JP2002277586A - Spent fuel storage cask - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spent fuel storage cask capable of preventing the corrosion by salt damage of a canister to allow a long-term storage at a low cost. SOLUTION: Austenite-based stainless steel or carbon steel with good weldability is used for a base metal 16 for imparting strength to the canister 1, and a metal resistant to corrosion by salt damage such as SUS239J, hastelloy or the like is used for an outside clad material 17 and an inside clad material 18. Since the base metal 16 covers the strength to falling in transportation, and the clad materials 17 and 18 cover the corrosion by salt damage, the canister can be thinned.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radioactive waste generated from a facility such as a nuclear power plant, which has a high radiation dose such as spent fuel, and which is carried out from the facility such as a nuclear power plant. The present invention relates to a spent fuel storage cask of a concrete cask system configured to be able to store for a temporary period until reuse or disposal by appropriately performing storage management in a storage facility or the like.

[0002]

2. Description of the Related Art Spent fuel storage facilities planned or operated in Japan and the like generally use ships and the like to easily transport radioactive waste generated from nuclear power plant facilities. It is located near the coast. For this reason, many damages due to salt damage have occurred around the storage facility.

[0003] Conventional spent fuel storage casks include a metal cask body in which the body of the cask is made of metal and the spent fuel is stored directly in the cask body, or a cask body made of inexpensive concrete instead of the metal cask. Concrete cask systems, in which canisters containing fuel are stored, are widely used in Japan and overseas.

[0004]

In the case of the former metal cask, since it is used consistently from the power plant to the storage facility, it is a cask that requires transport and storage functions. Yes, the equipment cost of storage casks accounts for almost all construction costs.

Further, in the case of the latter concrete cask system, concrete containing a component for shielding neutron rays is used instead of iron and resin for shielding gamma rays and neutron rays, and the production cost per unit is made of metal. Although it is much cheaper than a cask, it is necessary to directly cool the canister, which is a container, in order to eliminate the calorific value of the spent fuel stored inside.

[0006] Since the outside air comes into direct contact with the canister, which is a container for storing the spent fuel, in Japan and the like, the use of outside air containing salt in seawater near the spent fuel storage facility causes corrosion due to salt damage. However, thin-walled containers cannot withstand long-term storage.

As an example, about 5 mm of wall thinning occurs every 40 years. For this reason, in order to store the fuel for a long period of time, it is necessary to take measures such as increasing the thickness of the canister, which is a storage container, from the beginning. Due to the significant increase in weight, it is necessary to reduce the amount of spent fuel built in from the limited weight of transport vessels, heavy equipment at the port and transport vehicles, etc. to keep it to the limited weight, and this storage method requires a large amount of stored spent fuel. There is a problem that is not economical because it is reduced.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. By using a concrete cask as a cask, equipment costs can be kept lower than that of a metal spent fuel storage cask, and the same scale of spent fuel storage can be achieved. Use a method that increases the fuel capacity of the facility and removes the calorific value from the spent fuel by directly removing the outer surface of the canister, which is the storage container, by natural convection. An object of the present invention is to provide an inexpensive and highly reliable spent fuel storage cask that is sufficiently resistant to corrosion caused by salt contained therein.

[0009]

According to the first aspect of the present invention,
In a spent fuel storage cask of a concrete cask system for storing and storing spent fuel in a canister body constituting a canister of a concrete cask, the canister body is made of a composite structure material in which a base material is coated with a clad material, The base material is made of austenitic stainless steel, and the clad material is made of nickel-based Hastelloy on at least one surface that is in contact with the atmosphere outside the base material.

According to the present invention, by cladding austenitic stainless steel as a base metal with nickel-based metal Hastelloy, it is sufficiently resistant to salt damage, has good corrosion resistance, and can be stored for a long period of time.

Further, since there is no need to consider corrosion due to salt damage, the thickness of the canister can be reduced as in the prior art.
As a result, the fuel that can be stored during transportation from the nuclear power plant to the storage facility does not need to be reduced, so that it is economical.

