JP2016130744A - Covering apparatus of thermal neutron absorption film, method thereof and collection method of core meltdown matter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique to cover core meltdown matter which has complicated surface shape with a thermal neutron absorption film even under water conditions.SOLUTION: A covering apparatus 10 of thermal neutron absorption film includes: a supply means 20 that mixes a particulate matter 31 containing an element the thermal neutron absorption cross section of which is 100 barn or more as a major component and a binder 32 for fixing the particulate matter 31 on the surface of the core meltdown matter 30 and stirs the mixture 15 in a mixing part 23 to adjust the viscosity and supplies the same in a slurry state; and a nozzle 11 for ejecting the supplied mixture 15 over the surface of the core meltdown matter 30. The supply means 20 has a hardening unit 27 for supplying hardening means for hardening the binder 32.SELECTED DRAWING: Figure 1

Description

  Embodiments of the present invention relate to a technique of coating a surface of an object that causes fission when thermal neutrons are absorbed with a thermal neutron absorption film.

  If a severe accident occurs at a nuclear power plant, the core may not be sufficiently cooled, and the core may melt. If the fuel shape changes due to core melting, the possibility of recriticality occurring even when the reactor is shut down cannot be denied. If this re-criticality occurs, the reactor pressure vessel, containment vessel, and reactor building may be damaged, and radioactive materials may be released to the environment. Therefore, it is important from the viewpoint of containment of radioactive materials to take recriticality prevention measures after the occurrence of severe accidents.

  On the other hand, when core melting occurs, it is necessary to carry out the cold temperature stop and then carry the molten core out of the pressure vessel and the containment vessel and seal it in a long-term storage vessel such as a cask. However, it is assumed that the melting core is integrated with the pressure vessel or the containment vessel by melting and reacting, and it may be necessary to cut and divide in the furnace for carrying out.

By the way, even in the cold shutdown state, it is considered that very small-scale fission has occurred in the molten core. Fast neutrons generated by this fission are decelerated by water and become thermal neutrons that cause the next fission.
Usually, since cooling water exists inside the pressure vessel or the containment vessel, it is considered that the cutting operation of the melting core is performed in a state of being immersed in water.
Therefore, when the molten core is cut and divided, water is brought into contact with the cut surface, and the assumption is made that the fission reaction is activated and the criticality is reached.

Therefore, it is conceivable to cover the cut surface of the molten core that has been cut and divided with a thermal neutron absorption film. It is possible to effectively suppress the fission reaction by covering the melt core having a complicated shape as well as the cut surface over a wide range.
As a technique for absorbing and shielding radiation, a method of using spherical lead powder having a diameter of 0.2 to 2 mm whose surface is coated with boride has been proposed (for example, Patent Document 1).
In addition, a technique has been proposed in which metal aluminum powder and boron carbide (B ₄ C) powder are coated on the surface of a metal substrate by thermal spraying (for example, Patent Document 2).
Furthermore, a method using composite fine particles in which the surface of inorganic core particles (radiation absorption / shielding material) is coated with an organic polymer has been proposed (for example, Patent Document 3).

JP 2011-7510 A JP 2007-290017 A JP 2008-81728 A

However, in the shielding material of the above-mentioned Patent Document 1, thermal neutrons cannot be shielded / absorbed by the main component lead powder, and borides having a thermal neutron shielding effect are only covered with lead powder. It is insufficient in quantity to obtain.
Further, in the technique of Patent Document 2 described above, boron carbide is thermally decomposed before reaching the core melting temperature, and it is impossible to coat boron alone on the metal surface by thermal spraying.
Furthermore, in the technique of Patent Document 3 described above, it is easy to solidify polymer particles to produce a block-shaped or sheet-shaped product, but it is difficult to coat the surface of the molten core.

  Embodiments of the present invention have been made in view of such circumstances, and an object thereof is to provide a technique for coating a thermal neutron absorbing film on an object having a complicated surface shape even in an underwater environment. .

  In a thermal neutron absorption film coating apparatus, a mixture of a granular material whose main component is an element having a thermal neutron absorption cross-section of 100 burns or more and a binder for immobilizing the granular material on the surface of the core melt is stirred and mixed in a kneading section. A supply means for adjusting the viscosity and supplying the mixture in a slurry state, and a nozzle for discharging the supplied mixture to the surface of the core melt, and the supply means supplies a curing means for curing the binder. It has a hardened part.

