JP2014092530A - Neutron absorption member, critical state occurrence preventing method, and fissile material recovery method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a neutron absorption member capable of recovering, without causing recriticality, debris that contains a fissile material and exists in a pressure vessel or containment vessel in a nuclear reactor, and to provide a method of recovering the debris from a reactor pressure vessel or containment vessel using the neutron absorption member.SOLUTION: The present invention provides a neutron absorption member including a heat-resistant and radiation-resistant sheet-like material and a neutron absorber fixed on the sheet-like material, a fissile material recovery method of making the neutron absorption member absorb a fissile material inclusion and recovering the fissile material inclusion, and a critical state occurrence preventing method of preventing occurrence of a critical state with the neutron absorption member.

Description

  The present invention relates to a neutron absorbing member, and more particularly to a critical state generation prevention method and a fissile material recovery method for ensuring that damaged nuclear fuel present inside a nuclear reactor does not reach a critical state.

  Even during a nuclear accident, core melting is critical. This is because it causes large-scale leakage of radioactive materials to the outside, causing radioactive contamination to a wide area including the nuclear reactor, resulting in a large environmental problem.

  When a nuclear accident occurs, when the nuclear fuel rod melts and stays at the bottom of the reactor pressure vessel or containment, the decay heat generated from the nuclear fuel by storing a large amount of water in the reactor pressure vessel or containment It is necessary to remove the fissile material and to collect the fissile material staying at the bottom of the reactor pressure vessel or the containment vessel.

  The fissile material present at the bottom of the reactor pressure vessel or containment vessel in the water stored in the reactor pressure vessel or containment vessel is a large lump with very fine material particles and a rough surface. It is presumed that it exists in a mixed state of rocks and hard walls like volcanic rocks. A material containing such a fissile material is called debris.

  The fissile material that sinks to the bottom of a large amount of water stored in a reactor pressure vessel or containment vessel emits a large amount of radiation, and humans cannot directly recover it.

  If the fissile material existing at the bottom of the water in the reactor pressure vessel or the containment vessel is collected by some method like collecting dust and collected, it will cause recriticality and again fission reaction May cause a runaway.

  Even if the fissile material present in the water in the reactor pressure vessel or the containment vessel is kept so as not to reach criticality, the fissile material may be moved in some way, causing cracks or cracks. In this case, the ratio of water to fissile material changes, so that it may change from a steady state to an unsteady state, resulting in recriticality.

  Examples of nuclear accidents include the nuclear power plant accident on Three Mile Island in the United States and the Fukushima Daiichi Nuclear Power Plant accident.

  As shown in Non-Patent Documents 1 to 3, in the reactor accident on Three Mile Island, the reactor pressure vessel or containment vessel is obtained by adding a large amount of boron to the water stored in the reactor pressure vessel or containment vessel. There is an example in which the debris containing a fissile material is recovered by making the water in the inside into a high concentration boron aqueous solution.

  However, when the reactor pressure vessel or containment vessel of the reactor is damaged, it is difficult to keep the concentration of boron introduced into the water in the reactor pressure vessel or containment vessel constant.

  To date, no technology has been established to recover debris containing fissile material deposited on the bottom of a damaged reactor pressure vessel or containment vessel. The nuclear accidents at nuclear power plants that have occurred so far are all in different situations, and it can be said that the technology for recovering debris deposited at the bottom of a damaged reactor pressure vessel or containment vessel is under development.

  Non-Patent Documents 1 to 3 relating to a nuclear power plant accident on Three Mile Island are cited as documents describing the most recent invention for the present invention.

EPRI NP-6931 Research Project 2558-8 Final Report `` The Cleanup of ThreeMile Island Unit2 A technical History: 1979 to 1990 '' (Sep. 1990) JAERI-M-93-111 Results and Lessons Learned from TMI-2 Accident Investigation and Recovery -Introduction of Special Issue on Nuclear Technology TMI- (June 1993) CRITICALITY PREVENTION DURING POSTACCIDENT DECONTAMINATION OF THREE MILE ISLAND UNIT 2 PLANT SYSTEMS / Gerald L. Palau, Bechtel National. Inc. “NUCLEAR TECHNOLOGY” Vol.87, PP679, (Nov. 1989)

  An object of the present invention is to provide a neutron absorbing member capable of recovering debris containing a fissile material present in a pressure vessel or a containment vessel in a nuclear reactor without causing recriticality, It is to provide a method for recovering the debris from a reactor pressure vessel or a containment vessel using the neutron absorbing member, and to provide a critical state generation preventing method for preventing the occurrence of a critical state. .

