JPS5952225B2 - Neutron absorber - Google Patents

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 7% maintained.

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 an almost cylindrical cross section, and inside it is made of stainless steel with an average grain size of about 1.
Neutron absorber powder 1 made of 00μ boron carbide
3 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, but the poison tube 14 is used to suppress this movement.
Ball-shaped neutron absorbing material movement prevention bodies 10 are fixed at various locations in the middle part of the poison chive by deforming a part of the poison chive 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 concentrates only in the upper part of the movement preventer 10, as shown in the figure. In extreme cases, there is no absorbing material below the neutron absorbing material 13, and the neutron absorbing ability in this area is lost, resulting in the neutron The 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 neutron absorbing material 13, has a large neutron absorption cross section and is therefore advantageous as an absorbing material, but it reacts with neutrons (n.

a) The reaction, QBMV + JnM = CLiS + BHeP, is an exothermic reaction, and riboron carbide swells due to the temperature rise due to the heat generation and the generation of helium gas, causing undesired movement of the powder in the poison tube as described above, or In some cases, the tube may be destroyed by increasing the internal pressure of the tube.

Therefore, the poison tube having the above-mentioned neutron absorbing material 13 has the disadvantage 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.

[Purpose of the invention]

The purpose of the present 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.

The present invention is TMloo-a-bBaXb TM is Fe, and at least one of Ni
, Rh, Re.

At least one of Fr, Au, Ag, 10 atomic % or less (c) At least one of Li, Cd, In, Hg, 5 atomic % or less) Hf, 15 atomic % or less of the above (a), (b), (c) , at least one selected from the group of (a) is 10 to 30 atom % b is 50 atom % or less or TMloo a b cBaXbYcTM is Fe
, at least one type of Ni
, Rh, Re.

At least one of Ir, Au, Ag, 10 atomic % or less (c) At least one of Li, Cd, In, Hg, 5 atoms or less) Hf, 15 atomic % or less At least one type Y selected from the group (2) is P, C, Si, AI, Sn, Sh, Ge
The neutron absorbing material is characterized in that it is made of an amorphous alloy in which at least one of Be is contained in an amount of 5 to 30 atom %, b is 50 atom % or less, and C is 0.1 to 15 atom %.

That is, in the present invention, the tron 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, boron B, which is an element with a large neutron absorption cross section, is used as a second component of 10 to 30 at% (5 to 30 at% if the above Y component is included) and the above X as a third component. An amorphous alloy was prepared by mixing the first component of iron (Fe), nickel (Ni), or iron-nickel element to 50 atomic % or less of the component.

This amorphous alloy has a width of about 100 mm and an original diameter of about 20 to 80 μm.
A neutron absorbing material is obtained which is formed into a uniform ribbon shape and in which boron, which is a neutron absorbing element, is also uniformly dispersed.

The amount of boron added above is 10% in atomic ratio (note that the above Y
If the amount is less than 5%, the neutron absorbing ability cannot be expected, and a large number of Okitron absorbing materials must be stacked together, which is uneconomical.

In practice, it is preferable that the boron content be 15% or more in terms of neutron absorption capacity, ease of production, etc.

Moreover, if it exceeds 30%, it is difficult with current technology to obtain an amorphous thin plate with excellent mechanical properties and uniform boron distribution.

In addition to the boron mentioned above, additional components Y include phosphorus (P), carbon (C), silicon (Si), and aluminum (
Al), tin (Sn), antimony (Sb), germanium (Ge) and beryllium (Be) in an atomic ratio of 0.1 to
Add 15%.

In this case, when at least one of the above elements is added in the above amount range, the crystallization temperature is increased and further stabilized, so that the amorphous state is maintained for a long time.

Furthermore, chromium can be added as one of the X components while keeping the atomic ratio of chromium at 20% or less.

In this case, care must be taken in terms of the law if it exceeds 20%.

The above-mentioned chromium (Cr) can improve corrosion resistance and is suitable for use in severe usage conditions.