Further, when applied to a concrete cask using a clad material containing a corrosion resistant alloy, the calorific value of the internal fuel can be made to be natural convection using general outside air, so that no additional equipment is required. In addition, it exhibits sufficient performance against corrosion caused by salt contained in the outside air, and greatly improves reliability even during long-term storage.

According to a second aspect of the present invention, there is provided a spent fuel storage cask of a concrete cask system in which spent fuel is stored and stored in a canister body constituting a canister of a concrete cask, wherein the canister body is a base material. The base material is composed of an austenitic stainless steel, and the clad material is formed of an austenitic and ferritic duplex stainless steel on at least one surface of the clad material that is in contact with the atmosphere outside the base material. It is characterized by comprising.

According to the present invention, sufficient corrosion resistance against salt damage can be obtained by using an austenitic ferritic stainless steel for the clad material. Others are the same as those of the first aspect, and the description thereof is omitted.

According to a third aspect of the present invention, there is provided a spent fuel storage cask of a concrete cask system in which spent fuel is stored and stored in a canister body constituting a canister of a concrete cask, wherein the canister body is a base material. The base material is made of carbon steel having good weldability and a carbon content of 0.3% or less (excluding 0), and the clad material on both sides of the base material is a nickel-based metal. The welded portion that is made of Hastelloy and forms the composite structural material on the cylindrical canister body by welding is welded only with the carbon steel, and the portion where the clad material is not present is subjected to buttering Hastelloy or subjected to a corrosion-resistant paint. It is characterized by becoming. ADVANTAGE OF THE INVENTION According to this invention, a welding operation | work is easy and an inexpensive cask can be provided, and the reliability with respect to the corrosion by salt damage improves significantly.

According to a fourth aspect of the present invention, there is provided a spent fuel storage cask of a concrete cask type in which spent fuel is stored and stored in a canister body constituting a canister of a concrete cask, wherein the canister body is a base material. The base material is composed of carbon steel having good weldability and a carbon content of 0.3% or less (excluding 0), and both surfaces of the base material are austenitic two-phase alloys. A welded part which is coated with a clad material of ferritic duplex stainless steel and forms the composite structural material into a cylindrical canister body by welding, only the carbon steel is welded,
Austenitic / ferritic duplex stainless steel is buttered on the part where the clad material does not exist,
Alternatively, a corrosion-resistant paint is applied.

According to this invention, the same function and effect as those of the first aspect can be obtained by using the austenitic ferritic stainless steel of the first aspect instead of Hastelloy as the cladding material.

According to a fifth aspect of the present invention, the thickness of the base material is reduced.
The thickness is selected from 10 to 20 mm and the thickness of the cladding material is selected from 0.1 to 2 mm. In the present invention, the reason why the thickness of the canister base material is selected to be 10 to 20 mm is that the problems of corrosion resistance, ease of assembly, work safety, strength, weight, transportation cost, etc. are comprehensively considered from the viewpoint of configuration. It is decided by considering that if it is less than 10 mm, it is inappropriate due to strength
If the number exceeds the limit, it is unsuitable from the viewpoint of cost and the safety of transportation, assembling, and work due to the large size of a heavy product.

The reason why the thickness of the clad material is selected to be 0.1 to 2 mm is substantially the same as that of the canister base material.
If it is less than m, it is inappropriate from the point of strength and welding work,
If it exceeds 2 mm, it is unsuitable in terms of cost and assembly work.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a spent fuel storage cask according to the present invention will be described with reference to FIGS. 1, 2, 3 and 4. FIG. FIG. 1 shows an embodiment in which spent fuel (hereinafter referred to as fuel) 7 is stored in a canister 1 and stored in a concrete cask 2 for a long time. The canister 1 for storing the fuel 7 forms a sealed container by the canister trunk 3, the canister bottom plate 4 and the canister lid 5,
The fuel 7 is stored at equal intervals inside the fuel tank.
The basket 6 is provided in order to prevent the critical state due to.

