NEUTRON SHIELDING MATERIAL, METHOD OF MANUFACTURING THE SAME, AND CASK FOR SPENT FUEL

• US 20120187315A1
• Filed: 01/27/2012
• Published: 07/26/2012
• Est. Priority Date: 07/28/2009
• Status: Active Grant

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: SAITO, Yuuji, TSUBOTA, Motoji, SATO, Makoto, KIBATA, Masanori, DOKEN, Yoshitaka, HATANO, Shunichi, ISHIGA, Masanori, ONO, Go
• Granted Patent: US 8,481,986 B2
• Time in Patent Office: Days
• US Class Current: 250/506.1
• CPC Class Codes: C21C 7/00 Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00 treating molten metals during moulding B22D1/00, B22D27/00; remelting ferrous metals C22B
• CPC Class Codes: C21D 6/002 containing Cr C21D6/004 takes precedence
• CPC Class Codes: C21D 8/0226 Hot rolling
• CPC Class Codes: C21D 8/0263 following hot rolling
• CPC Class Codes: C21D 9/46 for sheet metals
• CPC Class Codes: C22C 1/02 by melting C22C1/1036 takes precedence
• CPC Class Codes: C22C 38/004 Very low carbon steels, i.e. having a carbon content of less than 0,01%
• CPC Class Codes: C22C 38/02 containing silicon
• CPC Class Codes: C22C 38/04 containing manganese
• CPC Class Codes: C22C 38/54 with boron
• CPC Class Codes: G21F 1/08 Metals; Alloys; Cermets, i.e. sintered mixtures of ceramics and metals
• CPC Class Codes: G21F 1/085 Heavy metals or alloys
• CPC Class Codes: G21F 5/012 Fuel element racks in the containers
• CPC Class Codes: G21F 9/36 by packaging; by baling

Abstract

In one embodiment, a neutron shielding material is formed of boron-adding stainless steel of either austenite-ferrite two-phase stainless steel or ferritic stainless steel, the austenite-ferrite two-phase stainless steel containing, in mass %, B: 0.5% to 2.0%, Ni: 3.0 to 10.0%, and Cr: 21.00 to 32.00%, the ferritic stainless steel containing, in mass %, B: 0.5% to 2.0%, Ni: 4.0% or less, and Cr: 11.00 to 32.00%, and the boron-adding stainless steel being well in ductility and thermal conduction property.

Claims

1. A neutron shielding material made of boron-adding stainless steel of either austenite-ferrite two-phase stainless steel or ferritic stainless steel,

the austenite-ferrite two-phase stainless steel containing, in mass %, B:

0.5% to 2.0%, Ni;

3.0 to 10.0%, and Cr;

21.00 to 32.00%,

the ferritic stainless steel containing, in mass %, B;

0.5% to 2.0%, Ni;

4.0% or less, and Cr;

11.00 to 32.00%, and

the boron-adding stainless steel being well in ductility and thermal conduction property.

2. The neutron shielding material according to claim 1,

wherein either the austenite-ferrite two-phase stainless steel or the ferritic stainless steel contains, in mass %, P:

0.010% or less, S;

0.002% or less, Al;

0.05% or less, O;

0.008% or less, and N;

0.005% or less as inevitable impurities.

3. The neutron shielding material according to claim 1,

wherein either the austenite-ferrite two-phase stainless steel or the ferritic stainless steel contains, in mass %, C:

0.030% or less, Si;

1.00% or less, Mn;

1.50% or less, and Mo;

3.50% or less.

4. The neutron shielding material according to claim 2,

wherein either the austenite-ferrite two-phase stainless steel or the ferritic stainless steel contains, in mass %, C:

0.030% or less, Si;

1.00% or less, Mn;

1.50% or less, and Mo;

3.50% or less.

5. The neutron shielding material according to claim 1,

wherein a ferrite phase ratio of the austenite-ferrite two-phase stainless steel falls within a range of 7 to 98%.