Means for solving the problems are as follows:
(1) A neutron absorbing member comprising a heat-resistant and radiation-resistant sheet-like material and a neutron absorbing material fixed to the sheet-like material,
(2) The neutron absorbing member according to (1), wherein the sheet-like object is an object formed in a planar shape object and a three-dimensional shape object,
(3) The sheet-like material has a mechanical property of at least 20 hours even in a high radiation environment in which the melting temperature is 200 ° C. even when the melting temperature is low and a radiation dose of at least 10 ⁶ [Gy / hr] is emitted. The neutron absorbing member according to (1) or (2), wherein the neutron absorbing member is formed of a material that does not change,
(4) The neutron absorbing member according to any one of (1) to (3), wherein the sheet is formed of carbon fiber or glass fiber.
(5) The neutron absorbing member according to any one of (1) to (4), wherein the sheet-like material includes an accommodating portion that accommodates the neutron absorber.
(6) The sheet-like material is formed by dividing a gap sandwiched between a plurality of stacked sheets and a stacked sheet by integrating the stacked sheets into small regions. The neutron absorbing member according to any one of (1) to (5), comprising a housing part,
(7) The sheet-like object includes a plurality of stacked sheets, a sewing thread that integrates the stacked sheets, and a storage portion that is formed by overlapping sheets and stitches of the sewing thread. The neutron absorbing member according to any one of (1) to (5),
(8) The sheet-like material is the neutron absorbing member according to any one of (1) to (5), which includes a gap through which water passes.
(9) The neutron absorbing member according to any one of (1) to (7), wherein the neutron absorber is particulate.
(10) A fissile material recovery method, wherein the neutron absorbing member according to any one of (1) to (7) includes a fissile material inclusion and recovers the fissile material inclusion. And
(11) A critical state generation preventing method for preventing a critical state from being generated by the neutron absorbing member according to any one of (1) to (8).

  According to the present invention, a fissile material can be contained in a sheet-like material on which a neutron absorbing material is fixed, and neutrons absorbed from the fissile material can be absorbed even if debris containing the fissile material is moved in water. Because it can be absorbed by the material, it does not cause recriticality, and even if a sheet-like material containing fissile material is exposed from water, neutrons released from the fissile material can be absorbed by the neutron absorber. Therefore, it is possible to provide a neutron absorbing member capable of recovering debris containing fissile material from, for example, a reactor pressure vessel or a containment vessel without causing recriticality.

According to the present invention, when the sheet-like material is formed into a planar shape, the sheet-like material for fixing the neutron absorbing material is placed on a large debris mass containing, for example, a fissile material, and the debris is sheeted. Since the debris is included in the sheet-like material so as to be wrapped in the shape-like material, the debris is recovered after the sheet-like material containing the debris is transferred out of the pressure vessel or the containment vessel of the nuclear reactor, Even if the debris is cut or cracked with neutrons, the neutrons released from the fissile material can be absorbed by the neutron absorber fixed to the sheet, so work can be done safely without causing recriticality. A neutron absorbing member that can be provided can be provided.
According to the present invention, when the sheet-like material is formed into a planar shape, the sheet-like material for fixing the neutron absorbing material is placed on, for example, debris containing a fissile material, and the debris is wrapped with the sheet-like material. In this way, the debris can be secured with a sheet-like material, and neutrons released from the fissile material can be absorbed by the neutron absorber fixed to the sheet-like material, so that the debris moves in the water, Further, it is possible to provide a neutron absorbing member that can recover debris without causing recriticality, for example, from a reactor pressure vessel or containment vessel without causing recriticality even if the debris is moved from water to air. .