The block diagram which shows 1st Embodiment of the coating | coated apparatus of the thermal neutron absorption film which concerns on this invention. (A) A cross-sectional view showing a state in which a thermal neutron absorbing film is coated on the surface of an object that causes fission when absorbing thermal neutrons, and (B) a protective coating further containing an environmentally resistant substance on the surface of the thermal neutron absorbing film. Sectional drawing which shows the state formed. The table | surface of the element which can be employ | adopted as a main component of a granular material in each embodiment. The partial enlarged view of the nozzle applied to the coating apparatus of the thermal neutron absorption film which concerns on 2nd Embodiment. Explanatory drawing explaining embodiment of the collection | recovery method of the molten core which concerns on this invention. Explanatory drawing explaining embodiment of the collection | recovery method of the molten core which concerns on this invention.

(First embodiment)
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
As shown in FIG. 1, the thermal neutron absorption film coating apparatus 10 according to the first embodiment includes a granular material 31 whose main component is an element having a thermal neutron absorption cross-sectional area of 100 burns or more, and the granular material 31 as an object 30. Supply means 20 for supplying the mixture 15 of the binder 32 to be immobilized on the surface, and a nozzle 11 for discharging the supplied mixture 15 to the surface of the object 30.

  FIG. 2A is a cross-sectional view showing a state in which a thermal neutron absorption film 33 is coated on the surface of an object 30 that causes fission when absorbing thermal neutrons. FIG. 2B is a cross-sectional view showing a state in which a protective coating 34 further containing an environmental resistant material is formed on the surface of the thermal neutron absorption film 33.

The nozzle 11 is, for example, a spray gun, and sprays the mixture 15 of the particulate material 31 and the binder 32 on the surface of the object 30 with a pressure gas. Thereby, the favorable thermal neutron absorption film 33 with few voids can be formed on the surface of the object 30.
The mixture 15 is not limited to being sprayed by pressure such as pressure gas, but may be discharged from the nozzle 11 by gravity.

The supply unit 20 includes a storage unit 21 that stores the mixture 15 of the particulate material 31 and the binder 32, a gas compressor 26 that sprays the mixture 15, and a curing unit 27 that supplies a curing unit that cures the binder 32. ing.
In addition, the hose 12 that guides the mixture 15 that is contained to the nozzle 11 is connected to the containing portion 21, the hose 13 that guides the pressure gas to the nozzle 11 is connected to the gas compressor 26, and the curing means is the curing means 27. Is connected to the nozzle 11.

Various curing means are applied depending on the type of the binder 32.
For example, if the inorganic compound of sodium silicate-based _{(Na 2 O · nSiO 2 ·} mH 2 O) is used as the binder 32 may be carbon dioxide, UV, the curing means such as cement.
When the binder is cured by moisture, the curing unit 27 supplies a humidified gas. When the binder is a UV curable binder, the curing unit 27 is a UV lamp or the like.
By supplying such a curing means, the curing reaction of the inorganic or organic binder 32 can be controlled, and the thermal neutron absorption film 33 can be immobilized on the surface of the object 30 at the same time as the coating. This shortens the construction cost.

The supply unit 20 may further include a kneading unit 23 that kneads the particulate material 31 and the binder 32 to form a mixture.
In this case, the granular material 31 and the binder 32 are held in separate containers 24 and 25, respectively, and are agitated and mixed by the kneading unit 23 in a slurry state and stored in the storage unit 21 as appropriate.
The stirring and mixing in the kneading unit 23 is adjusted according to the surface shape of the object 30 so that the mixture 15 has an appropriate viscosity range.

That is, when the surface of the object 30 is complicated, the slurry is adjusted to a low viscosity so that the mixture 15 penetrates to the finest details. On the other hand, when it is nearly flat, the slurry is adjusted to a high viscosity to prevent the mixture 15 from flowing around due to surface tension.
Thereby, as shown in FIG. 2A, the thermal neutron absorption film 33 is formed on the surface of the object 30 with a substantially uniform thickness. In the thermal neutron absorption film 33, the particulate matter 31 is dispersed in a binder 32 in a uniform state.

As shown in FIG. 2B, a protective coating 34 containing an environmental resistant material may be formed on the surface of the thermal neutron absorption film 33 formed on the surface of the object 30.
Depending on the components of the binder 32 constituting the thermal neutron absorption film 33, there are substances that react and elute with water and hot water, and there are substances that deteriorate due to neutrons emitted from the molten core. Therefore, by forming the protective film 34 on the surface, the long-term soundness of the thermal neutron absorption film 33 is ensured or the cooling water is prevented from being contaminated.

