JP7182529B2 - Neutron shielding material, storage container, and method for producing neutron shielding agent - Google Patents

Description

The present invention relates to a neutron shielding material, a storage container, and a method for producing a neutron shielding agent.

The combustion assembly storage vessel (eg, cask) includes a neutron shielding material that shields neutrons emitted from the fuel assembly. As a technique related to neutron shielding materials, the technique described in Patent Document 1 is known.

In Patent Document 1, each powder including a neutron absorbing boron compound powder, a high density metal powder for gamma ray shielding and a flame retardant powder optionally included, or a mixture of the powders is mixed with an amine curing agent to obtain a curing agent. A mixing step of obtaining a mixture of and a powder, an ultrasonic treatment step of applying ultrasonic waves to the mixture to coat the powder surface with an amine-based curing agent and dispersing it in the curing agent, and the ultrasonically treated powder and a dispersing step of mixing and dispersing an amine-based curing agent dispersed with an epoxy resin.

Japanese Patent Application Publication No. 2014-514587 (especially see claim 1)

In the technique described in Patent Document 1, the flame retardant is contained in the resin composition at a rate of 10% or more and 30% or less with respect to the entire resin composition (see paragraph 0047 of Patent Document 1). Therefore, the technique described in Patent Document 1 requires a small amount of flame retardant and has a problem of heat resistance.

The problem to be solved by the present invention is to provide a neutron shielding material, a storage container, and a method for producing a neutron shielding agent that can improve heat resistance more than conventional ones.

The neutron shielding material of the present invention is composed of a resin composition containing a flame retardant, an epoxy resin containing a unit skeleton derived from an acid anhydride as a curing agent, and a curing accelerator that is only a non-imidazole compound. , the epoxy resin includes a unit skeleton derived from a hydrogenated epoxy main agent containing two or more epoxy groups in the molecule, and the flame retardant has a ratio of 40% by mass or more and 60% by mass or less with respect to the resin composition. included in Other solutions will be described later in the detailed description.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the neutron shielding material which can improve heat resistance conventionally, a storage container, and a neutron shielding agent can be provided.

It is a perspective view which shows the storage container of this embodiment typically. 4 is a flow chart showing a method for manufacturing the neutron shielding material of this embodiment. 4 is a graph showing the oxygen index with respect to the blending amount of flame retardant. 4 is a graph showing the viscosity of the raw material mixture with respect to the amount of flame retardant compounded. 4 is a graph showing the oxygen index with respect to the average particle size of flame retardants. 4 is a graph showing the viscosity of the raw material mixture with respect to the average particle size of the flame retardant.

Hereinafter, the form (this embodiment) for carrying out the present invention will be described with reference to the drawings as appropriate, but the present invention is not limited to the following contents, and can be arbitrarily modified within a range that does not significantly impair the effects of the present invention. can be implemented by In different embodiments, the same members shall be given the same reference numerals, and overlapping descriptions will be omitted. The present invention can be practiced by combining different embodiments.

<Storage container 10>
(Container body 11)
FIG. 1 is a perspective view schematically showing a storage container 10 of this embodiment. In FIG. 1, a portion of the storage container 10 having a substantially cylindrical shape is cut away to show its internal structure and cross-sectional structure. The storage container 10 includes a container main body 11 for storing fuel assemblies (not shown), and a neutron shielding material 6 arranged around the fuel assemblies. The fuel assembly referred to here is, for example, a spent fuel assembly, and the same applies hereinafter. However, the fuel assemblies that can be stored in the storage container 10 are not limited to spent fuel assemblies.

The container main body 11 includes a bottomed inner cylinder (inner container) 2, an outer cylinder (outer container) 3 installed outside the inner cylinder 2, and an outer cylinder 3 installed inside the inner cylinder 2, and stores the fuel assembly. and a basket 5 for storage. The container body 11 also includes heat transfer fins 4 , a primary lid 7 , a secondary lid 8 , and a trunnion 9 . In the illustrated example, the neutron shielding material 6 is arranged between the inner cylinder 2 and the outer cylinder 3, the primary lid 7, and the secondary lid so as to be arranged around the fuel assembly when the fuel assembly is stored. 8 inside. The neutron shielding material 6 suppresses the movement of neutrons into and out of the storage container 10 by absorbing neutrons, and is composed of neutron shielding materials 6A and 6B described later. The neutron shielding materials 6, 6A, 6B will be described later.

The inner cylinder 2 is made of carbon steel or the like to shield gamma rays. A side surface of the inner cylinder 2 is provided with heat transfer fins 4 for radiating heat from the fuel assembly. The heat transfer fins 4 are made of, for example, metal plates such as copper, aluminum, and alloys thereof. The side surface of the inner cylinder 2 is covered with the outer cylinder 3 installed outside the heat transfer fins 4 .

The basket 5 is installed inside the inner cylinder 2 and has a grid-like compartment. The basket 5 accommodates the fuel assemblies stored in the storage container 10 so that the number of loaded fuel assemblies is, for example, about 30 to 70. The fuel assemblies are stored while being separated from each other by metal partition plates 5a provided in a grid pattern.

A primary lid 7 and a secondary lid 8 are attached to an upper opening (not shown) of the inner cylinder 2 that constitutes the container body 11 of the storage container 10 . The fuel assembly housed in the storage container 10 is hermetically sealed in the inner cylinder 2 with a double structure consisting of an inner primary lid 7 and an outer secondary lid 8 . A predetermined number of trunnions 9 are provided on the side surface of the outer cylinder 3 as a part for supporting the storage container 10 on a support frame or the like and for fixing the storage container 10 to a transport hanger or the like.

A plurality of heat transfer fins 4 radially extend between the inner cylinder 2 and the outer cylinder 3 at equal intervals in the circumferential direction of the inner cylinder 1 and the outer cylinder 2 . The heat transfer fins 4 are arranged at intervals, and a space is provided between the inner cylinder 2 and the outer cylinder 3 so as to surround the inner cylinder 2 . The primary lid 7 and the secondary lid 8 can be provided in a hollow structure while ensuring shielding performance against radiation and secondary gamma rays from the fuel assembly. A neutron shielding material 6 is arranged in the hollow portions of the primary lid 7 and the secondary lid 8 so as to surround the fuel assembly.

In the storage container 10, for example, the neutron shielding material 6, which has high heat resistance and does not easily deteriorate in neutron shielding performance even in a high temperature environment, is provided at a position surrounding the inner cylinder 2. Therefore, even if the fuel assembly, which is generally assumed to have a storage period of about 50 years, continues to generate heat during storage, the thermal aging of the neutron shielding material 6 is suppressed, and the neutron shielding performance of the storage container 10 is reduced. The storage of the fuel assembly can be safely continued for a long period of time.

In addition, when the number of fuel assemblies loaded in the storage container 10 is increased, the storage container 10 can be provided in which the neutron shielding performance is less likely to deteriorate even when storing high-burnup nuclear fuel assemblies. That is, when the cooling period in the cooling pool in the nuclear power plant is short, even when storing high-burnup nuclear fuel assemblies, it is possible to increase the number of nuclear fuel assemblies loaded in the storage container 10. , the weight of the storage container 10 can be reduced, and the volume occupied for storage can be reduced.

(Neutron shielding material 6)
The neutron shielding material 6 is composed of a resin composition containing a flame retardant and an epoxy resin, and the epoxy resin contains a unit skeleton derived from a hydrogenated epoxy main agent containing two or more epoxy groups in the molecule. Hereinafter, for convenience of explanation, the epoxy resin contains (a) a unit skeleton derived from a hydrogenated epoxy main agent containing two epoxy groups in the molecule (neutron shielding material 6A), and (b) in the molecule The neutron shielding material 6 will be described separately from the case (neutron shielding material 6B) containing a unit skeleton derived from a hydrogenated epoxy main agent containing three or more epoxy groups.

(a) When the epoxy resin contains a unit skeleton derived from a hydrogenated epoxy main agent containing two epoxy groups in the molecule. . The neutron shielding material 6A is used by blending a flame retardant, a neutron absorbing material, etc. in an epoxy resin forming a resin matrix, and molding it into an appropriate shape. The neutron shielding material 6A can be used for various applications for shielding neutrons, but in particular, the neutron shielding material 6A, which has excellent heat resistance, is suitable for applications where high temperatures of 150° C. or higher and 300° C. or lower may continue. Suitable for use in storage vessels 10 such as dry casks.

As used herein, "heat resistance" means a property evaluated using the glass transition temperature or heat distortion temperature as an index. Therefore, the heat resistance of the cured resin composition can be evaluated by measuring the glass transition temperature or heat distortion temperature. Also, the heat resistance of the neutron shielding material 6A can be indirectly evaluated using the reduction rate of the hydrogen density or number of hydrogen or the mass depletion rate with temperature change as an index. Note that "flame retardancy" is one of the classifications representing the degree of "heat resistance". Therefore, it can be said that if the flame retardancy is inferior, the heat resistance is also inferior.

The epoxy resin contained in the neutron shielding material 6A is composed of, for example, a cured material cured by a polymerization reaction of a raw material mixture. The raw material mixture contains a main agent containing at least a hydrogenated epoxy main agent (bifunctional hydrogenated epoxy main agent) containing two epoxy groups in the molecule, and a curing accelerator that accelerates polymerization via the epoxy groups, for example. . Therefore, the resin composition, which is the cured product of the raw material mixture, contains an epoxy resin containing a unit skeleton derived from the main agent and a curing accelerator not contained in the constituent skeleton of the epoxy resin.

