KR20220019399A - Rolled steel plate having Gadolinium for neutron shielding and method of manufacturing the same - Google Patents

Abstract

The present invention provides a rolled steel plate containing gadolinium having high neutron shielding performance. The rolled steel plate containing gadolinium for neutron shielding comprises: 0.005-0.2 wt% of carbon (C); 15-25 wt% of chromium (Cr); 17-30 wt% of Nickel (Ni); 0.1-6 wt% of gadolinium (Gd); and the remaining of iron and inevitable impurities.

Description

Rolled steel plate having Gadolinium for neutron shielding and method of manufacturing the same

The present invention relates to a neutron shielding structure, and more particularly, to a gadolinium-containing rolled steel sheet for neutron shielding and a method for manufacturing the same.

In the case of a nuclear power plant, a large amount of thermal neutrons is generated from the spent nuclear fuel, and the spent nuclear fuel is stored and stored underwater in order to prevent the thermal neutrons from being emitted to the outside. However, as the amount of spent nuclear fuel is continuously increased due to the continuous use of electricity, the storage space is saturated and the problem of securing the storage space is emerging as a big issue.

Therefore, high efficiency and high density of the spent nuclear fuel storage structure capable of efficiently storing a large amount of spent nuclear fuel in a narrow space is inevitable, and high performance of the structure material is required. Materials used as spent nuclear fuel storage containers are required to have excellent thermal neutron absorption capacity. In addition, materials with excellent corrosion resistance should be applied so that the storage container is not damaged by corrosion. As other selection criteria, resistance to neutrons, mechanical stability, material weight, moderator consumption, gas generation rate, use cases and history of problems should be included.

In addition, it should be possible to manufacture parts such as dense racks because processing and welding/joining are easy in terms of manufacturing the material. For this purpose, recently, as a material for thermal neutron shielding, boron (B), which has excellent neutron absorption ability, is compounded with aluminum alloy and stainless steel, which has excellent corrosion resistance, and is accelerating research on the development of new material technology having high efficiency shielding performance. The use of shielding materials is gradually restricted due to problems such as hydrogen generation being exposed.

In most cases, as a shielding material, boron or a boron compound (B ₄ C) is added to aluminum alloy or stainless steel as a base metal. There is a problem that it is very difficult to add more than a certain amount.

Among them, in the case of stainless steel, since there is almost no solubility of boron in the austenite phase, a very small amount of boron, for example, less than 2% by weight of boron, is inevitably added, and it is difficult to expect high shielding performance. B ¹⁰ and B ¹¹ are isotopes of boron, and natural boron contains about 20% of B ¹⁰ having a large neutron absorption cross-sectional area. Among the isotopes of boron, B ¹¹ hardly absorbs neutrons, so it is common to use concentrated B ¹⁰ depending on the purpose. In the case of boron, the content of boron itself exhibits a neutron shielding effect, regardless of what kind of compound is present. Therefore, from the standpoint of neutron shielding, the higher the boron content, the better.

In particular, in the case of stainless steel, when manufactured by casting, chromium (Cr) and boron (B) react and the Cr ₂ B compound formed by precipitation increases brittleness, so that hot workability and tensile properties are remarkably reduced. Therefore, in order to add boron in a high content, it is mainly manufactured by powder metallurgy, but this is a very expensive manufacturing process, and there is a problem in that the product price is greatly increased.

An object of the present invention is to solve various problems including the above problems, and to provide a rolled steel sheet having high neutron shielding performance so that a large amount of spent nuclear fuel can be efficiently stored in a narrow space and a method for manufacturing the same do it with However, these problems are exemplary, and the scope of the present invention is not limited thereto.

According to one aspect of the present invention, a gadolinium-containing rolled steel sheet for neutron shielding and a method for manufacturing the same are provided.

According to an embodiment of the present invention, the gadolinium-containing rolled steel sheet for neutron shielding, carbon (C) in the range of 0.005 wt% to 0.2 wt%; chromium (Cr) in the range of 15% to 25% by weight; nickel (Ni) in the range of 17% to 30% by weight; gadolinium (Gd) in the range of 0.1% to 6% by weight; and the remainder may include iron and unavoidable impurities.