  According to the present invention, when the sheet-like material is a three-dimensional object such as a bag or a container, for example, debris containing a fissile material can be accommodated in the bag or container. In addition, since a bag or container is formed of a sheet that fixes the neutron absorber, the debris containing fissile material can be pressurized from within the reactor pressure vessel or containment vessel without causing recriticality. It is possible to provide a neutron absorbing member that can be recovered from the container or the containment vessel.

  When the sheet-like material is a rod-like material that is an example of a three-dimensional object, the rod-like sheet-like material is inserted into a crack or a gap portion of the debris containing fissile material, or a hole is made in the debris with a tool. The neutron absorber that can be inserted into the hole and fixed to the rod-shaped sheet can absorb the neutrons released from the fissile material. It is possible to provide a neutron absorbing member capable of recovering debris without causing recriticality, for example, from a reactor pressure vessel or containment vessel without causing recriticality even if the debris is moved into the air.

According to the present invention, the sheet-like material has a melting temperature of 200 ° C. even if it is low, and a period of at least 20 hours even in a high radiation environment where a radiation dose of at least 10 ⁶ [Gy / hr] is emitted. Because it is made of a radiation-resistant material that does not change its mechanical properties, the fissile material is not melted or deteriorated during the operation of recovering the fissile material. A neutron absorbing member that can be recovered without losing inclusions of fissile material therein can be provided.

  According to the present invention, since the sheet-like material is formed of carbon fiber or glass fiber, the sheet-like material does not melt or deteriorate during the operation of recovering the fissile material. A neutron absorbing member that can be recovered without losing fissile material inclusions during the recovery operation can be provided.

  According to the present invention, since the sheet-like material has the accommodating portion that accommodates the neutron absorber, the neutron absorber is not detached from or separated from the sheet-like material, and the neutron absorber is a sheet-like material. It is possible to provide a neutron absorbing member that can recover fissile material inclusions such as debris without recriticality without being unevenly distributed in a part of the object.

  According to the present invention, a plurality of sheet-like materials sandwiched with neutron absorbers are sewn with sewing threads, and are sandwiched between the sheet-like materials and the sheet-like materials, in an accommodating portion that is an internal space partitioned by the sewing threads. Since the neutron absorber is housed, the neutron absorber can be recovered without re-criticalizing the inclusion of fissile material, for example, debris, without the neutron absorber being unevenly distributed in a part of the sheet. Can be provided.

  According to the present invention, since the neutron absorbing material is in the form of particles, the neutron absorbing material can be uniformly fixed to the sheet-like material, and thus the fissionable substance inclusion such as debris can be recovered without recriticality. The neutron absorption member which can be provided can be provided.

  According to the present invention, even when convection of water occurs in a high-temperature fissile material inclusion such as debris by forming a sheet-like material having a gap through which water passes, the debris deposited on the bottom of the water does not float even when water convection occurs. It is possible to provide a neutron absorbing member that can be recovered without recriticality of fissionable substance inclusions, for example, debris, by being surely encased.

  According to the present invention, it is possible to provide a fissile material recovery method and a critical state generation prevention method capable of recovering a fissile material without recriticality.

FIG. 1 is a perspective view showing a sheet-like object that is a planar object. FIG. 2 is a perspective view showing a sheet-like material in the form of a bag-like material. FIG. 3 is a perspective view showing a sheet-like material in the form of a container-like material. FIG. 4 is an explanatory diagram showing a state in which a particulate neutron absorber is interposed between sheets. FIG. 5 is a photograph showing gadolinia particles that are actually manufactured neutron absorbers. FIG. 6 is a photographic diagram showing a neutron absorber formed of carbon fiber sheets and gadolinia particles sewn with carbon fiber cloth and carbon fiber yarns.

  The neutron absorbing member according to the present invention has a sheet-like material and a neutron absorbing material.

  The sheet-like material is formed in a sheet shape and has heat resistance and radiation resistance.

  The form of the sheet-like material may be a form formed of one sheet or a plurality of sheets. As a sheet-like material, a single object formed by a single sheet, a combination of a plurality of single objects that are sheets, a laminate formed by laminating a plurality of sheets, and a plurality of sheets are laminated. It may be a laminated body formed by bonding the laminated bodies to each other or by combining the laminated body with a single body or a combined body.