A curing agent for ring-opening polymerization of the epoxy group of the epoxy compound is optionally added to the raw material mixture depending on the type of main agent, curing conditions, required performance, and the like. When the raw material mixture contains a curing agent, the epoxy resin contains a unit skeleton derived from the main agent and a unit skeleton derived from the curing agent.

The epoxy resin contains a unit skeleton derived from a hydrogenated epoxy main agent containing two epoxy groups in the molecule. In this specification, the term "hydrogenation" refers to a state in which an aromatic ring present in the molecule is hydrogenated so that the double bond constituting the aromatic ring becomes a single bond. In this specification, hydrogenated compounds and resins are referred to as hydrogenates. A hydrogenated epoxy compound is an epoxy compound in which the aromatic ring is hydrogenated. Furthermore, a hydrogenated epoxy resin refers to a polymer of an epoxy compound having a hydrogenated aromatic ring. It should be noted that not all the aromatic rings contained in the epoxy resin need to be hydrogenated, and only some of the aromatic rings may be hydrogenated.

The hydrogenated epoxy main agent forming such a unit skeleton is at least one of hydrogenated bisphenol A diglycidyl ether (hydrogenated BADGE) and hydrogenated bisphenol F diglycidyl ether (hydrogenated BFDGE). is preferred. Epoxy resins are nuclear hydrogenated and exhibit high hydrogen densities. Therefore, it is suitable for achieving both high neutron shielding performance and high heat resistance. Hydrogenated bisphenol A diglycidyl ether is particularly preferable as the main agent because higher hydrogen density can be obtained.

In addition to the above-described unit skeleton, the unit skeleton may further include a unit skeleton derived from other epoxy compounds and an epoxy resin skeleton that is a polymer of an epoxy compound. For example, when a unit skeleton derived from a bisphenol-type epoxy compound that is not hydrogenated at the nucleus, or a resin (prepolymer) skeleton that is a polymer of such an epoxy compound is used in combination, the viscosity of the resin composition can be adjusted and the resin composition can be improved. It is possible to improve the strength and toughness of the steel.

As other epoxy compounds, a bifunctional epoxy compound containing two epoxy groups in the molecule may be used, or a polyfunctional epoxy compound containing three or more epoxy groups in the molecule may be used. Other epoxy compounds may be non-hydrogenated or may be hydrogenated. Other resins can be polymers of these epoxy compounds. Each of the other epoxy compounds or resins may be one kind, or two or more kinds.

Other epoxy compounds include, for example, glycidyl ether-type epoxy compounds, glycidyl ester-type epoxy compounds, glycidylamine-type epoxy compounds, alicyclic epoxy compounds, and the like. Other epoxy resins include polymers of these epoxy compounds, such as glycidyl ether type epoxy resins, glycidyl ester type epoxy resins, glycidyl amine type epoxy resins, alicyclic type epoxy resins, and phenol resin type epoxy resins. Epoxy resins, which are modified resins and the like and correspond to prepolymers, can be mentioned.

Examples of glycidyl ether type epoxy compounds include tetrabromobisphenol A diglycidyl ether, bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, 4,4'-biphenyldiyl bis(glycidyl ether), naphthalenediyl bis(glycidyl ether). , dicyclopentadiene diglycidyl ether, hydroquinone diglycidyl ether, resorcinol diglycidyl ether, cyclohexanediol diglycidyl ether, biphenol diglycidyl ether, diglycidylphenyl glycidyl ether, 4,4'-dihydroxybenzophenone diglycidyl ether, triglycidyl cyanurate. ether, tris(4-hydroxyphenyl)methane triglycidyl ether, 1,1,1-tris(4-hydroxyphenyl)ethane triglycidyl ether, 1,1,1-tris(4-hydroxyphenyl)propane triglycidyl ether, Examples include 1,1,2,2-tetra(p-hydroxyphenyl)ethane tetraglycidyl ether and derivatives thereof.

Examples of glycidyl ether type epoxy resins include brominated epoxy resins, bisphenol A type epoxy resins, bisphenol F type epoxy resins, biphenyl type epoxy resins, naphthalene type epoxy resins, and dicyclopentadiene type epoxy resins, which are polymers of these epoxy compounds. Epoxy resins, trisphenolmethane-type epoxy resins, phenol resin-type epoxy resins, and the like are included.

Examples of phenol resin-type epoxy resins include phenol novolak, which is a polymer of phenols and aldehydes, and xylylene into which a 1,2-xylylene group, a 1,3-xylylene group, or a 1,4-xylylene group is introduced. Novolacs, bisphenol A novolacs that are polymers of bisphenol A and aldehydes, triphenylmethane novolaks that are polymers of phenols, salicylaldehyde and hydroxybenzaldehyde, biphenyl novolaks modified with biphenyls, and dicyclopentadienes. Epoxy resins obtained by reacting phenol resins such as modified dicyclopentadiene phenol novolac and terpene phenol novolak modified with terpenes with epichlorohydrin or the like to epoxidize the resins may be mentioned.

Examples of glycidyl ester type epoxy compounds include diglycidyl phthalate, diglycidyl isophthalate, diglycidyl terephthalate, diglycidyl tetrahydrophthalate, diglycidyl hexahydrophthalate, and 1,2,4-benzene. Tricarboxylic acid triglycidyl ester, cyclohexanedicarboxylic acid diglycidyl ester, naphthalenedicarboxylic acid diglycidyl ester, and derivatives thereof.

Examples of glycidyl ester type epoxy resins include cyclic glycidyl ester type epoxy resins, which are polymers of these epoxy compounds.

Examples of glycidylamine type epoxy compounds include N,N-diglycidylaniline, N,N-diglycidyltoluidine, 1,3-phenylenebis(N,N-diglycidylmethanamine), 4,4-methylenebis(N , N-diglycidylaniline), N,N,N′-triglycidyl-4,4′-diaminodiphenylmethane, N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenylmethane, N,N ,N′,N′-tetraglycidylxylene diamine, N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenyl ether, diglycidylaminophenol, triglycidylaminophenol, triglycidyl isocyanurate, N, N-diglycidyl-4-glycidylaniline, N,N-diglycidyl-4-glycidyloxyaniline, N,N-diglycidyl-4-oxiraneroxyaniline, N,N-diglycidyl-4-phenoxyaniline, diglycidylpiperazine, N , N-bis(2,3-epoxypropyl)-4-(2,3-epoxypropoxy)aniline and derivatives thereof.

Examples of glycidylamine type epoxy resins include aromatic amine type epoxy resins, aminophenol type epoxy resins, and aliphatic amine type epoxy resins, which are polymers of these epoxy compounds.

Alicyclic epoxy compounds include, for example, 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate, 3,4-epoxy-6methyl-cyclohexylmethyl-3′,4′-epoxy-6 methyl-cyclohexanecarboxylate, bis(3,4-epoxycyclohexylmethyl)adipate, bis(3,4-epoxy-6-methyl-cyclohexylmethyl)adipate, ethyleneoxy-3,4-epoxycyclohexane, bis(3,4-epoxy)carboxylate 4-epoxycyclohexan-1-ylmethyl)ester, 1,1'-bi(2,3-epoxycyclohexane), 4,4'-bi(1,2-epoxycyclohexane), limonene diepoxide, dicyclopentadiene diepoxide , 1,4-cyclohexadiene diepoxide, 4-vinylcyclohexane diepoxide, 1,5-cyclooctadiene diepoxide, and derivatives thereof.

The alicyclic epoxy resins include, for example, oligomer-type alicyclic epoxy resins that are polymers of these epoxy compounds.

Since the epoxy resin contained in the resin composition has fluidity near room temperature and can be cured at room temperature, it is excellent in filling the space in which the neutron shielding material 6A is to be arranged. Therefore, when the neutron shielding material 6A is applied to a cask or the like, even if the space is narrow or has a complicated shape, the resin composition has a high filling rate and exhibits good neutron shielding performance. can be formed.

The curing agent forms the unit skeleton of the epoxy resin together with the main agent. The epoxy resin preferably contains a unit skeleton derived from a curing agent that is at least one of acid anhydride, dicyandiamide, and phenolic resin (prepolymer). Among them, the epoxy resin preferably contains a unit skeleton derived from an acid anhydride as a curing agent as a unit skeleton of the epoxy resin. In addition, one type of curing agent may be used, or two or more types may be used.

Examples of acid anhydrides include tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methylnadic anhydride, hydrogenated methylnadic anhydride, and trialkyltetrahydrophthalic anhydride. Acid, methylcyclohexene tetracarboxylic dianhydride, phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, benzophenone tetracarboxylic dianhydride, ethylene glycol bisanhydro trimellitate, dodecenyl succinic anhydride, maleic anhydride , succinic anhydride, chlorendic anhydride and the like. Among these, the acid anhydrides include tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methylnadic anhydride, hydrogenated methylnadic anhydride, trialkyltetrahydro Phthalic anhydride, methylcyclohexenetetracarboxylic dianhydride, phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, benzophenone tetracarboxylic dianhydride, ethylene glycol bisanhydrotrimellitate, and dodecenyl succinic anhydride is preferred.

The acid anhydride is preferably used in combination with another curing accelerator that accelerates the polymerization reaction. By using an acid anhydride, the neutron shielding material 6A having a relatively high glass transition point and heat resistance can be obtained at a relatively low cost.