According to an embodiment of the present invention, the gadolinium-containing rolled steel sheet for neutron shielding, as gadolinium precipitates in the matrix, Fe ₃ Gd precipitates, Ni ₃ Gd precipitates, Fe ₄ Gd precipitates, Ni ₄ Gd precipitates, Fe ₇ Gd ₂ precipitates , and at least one of Ni ₇ Gd ₂ precipitates may be distributed.

According to an embodiment of the present invention, the gadolinium-containing rolled steel sheet for neutron shielding may satisfy a tensile strength in a range of 450 MPa to 650 MPa and an elongation in a range of 4% to 50%.

According to an embodiment of the present invention, the gadolinium-containing rolled steel sheet for neutron shielding may be manufactured by rolling a cast material.

According to an embodiment of the present invention, the rolled steel sheet containing gadolinium for neutron shielding may have stainless properties.

According to an embodiment of the present invention, the neutron shielding gadolinium-containing rolled steel sheet. carbon (C) in the range of 0.005% to 0.2% by weight; chromium (Cr) in the range of 15% to 25% by weight; nickel (Ni) in the range of 17% to 30% by weight; manganese (Mn) in the range of 0.1% to 5% by weight; gadolinium (Gd) in the range of 0.1% to 6% by weight; and the remainder may include iron and unavoidable impurities.

According to an embodiment of the present invention, the method for manufacturing the gadolinium-containing rolled steel sheet for neutron shielding includes: forming a gadolinium-containing iron-based casting material by casting an iron-based molten metal containing gadolinium; homogenizing the gadolinium-containing iron-based cast material; and hot-rolling the gadolinium-containing iron-based cast material to form a gadolinium-containing rolled steel sheet for neutron shielding.

According to an embodiment of the present invention, the gadolinium-containing rolled steel sheet for neutron shielding, carbon (C) in the range of 0.005 wt% to 0.2 wt%; chromium (Cr) in the range of 15% to 25% by weight; nickel (Ni) in the range of 17% to 30% by weight; gadolinium (Gd) in the range of 0.1% to 6% by weight; and the remainder may include iron and unavoidable impurities.

According to an embodiment of the present invention, the homogenizing treatment may be performed at a temperature in the range of 1100° C. to 1400° C. for 10 minutes to 24 hours.

According to an embodiment of the present invention, the hot rolling may be performed after reheating at a temperature in the range of 1100°C to 1400°C for 10 minutes to 24 hours.

According to an embodiment of the present invention, the gadolinium-containing rolled steel sheet for neutron shielding, as gadolinium precipitates in the matrix, Fe ₃ Gd precipitates, Ni ₃ Gd precipitates, Fe ₄ Gd precipitates, Ni ₄ Gd precipitates, Fe ₇ Gd ₂ precipitates , and at least one of Ni ₇ Gd ₂ precipitates may be distributed.

According to the embodiment of the present invention made as described above, a stainless steel rolled steel sheet for neutron shielding containing gadolinium having a higher neutron shielding performance than boron, and having excellent castability, hot-rollability, workability, toughness and weldability, etc. A manufacturing method can be implemented. Of course, the scope of the present invention is not limited by these effects.

1 is a flowchart illustrating a method of manufacturing a gadolinium-containing rolled steel sheet for neutron shielding according to an embodiment of the present invention.
2 is a photograph showing a state after hot rolling of a rolled steel sheet containing gadolinium for neutron shielding according to an embodiment of the present invention.
3 is a photograph showing the state after hot rolling and after cold rolling of the rolled steel sheet containing gadolinium for neutron shielding according to an embodiment of the present invention.
4 is a scanning electron microscope photograph showing the microstructure of a rolled steel sheet containing gadolinium for neutron shielding according to an embodiment of the present invention.
5 is a graph showing the results of differential scanning calorimetry of the rolled steel sheet containing gadolinium for neutron shielding according to an embodiment of the present invention.
6 is a photograph showing the SEM-EDS analysis of the rolled steel sheet containing gadolinium for neutron shielding according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various different forms. It is provided to fully inform the In addition, in the drawings for convenience of description, the size of the components may be exaggerated or reduced.

As a material for absorbing and shielding neutrons, boron is generally used. In boron, B ¹⁰ absorbs neutrons among isotopes, and it is present in a ratio of 19.8% with respect to the total boron content. The B ¹⁰ has a density of 2.46 g/cm ³ , a neutron absorption cross-sectional area of 3835 barn, and an effective neutron cross-sectional area of 767 barn.