  The sheet-like material may be a flat shape by itself, a bonded material, a laminated material, or a laminated material, and a three-dimensional object using the single material, the bonded material, the laminated material, and the laminated material. It may be a shape. As a three-dimensional shape, a bag-like product processed into a bag-like shape, and a container-like product processed into a container-like shape using the above-mentioned simple substance, combination, laminate, and laminate combination, Moreover, a rod-shaped object may be sufficient.

  The sheet-like material may be either a planar shape or a three-dimensional shape.

  Examples of the planar shape include the simple substance, the bonded product, the stacked product, and the stacked bonded product.

  In addition, examples of the three-dimensional object include a bag-like object, a container-like object, and a rod-like object.

  In addition, the meaning of the "planar shape" and "three-dimensional shape" when calling it a planar shape thing and a solid shape object is relative according to the magnitude | size etc. of a sheet-like thing. The meaning of ordinary geometrical terms is that the plane is a two-dimensional shape without thickness, and the solid is a three-dimensional shape, but real objects always have a three-dimensional shape, compared to the thickness on the plane. If the dimension of the plane is sufficiently large, the sheet can be referred to as a planar shape, and the thickness of the plane is not negligible with respect to the dimension of the plane in the plane, for example, the vertical dimension and the horizontal dimension. In terms of size, it is appropriate to call the sheet-like object a three-dimensional object rather than a planar object.

  FIG. 1 shows a sheet-like object that is a planar object. The sheet-like material is a thin film-like sheet material 1 having a flat plane as shown in FIG. 1 (a), a thick anti-material sheet-like material 1 as shown in FIG. 1 (b), It can take a form such as a thick plate. This is because a sheet-like material having a planar shape envelops debris having a fissile material. Since it is necessary to wrap debris having a fissile material in a sheet-like material having a planar shape, it is desirable that any sheet-like material having a planar shape has flexibility. The size of the sheet-like material that is a planar shape is arbitrarily determined by the volume of the debris to be included. If an example is given, the planar shape object of length 120cm and width 120cm can be mentioned.

  As shown in FIG. 2, the sheet-like object 1 can take a bag-like form. The sheet-like material 1 in the form of a bag is formed into a bag having one end as an opening 3 using, for example, a plurality of sheets 2. The internal space of the bag is a part that accommodates debris. The size or the internal volume of the bag portion can be appropriately determined according to the capacity of the debris to be accommodated.

  As shown in FIG. 3, the sheet-like object 1 may be formed in a container shape having a plurality of sheets 2 and one end at an opening 3. In FIG. 3, reference numeral 4 denotes a shovel plate formed of the sheet 2. It is desirable that the sheet-like material formed in a container shape is hard. Moreover, the sheet-like material may be formed in the inner container of the metal container by being attached to the inner surface of the metal container.

  It is preferable that the sheet-like material has water permeability through which water passes. The sheet-like material having water permeability may be a woven fabric, a knitted fabric, or a non-woven fabric. In addition, when the material forming the sheet-like material is a synthetic resin having heat resistance and radiation resistance, the sheet-like material may be a sheet formed and processed at a melting temperature not higher than heat resistance.

  Water permeability can be realized by the gap between the warp and weft in the woven fabric, the gap in the knitted fabric, and the gap in the nonwoven fabric, and may be an opening formed by processing as shown in FIG. .

  This sheet-like material has a property of melting at 200 ° C. even if it has low heat resistance. Since this sheet-like material has heat resistance, this sheet-like material releases the fissile material during the operation of collecting debris containing the fissile material existing in water with this sheet-like material. The degree of melting or deterioration by the decay heat is extremely low.

  The sheet-like material having heat resistance preferably has a melting temperature of 200 ° C. or higher.

  When enveloping the fissile material with the neutron absorbing member of the present invention, the debris includes the actinide generated by the absorption of neutrons together with the fissile material and the fission parent material. In addition, fission products produced by fission of nuclear material are included. Some of them cause radioactive decay, and the energy of the radiation generated during the radioactive decay is changed into thermal energy during the debris, so that the debris may be at a high temperature. Moreover, when the radiation emitted from the debris hits the neutron absorbing member, the temperature of the neutron absorbing member may increase. Even in such a case, heat resistance is required in order not to impair the function of the neutron absorbing member.