The basket 6 is mainly made of a material having excellent heat conductivity, such as aluminum. Then, the canister 1 containing the fuel 7 is fitted into the canister supporting portion 8 in the concrete cask 2 containing a component for shielding radiation emitted from the fuel 7 loaded therein, and is stored vertically.

The amount of heat generated from the internal fuel 7 is reduced by a plurality of coolant inlets 9 at the lower end of the concrete cask 2.
From the coolant outlet 10 near the upper end of the concrete cask 2. Heat is removed between the cooling air and the canister 1 by natural convection.

FIG. 2 shows a cross section of the concrete cask 2. Baskets 6 are regularly arranged in a canister 1 like a grid pattern, and fuels 7 are stored at regular intervals in the lattice-like basket 6 to prevent a criticality accident.

The amount of heat generated from the internal fuel 7 is transmitted from the lattice-shaped basket 6 to the canister 1 by radiation and heat conduction, and the outside air from a plurality of coolant inlets 9 provided in the concrete cask 2 is used. Heat is removed by heat exchange in natural convection. The outside air from which heat has been removed is discharged from a plurality of cooling hole outlets 10 provided in another direction of the concrete cask 2. Reference numeral 11 denotes a canister hanging bracket, 12 denotes a cask lid, and 13 denotes a cask lid hanging tool.

Next, the canister 1 will be described with reference to FIGS. FIG. 3 is a cross-sectional view of the canister 1, and FIG. 4 is an enlarged cross-sectional view of a portion A in FIG. In FIG. 3, reference numeral 14 is a lid support member, and 15 is a basket support member. In FIG. 4, reference numeral 16 denotes a base material, 17 denotes an outer clad material, 18 denotes an inner clad material, and 19 denotes a body joint (welding).
It is.

As shown in FIGS. 3 and 4, the canister body 3 of the canister 1 has an outer clad material 17 outside the base material 16.
And a three-phase clad steel coated with an inner clad material 18 on the inside.

The base material 16 is made of austenitic stainless steel or carbon steel which has good weldability in order to have strength and weldability, and the surface of the base material 16 is made of a two-phase alloy SU which is resistant to salt damage.
S329J or Hastelloy having good corrosion resistance is coated with the outer cladding material 17 and the inner coating material 18.

FIG. 5 shows an example in which only the outer cladding material 17 is coated on the base material 16 and the inner coating material 18 is omitted in FIG. Also in this example, the base material 16 is made of austenitic stainless steel or carbon steel, and the outer clad material 17 is made of a two-phase alloy, SUS329J or Hastelloy, as described above.

In the above configuration, when transporting from the nuclear power plant, the canister 1 storing the fuel 7 in the transport container is stored in the concrete cask 2 using a cask for transport only. Since the base material 16 is responsible for the strength of falling during transportation and the like, and the clad material made of the corrosion-resistant alloy can be responsible for corrosion due to salt damage, a thin canister can be configured.

Next, the handling from the reactor building to the storage facility will be described with reference to FIG. The fuel 7 is stored between the baskets 6 in the canister 1 in the reactor building, the canister lid 5 is placed on the canister 1, and the canister body 3 is sealed with an automatic welding machine or the like (not shown).

Further, the transport cask 20 is housed in the main body 21 of the transport cask 20 by a hanging tool 22 of a canister handling machine (not shown), and the upper lid 23 on the cask main body 21 is sealed with bolts and sealing parts (not shown). It has a structure.

The transport cask 20 is transported from a reactor building to a storage facility by using a trunnion 24 installed outside the transport cask 20 to stand up and fall down, and to be transported using a transport ship or the like. With the transport cask 20 transported to the storage facility, the upper cover 23 of the transport cask 20 is removed in a vertically installed state.