Another material that absorbs and shields neutrons is gadolinium. Among the isotopes of gadolinium, Gd ¹⁵⁵ and Gd ¹⁵⁷ absorb neutrons. The Gd ¹⁵⁵ is present in a ratio of 14.8% with respect to the total gadolinium content, and has a neutron absorption cross-sectional area of 61,100 barn. The Gd ¹⁵⁷ is present in a ratio of 15.7% with respect to the total gadolinium content, and has a neutron absorption cross-sectional area of 259,000 barn. The gadolinium has a density of 7.90 g/cm ³ and an effective neutron cross-sectional area of 49700 barn. Accordingly, the gadolinium may have about 65 times the neutron shielding performance per the same atomic ratio compared to the boron. Since the atomic weight of gadolinium is about 15 times greater than that of boron, it can be seen that it has about 4.4 times of neutron shielding performance per 1 wt%.

In order to form a steel sheet for neutron shielding, an attempt has been made to make a sheet including gadolinium in 304 stainless steel, but since the gadolinium precipitate has a low melting point of about 1060° C., there is a problem in that hot-rollability and weldability are deteriorated. . Therefore, the technical idea of the present invention is to change the gadolinium precipitate generated through the change of the alloy composition and increase the melting point of the gadolinium precipitate to form a rolled steel sheet for neutron shielding that secures excellent hot rolling properties and excellent weldability. The purpose.

1 is a flowchart illustrating a method (S100) of manufacturing a gadolinium-containing rolled steel sheet for neutron shielding according to an embodiment of the present invention.

Referring to FIG. 1 , the method for manufacturing a gadolinium-containing rolled steel sheet for neutron shielding (S100) includes: casting an iron-based molten metal containing gadolinium to form a gadolinium-containing iron-based casting material (S110); Homogenizing the gadolinium-containing iron-based cast material (S120); and hot-rolling the gadolinium-containing iron-based cast material to form a gadolinium-containing rolled steel sheet for neutron shielding (S130).

The homogenizing treatment may be performed at a temperature ranging from 1100° C. to 1400° C. for 10 minutes to 24 hours.

The hot rolling may be performed after reheating at a temperature in the range of 1100° C. to 1400° C. for 10 minutes to 24 hours.

The neutron shielding gadolinium-containing rolled steel sheet, carbon (C) in the range of 0.005 wt% to 0.2 wt%; chromium (Cr) in the range of 15% to 25% by weight; nickel (Ni) in the range of 17% to 30% by weight; gadolinium (Gd) in the range of 0.1% to 6% by weight; and the remainder may include iron and unavoidable impurities. This composition range may be referred to as stainless steel.

The gadolinium-containing rolled steel sheet for neutron shielding, as gadolinium precipitates in the matrix, at least among Fe ₃ Gd precipitates, Ni ₃ Gd precipitates, Fe ₄ Gd precipitates, Ni ₄ Gd precipitates, Fe ₇ Gd ₂ precipitates, and Ni ₇ Gd ₂ precipitates Either one can be distributed.

The gadolinium-containing rolled steel sheet for neutron shielding may satisfy a tensile strength in a range of 450 MPa to 650 MPa and an elongation in a range of 4% to 50%.

The gadolinium-containing rolled steel sheet for neutron shielding may be manufactured by rolling a cast material.

According to an embodiment of the present invention, the rolled steel sheet containing gadolinium for neutron shielding may have stainless properties.

In addition, the gadolinium-containing rolled steel sheet for neutron shielding may further include manganese (Mn). For example, the gadolinium-containing rolled steel sheet for neutron shielding, carbon (C) in the range of 0.005 wt% to 0.2 wt%; chromium (Cr) in the range of 15% to 25% by weight; nickel (Ni) in the range of 17% to 30% by weight; manganese (Mn) in the range of 0.1% to 5% by weight; gadolinium (Gd) in the range of 0.1% to 6% by weight; and the remainder may include iron and unavoidable impurities.