The reason why chromium is limited to 20% or more is due to problems with the manufacturing technology of amorphous alloys, and if it is added more than this, it is difficult to form an alloy even though it is amorphous.

Furthermore, as one of the X components, samarium (Sm), cadrium (Gd), europium (Eu), erbium (Er), dysprosium (Dy), rhodium (Rh)
, rhenium (Re), iridium (■r), gold (Au)
, one or more types of silver (Ag) should be 10% or less.

This makes it possible to further increase the neutron absorption capacity.

However, if it exceeds 10%, it is difficult to obtain a uniform amorphous thin plate due to manufacturing problems.

Furthermore, lithium (Li) and cadmium (
When Cd), indium (In), and mercury (Hg) are added, the properties are improved as follows.

However, the amount added must be limited.

In other words, it must not exceed 5% in terms of atomic ratio.

One of the above may be used, or four types may be freely combined.

In this case, both exhibit similar characteristics.

Since lithium, cadmium 1, indium, and mercury are elements each having a large neutron absorption ability, the neutron absorption effect can be further enhanced by further adding them to the above-mentioned neutron absorbing material.

Furthermore, hafnium (Hf) can be added as the above-mentioned X component in an amount of 15% or less.

The reason for this is that hafnium is also an element with a high neutron absorption ability, and further effects are expected by adding hafnium.

However, if the total of the above-mentioned X components exceeds 50%, it is unfavorable for the following reasons.

However, the intended purpose of the present application can be achieved with any combination within the above range.

That is, if the total of the elements of the X component exceeds 50%, even though the material is amorphous, it is difficult to industrially obtain a uniform thin plate shape using current technology.

All of the above have uniform neutron absorption capacity as a whole, are made into a foil-like ribbon that is lightweight, and do not cause undesired movement of neutron-absorbing elements, or are made into an amorphous alloy that absorbs neutrons. It was confirmed that manufacturing is easy because the elements can be dispersed.

In addition, if the neutron absorbing element is made amorphous, it can be contained in an amount tens of times more than in the crystalline case, as mentioned above, but there is a limit to this, but in order to further increase the ability, other elements can be added. It has the characteristic that it can be dispersed in a much larger amount than conventional methods.

[Embodiments of the invention]

Next, an example will be described.

Example 1 As an element with a large neutron absorption cross section, boron (
B) 5%, cadrium (Gd) 3%, cadmium (C
d) 5%, gold (Au) 5%, hafnium (Hf)
15% iron (Fe) 57%, rim (Cr) 10%
As shown in FIG. 3, this is heated and melted by a heating device 2 inside the container, and the alloy 4 in the molten state is brought into contact with two high speed rotating (2000rI) rolling rollers 3, 3. A ribbon-shaped amorphous alloy neutron absorbing material 5 with a thickness of about 40 μm and a width of about 150 mm is inserted between the holes and rapidly cooled.
was formed.

In this amorphous alloy neutron absorbing material 5, the boron element is well dispersed and uniform throughout, so that elongation absorption is averaged and it has sufficient neutron absorption ability.

Further, a ribbon having the same length as the poise tube shown in FIG. 1 was formed, and the neutron absorption capacity was measured. As a result, it was confirmed that the ribbon had an extremely uniform absorption capacity as shown by curve B in FIG. 2.

Example 2 Boron (B) 5%, aluminum (AI) in atomic ratio
2%, chromium (Cr) 5%, cadrinium (Ga) 1
0%, indium (In) 2%, hafnium (Hf)
An alloy consisting of 3% nickel (Ni), 15% silver (Ag), and the balance iron (Fe) was made into an amorphous alloy in the same manner as described above to form an amorphous alloy neutron absorbing material.

This is a neutron absorbing material that contains 20% of neutron absorbing elements and exhibits an extremely high neutron absorbing ability, and has excellent stability due to the thermal stability of aluminum and the corrosion resistance of chromium.

Next, Table 1 shows the neutron absorption cross sections of amorphous alloys of various compositions, including the above examples, in comparison with conventional B4C1 and Hf, which has been considered for use in recent years.

