare earth element, which is a neutron absorbing element, is also uniformly dispersed. 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, and therefore a large number of neutron absorbing materials must be stacked and used, which is uneconomical. Furthermore, 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 above-mentioned rare earth elements Sm, Gd, Er, Eu, and Dy are all elements with high neutron absorption ability, 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, approximately 10% or less of B as an additive component (AD),
An amorphous alloy neutron absorbing material can be formed by adding 20% or less of Cr and 10% or less of at least one of Rh, Re, In, Ag, and Au. In this case, it is necessary to monitor so that the total of these added components does not exceed about 40%. Cr is added to improve corrosion resistance.
Rh, Re, In, Ag, and Au are added because they are elements with high neutron absorption ability. Each upper limit is the maximum amount that can be added in an amorphous state with good stability. All of the above have a uniform neutron absorption capacity as a whole, and are made into a foil-like ribbon to reduce weight, and there is no undesired movement of the neutron-absorbing element, or the neutron-absorbing element is only made into an amorphous alloy. It was confirmed that manufacturing is easy because the components can be distributed and arranged. Furthermore, when the neutron-absorbing element is made amorphous, it can be contained in an amount several tens of times more than when it is crystalline, as mentioned above, but there is a limit to this.
Furthermore, by adding other elements to increase the ability, it has the characteristic that it can be dispersed in an incomparably large amount compared to conventional methods. [Embodiments of the Invention] Next, embodiments will be described. Example 1 As an element with a large neutron absorption cross section, samarium (Sm) was used at an atomic ratio of 40%, and nickel (Ni) was used at the same rate.
40% and iron (Fe), also 20%, were mixed and heated and melted in a quartz container 1 to 1250° C. using a heating device 2, as shown in FIG. This molten alloy has a diameter
A pressure of 0.2 atm is extruded from a 0.4 mm nozzle 5, and it is inserted between rotating rolling rollers 3 and 3 with a diameter of 200 mm, and is rapidly cooled at a high speed of 2000 rpm to a width of 3 mm and a thickness.
A 40 μm ribbon-shaped neutron absorbing material 5 made of an amorphous alloy was formed. Since samarium has a large neutron absorption cross section, it is uniformly dispersed in the neutron absorbing material, so it is used in the control rods of nuclear reactors to efficiently exert its neutron absorption ability, and it also prevents undesirable reactions in neutron reactions. Since there is no physical movement, it has a long lifespan. 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 ability, it was confirmed that the ribbon had an extremely uniform absorption ability as shown by curve B in FIG. Example 2 Boron (B) 10%, chromium (Cr) 15% in atomic ratio
%, dysprosium (Dy) 55% and the remainder iron (Fe) to form an amorphous alloy in the same manner as in the first example to form an amorphous alloy 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
%, 50% europium (Eu), 5% rhenium (Re), 10% nickel (Ni), and the balance is made into an amorphous alloy as described above to produce an amorphous alloy neutron. I made an absorbent material. In this case as well, the same effect as above was obtained. Next, Table 1 shows the neutron absorption cross sections of amorphous alloys of various compositions, including the above examples, in comparison with conventional B ₄ C and Hf, which has been considered for use in recent years.

【table】

[Table] As is clear from this result, the neutron absorption capacity is sometimes inferior to the neutron absorption capacity of B ₄ C itself, but it can be said that it is practically effective as it can obtain a uniform absorption capacity as shown in Figure 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 making use of its amorphous characteristics to absorb neutrons. We were able to obtain a neutron absorbing material with high absorption capacity. 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 is 20~
It is 80 μm 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 they do not migrate due to reactions with neutrons, so the desired characteristics can be maintained over a long period of time. This makes it possible to extend the service life. Furthermore, since it is in the form of an extremely thin foil of 20 to 80 μm, it has the advantage of being much lighter in weight as a neutron absorbing material, compared to 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. Further, the ability of the neutron absorbing material can be adjusted by laminating the neutron absorbing materials as necessary. 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 achieved by partially changing the lamination 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. Furthermore, the lighter control rod is easier to drive, the drive mechanism is simplified, and a speed limiter can be omitted. The operating temperature in this case is approx.
280° C., and the crystallization temperature of the neutron absorbing material is about 400° C. or higher, so there is almost no undesirable decrease in the effect of the neutron absorbing element. It can also be used as a clinical neutron shielding material. In other words, the neutron absorbing material is foil-shaped and has excellent mechanical strength.
Taking advantage of its excellent workability, for example, a neutron absorbing material is made of a wide material with a width of 300 to 400 mm, a hole is formed in a part of the material using a press, etc., and neutrons are absorbed through this hole. It can be used to protect other areas from neutrons when irradiating diseased areas. That is, for example, when neutrons are used to irradiate an affected area in 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 gamma ray shielding body using a gamma ray shielding material containing lead and the neutron absorbing material of the present invention in combination. In this case as well, it is extremely effective to incorporate the material by taking advantage of the flexibility of the amorphous material. Spent fuel from current nuclear reactors is highly radioactive and is stored in a tank in a spent fuel rack for several years to reduce its radioactivity before it can be treated as waste or recovered for reuse. At that time, the fuel assemblies are stored in a water tank, and boron-containing aluminum is inserted between the assemblies as a partition.
It absorbs the neutrons that fly out and prevents the reaction from occurring. If an absorbing material containing an element having a large neutron absorption cross section among the amorphous neutron absorbing materials of the present invention is used as a partition between the aggregates, the distance between the aggregates can be shortened. This will economically contribute to expanding the capacity of spent fuel racks for storing spent fuel due to the ever-increasing demand for nuclear power generation.

[Brief explanation of the drawing]

Figure 1 is a side view showing the inside of a poison tube, which is a conventional neutron absorbing material, partially cut away.
The figure is a characteristic diagram of its neutron absorption capacity, and FIG. 3 is a side view showing a part of the neutron absorbing material manufacturing apparatus according to the present invention.

Claims (1)

[Claims] 1 TM _100-a RE _a TM is at least one of Fe and Ni RE is at least one of Sm, Gd, Er, Eu, and Dy A is an amorphous alloy represented by 40 to 70 atomic % A neutron absorbing material characterized by comprising: 2 TM _100-ab AD _b RE _a TM is at least one of Fe and Ni RE is at least one of Sm, Gd, Er, Eu, and Dy AD is A Exceeds B0 and 10 atomic% or less B Exceeds Cr0 and 20 atomic% (c) At least one of Rh, Re, In, Ag, and Au selected from the group of (a), (b), and (c) above, exceeding 0 and up to 10 atomic %; a is 40 to 70 atomic %; b is A neutron absorbing material characterized by being made of an amorphous alloy with a content of 40 atomic % or less.