Dicyandiamide may be used alone or in combination with other curing accelerators that accelerate the polymerization reaction. When dicyandiamide is used, the usable life of the resin composition is relatively long, and it is easy to obtain an epoxy resin having high mechanical strength. In addition, since it reacts at a high temperature of about 180° C. or higher, the heat resistance of the neutron shielding material 6A can be improved by performing heat curing at a temperature higher than room temperature.

Examples of phenolic resins include phenol novolak, cresol novolak, naphthol novolak, xylylene novolak, bisphenol A novolak, bisphenol F novolak, triphenylmethane novolak, biphenyl novolak, dicyclopentadiene novolak, and terpene phenol novolak. As a phenol resin, only 1 type may be used and multiple types may be used together. Phenol resin is a polymer obtained by polymerizing phenol or a nucleus-substituted phenol derivative, a compound having a ring structure that serves as a cross-linking group, and aldehydes such as formaldehyde, acetaldehyde, benzaldehyde, and salicylaldehyde in the presence of an acid catalyst. is.

The phenol resin is preferably used in combination with another curing accelerator that accelerates the polymerization reaction. When non-hydrogenated phenol resin is used, a rigid ring structure is introduced, so that the heat resistance and mechanical strength of the neutron shielding material 6A can be improved. As the phenol resin, a resin having high hydrogen density and high rigidity is preferred, and phenol novolac is particularly preferred.

When the epoxy resin contains a unit skeleton derived from an acid anhydride as a curing agent (that is, when an acid anhydride is used as a curing agent), the curing accelerator contained in the resin composition is only a non-imidazole compound. is preferred. The term "non-imidazole compound" as used herein means a compound that does not have an imidazole structure, that is, a structure having nitrogen atoms at positions 1 and 3 of a 5-membered ring. The non-imidazole compound may be either a low-molecular compound or a high-molecular compound.

In the case where the raw material liquid mixture that becomes the resin composition by curing contains an imidazole compound, an unreacted imidazole compound or a reactant of the imidazole compound remains in the resin composition. When the neutron shielding material 6A is exposed to a high temperature of, for example, 150° C. or higher and 300° C. or lower, the neutron shielding material 6A exhibits high reaction activity. This causes a decrease in density or deformation of the neutron shielding material 6A. On the other hand, if only a non-imidazole compound is used as a curing accelerator, the active sites of the imidazole structure in the resin composition will not exist, so in a high temperature environment such as dry storage where the fuel assembly continues to generate heat. Also, it is possible to suppress the decrease in the hydrogen density due to the vaporization of the unreacted epoxy compound and the curing agent, and the generation of the non-shielding portion due to the deformation of the neutron shielding material 6A. As a result, even in a high-temperature environment, progress of thermal aging can be suppressed, and the high hydrogen density and shape of the neutron shielding material 6A can be maintained.

Among the non-imidazole compounds, at least one of tertiary amines, tertiary amine salts, phosphines and phosphonium salts is preferred, and at least one of tertiary amines and tertiary amine salts is more preferred. By using at least one of tertiary amines, tertiary amine salts, phosphines or phosphonium salts, more preferably tertiary amines or tertiary amine salts, when exposed to high temperatures, imidazole compounds Unlike the case, the reaction activity does not become high, so high heat resistance can be obtained while securing the hydrogen density.

Examples of tertiary amines and tertiary amine salts include 2,4,6-tris(dimethylaminomethyl)phenol, 2,3,4-tris(dimethylaminomethyl)phenol, 2,4,5-tris(dimethyl aminomethyl)phenol, N-benzyldimethylamine, 1,8-diazabicyclo[5.4.0]-7-undecene, salts thereof (eg hydrochlorides), organic acid salts and the like.

Among these, tertiary amines and tertiary amine salts include tris(dimethylaminomethyl)phenol and its salts, N-benzyldimethylamine and its salts, 1,8-diazabicyclo[5.4.0]-7- At least one of undecene and its salts is preferred, and tris(dimethylaminomethyl)phenol and its salts are particularly preferred. With such a combination, the cost of raw materials is reduced, and a raw material mixed solution that hardens at room temperature can be obtained easily. In addition, unlike the case of using an imidazole compound, even when the neutron shielding material 6A is exposed to high temperatures, thermal decomposition of the components present in the resin composition is reduced, so high heat resistance can be obtained. can.

Tertiary amines and tertiary amine salts are preferably used in combination with other curing agents that form crosslinks. The use of a tertiary amine and a tertiary amine salt makes it possible to suppress the compounding amount compared to other compounds that cause an addition reaction, thus facilitating the improvement of the hydrogen density of the neutron shielding material 6A. In addition, since it tends to exhibit activity at high temperatures, the heat resistance of the neutron shielding material 6A can be further improved by performing heat curing at a temperature higher than room temperature.

Phosphines and phosphonium salts include, for example, phosphine, triphenylphosphine, salts thereof (eg, hydrochlorides), hydrobromides, organic acid salts, etc., and at least one of tetra-n-butylphosphonium tetraphenylborate. one is preferred. Phosphines and phosphonium salts are preferably used in combination with other curing agents that form crosslinks. When phosphines and phosphonium salts are used, the amounts to be added can be suppressed as compared with other compounds that undergo addition reactions, so the hydrogen density of the neutron shielding material 6A can be easily improved.

When an imidazole compound is used as the curing accelerator, examples of the imidazole compound include 2-ethyl-4-methylimidazole.

A combination of a curing agent and a curing accelerator includes a combination of an acid anhydride and one or more of a tertiary amine and a tertiary amine salt, and a combination of dicyandiamide and one or more of a tertiary amine and a tertiary amine salt. and phenolic resins with one or more of tertiary amines and tertiary amine salts. One or more of tertiary amines and tertiary amine salts and one or more of phosphines and phosphonium salts may be used in combination. That is, the epoxy resin contains a unit skeleton derived from an acid anhydride as a curing agent as a unit skeleton of the epoxy resin, and the resin composition contains at least one of a tertiary amine and a tertiary amine salt as a curing accelerator. preferably include one.

According to such a combination, the polymerization reaction can proceed in a short period of time even when curing at normal temperature or at low temperature, and a resin composition having high heat resistance can be obtained. Further, with such a combination, the dilution of the hydrogen density by the curing agent or curing accelerator can be reduced by adjusting the compounding ratio of the curing agent or by selecting a type with a large number of hydrogen atoms.

The content ratio of the unit skeleton derived from the main agent and the unit skeleton derived from the curing agent (usually corresponding to the usage ratio of the main agent and the curing agent) is 0.7 in terms of the equivalent ratio between the epoxy equivalent and the active hydrogen equivalent. It is preferable to mix in the range of 1.3 or less. The equivalent ratio is more preferably 0.8 or more and 1.2 or less, still more preferably 0.9 or more and 1.1 or less. Within such a range, the amount of unreacted epoxy compound and curing agent remaining in the resin composition after the polymerization reaction is reduced. Therefore, it is possible to suppress the hydrogen density from decreasing due to the vaporization of the unreacted epoxy compound and the curing agent. The amount of the curing accelerator that mainly acts as a catalyst can be appropriately adjusted according to the type, curing conditions, and the like.

Flame retardants are also called refractory materials. One kind of flame retardant may be used, or two or more kinds thereof may be used. The flame retardant is included in the resin composition in a proportion of 40% by mass or more, preferably 45% by mass or less, and the upper limit is 60% by mass or less, preferably 55% by mass or less. When the content of the flame retardant is 40% by mass or more, the heat resistance of the neutron shielding material 6A can be improved. On the other hand, when the content of the flame retardant is 60% by mass or less, it is possible to suppress excessive reduction of other components (epoxy resin, etc.) in the resin composition, and the neutron shielding ability of the medieval shielding material 6A is improved. I can do it.

The flame retardant is preferably at least one of magnesium hydroxide, aluminum hydroxide, calcium hydroxide, ammonium polyphosphate, inorganic phosphoric acid compound, phosphoric acid ester, hexabromobenzene, or tetrabromobisphenol A. Among others, at least one of hydroxyl-containing flame retardants such as aluminum hydroxide, calcium hydroxide, ammonium polyphosphate, inorganic phosphoric acid compounds, and tetrabromobisphenol A is more preferable, and aluminum hydroxide is particularly preferable. By including a flame retardant containing a hydroxyl group, the hydrogen density of the neutron shielding material 6A can be increased, and the heat resistance of the neutron shielding material 6A can be improved.

The flame retardant is preferably a particulate flame retardant. The average particle size of the flame retardant measured by a laser diffraction scattering method is, for example, 0.2 μm or more, preferably 0.5 μm or more, and the upper limit thereof is, for example, 10 μm or less, preferably 7 μm or less. Among these, by setting the average particle diameter to, for example, 0.5 μm or more, the viscosity of the mixed solution of the epoxy resin and the curing agent can be reduced, and heat curing during the stirring process can be suppressed. In addition, molding becomes easier. On the other hand, by setting the average particle size to, for example, 7 μm or less, the flame retardancy can be improved without excessively increasing the viscosity.

Moreover, the particle size distribution of the flame retardant measured based on the laser diffraction scattering method is preferably a unimodal distribution. In the case of a bimodal distribution, the amount of the flame retardant outside the preferred range tends to increase. However, by adopting a unimodal distribution, it is possible to improve the heat resistance of the medieval shielding agent 6A while maintaining the fluidity of the resin composition within an appropriate range.