FIG. 3 shows a list of elements that can be employed as the main component of the granular material 31 in each embodiment.
By forming the thermal neutron absorption film 33 in which the particulate matter 31 containing the element having a large thermal neutron absorption cross section is dispersed on the surface of the object 30 such as a molten core, thermal neutrons can be effectively absorbed even in a small amount. .
Thus, recriticality can be prevented without increasing the thickness of the thermal neutron absorption film 33, and a great effect can be obtained in terms of construction cost.

The main component of the particulate material 31 is preferably gadolinium oxide or boron carbide from the viewpoint of thermal neutron absorption cross section, chemical stability, availability, cost, and the like.
In addition, since gadolinium and boron have different thermal neutron spectra, it is possible to effectively prevent recriticality by optimizing the composition of both according to the spectrum of thermal neutrons emitted from the molten core. Can do.

  In addition, since gadolinium oxide and boron carbide have a high melting point of 2000 ° C. or higher, it is difficult to immobilize on the surface of the object 30 by a thermal process such as melting, thermal spraying, and sintering. For this purpose, the particulate material 31 is stably fixed to the surface of the object 30 by being discharged from the nozzle 11 together with the binder 32.

The main component of the particulate material 31 is not limited to gadolinium oxide, boron carbide, or a combination thereof, and can be selected from the group of gadolinium, gadolinium compounds, boron, and boron compounds.
Further, as neutron absorbing elements applicable to the present invention, boron (B), gadolinium (Gd), hafnium (Hf), erbium (Er), silver (Ag), indium (In), cadmium (Cd), europium ( Examples are those having a thermal neutron absorption cross section of 100 burns or more, such as Eu).
And the granular material 31 which has as a main component what combined these single substance and multiple compounds can be employ | adopted suitably.

  The granular material 31 is preferably spherical particles having a particle diameter in the range of 10 to 100 μm. If it deviates from this range, any of various properties such as fluidity, dispersibility, homogeneity, and fillability of the mixture 15 with the binder 32 may decrease.

The binder 32 can be mainly composed of an organic compound such as a vinyl monomer such as cyanoacrylate that is cured by reacting with moisture or a modified acrylate that is cured by ultraviolet rays.
The organic compound binder component reacts with moisture in the environment or UV irradiation, and may be cured before the thermal neutron absorption film 33 conforms to the surface of the object 30. Construction is preferable.
In addition, the binder 32 can contain, as a main component, a sodium silicate-based (Na ₂ O.nSiO ₂ .mH ₂ O) inorganic compound that is hardened with carbon dioxide, ultraviolet light, cement, or the like.

According to such a binder 32, since the gel state is rich in deformability immediately after the object 30 is coated, the uniform thermal neutron absorption film 33 can be formed for a complicated surface shape.
And when this gel state has become familiar with the surface of the target object 30, it can harden | cure without using a thermal process and the thermal neutron absorption film | membrane 33 with strong adhesive force can be obtained.

(Second Embodiment)
FIG. 4 is a partially enlarged view of the nozzle 11 of the thermal neutron absorption film coating apparatus according to the second embodiment. 4, parts having the same configuration or function as those in FIG. 1 are denoted by the same reference numerals, and redundant description is omitted.

In the second embodiment, the nozzle 11 is provided inside a chamber 16 having an opening on the object 30 side.
When the object 30 is a melting core, the periphery is covered with cooling water. Thus, when the surface of the object 30 is wet, the thermal neutron absorption film 33 may not have sufficient adhesion. As a countermeasure in such a case, the moisture on the surface of the object 30 is removed using the chamber 16 in the coating construction.

The gas compressor 26 of the supply means 20 (FIG. 1) also supplies a purge gas 17 that purges the inside of the chamber 16.
In the case of construction in the atmosphere, there is no particular problem, but in the case of construction in water, the kinetic energy of the mixture 15 sprayed from the nozzle 11 is attenuated by the resistance of water, and the adhesion and denseness of the thermal neutron absorption film 33 are impaired. There is a fear.
Since the inside of the chamber 16 is purged with gas, the mixture 15 is directly discharged from the nozzle 11 to the surface of the object 30, so that a good thermal neutron absorption film 33 is formed.

A method for recovering the molten core will be described with reference to FIGS. 5 and 6.
As shown in FIG. 5, when a severe accident occurs at a nuclear power plant and core melting occurs, the molten core (object 30) integrated with the reactor structure 36 is cooled and stopped by melting and reacting. After that, it is cut and divided in a furnace for carrying out.
By the way, even in the cold shutdown state, it is considered that very small-scale nuclear fission has occurred inside the molten core (object 30). For this reason, it is assumed that when the cooling water 18 comes into contact with the cut surface 35 when the molten core (object 30) is cut and divided, the fission reaction is activated and the criticality is reached.