Experimental example

Hereinafter, experimental examples for understanding the characteristics of the neutron shielding gadolinium-containing rolled steel sheet material implemented by the manufacturing method of the neutron shielding gadolinium-containing rolled steel sheet according to the technical spirit of the present invention will be described. However, the following experimental examples are only for helping the understanding of the present invention, and the embodiments of the present invention are not limited to the following experimental examples only.

Comparative Examples and Examples of the present invention are prepared by combining Fe alloy and pure metal in the composition ratios listed in Table 1 below, heating to about 1500° C. or higher in a melting furnace to make a molten metal, and then charging it in a mold. Each ingot was prepared. Then, after being cooled to room temperature, the homogenization treatment was performed at a temperature of 1100° C. for 1 hour, and after reheating at a temperature of 1100° C. for 2 hours, hot rolling was performed to process the plate material. The thickness was reduced from 30 mm to 5 mm by the hot rolling. Then, the thickness was reduced from 5 mm to 2.5 mm through cold rolling.

Table 1 is a table showing the composition and hot rolling characteristics of the rolled steel sheet containing gadolinium for neutron shielding according to an embodiment of the present invention. The remainder in Table 1 includes iron (Fe) and unavoidable impurities.

division Composition (wt%) hot
rolled
characteristic Seal
burglar
(MPa) elongation
(%) C Mn Cr Ni Gd Comparative Example 1 0.008 1.5 16.5 11.9 0.01 O - - Comparative Example 2 0.008 1.5 16.8 12.0 0.58 X - - Comparative Example 3 0.008 1.5 18.1 12.0 4.33 X - - Comparative Example 4 0.008 1.5 7.9 19.8 5.0 O - - Comparative Example 5 0.008 1.5 0 26.0 5.0 O - - Comparative Example 6 0.008 1.5 12.0 12.0 4.1 X - - Comparative Example 7 0.008 1.5 18.0 4.5 1.8 X - - Comparative Example 8 0.008 1.5 18.0 16.0 4.2 X - - Comparative Example 9 0.008 10.0 18.0 4.0 1.0 X - - Comparative Example 10 0.008 10.0 18.0 4.0 3.0 X - - Comparative Example 11 0.008 10.0 18.0 4.0 5.0 X - - Comparative Example 12 0.008 0 8.0 20.0 2.2 O 465 27 Comparative Example 13 0.008 0 12.0 20.0 2.4 O 477 20 Comparative Example 14 0.08 0 12.0 20.0 1.44 O 516 25 Example 1 0.008 0 16.0 20.0 2.4 O 499 17 Example 2 0.008 0 18.0 20.0 2.6 O 463 12 Example 3 0.008 0 21.0 20.0 2.5 O 513 13 Example 4 0.008 0 25.0 20.0 2.2 O 647 4 Example 5 0.08 0 16.0 20.0 1.48 O 527 21 Example 6 0.08 0 18.0 20.0 1.12 O 543 27 Example 7 0.08 0 21.0 20.0 1.26 O 547 25 Example 8 0.08 0 25.0 20.0 1.20 O 539 19 Example 9 0.08 1.0 21.0 20.0 1.21 O 510 18

In Table 1, in the hot rolling characteristics, "O" means no or insignificant surface cracks after hot rolling, and "X" means a case in which severe surface cracks occur after hot rolling. Comparative Example 1 is a case in which the content of gadolinium (Gd) is very low, Comparative Examples 2, 3, 6 and 11 are cases where the lower limit of the nickel content is reviewed, and Comparative Examples 4, 5, 12, 13, and 14 are chromium content This is the case when the lower limit of

2 is a photograph showing a state after hot rolling of a rolled steel sheet containing gadolinium for neutron shielding according to an embodiment of the present invention.

Referring to FIG. 2 , (a) is the case of Comparative Example 2, and shows a fractured shape due to a severe level of surface cracks generated by hot rolling. On the other hand, (b) is the case of Example 1, and since surface cracks hardly occur by hot rolling, it shows that hot rolling was successfully performed.

Again, referring to Table 1, it is noted that all of Comparative Examples 1 to 8 contained 1.5 wt% of manganese. Comparative Example 1 is a case in which the content of gadolinium is very low as 0.01 wt%. In this case, hot rolling was successful, but the neutron shielding ability was lowered. For reference, it is necessary to include gadolinium in the range of 0.5 wt% to 6 wt% in order to secure neutron shielding performance.