The canister 1 is taken out of the transport cask 20 by a dedicated crane (not shown) and stored in a separate concrete cask 2 shown in FIG. Further, the cask lid 12 is placed on the canister 1 by using the lid hanging member 13 to be in a state of long-term storage. In FIG. 6, reference numeral 25 is a heat transfer space, 26 is a cooling fin, 27 is a metal outer cylinder, and 28 is an outer lid.

The canister 1 stores the fuel 7 and the like inside, and also withstands the acceleration generated when dropping during transportation.
The base material 16 has a thickness of about several tens of millimeters due to weight restrictions, and is mainly made of stainless steel such as SUS316. Furthermore, torso 3
The inner and outer surfaces of the base material 16 have a three-phase clad structure of an outer clad material 17 and an inner clad material 18 as shown in FIG. 4 in order to prevent corrosion due to salt damage of the outside air.

The canister 1 has an outer diameter of about 1700 mm in the currently planned 61-body system, and a plurality of longitudinal joints are required for the body joint (welding) 19 as shown in FIG. This portion is mainly assembled by welding, and the outer clad material 17 and the inner clad material 18 near the welded portion are removed so as to facilitate welding. This part will batter the corrosion resistant alloy after welding.

The canister 1 for a spent fuel storage cask according to the present embodiment has been described as a clad steel having a corrosion-resistant alloy attached to the inner and outer surfaces, but a clad steel provided with a corrosion-resistant alloy only on the outer surface and a tubular corrosion-resistant alloy. The same applies to the canisters combined in the above.

The embodiments of the present invention are summarized as follows. (1) In a canister for a spent fuel storage cask in which fuel is stored inside, when the canister is directly cooled by a natural convection with outside air, a metal for preventing salt damage is formed on the surface of the canister base material. Cladding.

(2) In the canister for a spent fuel storage cask, the canister has a double structure of a base metal for strength, a corrosion resistant alloy against salt damage by natural air and natural convection cooling, and a corrosion resistant alloy for salt damage also inside. Cladding or assembling a triple metal using the above cladding material.

(3) Nickel 6- having good corrosion resistance as base material
Austenitic stainless steel containing 18%, 15-20% chromium, Hastelloy containing 12-20% chromium, 14-18% molybdenum, 50-60% nickel, 4-7% iron, etc. Constructing the canister body using a corrosion resistant alloy.

(4) Nickel 6 ~ with good corrosion resistance as base material
Construct a canister body using austenitic stainless steel containing 18% and 15-20% chromium, and a corrosion-resistant alloy such as a two-phase alloy containing 20-28% chromium as the canning material.

(5) The base material is made of 0.3% carbon having excellent weldability.
Using carbon steel containing below, chrome 12 ~ 20 for canning material
%, Molybdenum 14-18%, nickel 50-60%, iron 4-7
The canister body is made of a corrosion-resistant alloy such as Hastelloy containing 0.1%.

(6) The base material is made of 0.3% carbon with excellent weldability.
Use carbon steel containing
Constructing the canister body using a corrosion-resistant alloy such as a two-phase alloy containing 28%. (7) The thickness of the base material is 10 to 20 mm, and the thickness of the clad material is
Must be in the range of 0.1 to 2 mm.

(8) Only the base metal is welded at the connection portion of the canister body, and the canning material portion is not welded. (9) After welding the base material to the connecting portion of the canister body, buttering the canning material to the welded portion.

[0044]

According to the present invention, the following effects can be obtained. (1) By cladding (coating) the base material with a clad material containing a corrosion-resistant alloy for long-term storage, a concrete cask cheaper than a metal cask can be used, and equipment costs can be greatly reduced. Therefore, the accommodation of spent fuel can be significantly increased at the same construction cost.

(2) By using a clad material containing a corrosion-resistant alloy, it is not necessary to consider corrosion due to salt damage, so that the thickness of the canister can be made thinner as before, thereby transporting the canister from a nuclear power plant to a storage facility. It is economical because sometimes the fuel that can be stored does not need to be reduced.