The resin composition preferably contains a neutron absorber. As the neutron absorbing material, an appropriate material having a large neutron absorption cross section can be used as long as it does not impair the mechanical properties of the epoxy resin and is chemically stable. One type of neutron absorbing material may be used, or two or more types may be used. The neutron absorbing material may not be blended depending on the application of the neutron shielding material, usage conditions, usage environment, and the like.

Examples of neutron absorbers include boron compounds such as boron carbide, boron nitride, boric anhydride, metaboric acid, and perovskite, elemental metals such as cadmium, gadolinium, and samarium, and compounds such as oxides containing these elements. mentioned.

Preferably, the neutron absorber is at least one of boron carbide and boron nitride. These neutron absorbing materials hardly react with curing agents such as epoxy compounds and acid anhydrides, and flame retardants such as magnesium hydroxide, even when high-temperature curing is performed. Therefore, the neutron shielding performance can be further improved without significantly deteriorating the mechanical properties, hydrogen density, heat resistance, and the like.

The neutron absorbing material is preferably added in an amount of 0.1% by mass or more and 10% by mass or less based on the neutron shielding material. With such a compounding amount, neutrons can be efficiently absorbed without greatly impairing the moderation performance of the neutron shielding material 6A, the kneadability of the resin composition, and the like.

The neutron shielding material 6A preferably has a hydrogen density of 5×10 ²² /cm ³ or more. Further, it is preferable that the mass loss rate when exposed to a high temperature of 190° C. for 200 hours is 0.5% or less. The mass depletion rate can be measured according to the method described in Examples below. Generally, the maximum operating temperature of the storage container 10 such as a dry cask is assumed to be about 170°C or higher and 200°C or lower. If the neutron shielding material 6 has such a mass depletion rate, it is possible to sufficiently suppress thermal aging in the operating temperature range of the storage container 10 while maintaining a high neutron shielding ability.

Furthermore, the oxygen index of the neutron shielding material 6A is preferably 26 or more. When the oxygen index is 26 or more, particularly good heat resistance can be achieved. The oxygen index can be measured according to the method described in Examples below.

The neutron shielding material 6A can be applied to, for example, the storage container 10 as well as the radiation shielding portion of containers for storing and transporting radioactive substances, such as radioactive substance transport containers, radioactive substance storage containers, and nuclear reactor vessels. It can also be applied to radiation shielding units installed in radioactive material handling facilities such as nuclear fuel reprocessing facilities, spent nuclear fuel storage facilities, accelerator facilities and the like.

(b) When the epoxy resin contains a unit skeleton derived from a hydrogenated epoxy main agent containing three or more epoxy groups in the molecule The neutron shielding material 6B, like the neutron shielding material 6A, contains an epoxy resin as a main component (e.g. 50% by mass or more). However, the epoxy resin constituting the neutron shielding material 6B includes a unit skeleton derived from a hydrogenated epoxy main agent (polyfunctional hydrogenated epoxy main agent) containing three or more epoxy groups in the molecule. The "polyfunctional hydrogenated epoxy main agent" used herein contains three or more epoxy groups, usually four or less, in the molecule. The polyfunctional hydrogenated epoxy main agent may be either a low-molecular-weight epoxy (epoxy compound), a high-molecular-weight epoxy (epoxy resin prepolymer), or the like, and may be of one type or two or more types.

By including three or more epoxy groups, the glass transition temperature of the epoxy resin can be increased, the amount of unreacted epoxy compound or epoxy resin remaining can be reduced, and the molecular weight and crosslink density can be increased. Therefore, even in a high-temperature environment such as dry storage where the fuel assembly continues to generate heat, it is possible to suppress the decrease in hydrogen density due to vaporization or the generation of non-shielded portions due to deformation of the neutron shielding material. As a result, it is possible to obtain the neutron shielding material 6B which has higher heat resistance and whose neutron shielding performance is less likely to deteriorate even in a high temperature environment.

The neutron shielding material 6B will be described below, focusing on the differences from the neutron shielding material 6A described above, and the description of the common points will be omitted. Therefore, even if the items are not described below, the same items as those described for the neutron shielding material 6A can be applied to the neutron shielding material 6B within the range that does not significantly impair the effects of the present invention.

As the polyfunctional hydrogenated epoxy main agent forming the unit skeleton, water of at least one epoxy compound selected from a glycidyl ether type epoxy compound, a glycidyl ester type epoxy compound, a glycidyl amine type epoxy compound, and an alicyclic type epoxy compound. A polyfunctional hydrogenated epoxy compound as an additive is preferred. As the polyfunctional hydrogenated epoxy main agent, resins (prepolymers) that are polymers of these compounds are also preferable.

Examples of polyfunctional hydrogenated epoxy resins include glycidyl ether-type epoxy resins, glycidyl ester-type epoxy resins, glycidyl amine-type epoxy resins, alicyclic epoxy resins, phenol, and phenol, all of which are hydrogenated products and are polymers of epoxy compounds. Hydrogenated products of epoxy resins, such as resin-type epoxy resins, which are modified products of these epoxy resins and correspond to prepolymers, can be mentioned.

As polyfunctional glycidyl ether type epoxy compounds, all of them are hydrogenated products, and examples thereof include cyanuric acid triglycidyl ether, tris(4-hydroxyphenyl)methane triglycidyl ether, 1,1,1-tris(4- hydroxyphenyl)ethane triglycidyl ether, 1,1,1-tris(4-hydroxyphenyl)propane triglycidyl ether, 1,1,2,2-tetra(p-hydroxyphenyl)ethane tetraglycidyl ether, and derivatives thereof etc.

Polyfunctional glycidyl ether type epoxy resins are all hydrogenated products, for example, brominated epoxy resins (brominated phenol novolak type epoxy resins), which are polymers of polyfunctional epoxy compounds, bisphenol A type epoxy Resin, bisphenol F type epoxy resin, biphenyl type epoxy resin, naphthalene type epoxy resin, dicyclopentadiene type epoxy resin, trisphenolmethane type epoxy resin, phenol resin type epoxy resin, cresol novolac type epoxy resin, phenol-biphenylene type epoxy resin etc. Among these, polyfunctional glycidyl ether type epoxy resins include brominated epoxy, cresol novolac type epoxy, trisphenolmethane type epoxy, dicyclopentadiene type epoxy, naphthalene type epoxy (1,1-bis(2,7- Diglycidyloxy-1-naphthyl)methane) or at least one of phenol-biphenylene type epoxy is preferred.

Examples of the phenolic resin-type epoxy resins include hydrogenated products such as phenol novolac, which is a polymer of phenols and aldehydes, cresol novolac, which is a polymer of cresol and aldehydes, xylylene group, xylylene novolak into which a 1,3-xylylene group or 1,4-xylylene group is introduced, bisphenol A novolac which is a polymer of bisphenol A and aldehydes, polymerization of phenols, salicylaldehyde and hydroxybenzaldehyde Phenolic resins such as triphenylmethane novolak, biphenyl novolak modified with biphenyls, dicyclopentadiene phenol novolac modified with dicyclopentadienes, and terpenephenol novolac modified with terpenes are reacted with epichlorohydrin, etc. and epoxidized epoxy resins.

As the polyfunctional glycidyl ester type epoxy compounds, all of them are hydrogenated products, and examples thereof include 1,2,4-benzenetricarboxylic acid triglycidyl ester, 1,3,5-benzenetricarboxylic acid triglycidyl ester, and trimellit. Acid glycidyl esters, pyromellitic acid glycidyl esters, and derivatives thereof.

As polyfunctional glycidyl ester type epoxy resins, for example, cyclic polyfunctional glycidyl ester type epoxy resins, which are both hydrogenated products and polymers such as allyl esters of epoxy compounds, are preferable.

As polyfunctional glycidylamine type epoxy compounds, all of them are hydrogenated products such as 1,3-phenylenebis(N,N-diglycidylmethanamine), 4,4′-methylenebis[N,N- bis(oxiranylmethyl)aniline], N,N,N'-triglycidyl-4,4'-diaminodiphenylmethane, N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenylmethane, N , N,N′,N′-tetraglycidyl-1,3-benzenedi(methanamine), N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenyl ether, triglycidyl-p-aminophenol, triglycidyl-m-aminophenol, triglycidyl-p-aminocresol, triglycidyl isocyanurate, N,N-diglycidyl-4-glycidylaniline, N,N-diglycidyl-4-oxiranyloxyaniline, N,N- Examples include bis(2,3-epoxypropyl)-4-(2,3-epoxypropoxy)aniline and derivatives thereof. Among these, glycidylamine type epoxy compounds include 4,4′-methylenebis[N,N-bis(oxiranylmethyl)aniline], triglycidyl-p-aminophenol, triglycidyl-m-aminophenol, tri at least one of glycidyl-p-aminocresol, N,N,N',N'-tetraglycidyl-1,3-benzenedi(methanamine) and 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane one is preferred.

Polyfunctional glycidylamine epoxy resins include, for example, aromatic amine epoxy resins, aminophenol epoxy resins, and aliphatic amine epoxy resins, all of which are hydrogenated products and are polymers such as polyfunctional epoxy compounds. At least one of resins is preferred.

As the alicyclic epoxy compound, for example, a hydrogenated product of an oligomer-type alicyclic epoxy resin, which is a polymer such as an allyl ester of epoxycyclohexanecarboxylic acid, is preferable.