Therefore, as shown in FIG. 6, not only the cut surface of the cut / divided molten core (object 30) but also the molten core having a complicated shape is covered with a thermal neutron absorption film 33 over a wide range to effectively perform the fission reaction. Suppress.
Further, the formation of the thermal neutron absorption film 33 with the object 30 as a nuclear fuel storage cask or reactor fuel demolition work equipment / equipment is not limited to the molten core, thereby enhancing the prevention of recriticality. it can.

The thermal neutron absorption film 33 needs to have a sufficient thickness to prevent recriticality. When the thickness of the thermal neutron absorption film 33 increases, it becomes difficult to maintain the film thickness due to surface tension. Therefore, it is preferable to perform a construction in which the mixture 15 is cured simultaneously with the release.
Alternatively, the construction may be performed a plurality of times so as to be laminated on the cured thermal neutron absorption film 33.

  According to the thermal neutron absorption film coating apparatus of at least one embodiment described above, the particulate matter whose main component is an element having a thermal neutron absorption cross-sectional area of 100 burns or more is discharged from the nozzle together with the binder onto the surface of the object. This makes it possible to reliably prevent the recriticality of an object having a complicated surface shape.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, changes, and combinations can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 10 ... Coating | coated apparatus, 11 ... Nozzle, 12, 13, 14 ... Hose, 15 ... Mixture, 16 ... Chamber, 17 ... Purge gas, 18 ... Cooling water, 20 ... Supply means, 21 ... Storage part, 23 ... Kneading part, 24 DESCRIPTION OF SYMBOLS ... Container for particulate matter, 25 ... Container for binder, 26 ... Gas compressor, 27 ... Curing part, 30 ... Object, 31 ... Particulate matter, 32 ... Binder, 33 ... Thermal neutron absorption film, 34 ... Protective coating, 35 ... Cut surface, 36 ... reactor structure.

Claims (12)

A mixture of a particulate material whose main component is an element having a thermal neutron absorption cross-section of 100 burns or more and a binder for immobilizing this particulate material on the surface of the core melt is agitated and mixed in a kneading section to adjust the viscosity to form a slurry. Supply means for supplying;
A nozzle for discharging the supplied mixture to the surface of the core melt,
The apparatus for coating a thermal neutron absorption film, wherein the supply means has a curing unit for supplying a curing means for curing the binder.   2. The thermal neutron absorption film coating apparatus according to claim 1, wherein the nozzle sprays the mixture onto a surface of the core melt with a pressure gas. 3.   The thermal neutron absorption film coating apparatus according to claim 1 or 2, wherein a protective coating containing an environmentally resistant substance is formed on the surface of the thermal neutron absorption film formed on the surface of the core melt.   4. The thermal neutron absorption film according to claim 1, wherein the main component of the particulate material is at least one selected from the group consisting of gadolinium, a gadolinium compound, boron, and a boron compound. 5. Coating equipment.   The thermal neutron absorption film coating apparatus according to claim 4, wherein the gadolinium compound is gadolinium oxide and the boron compound is boron carbide.   The thermal neutron absorption film coating apparatus according to any one of claims 1 to 5, wherein the binder contains a compound that is cured by a chemical reaction accelerated by moisture, ultraviolet rays, or carbon dioxide gas.   The thermal neutron absorption film coating apparatus according to any one of claims 1 to 5, wherein the binder is made of a substance mainly composed of sodium silicate.   The thermal neutron absorption film coating apparatus according to claim 1 or 7, wherein the curing means is cement.   The thermal neutron absorbing film coating apparatus according to any one of claims 1 to 8, wherein the nozzle is provided inside a chamber having an opening on the core melt side.   The thermal neutron absorption film coating apparatus according to claim 9, wherein the supply unit also supplies a purge gas for purging the inside of the chamber. A mixture of a particulate material whose main component is an element having a thermal neutron absorption cross-section of 100 burns or more and a binder for immobilizing this particulate material on the surface of the core melt is agitated and mixed in a kneading section to adjust the viscosity to form a slurry. Supplying step;
Discharging the supplied mixture to the surface of the core melt;
Supplying a curing means for curing the inorganic binder constituting the supplied mixture, and a method for coating a thermal neutron absorption film.   A method for recovering a molten core, wherein recriticality is prevented by using the coating method of a thermal neutron absorption film according to claim 11.

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