This sheet-like material has radiation resistance. The sheet-like material only needs to have radiation resistance to such an extent that the mechanical properties are not substantially deteriorated even in a high radiation environment. For example, a radiation-resistant sheet may have its mechanical properties for at least substantially 20 hours when placed in a high radiation environment in which a radiation dose of at least substantially 10 ⁶ [Gy / hr] is emitted. However, it is desirable not to deteriorate to such an extent that it cannot be transported in a state including debris.

  In the present invention, when the material forming the sheet-like material is a polymer compound, the initial value of the tensile elongation when irradiated with a high dose rate electron beam (5 kGy / s) in air is used. The polymer compound can have radiation resistance when the dose that decreases to 50% of the above is at least 20 MGy. A sheet formed of such a polymer compound envelops debris in water containing a fissile material, and this sheet for at least 20 hours including the work time of removing the debris from the reactor pressure vessel or containment vessel This is because the tensile elongation of the product does not decrease so as to be difficult to work. Examples of such a polymer compound having radiation resistance include engineering plastics such as non-crystalline PEEK, crystalline PEEK, polyamide, and polyimide.

  Moreover, this sheet-like material can be formed of carbon fiber alone, or can be formed of a composite material of carbon fiber and epoxy resin. In general, when an organic compound is used in a radiation field, the mechanical properties and electrical properties of the material are often lowered due to an increase in bonds (crosslinking) between polymer chains, molecular chain breaks, double bonds, and the like. Carbon fibers are composed of only covalent bonds between carbons, and are less likely to cause molecular chain breakage. Therefore, carbon fibers are superior in radiation resistance to the engineering plastics described above. When the sheet-like material is formed of carbon fiber, it can be in the form of carbon fiber woven fabric, knitted fabric, or non-woven fabric. The sheet-like material can also be formed of a composite material of carbon fiber and an engineering plastic such as epoxy resin, PEEK, polyamide, or polyimide. As Non-Patent Document 4, “Nuclear Research Institute JAERI-Data / Code 2003-015 Radiation Resistance Properties and Data Collection of Polymer Materials (July 2003)” is shown.

  The neutron absorber may be any substance that absorbs neutrons, such as borax, sodium polyborate, boric acid, gadolinium nitrate, etc., and rhodium, cadmium, indium, Examples include elemental elements such as samarium, europium, dysprosium, erbium, thulium, hafnium, mercury, and compounds of these elements. Among these, gadolinium oxide is preferable.

  As a form of the neutron absorbing material used in the present invention, various forms such as a particulate form, a flake form, a strip form, a plate form, and a needle form can be taken.

  The form of the neutron absorber can be appropriately determined according to the form of the sheet. For example, when the sheet-like material is a laminate obtained by laminating a plurality of sheets, a form of particles dispersed almost uniformly between the sheets is preferable. This is because the particles are easy to handle and the particles of the neutron absorber can be easily dispersed between the sheets. As shown in FIG. 4, a neutron absorber 6 formed in a spherical shape between a carbon fiber sheet 5A, which is a sheet formed of carbon fibers, and a carbon fiber sheet 5B similar to the carbon fiber sheet 5A. Then, the two carbon fiber sheets 5A and 5B are sewn with the carbon fiber yarn 7 to obtain the neutron absorbing member 8 formed in a planar shape. In FIG. 4, the carbon fiber yarn is sewn in the vertical direction and the horizontal direction, but the sewing direction may be arbitrary. If the neutron absorber can be formed into a thin piece depending on the type of the neutron absorber, the neutron absorber made into a thin piece can be interposed between the sheets.

  In the neutron absorbing member according to the present invention, a neutron absorbing material is fixed to a sheet-like material. The neutron absorbing member is fixed so as to be integrated with the sheet-like material so that the neutron-absorbing material does not fall off from the sheet-like material, is separated, and moves and is unevenly distributed during the recovery operation.