6. The neutron shielding material according to claim 1,

wherein the austenite-ferrite two-phase stainless steel contains Cr, Mo, Si, Ni, C, and Mn falling within a range surrounded by a straight line passing through a point A (Ni equivalent weight:

7.95%, Cr equivalent weight;

25.88%), a point B (Ni equivalent weight;

9.73%, Cr equivalent weight;

25.98%), a point C (Ni equivalent weight;

7.91%, Cr equivalent weight;

28.72%), a point D (Ni equivalent weight;

6.04%, Cr equivalent weight;

28.10%), and a point E (Ni equivalent weight;

6.12%, Cr equivalent weight;

26.32%) that are shown in FIG. 1, and the remainder is composed of Fe and as inevitable impurities, in mass %, P;

0.010% or less, S;

0.002% or less, Al;

0.05% or less, O;

0.008% or less, and N;

0.005% or less.

7. The neutron shielding material according to claim 5,

wherein the austenite-ferrite two-phase stainless steel contains Cr, Mo, Si, Ni, C, and Mn falling within a range surrounded by a straight line passing through a point A (Ni equivalent weight:

7.95%, Cr equivalent weight;

25.88%), a point B (Ni equivalent weight;

9.73%, Cr equivalent weight;

25.98%), a point C (Ni equivalent weight;

7.91%, Cr equivalent weight;

28.72%), a point D (Ni equivalent weight;

6.04%, Cr equivalent weight;

28.10%), and a point E (Ni equivalent weight;

6.12%, Cr equivalent weight;

26.32%) that are shown in FIG. 1, and the remainder is composed of Fe and as inevitable impurities, in mass %, P;

0.010% or less, S;

0.002% or less, Al;

0.05% or less, O;

0.008% or less, and N;

0.005% or less.

8. The neutron shielding material according to claim 1,

wherein the boron-adding stainless steel is manufactured by melting a raw material for the boron-adding stainless steel to form a melted material, and performing a homogenized heat treatment to the melted material in a range of 1050 to 1350°

C. to stabilize a material property.

9. A method of manufacturing a neutron shielding material, comprising:

preparing a raw material for forming either austenite-ferrite two-phase stainless steel containing, in mass %, Ni;

3.0 to 10.0% and Cr;

21.00 to 32.00%, or ferritic stainless steel containing, in mass %, Ni;

4.0% or less and Cr;

11.00 to 32.00%; and

adding 0.5% to 2.0% in mass % of boron (B) to the raw material to manufacture boron-adding stainless steel being well in ductility and thermal conduction property.

10. The method of manufacturing the neutron shielding material according to claim 9, further comprising

melting the boron and the raw material to form a melted material;

and

performing a homogenized heat treatment to the melted material in a range of 1050 to 1350°

C. to stabilize a material property.

11. A cask for spent fuel, comprising:

a cylindrical container;

a lattice-shaped basket that is housed in the container and is for housing spent fuel therein;

a lid for sealing the container;

an outer cylinder covering the entire container;

a resin for absorbing neutrons that is housed between the container and the outer cylinder;

cooling fins provided in the resin in order to connect the container and the outer cylinder; and

the basket being manufactured of a neutron shielding material made of boron-adding stainless steel of austenite-ferrite two-phase stainless steel or ferritic stainless steel, the austenite-ferrite two-phase stainless steel containing, in mass %, B;

0.5% to 2.0%, Ni;

3.0 to 10.0%, and Cr;

21.00 to 32.00%, the ferritic stainless steel containing, in mass %, B;

0.5% to 2.0%, Ni;

4.0% or less, and Cr;

11.00 to 32.00%, and the boron-adding stainless steel being well in ductility and thermal conduction property.

12. The cask for spent fuel according to claim 11,

wherein either the austenite-ferrite two-phase stainless steel or the ferritic stainless steel contains, in mass %, P:

0.010% or less, S;

0.002% or less, Al;

0.05% or less, O;

0.008% or less, and N;

0.005% or less as inevitable impurities.

13. The cask for spent fuel according to claim 11,

wherein either the austenite-ferrite two-phase stainless steel or the ferritic stainless steel contains, in mass %, C:

0.030% or less, Si;

1.00% or less, Mn;

1.50% or less, and Mo;

3.50% or less.

14. The cask for spent fuel according to claim 12,

wherein either the austenite-ferrite two-phase stainless steel or the ferritic stainless steel contains, in mass %, C:

0.030% or less, Si;

1.00% or less, Mn;

1.50% or less, and Mo;

3.50% or less.

15. The cask for spent fuel according to claim 11,

wherein a ferrite phase ratio of the austenite-ferrite two-phase stainless steel is within a range of 7 to 98%.