Comparative Example 2 is a case in which the gadolinium content is increased to 0.58 wt%, and Comparative Example 3 is a case in which the gadolinium content is increased to 4.33 wt%. In both cases, it can be seen that hot rolling is impossible. Therefore, in order to enable hot rolling and to increase the content of gadolinium for increasing the neutron shielding rate, it is necessary to control the relative content of chromium and nickel.

In Comparative Examples 4 and 5, the content of chromium was decreased, the content of nickel was increased, and the content of gadolinium was increased to 5.0% by weight. In both cases, hot rolling is possible, but there is a limit in that stainless steel properties cannot be provided due to a decrease in chromium. In general, the stainless properties are exhibited when it contains 12 wt% or more of chromium. Therefore, the content of chromium may be limited to 12 wt% or more.

Comparative Examples 6 to 8 are cases in which the content of chromium is 12 wt% or more and the content of nickel is changed. When nickel contained 12 wt%, 4.5 wt%, or 16 wt%, it was confirmed that hot rolling was impossible. Therefore, the content of nickel may be limited to 17% by weight or more.

In Comparative Examples 9 to 11, the manganese content was as high as 10 wt%, indicating that hot rolling was impossible. Accordingly, the manganese content can be controlled to a low level or eliminated.

Comparative Example 12, Comparative Example 13, and Comparative Example 15 are cases in which manganese is excluded, nickel is set to 20 wt%, and the chromium content is changed to 8 wt% and 12 wt%. The content of gadolinium ranged from 1.44% to 2.4% by weight. In all of these cases, hot rolling was successful, but since chromium is 12 wt % or less, stainless properties may be deteriorated.

In Examples 1 to 4, the nickel content is set to 20 wt% and the chromium content is changed to 16 wt% to 25 wt%. The content of carbon was 0.008% by weight, and the content of gadolinium was in the range of 2.2% to 2.6% by weight. In Examples 5 to 8, the nickel content was set to 20 wt% and the chromium content was changed to 16 wt% to 25 wt%. In particular, the carbon content was 0.08 wt%, which was higher than in Examples 1 to 4 above. The content of gadolinium was in the range of 1.12 wt% to 1.48 wt%, which was lower than in Examples 1 to 4 above.

In all of Examples 1 to 8, hot rolling was successful. In addition, as mechanical properties, tensile strength in the range of 450 MPa to 650 MPa and elongation in the range of 4% to 50% were satisfied.

In Example 9, manganese was added in 1 wt%, nickel was 20 wt%, chromium was 21 wt%, and gadolinium was 1.21 wt%. In Example 9, the hot rolling was also successful, and the tensile strength and elongation ratio satisfies the above ranges.

3 is a photograph showing the state after hot rolling and after cold rolling of the rolled steel sheet containing gadolinium for neutron shielding according to an embodiment of the present invention.

Referring to Figure 3, it shows the rolled state of the gadolinium-containing rolled steel sheet for neutron shielding after hot rolling from 30T to 5T and cold rolling from 5T to 2.5T. In Comparative Example 13, Comparative Example 14, and Examples 1 to 4, it can be seen that hot rolling and cold rolling were successful. This is consistent with the results in Table 1 above.

4 is a scanning electron microscope photograph showing the microstructure of a rolled steel sheet containing gadolinium for neutron shielding according to an embodiment of the present invention.

4, (a) and (b) are comparative examples, (c), (d), (e), (f) are examples. In embodiments, it can be confirmed that at least one of M ₃ Gd precipitates, M ₄ Gd precipitates, and M ₇ Gd ₂ precipitates are distributed as gadolinium precipitates in the matrix. Specifically, it was analyzed that at least one of Fe ₃ Gd precipitate, Ni ₃ Gd precipitate, Fe ₄ Gd precipitate, Ni ₄ Gd precipitate, Fe ₇ Gd ₂ precipitate, and Ni ₇ Gd ₂ precipitate was distributed.

5 is a graph showing the results of differential scanning calorimetry of the rolled steel sheet containing gadolinium for neutron shielding according to an embodiment of the present invention.

Referring to FIG. 5 , from the differential scanning calorimetry (DSC) results, it can be seen that the melting point of Example 6 is higher than that of Comparative Example 2, and has a melting point of about 1100° C. or higher.