As is clear from this result, although it is inferior to the neutron absorption ability of B4C itself, an extremely uniform absorption ability can be obtained as shown in FIG. 2, and it can be said to be practically effective.

Example 8 Fe8o-bB2oX produced by the same manufacturing method as Example 1
A neutron absorbing material having the composition shown by b was manufactured, and the rate of increase in its neutron absorption capacity is shown in FIG. 4 as a relative value to the neutron absorption capacity where b=o.

Note that curves a, b, c, d5. f is each X=
The cases of In, In, Cd, Sm, Eu, and Gd are shown.

Example 9 Fe73-CB2oEu produced by the same manufacturing method as Example 1
A neutron absorbing material having the composition shown by 7YC was produced, and its crystallization temperature was measured as a method of evaluating its thermal stability, as shown in FIG.

In addition, curves g and h in Fig. 5 are Y=AI and S, respectively.
The case of i is shown.

〔Effect 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 the most of its amorphous characteristics. I was able to obtain.

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-mentioned neutron absorbing material has a thickness of 20 to 80 μm, is in the form of a foil, has high mechanical strength, 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 are maintained over a long period of time without being transferred due to reactions with neutrons. This makes it possible to extend the lifespan.

Moreover, since it is in the form of an extremely thin foil of 20 to 80 μm, it has the characteristic that it is much lighter in weight than a poison tube or the like as an Okishiko absorbing material.

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 can be greatly simplified in part, 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, it 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 about 280° C., and the crystal temperature of the neutron absorbing material is about 400° C. or more, so there is almost no undesirable deterioration in the action of the neutron absorbing element.

It can also be used as a clinical neutron shielding material.

That is, taking advantage of the fact that the above-mentioned neutron absorbing material is in the form of a foil, has excellent mechanical strength, and is extremely easy to process, the neutron absorbing material can be
It is made of a wide material with a width of ~400 mm, and a through hole is formed in a part using a press or the like, and when neutrons are irradiated to a diseased area through this through hole, it can be used to protect other parts from the neutrons.

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 spent fuel lag tanks for several years to reduce its radioactivity 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 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.

The distance between the assemblies can be shortened by using the amorphous neutron absorbing material of the present invention to which an element with a large neutron absorption cross section is added as a partition between the assemblies.

This contributes economically to expanding the capacity of spent fuel racks for storing spent fuel due to the increasing demand for nuclear power generation.

[Brief explanation of the drawing]

Fig. 1 is a side view showing the inside of a conventional neutron absorbing poison tube with a part cut away, Fig. 2 is a characteristic diagram of its neutron absorption capacity, and Fig. 3 is a manufacturing apparatus for a neutron absorbing material according to the present invention. 4 and 5 are curve diagrams showing characteristic examples of the neutron absorbing material according to the present invention.

Claims (1)

[Claims] 1TM1oo-a-bBaXb TM is Fe, and at least one of Ni is (a) Cr 20 atomic % or less (o) Sm, Gd, Eu, Er, Dy
, Rh, Re, Ir. At least one of Au and Ag 10 atomic % or less (c) L
i, Cd, In, Hg, 1 type, 5 atomic%
(below) at least one type selected from the groups (a), (b), (c), and (b) above, containing Hf of 15 at % or less, a of 10 to 30 at %, and b of 50 at % or less of Neutron absorbing material 2 characterized by being made of a crystalline alloy TM□oo-a -b -cBaXbYc TM
is Fe, at least one of Ni
, Rh, Re, Ir. At least one of Au and Ag 10 atomic % or less (c) L
i, Cd, In, Hg, at least one type selected from the group of (a), (b), (c), and (i), containing at least 5 at% of Hf, and at least one type of Hf, at most 15 at%, Y is p , c, Si, AI, Sn, Sb, G
A neutron absorbing material comprising an amorphous alloy in which at least one of e and Be is present in an amount of 5 to 30 atomic %, b is 50 atomic % or less, and C is 0.1 to 15 atomic %.