  As a fixed aspect, various aspects can be mentioned according to the form of a neutron absorber. When the neutron absorbing material is in the form of particles, the neutron absorbing material is accommodated in the accommodating portion formed in the sheet-like material that is a laminate formed by laminating the sheets. Can be fixed to.

  As shown in FIG. 4, as an example of the accommodating portion, a particulate neutron absorber 6 is formed between stacked sheets such as a carbon fiber sheet 5A and another sheet such as a carbon fiber sheet 5B, which form a laminate. The carbon fiber sheet 5A and the carbon fiber sheet 5B are integrated by sewing the carbon fiber sheet 7 with the sewing sheet, for example, the carbon fiber thread 7, and then sandwiched between the carbon fiber sheet 5A and the carbon fiber sheet 5B. Thus, a space formed by the sewing thread, for example, the seam of the carbon fiber thread 7 can be used as the accommodating portion 9.

The particle size of the particulate neutron absorbing material accommodated in the accommodating portion formed by sandwiching the neutron absorbing material between the sheets in the laminate of such sheets and integrating the plurality of sheets with the sewing thread is as follows: For example, it is preferably 5 mm or less, particularly 0.1 to 3 mm. Further, the amount of neutron absorbing material which is accommodated in the accommodating portion formed between the sheets, e.g. 0.7~2.7g weight / cm ^2, preferably cited 0.7~0.9g mass / cm ² be able to. It is preferable that an amount sufficient to break the interaction between the debris and the fissile material existing in the vicinity thereof and neutrons is contained.

  If the neutron absorbing material can be formed in an elongated foil shape, the foil-like neutron absorbing material can be attached to the surface of a sheet-like material that is a single sheet. If the neutron absorber can be formed into a slender thread, the neutron absorber can be fixed to the sheet by sewing the thread neutron absorber on the sheet.

  Using the neutron absorbing member according to the present invention, debris containing a fissile material can be recovered as follows.

  Remote control is possible when debris containing fissile material is present at the bottom of the reactor pressure vessel or containment vessel, and the debris is submerged in the water stored in the reactor pressure vessel or containment vessel The debris is covered with a neutron absorbing member having a sheet-like material in the form of, for example, a planar shape according to the present invention using a robot hand.

  A neutron absorbing member is submerged in water stored in a reactor pressure vessel or a containment vessel using a multi-fingered robot hand that can be remotely operated, and a neutron absorbing member having a planar shape is placed on the debris. By operating the multi-fingered robot hand, the debris is covered with a neutron absorbing member, and then the neutron absorbing member is operated so that the debris is wrapped with the neutron absorbing member. Fissile material is separated from the neutron absorber in place.

  In this way, the fissile material can be recovered from the inside of the reactor using the neutron absorbing member, and the fissionable material in the debris contained in the neutron absorbing member causes recriticality because it has the neutron absorbing member. The nuclear reactor can safely recover fissile material.

  When the neutron absorbing member is a bag-like material, for example, using two multi-fingered robot hands, the neutron absorbing member is gripped by one multi-fingered robot hand and the neutron absorbing member is A neutron absorbing member is disposed near the debris in the containment vessel. The other multi-fingered robot hand, for example, holds a scoop or the like and places it near the debris. The debris is crushed by a scoop or the like held by the multi-fingered robot hand, and the crushed debris is stored in a bag-like neutron absorbing member held by the other multi-fingered robot hand. The debris accommodated in the bag-like neutron absorbing member is recovered from the reactor pressure vessel or the containment vessel together with the neutron absorbing member. Even in this case, since the neutron absorbing member contains the neutron absorbing member, the fissile material in the debris does not cause recriticality even if the bag-like neutron absorbing member that contains the debris is moved.

  When the neutron absorbing member is a container, for example, a neutron absorbing member that is a container is used as an inner attachment of a metal bucket. If the neutron absorbing member is attached to the inner surface of the metal bucket as an inner vessel, the metal bucket can scrape debris present at the bottom of the reactor pressure vessel or containment vessel, The debris can be recovered by moving from the bottom of the reactor pressure vessel or containment vessel to the outside of the pressure vessel or containment vessel with the debris contained in the bucket. Since the neutron absorbing member is provided inside the metal bucket, recriticality of the fissile material does not occur.