As the polyfunctional hydrogenated epoxy main agent, those which are liquid and whose cured products have a high glass transition temperature are particularly desirable in order to achieve both high heat resistance and good manufacturability required for the neutron shielding material 6B. As such a polyfunctional hydrogenated epoxy base material, for example, among glycidylamine type epoxy compounds and resins (prepolymers), which are both hydrogenated products, compounds and resins that are liquid and have a benzene ring in the molecule are used. preferable. Glycidylamine-type epoxy compounds and resins do not have repeating units in their molecules, so they have relatively small molecular weights and tend to be liquid. Further, 4,4′-methylenebis[N,N-bis(oxiranylmethyl)aniline] which is an aromatic amine type epoxy compound, triglycidyl-p-aminophenol which is an aminophenol type epoxy compound, or triglycidyl- Preferred are m-aminophenol, triglycidyl-p-aminocresol, and N,N,N',N'-tetraglycidyl-1,3-benzenedi(methanamine), which is an aliphatic amine type epoxy compound.

The epoxy resin contains a unit skeleton derived from one or more epoxy compounds selected from hydrogenated bisphenol A diglycidyl ether and hydrogenated bisphenol F diglycidyl ether, in addition to a unit skeleton derived from a polyfunctional hydrogenated epoxy base material. is preferred. Among these, hydrogenated bisphenol A diglycidyl ether is particularly preferable in that higher hydrogen density can be obtained.

The epoxy resin, in addition to the unit skeleton derived from the polyfunctional hydrogenated epoxy main agent, further, other epoxy compounds and resins, such as bifunctional epoxy compounds, units derived from bifunctional epoxy resin polymer of bifunctional epoxy compounds. It may contain one or more skeletons. For example, when a bisphenol-type epoxy compound that is not hydrogenated at the nucleus, a prepolymer that is a polymer of the epoxy compound, or the like is used in combination, it may be possible to adjust the viscosity of the resin composition and improve the strength, toughness, etc. of the resin composition. .

Other bifunctional epoxy compounds and bifunctional epoxy resins include, for example, bisphenol A type epoxy compounds, bisphenol A type epoxy resins, bisphenol F type epoxy compounds, bisphenol F type epoxy resins, glycidyl ether type epoxy compounds, glycidyl ether type epoxy compounds. Resin, glycidyl ester type epoxy compound, glycidyl ester type epoxy resin, glycidylamine type epoxy compound, glycidylamine type epoxy resin, alicyclic epoxy compound, alicyclic epoxy resin, biphenyl type epoxy compound, biphenyl type epoxy resin, naphthalene type Epoxy compounds, naphthalene-type epoxy resins, derivatives of these epoxy compounds, modified products of epoxy resins, and the like can be used in combination.

Examples of bifunctional glycidyl ether type epoxy compounds include tetrabromobisphenol A diglycidyl ether, bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, 4,4′-biphenyldiyl bis (glycidyl ether), naphthalenediyl bis ( glycidyl ether), dicyclopentadiene diglycidyl ether, hydroquinone diglycidyl ether, resorcinol diglycidyl ether, cyclohexanediol diglycidyl ether, biphenol diglycidyl ether, diglycidylphenyl glycidyl ether, 4,4′-dihydroxybenzophenone diglycidyl ether, etc. Derivatives of these and the like are included.

Examples of bifunctional glycidyl ether type epoxy resins include brominated epoxy resins, bisphenol A type epoxy resins, bisphenol F type epoxy resins, biphenyl type epoxy resins, naphthalene type epoxy resins, di A cyclopentadiene type epoxy resin and the like can be mentioned.

Examples of bifunctional glycidyl ester type epoxy compounds include diglycidyl phthalate, diglycidyl isophthalate, diglycidyl terephthalate, diglycidyl tetrahydrophthalate, diglycidyl hexahydrophthalate, and dicyclohexanedicarboxylic acid. Examples thereof include glycidyl esters, diglycidyl naphthalene dicarboxylic acid esters, and derivatives thereof.

Examples of bifunctional glycidyl ester type epoxy resins include glycidyl ester type epoxy resins that are polymers of these epoxy compounds.

Examples of bifunctional glycidylamine type epoxy compounds include N,N-diglycidylaniline, N,N-diglycidyltoluidine, diglycidylaminophenol, diglycidylaminocresol, N,N-diglycidyl-4-phenoxyaniline, Derivatives thereof such as diglycidylpiperazine and the like are included.

Examples of bifunctional glycidylamine epoxy resins include aromatic amine epoxy resins, aminophenol epoxy resins, and aliphatic amine epoxy resins, which are polymers of these epoxy compounds.

Examples of bifunctional alicyclic epoxy compounds include 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate, 3,4-epoxy-6methyl-cyclohexylmethyl-3′,4′- Epoxy-6-methyl-cyclohexanecarboxylate, bis(3,4-epoxycyclohexylmethyl)adipate, bis(3,4-epoxy-6-methyl-cyclohexylmethyl)adipate, ethyleneoxy-3,4-epoxycyclohexane, bis carboxylate (3,4-epoxycyclohexan-1-ylmethyl)ester, 1,1′-bi(2,3-epoxycyclohexane), 4,4′-bi(1,2-epoxycyclohexane), limonene diepoxide, dicyclo Examples include pentadiene diepoxide, 1,4-cyclohexadiene diepoxide, 4-vinylcyclohexane diepoxide, 1,5-cyclooctadiene diepoxide, and derivatives thereof.

Examples of bifunctional alicyclic epoxy resins include alicyclic epoxy resins that are polymers of these epoxy compounds.

The epoxy resin contained in the neutron shielding material 6B may contain a unit skeleton derived from a curing agent.

The unit skeleton derived from the curing agent is preferably a unit skeleton derived from at least one of acid anhydride, dicyandiamide, and phenol resin. Since these do not have an imidazole structure, unlike imidazole compounds having nitrogen atoms at the 1 and 3 positions of the 5-membered ring, active sites are less likely to remain after curing. Therefore, even if the neutron shielding material 6B is exposed to a high temperature of, for example, 150° C. or higher and 300° C. or lower, the reaction activity does not significantly increase, and the thermal decomposition of the epoxy resin or the like present in the cured product is reduced. . Therefore, it is possible to obtain the neutron shielding material 6B with high heat resistance that exhibits higher resistance to heat aging.

Examples of acid anhydrides include tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methylnadic anhydride, hydrogenated methylnadic anhydride, and trialkyltetrahydrophthalic anhydride. Acid, methylcyclohexene tetracarboxylic dianhydride, phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, benzophenone tetracarboxylic dianhydride, ethylene glycol bisanhydro trimellitate, dodecenyl succinic anhydride, maleic anhydride , succinic anhydride, chlorendic anhydride, methyl-3,6-endomethylene-1,2,3,6-tetrahydrophthalic anhydride and the like. The acid anhydride is preferably used in combination with another curing accelerator that accelerates the polymerization reaction. The use of an acid anhydride makes it possible to obtain the neutron shielding material 6B with a relatively high glass transition point and heat resistance at a relatively low cost.

Dicyandiamide may be used alone or in combination with other curing accelerators that accelerate the polymerization reaction. When dicyandiamide is used, the usable life of the resin composition is relatively long, and it is easy to obtain an epoxy resin having high mechanical strength. In addition, since it reacts at a high temperature of about 180° C. or higher, the heat resistance of the neutron shielding material 6B can be improved by performing heat curing at a temperature higher than room temperature.

Examples of phenolic resins include phenol novolak, cresol novolak, naphthol novolak, xylylene novolak, bisphenol A novolak, bisphenol F novolak, triphenylmethane novolak, biphenyl novolak, dicyclopentadiene novolak, and terpene phenol novolak. As a phenol resin, only 1 type may be used and multiple types may be used together. Phenol resin is a polymer obtained by polymerizing phenol or a nucleus-substituted phenol derivative, a compound having a ring structure that serves as a cross-linking group, and aldehydes such as formaldehyde, acetaldehyde, benzaldehyde, and salicylaldehyde in the presence of an acid catalyst. is.

The phenol resin is preferably used in combination with another curing accelerator that accelerates the polymerization reaction. When non-hydrogenated phenolic resin is used, a rigid ring structure is introduced, so that the heat resistance and mechanical strength of the neutron shielding material 6B can be improved. As the phenol resin, a resin having high hydrogen density and high rigidity is preferable, and phenol novolak is particularly preferable.

In the neutron shielding material 6B, the resin composition may contain a curing accelerator. The resin composition preferably contains at least one curing accelerator selected from imidazoles, imidazole salts, phosphines, phosphonium salts, tertiary amines, and tertiary amine salts. Among them, it is more preferable to use one or more of phosphines, phosphonium salts, tertiary amines, and tertiary amine salts. Since these do not have an imidazole structure, unlike imidazole compounds having nitrogen atoms at the 1 and 3 positions of the 5-membered ring, active sites are less likely to remain after curing. Therefore, even if the neutron shielding material 6B is exposed to a high temperature of, for example, 150° C. or higher and 300° C. or lower, the reaction activity does not significantly increase, and the thermal decomposition of the epoxy resin or the like present in the cured product is reduced. . Therefore, the neutron shielding material 6B exhibiting high resistance to heat aging can be obtained.

Examples of imidazoles and imidazole salts include 2-ethyl-4-methylimidazole and salts thereof.