(3) The clad material containing the corrosion-resistant alloy can be applied to a concrete cask and the calorific value of the internal fuel can be natural convection using general outside air, so that extra equipment is required. It is not necessary and exhibits sufficient performance against corrosion due to salt contained in the outside air, so that the reliability is greatly improved even during long-term storage.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view for explaining a first embodiment of a spent fuel storage canister according to the present invention.

FIG. 2 is a cross-sectional view in FIG.

FIG. 3 is a transverse sectional view showing the canister barrel in FIGS. 1 and 2;

FIG. 4 is an enlarged cross-sectional view showing part A in FIG. 3;

FIG. 5 is a transverse sectional view showing another example of the canister in FIG. 4;

FIG. 6 is a longitudinal sectional view for explaining a state of the spent fuel storage canister according to the present invention at the time of transportation.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Canister, 2 ... Concrete cask, 3 ... Canister trunk, 4 ... Canister bottom plate, 5 ... Canister lid,
6 basket, 7 fuel, 8 canister support, 9
... Coolant inlet, 10 ... Coolant outlet, 11 ... Canister hanger, 12 ... Cask lid, 13 ... Hook for lid, 14 ... Lid support member,
15 ... Basket support member, 16 ... Base material, 17 ... Outer clad material, 18 ... Inner clad material, 19 ... Body joint (welding), 20
... Transport cask, 21 ... Cask body, 22 ... Hanging tool, 23
... top lid, 24 ... trunnion, 25 ... heat transfer space, 26 ... cooling fins, 27 ... metal outer cylinder, 28 ... outer lid.

Continued on the front page (72) Inventor Takashi Aizaka 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture Inside the Toshiba Yokohama Office (72) Inventor Motoyoshi Tsubota 2-4 Suehirocho, Tsurumi-ku, Yokohama-shi, Kanagawa Toshiba Keihin Office

Claims (5)

[Claims] 1. A spent fuel storage cask of a concrete cask system for storing and storing spent fuel in a canister body constituting a canister of a concrete cask, wherein the canister body is formed by coating a base material with a clad material. The base material is made of austenitic stainless steel, and the clad material is made of nickel-based metal Hastelloy on at least one surface in contact with the atmosphere outside the base material. Spent fuel storage cask. 2. A spent fuel storage cask of a concrete cask system for storing and storing spent fuel in a canister body constituting a canister of a concrete cask, wherein the canister body has a base material covered with a clad material. The base material is made of austenitic stainless steel, and the clad material is made of an austenitic and ferritic duplex stainless steel on at least one surface in contact with the atmosphere outside the base material. Characterized spent fuel storage cask. 3. A spent fuel storage cask of a concrete cask system for storing and storing spent fuel in a canister body constituting a canister of a concrete cask, wherein the canister body is formed by coating a base material with a clad material. The base material is made of carbon steel having good weldability and a carbon content of 0.3% or less (excluding 0), and the clad materials on both sides of the base material are made of nickel-based metal Hastelloy, The welded part forming the composite structural material on the cylindrical canister body by welding is welded only with the carbon steel,
A spent fuel storage cask characterized in that a portion where the clad material does not exist is provided by battering Hastelloy or by applying a corrosion-resistant paint. 4. A spent fuel storage cask of a concrete cask system for storing and storing spent fuel in a canister body constituting a canister of a concrete cask, wherein the canister body is formed by coating a base material with a clad material. The base material is made of carbon steel having good weldability and a carbon content of 0.3% or less (not including 0), and both surfaces of the base material are two-phase alloy austenitic / ferritic duplex stainless steel. A welded part coated with a steel clad material and forming the composite structural material into a cylindrical canister body by welding is welded only with the carbon steel, and a portion where the clad material does not exist is austenitic / ferritic duplex stainless steel. A spent fuel storage cask characterized by buttering or applying a corrosion-resistant paint. 5. The spent fuel storage cask according to claim 1, wherein the thickness of the base material is selected to be 10 to 20 mm, and the thickness of the cladding material is selected to be 0.1 to 2 mm.