  As a neutron absorber, granular gadolinia was manufactured as follows. A dripping stock solution was prepared by dissolving 70 to 130 g of gadolinia powder in 150 to 300 mL of an aqueous solution to which 35 to 55 g of a thickener (trade name Poval, manufactured by Kuraray Co., Ltd.) was added. The dripping stock solution was dropped into acetone to produce coarse gadolinia particles. The produced coarse gadolinia particles were collected, washed, dried, and then sintered at 1150 to 1750 ° C. to obtain gadolinia particles. The average particle diameter of the obtained gadolinia particles was 0.6 to 1.5 mm. The obtained gadolinia particles are shown in FIG.

  On the other hand, two pieces of cloth having a length of 15 cm, a width of 15 cm, and a thickness of 0.5 mm are cut from a carbon fiber woven cloth so that the surface of the obtained one piece of carbon fiber cloth is 0.8 g per unit area. The gadolinia particles were arranged. A second carbon fiber cloth was laminated on the carbon fiber cloth on which the gadolinia particles were spread so as to cover the gadolinia particles. Next, two carbon fiber fabrics were sewn with carbon fiber threads. In the sewing, the interval between the vertical sewing line of the carbon fiber yarn and the adjacent vertical sewing line is 1 to 5 cm, and the interval between the horizontal sewing line of the carbon fiber yarn and the adjacent horizontal sewing line is 1 to 5 cm. Was made to be 1-5 cm. A space between the two carbon fiber cloths and formed by the vertical sewing line and the horizontal sewing line is a storage unit that stores gadolinia particles.

  As shown in FIG. 6, the sheet-like material made of carbon fiber cloth thus obtained is flexible and has a plurality of concrete lumps (longitudinal length 2 cm, lateral length 2 cm, depth maximum 2 cm) that are regarded as solids such as debris. ).

DESCRIPTION OF SYMBOLS 1 Sheet-like object 2 Sheet | seat 3 Opening part 4 Shovel board 5A Carbon fiber sheet 5B Carbon fiber sheet 6 Neutron absorber 7 Carbon fiber yarn 8 Neutron absorption member 9 Accommodating part

Claims (11)

  A neutron absorbing member comprising: a heat-resistant and radiation-resistant sheet-like material; and a neutron absorbing material fixed to the sheet-like material.   The neutron absorbing member according to claim 1, wherein the sheet-like object is an object formed into a planar shape object and a three-dimensional shape object. The sheet-like material is 200 ° C. even when the melting temperature is low, and the mechanical properties do not change for at least 20 hours even in a high radiation environment where a radiation dose of at least 10 ⁶ [Gy / hr] is emitted. The neutron absorbing member according to claim 1 or 2, wherein the neutron absorbing member is made of a material.   The neutron absorbing member according to any one of claims 1 to 3, wherein the sheet-like material is formed of carbon fiber or glass fiber.   The neutron absorbing member according to any one of claims 1 to 4, wherein the sheet-like material has an accommodating portion for accommodating the neutron absorbing material.   The sheet-like material includes a plurality of stacked sheets, and a storage portion formed by dividing a gap sandwiched between stacked sheets by integrating the plurality of stacked sheets into small regions. The neutron absorbing member according to claim 1, comprising:   The sheet-like object includes a plurality of stacked sheets, a sewing thread that integrates the stacked sheets, and a storage portion that is formed by overlapping sheets and stitches of the sewing thread. Item 6. The neutron absorbing member according to any one of Items 1 to 5.   The neutron absorbing member according to any one of claims 1 to 5, wherein the sheet-like material has a gap through which water passes.   The neutron absorbing member according to any one of claims 1 to 7, wherein the neutron absorber is particulate.   A fissile material recovery method comprising recovering a fissile material inclusion by including the fissile material inclusion in the neutron absorbing member according to claim 1.   The critical state generation | occurrence | production prevention method which prevents generation | occurrence | production of a critical state with the neutron absorption member as described in any one of the said Claims 1-8.

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