6 is a photograph showing the SEM-EDS analysis of the rolled steel sheet containing gadolinium for neutron shielding according to an embodiment of the present invention.

Referring to FIG. 6 , it is a scanning electron microscope photograph showing the microstructure of a region for elemental analysis of Example 1, and EDS analysis and element content of the precipitates in the photograph are shown. The precipitate was analyzed to consist of 3.39 at% chromium, 23.76 at% iron, 52.59 at% nickel, and 20.26 at% gadolinium.

Although the present invention has been described with reference to the embodiment shown in the drawings, which is merely exemplary, those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention should be determined by the technical spirit of the appended claims.

Claims (10)

carbon (C) in the range of 0.005% to 0.2% by weight;
chromium (Cr) in the range of 15% to 25% by weight;
nickel (Ni) in the range of 17% to 30% by weight;
gadolinium (Gd) in the range of 0.1% to 6% by weight; and
The balance contains iron and unavoidable impurities,
Rolled steel sheet containing gadolinium for neutron shielding. The method of claim 1,
The rolled steel sheet containing gadolinium for neutron shielding,
As a gadolinium precipitate in the matrix, at least one of Fe ₃ Gd precipitate, Ni ₃ Gd precipitate, Fe ₄ Gd precipitate, Ni ₄ Gd precipitate, Fe ₇ Gd ₂ precipitate, and Ni ₇ Gd ₂ precipitate is distributed,
Rolled steel sheet containing gadolinium for neutron shielding. The method of claim 1,
The rolled steel sheet containing gadolinium for neutron shielding,
satisfying a tensile strength in the range of 450 MPa to 650 MPa and an elongation in the range of 4% to 50%;
Rolled steel sheet containing gadolinium for neutron shielding. The method of claim 1,
The gadolinium-containing rolled steel sheet for neutron shielding is manufactured by rolling a cast material,
Rolled steel sheet containing gadolinium for neutron shielding. The method of claim 1,
The gadolinium-containing rolled steel sheet for neutron shielding has stainless properties,
Rolled steel sheet containing gadolinium for neutron shielding. carbon (C) in the range of 0.005% to 0.2% by weight;
chromium (Cr) in the range of 15% to 25% by weight;
nickel (Ni) in the range of 17% to 30% by weight;
manganese (Mn) in the range of 0.1% to 5% by weight;
gadolinium (Gd) in the range of 0.1% to 6% by weight; and
The balance contains iron and unavoidable impurities,
Rolled steel sheet containing gadolinium for neutron shielding. forming a gadolinium-containing iron-based casting material by casting an iron-based molten metal containing gadolinium;
Homogenizing the gadolinium-containing iron-based cast material; and
and hot rolling the gadolinium-containing iron-based cast material to form a gadolinium-containing rolled steel sheet for neutron shielding;
The neutron shielding gadolinium-containing rolled steel sheet, carbon (C) in the range of 0.005 wt% to 0.2 wt%; chromium (Cr) in the range of 15% to 25% by weight; nickel (Ni) in the range of 17% to 30% by weight; gadolinium (Gd) in the range of 0.1% to 6% by weight; and the balance comprising iron and unavoidable impurities;
A method for manufacturing a rolled steel sheet containing gadolinium for neutron shielding. 8. The method of claim 7,
The homogenizing treatment is performed at a temperature in the range of 1100 ° C to 1400 ° C for 10 minutes to 24 hours,
A method for manufacturing a rolled steel sheet containing gadolinium for neutron shielding. 8. The method of claim 7,
The hot rolling is performed after reheating for 10 minutes to 24 hours at a temperature in the range of 1100 ° C to 1400 ° C,
A method for manufacturing a rolled steel sheet containing gadolinium for neutron shielding. 8. The method of claim 7,
The rolled steel sheet containing gadolinium for neutron shielding,
As a gadolinium precipitate in the matrix, at least one of Fe ₃ Gd precipitate, Ni ₃ Gd precipitate, Fe ₄ Gd precipitate, Ni ₄ Gd precipitate, Fe ₇ Gd ₂ precipitate, and Ni ₇ Gd ₂ precipitate is distributed,
A method for manufacturing a rolled steel sheet containing gadolinium for neutron shielding.

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