Phosphines and phosphonium salts include, for example, phosphine, triphenylphosphine, hydrochlorides, hydrobromides and organic acid salts thereof, tetra-n-butylphosphonium tetraphenylborate and the like. Phosphines and phosphonium salts may be used in combination with other curing agents that form crosslinks. When phosphines and phosphonium salts are used, the amount to be added can be suppressed as compared with other compounds that cause addition reactions, so the hydrogen density of the neutron shielding material 6B can be easily improved.

Examples of tertiary amines and tertiary amine salts include 2,4,6-tris(dimethylaminomethyl)phenol, 2,3,4-tris(dimethylaminomethyl)phenol, 2,4,5-tris(dimethyl aminomethyl)phenol, N-benzyldimethylamine, 1,8-diazabicyclo[5.4.0]-7-undecene, hydrochlorides and organic acid salts thereof. Tertiary amines and tertiary amine salts may be used in combination with other curing agents that form crosslinks. The use of a tertiary amine and a tertiary amine salt makes it possible to suppress the compounding amount compared to other compounds that cause an addition reaction, thus facilitating the improvement of the hydrogen density of the neutron shielding material 6B. In addition, since it tends to be active at high temperatures, the heat resistance of the neutron shielding material 6B can be further improved by performing heat curing at a temperature higher than room temperature.

A combination of a curing agent and a curing accelerator includes a combination of an acid anhydride with one or more of tertiary amines and tertiary amine salts, and a combination of an acid anhydride with one or more of phosphines and phosphonium salts. combinations, combinations of acid anhydrides with imidazoles and one or more of imidazole salts, combinations of dicyandiamide with tertiary amines and one or more of tertiary amine salts, dicyandiamide with phosphines and phosphonium salts combinations of dicyandiamide with one or more of imidazoles and imidazole salts; combinations of phenolic resins with one or more of tertiary amines and tertiary amine salts; phenolic resins and phosphines and one or more of phosphonium salts, and phenolic resins with one or more of imidazoles and imidazole salts are preferred.

According to such a combination, the polymerization reaction can proceed in a short period of time even when curing at normal temperature or at low temperature, and a cured product with high heat resistance can be obtained. Further, with such a combination, the dilution of the hydrogen density by the curing agent or curing accelerator can be reduced by adjusting the compounding ratio of the curing agent or by selecting a type with a large number of hydrogen atoms.

As a combination of the curing agent and the curing accelerator, it is preferable to use one or more of tertiary amine and tertiary amine salt, and acid anhydride and tertiary amine and one or more of tertiary amine salt A combination is more preferred. Acid anhydrides include tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methylnadic anhydride, hydrogenated methylnadic anhydride, trialkyltetrahydrophthalic anhydride, one of methylcyclohexenetetracarboxylic dianhydride, phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, benzophenone tetracarboxylic dianhydride, ethylene glycol bisanhydrotrimellitate, and dodecenyl succinic anhydride The above are particularly preferred. As the tertiary amine and tertiary amine salt, tris(dimethylaminomethyl)phenol or a salt thereof is particularly preferred.

With such a combination, the cost of raw materials is reduced, and a resin composition that is easily cured at room temperature can be obtained. In addition, unlike the case of using an imidazole compound, even when the neutron shielding material 6B is exposed to high temperatures, thermal decomposition of the components present in the cured product is reduced, so high heat resistance can be obtained. .

The epoxy resin may not contain a unit skeleton derived from a curing agent, and the resin composition may not contain a curing accelerator. For example, when the reactivity of polyfunctional epoxy is particularly high, depending on the type of main agent, the application of the neutron shielding material 6B, the usage conditions, the usage environment, etc., a resin composition containing an epoxy resin can be used without using a curing agent or a curing accelerator. can form objects. In such a case, it is possible to reduce the dilution of the hydrogen density by the curing agent or curing accelerator and obtain good neutron shielding performance. For example, polyfunctional hydrogenated epoxy compounds have three or more epoxy groups in the molecule, and are therefore highly reactive. Therefore, the resin composition can be produced without using a curing agent such as an acid anhydride. As a result, even curing accelerators that can decompose the curing agent by reaction with the curing agent can be used.

The content ratio of the unit skeleton derived from the main agent and the unit skeleton derived from the curing agent can be set in the same manner as in the neutron shielding material 6A. Also, the flame retardant and neutron absorber can be used in the same manner as the neutron absorber 6A.

(Manufacturing method of neutron shielding material 6)
FIG. 2 is a flow chart showing a method for manufacturing the neutron shielding material 6 of this embodiment. The illustrated example is composed of a resin composition containing a flame retardant and an epoxy resin. The present invention relates to a method for manufacturing a neutron shielding material 6 containing at a ratio of 60% by mass or more. The method for manufacturing the neutron shielding material 6 includes an epoxy reaction liquid preparation step S1, an addition step S2, a molding step S3, and a curing step S4.

The epoxy reaction liquid preparation step S1 prepares an epoxy reaction liquid containing at least a hydrogenated epoxy main agent (main agent: bifunctional hydrogenated epoxy main agent or multifunctional hydrogenated epoxy main agent). In the illustrated example, a curing agent and a curing accelerator are used, and the epoxy reaction liquid is prepared by mixing the main agent, the curing agent and the curing accelerator. However, if either one of the curing agent and the curing accelerator is not used, only the one to be used may be mixed with the hydrogenated epoxy main agent. When neither a curing agent nor a curing accelerator is used, the epoxy reaction liquid is composed of a hydrogenated epoxy base.

Mixing can be done using any solvent. The mixing ratio of the hydrogenated epoxy main agent and the curing agent is not particularly limited, and may be appropriately determined according to the molecular weight of the desired epoxy resin, the ratio of the constituent skeletons, and the like. Polymerization of at least the hydrogenated epoxy main agent is initiated in the epoxy reaction liquid by the epoxy reaction liquid preparation step S1.

In the addition step S2, a raw material mixed liquid of a resin composition is obtained by adding a flame retardant to the epoxy reaction liquid so that the final concentration is 40% by mass or more and 60% by mass or less. In the illustrated example, a neutron absorber is also added. After addition, mixing is performed as necessary. The above resin composition is obtained by curing the raw material mixture. The adding step S2 is preferably performed while the epoxy reaction liquid has fluidity.

By first mixing the hydrogenated epoxy main agent and the curing agent and then mixing the flame retardant, it is possible to prevent the flame retardant from being coated with the curing agent. Therefore, uneven distribution of the flame retardant in the epoxy resin can be suppressed, and the curing agent can be dispersed throughout the epoxy resin. In addition, when the flame retardant contains a hydroxyl group, even if water is released from the flame retardant when the neutron shielding material 6 is exposed to high temperatures, an excessive increase in internal pressure inside the curing agent due to the coating of the curing agent is suppressed. can. By suppressing an excessive increase in internal pressure inside the curing agent, it is possible to suppress the decomposition of the neutron shielding material 6 at low temperatures and improve the heat resistance.

The forming step S3 forms the raw material mixture into a desired shape. Specifically, for example, the neutron shielding material 6 can be molded by filling the space surrounding the inner cylinder 2 with the raw material mixed liquid and performing normal temperature curing or heat curing. Alternatively, a molding die may be filled with the raw material mixed liquid, cured at room temperature or cured by heating into a predetermined shape, and the molded cured product may be placed in the space surrounding the inner cylinder 2 .

The raw material mixture to be filled is preferably in a state in which polymerization has progressed to the extent that it has a viscosity that allows filling. For example, if the viscosity is 60,000 mPa·s or less (measured at 25° C., hereinafter the same), preferably 40,000 mPa·s or less, filling of the raw material mixture becomes easy. On the other hand, if the viscosity is, for example, 1000 mPa·s or more, the flame retardant and the neutron absorbent can be easily dispersed throughout the raw material mixture.

The curing step S4 obtains the neutron shielding material 6 containing the epoxy resin by curing (that is, polymerizing) at least the hydrogenated epoxy main agent in the raw material mixture.

The curing reaction can be carried out at an appropriate temperature depending on the application of the neutron shielding material 6, usage conditions, usage environment, and the like. As the curing temperature, for example, any of a low temperature range of 5° C. to less than 50° C., a medium temperature range of 50° C. to less than 80° C., and a high temperature range of 80° C. to 200° C. can be used. When the curing temperature is normal temperature, the heating cost and the dimensional change of the cured product can be reduced, but the higher the curing temperature, the higher the heat resistance of the epoxy resin tends to be.

When curing at a temperature higher than room temperature, for example, heating is performed at 50° C. or higher and 200° C. or lower, preferably 130° C. or higher and 170° C. or lower, for 1 hour or longer and 12 hours or shorter, preferably 1 hour or longer and 3 hours or shorter. . In addition, it is more preferable to carry out the curing step by step from the viewpoint of reducing thermal strain and achieving uniform curing. For example, two-stage heating of primary heating at 80° C. to 130° C. for 2 hours to 4 hours and secondary heating at 140° C. to 170° C. for 4 hours to 12 hours, at room temperature for 1 day or more. It is preferable to carry out three-stage heating including primary heating for about 7 days, secondary heating at 120° C. or higher and 150° C. or lower, and tertiary heating at 180° C. or higher and 200° C. or lower, or equivalent heating.

The neutron shielding material 6, the storage container 10, and the method of manufacturing the neutron shielding agent have been described above. included. For example, the above embodiments are not necessarily limited to having all the configurations described. It is also possible to replace part of the configuration of the embodiment with another configuration, or add another configuration to the configuration of the embodiment. Moreover, it is also possible to add other configurations, delete configurations, and replace configurations with respect to a part of the configurations of the embodiments.

EXAMPLES The present invention will be specifically described below by showing examples, but the technical scope of the present invention is not limited to these.

Neutron shielding materials (including neutron shielding materials 6A and 6B according to Examples) according to Examples (Tables 1 to 5) and Comparative Examples (Table 6) using raw materials in the combinations shown in Tables 1 to 6 The performance of the neutron shielding material was evaluated. All of the resins used as raw materials are prepolymers. A detailed description of Tables 1 to 6 will be given later together with the evaluation results.

<Production of neutron shielding material 6A>
As the main agent (hydrogenated epoxy main agent), either hydrogenated bisphenol A diglycidyl ether (hydrogenated BADGE) or hydrogenated bisphenol F diglycidyl ether (hydrogenated BFDGE), or these and other epoxy resins (EP) was used.

Acid anhydrides, phenol novolacs, or dicyandiamides were used as curing agents. Acid anhydrides include tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, hydrogenated methylnadic anhydride, trialkyltetrahydrophthalic anhydride (TATHPA), and methyl Either nadic anhydride was used. The blending amount of the curing agent was set so that the epoxy equivalent and the active hydrogen equivalent would be 1:1.

As the curing accelerator, a non-imidazole compound (when an acid anhydride is used as a curing agent) or an imidazole compound was used. Examples of non-imidazole compounds include phosphine, triphenylphosphine, tetra-n-butylphosphonium tetraphenylborate (PX4PB), N-benzyldimethylamine, 1,8-diazabicyclo[5.4.0]-7-undecene (DBU ), and 2,4,6-tris(dimethylaminomethyl)phenol (DMP30) were used. 2-Ethyl-4-methylimidazole (2E4MZ) was used as the imidazole compound. The amount of the curing accelerator compounded was 4 parts by mass with respect to 100 parts by mass of the main agent.

Granular aluminum hydroxide was used as the flame retardant. It was confirmed that the flame retardant had a unimodal particle size distribution measured by a laser diffraction scattering method. In addition, the average particle size of each flame retardant was 0.5 μm or more and 7 μm or less, and the average particle sizes shown in Tables 1 to 6 were used. The blending amount of the flame retardant was 50 parts by mass with respect to 100 parts by mass of the resin composition.

Particles of either boron nitride or boron carbide were used as neutron absorbers. The blending amount of the neutron absorber was 4 parts by mass with respect to 100 parts by mass of the resin composition.

The neutron shielding material 6A was produced by the following procedure. First, the main agent, the curing agent and the curing accelerator were weighed so as to have predetermined compounding amounts, and these components were mixed (kneaded) using a planetary mixer. Then, the flame retardant and the neutron shielding material were added so as to have a predetermined blending amount, and the mixture was further kneaded to obtain a raw material mixed liquid in which the flame retardant and the neutron shielding material were mixed. The obtained raw material mixed liquid was subjected to the viscosity measurement described later.

This raw material mixture was filled in a SUS pipe with a diameter of 20 mm and a length of 100 mm for measuring the mass of thermal deterioration. For oxygen index measurement, a strip-shaped mold with a thickness of 4 mm, a width of 10 mm, and a length of 100 mm was filled. The neutron shielding material 6A was obtained by curing the raw material mixture by standing at room temperature of 20° C. to 25° C. respectively.

<Production of neutron shielding material 6B>
As the main agent (hydrogenated epoxy main agent), a combination of either hydrogenated bisphenol A diglycidyl ether (hydrogenated BADGE) or hydrogenated bisphenol F diglycidyl ether (hydrogenated BFDGE) and a polyfunctional epoxy compound or resin, Alternatively, only hydrogenated bisphenol A diglycidyl ether was used. A glycidyl ether type epoxy resin, a glycidyl amine type epoxy compound, or an alicyclic type epoxy compound was used as the polyfunctional epoxy compound or resin. In addition, polyfunctional epoxy compounds or resins include bisphenol F type epoxy resin, polyfunctional epoxy resin, novolac type epoxy resin, bisphenol A type epoxy resin, cyclic polyfunctional glycidyl ester type epoxy resin, and diaminodiphenylmethane type epoxy resin. Using.

Among polyfunctional epoxy compounds or resins, glycidyl ether-type epoxy resins include brominated phenol novolac-type epoxy resins, cresol novolak-type epoxy resins, trisphenolmethane-type epoxy resins, dicyclopentadiene-type epoxy resins, 1,1-bis(2,7-diglycidyloxy-1-naphthyl)methane, which is a naphthalene type epoxy resin, and a phenol-biphenylene type epoxy resin were used.

Among polyfunctional epoxy compounds or resins, glycidylamine-type epoxy compounds include 4,4′-methylenebis[N,N-bis(oxiranylmethyl)aniline], which are aromatic amine-type epoxies, and aminophenol-type epoxy compounds. triglycidyl-p-aminophenol as epoxy (1), triglycidyl-m-aminophenol as aminophenol type epoxy (2), triglycidyl-p-aminocresol as aminophenol type epoxy (3), aliphatic 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane as amine type epoxy (1), N,N,N',N'-tetraglycidyl-1 as aliphatic amine type epoxy (2), 3-benzenedi(methanamine) was used.

Moreover, among polyfunctional epoxy compounds or resins, an oligomer type alicyclic epoxy resin was used as the alicyclic epoxy resin.

As a curing agent, either methylhexahydrophthalic anhydride or methylnadic anhydride (MNA) was used. In Examples 57 to 69 shown in Table 4, 2-ethyl-4-methylimidazole (2E4MZ) was used as a curing agent as an imidazole compound having an action as a catalytic curing agent, and a curing accelerator was used. was not used. The blending amount of the curing agent was set to 5 parts by mass with respect to 100 parts by mass of the main agent. In Examples 70 to 82 listed in Table 5, 2,4,6-tris(dimethylaminomethyl)phenol (DMP30) was used as a curing agent as a tertiary amine acting as a catalytic curing agent. , no curing accelerator was used.

In other respects, the neutron shielding material 6B was produced in the same manner as the above "<neutron shielding material 6A>".

<Neutron shielding material according to comparative example>
In the same manner as in Example 2 except that non-hydrogenated "bisphenol A diglycidyl ether" was used instead of "hydrogenated bisphenol A diglycidyl ether" shown in Example 2 in Table 1, Table 6 A neutron shielding material according to Comparative Example 1 was produced. Further, in the same manner as in Example 24 except that non-hydrogenated "bisphenol F diglycidyl ether" was used instead of "hydrogenated bisphenol F diglycidyl ether" shown in Example 24 in Table 2, A neutron shielding material according to Comparative Example 2 of No. 6 was produced.

<Performance evaluation>
As performance evaluations, the viscosity of the raw material mixture, the oxygen index of the neutron shielding material, and the mass depletion rate of the neutron shielding material were evaluated.

The viscosity of the raw material mixture was evaluated according to JIS K 7117-1, "Plastics-liquid, emulsified or dispersed resin-measuring method of apparent viscosity by Brookfield rotational viscometer". The viscosity measurement temperature was 25°C.

The oxygen index of the neutron shielding material is an index of flame retardancy, and was evaluated according to the combustibility test method based on the oxygen index specified in JIS K 7201-2. An oxygen index of 26 or more is preferable in order to exhibit excellent flame retardancy.

The mass depletion rate of the neutron shielding material is an index showing how much it is degraded by heating, and was evaluated based on thermal degradation mass measurement. The thermal deterioration mass measurement of the neutron shielding material 6 was performed as follows. The neutron shielding material 6 prepared for thermal degradation mass measurement was taken out from the pipe, placed in a constant temperature bath at 190° C. and heated. After cooling for 200 hours of heating, the mass of the neutron shielding material 6 was measured. Based on the mass of the neutron shielding material 6 after heating, the mass loss rate after heating for 200 hours was obtained. The mass loss rate was calculated according to the following formula (1), where X ₀ is the mass before the heating test, and X _t is the mass after heating for 200 hours.
Mass loss rate (%)=(X ₀ −X _t )/X ₀ ×100 (1)

<Evaluation results>
The results of performance evaluation are shown in Tables 1 to 6 together with the combinations of raw materials used. In Tables 1 to 6, Example No. 22 to 43 and 57 to 82 are Reference Example Nos. 22 to 43 and 57 to 82. The same applies to the following description. In Tables 1 to 6, "EP" is an abbreviation for "epoxy resin". In Tables 1 to 6, the "viscosity" was evaluated as ◯ if the viscosity was 1000 mPa·s or more and 60000 mPa·s or less, and × otherwise. When the viscosity is 1000 mPa·s or more and 60000 mPa·s or less, the flame retardant and the neutron absorber can be dispersed throughout the raw material mixture, and the raw material mixture can be easily molded.

If the "oxygen index" was 26 or more, it was evaluated as ◯, and if it was less than 26, it was evaluated as x. If the oxygen index is 26 or higher, it is considered that a particularly large amount of oxygen is required to sustain combustion. For this reason, if the amount of oxygen is the same, it can be said that it is relatively difficult to burn, and it is considered to be flame retardant.

If the "mass loss rate" was 0.5% or less, it was evaluated as ◯, and if it exceeded 0.5%, it was evaluated as x. If the mass depletion rate is 0.5% or less, the mass hardly changes even when heated, and it can be said that thermal decomposition does not occur. Therefore, it can be considered that the heat resistance is good.

As shown in Tables 1 to 6, the epoxy resin constituting the neutron shielding material 6 contains a unit skeleton derived from a hydrogenated epoxy main agent containing two or more epoxy groups in the molecule, and the flame retardant is a neutron shielding All of the results of ◯ were obtained by containing at a rate of 40% by mass or more and 60% by mass or less with respect to the resin composition constituting the material 6. On the other hand, the neutron shielding materials of Comparative Examples 1 and 2 (see Table 6 for both) using a non-hydrogenated epoxy base resin had x in the oxygen coefficient and the mass depletion rate. Therefore, according to the present invention, it was found that the neutron shielding material 6 excellent in flame retardancy and heat resistance can be provided.

<Difference in oxygen index and viscosity due to amount of flame retardant>
Neutron of Example 6 except that the amount of the flame retardant was 20% by mass, 30% by mass, 40% by mass, 50% by mass, 55% by mass, 60% by mass, and 70% by mass with respect to the resin composition A neutron shielding material 6 was produced in the same manner as the shielding material 6 . The oxygen index of the produced neutron shielding material 6 and the viscosity of the raw material mixture of the neutron shielding material 6 were measured in the same manner as the neutron shielding material 6 of Example 6. The results are shown in FIGS. 3 and 4. FIG.

FIG. 3 is a graph showing the oxygen index with respect to the blending amount of the flame retardant. As described above, the blending amount of the flame retardant in the neutron shielding material 6 is 40% by mass or more and 60% by mass or less. As shown in FIG. 3, the oxygen index was able to be 26 or more when the blending amount of the flame retardant was 40% by mass or more. On the other hand, when the blending amount of the flame retardant was 20% by mass and 30% by mass (both of the blending amounts described in Patent Document 1 above), the oxygen index was less than 26, indicating poor flame retardancy. Therefore, it was found that the flame retardancy can be improved more than before by setting the blending amount of the flame retardant to 40% by mass or more.

Regarding the upper limit of the amount of the flame retardant compounded, if the purpose is simply to improve flame retardancy, the more the flame retardant, the better. However, the larger the amount of flame retardant compounded, the smaller the relative amount of the epoxy resin, which contributes to neutron shielding, and the neutron absorber, if included. As a result, the neutron shielding performance of the neutron shielding material 6 deteriorates. Therefore, the content of the flame retardant is set to 60% by mass or less from the viewpoint of maintaining sufficient neutron shielding ability. By doing so, the flame retardancy can be improved and the neutron shielding ability can be exhibited.

FIG. 4 is a graph showing the viscosity of the raw material mixture with respect to the blending amount of the flame retardant. As described above, the viscosity of the raw material mixture is preferably 1000 mPa·s or more and 60000 mPa·s or less from the viewpoint of ease of molding. Therefore, by setting the blending amount of the flame retardant to 40% by mass or more and 60% by mass or less, the viscosity of the raw material mixed liquid can be made 1000 mPa·s or more and 60000 mPa·s or less as shown in FIG. However, from the viewpoint of facilitating molding, the upper limit of the viscosity range of the raw material mixture is preferably 40000 mPa·s or less as described above. Therefore, by setting the content of the flame retardant to 55% by mass or less, the viscosity of the raw material mixture can be reduced to 40000 mPa·s or less, as shown in FIG. 4 .

<Difference in viscosity of raw material mixture and oxygen index due to average particle size of flame retardant>
A neutron shielding material 6 was produced in the same manner as the neutron shielding material 6 of Example 1 above, except that the flame retardant had an average particle size of 0.2 μm, 0.5 μm, 2 μm, 4 μm, 7 μm, 10 μm, and 12 μm. The oxygen index of the produced neutron shielding material 6 and the viscosity of the raw material mixture of the neutron shielding material 6 were measured in the same manner as for the neutron shielding material 6 of Example 1 above. The results are shown in FIGS. 5 and 6. FIG.

FIG. 5 is a graph showing the oxygen index versus the average particle size of flame retardants. As described above, the average particle size of the flame retardant is preferably 0.5 μm or more and 7 μm or less. As shown in FIG. 5, when the average particle size of the flame retardant is 7 μm or less, the oxygen index can be increased to 26 or more. Therefore, it was found that the flame retardancy can be improved by setting the average particle size of the flame retardant to 7 μm or less.

FIG. 6 is a graph showing the viscosity of the raw material mixture with respect to the average particle size of the flame retardant. The viscosity of the raw material mixture is preferably 1000 mPa·s or more and 60000 mPa·s or less. For this reason, as shown in FIG. 6, when the average particle diameter of the flame retardant is in the range of 0.2 μm or more, the raw material mixed liquid can be adjusted to 1000 mPa·s or more and 60000 mPa·s or less. Therefore, it was found that molding can be facilitated by setting the average particle size of the flame retardant to 0.2 μm or more.

As shown in FIGS. 5 and 6, when the average particle size of the flame retardant is 0.5 μm or more and 7 μm or less, both the viscosity and the oxygen index of the raw material mixed liquid can be kept within the preferable ranges described above. Therefore, by setting the average particle diameter of the flame retardant to 0.5 μm or more and 7 μm or less, both the flame retardancy and the easiness of molding the raw material mixture can be improved.

2 Inner cylinder (container main body)
3 Outer cylinder (container body)
4 heat transfer fins (vessel body)
5 basket (container body)
5a Partition plate (container body)
6 Neutron shielding material 6A Neutron shielding material 6B Neutron shielding material 7 Primary lid (container body)
8 secondary lid (container body)
9 trunnion (container body)
10 Storage container 11 Container body S1 Epoxy reaction liquid preparation step S2 Addition step S3 Molding step S4 Curing step

Claims (12)

A resin composition containing a flame retardant, an epoxy resin containing a unit skeleton derived from an acid anhydride as a curing agent, and a curing accelerator that is only a non-imidazole compound ,
The epoxy resin contains a unit skeleton derived from a hydrogenated epoxy main agent containing two or more epoxy groups in the molecule,
Neutron shielding material, wherein the flame retardant is contained at a ratio of 40% by mass or more and 60% by mass or less with respect to the resin composition. The neutron shielding material according to claim 1, wherein the epoxy resin includes a unit skeleton derived from a curing agent that is at least one of acid anhydride, dicyandiamide, and phenol resin. The neutron shielding material according to claim 1 or 2, wherein the epoxy resin includes a unit skeleton derived from a hydrogenated epoxy main agent containing two epoxy groups in the molecule. The neutron shielding material according to claim 1 or 2 , wherein the non-imidazole compound is at least one of a tertiary amine, a tertiary amine salt, phosphines, and a phosphonium salt. The neutron shielding material according to claim 1 or 2, wherein the epoxy resin includes a unit skeleton derived from a hydrogenated epoxy main agent containing three or more epoxy groups in the molecule. The hydrogenated epoxy base compound is a hydrogenated epoxy compound of at least one of a glycidyl ether type epoxy compound, a glycidyl ester type epoxy compound, a glycidyl amine type epoxy compound, and an alicyclic type epoxy compound. Neutron shielding material as described. The resin composition contains a neutron absorber,
The neutron shielding material according to claim 1 or 2, wherein the neutron absorber is at least one of boron carbide and boron nitride. The neutron shielding material according to claim 1 or 2, wherein the flame retardant is a flame retardant containing a hydroxyl group. The resin composition contains the particulate flame retardant,
The neutron shielding material according to claim 1 or 2, wherein the particle size distribution of the flame retardant measured based on a laser diffraction scattering method is a unimodal distribution. The resin composition contains the particulate flame retardant,
The neutron shielding material according to claim 1 or 2, wherein the flame retardant has an average particle size of 0.5 µm or more and 7 µm or less as measured based on a laser diffraction scattering method. a container main body for storing fuel assemblies;
and a neutron shielding material disposed around the fuel assembly,
The neutron shielding material is
A resin composition containing a flame retardant, an epoxy resin containing a unit skeleton derived from an acid anhydride as a curing agent, and a curing accelerator that is only a non-imidazole compound ,
The epoxy resin contains a unit skeleton derived from a hydrogenated epoxy main agent containing two or more epoxy groups in the molecule,
The flame retardant is contained in a ratio of 40% by mass or more and 60% by mass or less with respect to the resin composition. A resin composition containing a flame retardant, an epoxy resin containing a unit skeleton derived from an acid anhydride as a curing agent, and a curing accelerator that is only a non-imidazole compound, and the epoxy resin is an intramolecular Manufacture of a neutron shielding material containing a unit skeleton derived from a hydrogenated epoxy main agent containing two or more epoxy groups, and wherein the flame retardant is contained in a proportion of 40% by mass or more and 60% by mass or less with respect to the resin composition. a method,
an epoxy reaction liquid preparation step of preparing an epoxy reaction liquid containing at least the hydrogenated epoxy main agent , the curing agent, and the curing accelerator ;
a step of adding the raw material mixture of the resin composition by adding the flame retardant to the epoxy reaction liquid so that the final concentration is 40% by mass or more and 60% by mass or less;
and a curing step of obtaining the neutron shielding material containing the epoxy resin by curing at least the hydrogenated epoxy main agent in the raw material mixture.

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