WO2021252112A1

WO2021252112A1 - Neutron shielding and radiation absorbing compositions

Info

Publication number: WO2021252112A1
Application number: PCT/US2021/031261
Authority: WO
Inventors: Danielle CASTLEY; William Woodward; Alex NEYMARK; Charles CASTLEY; Ian Mcdonald
Original assignee: Neutroelectric, Llc
Priority date: 2020-05-20
Filing date: 2021-05-07
Publication date: 2021-12-16

Abstract

A neutron shielding and neutron absorbing composition containing an olefin or polyolefin base material, at least one element for neutron absorption, and a catalyst is presented. The composition may include additional additives such as flame retardants, gamma radiation retardants, neutron shielding additives and neutron absorbing additives. Neutron absorbing additives for inclusion in the composition may be, for example, boron, gadolinium, samarium, cadmium, bismuth, iron, or lithium, compounds thereof, or isotopes thereof. The composition is simple to fabricate, low-density, effective at slowing and absorbing neutrons, and capable of operating at temperatures up to 350°C. Methods of preparing the neutron shielding and radiation absorbing composition are also described.

Description

TITLE OF THE INVENTION

[0001] Neutron Shielding and Radiation Absorbing Compositions

CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] The present application claims priority to U. S. Provisional Application No. 63/027,666, filed May 20, 2020, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

[0003] Radiation shielding and absorbing compositions are used in aerospace, space, medical, defense and military, scientific, and nuclear applications. Within many industries, such as the nuclear industry, there is a growing need for lightweight (e.g., density < 2.5 g/cm³ with effective neutron shielding properties) neutron shielding materials that can operate in a wide temperature range (e.g., -273°C to 350°C) to improve the safety and reduce costs for numerous applications, including, but not limited to new reactor designs and construction, nuclear fuel management, and nuclear plant operations. The most common neutron shielding materials are boron or lithium containing polyethylene, polyamide composites, or water. These common neutron shielding materials rely on slowing neutrons to a thermal state to increase the probability of absorption by the neutron absorbing isotopes, such as those in boron or lithium.

[0004] Neutron shielding and absorption materials prevent criticality in various nuclear applications and increase the safety of nuclear, research, medical, aerospace, and space applications. For example, in nuclear applications, spent nuclear fuel assemblies are taken out from an atomic reactor, stored in water-cooled pools at the atomic power plant site for a preset time period to attenuate radiation dose and calorific power, and then transported to a storage facility (e.g., dry storage facility) or a processing facility (e.g., fuel reprocessing factory). A specially designed container, often referred to as a cask, is used to store and/or carry the spent nuclear fuel assembly.

[0005] There are generally various types of nuclear fuel casks, such as, but not limited to, transfer casks, transport casks, storage casks, and dual-purpose storage and transport casks. Typically, transfer casks are designed to be lighter than storage casks because a transfer cask must be lifted, handled, and transported by, for example, a crane, or other machinery. [0006] Current neutron shielding materials have thermal properties that are design limiting and are susceptible to degradation from gamma and secondary gamma radiation. The secondary gamma radiation may be caused by isotope neutron capture. Neutron absorbers are often composed of metal matrix composites or ceramic metal matrix materials and are design limiting due to their high density. Such properties are concerns for nuclear fuel management. For example, borated polyethylene, water, and concrete are the most commonly used neutron shielding materials in spent fuel storage applications. Aluminum or steel materials with boron are the most common neutron absorbers. Concrete is multi-purpose in shielding neutron radiation, shielding gamma radiation, and providing structural support or protection from impact. Concrete and the aforementioned neutron absorbers are stable at high temperatures, but have relatively high densities and are thus too heavy for use in many applications.

[0007] Conversely, water has a lower density but begins to boil at 100°C, and therefore requires cumbersome mechanical cooling systems. The neutron attenuation abilities of both water and concrete have been leveraged with neutron absorbing additives such as boric acid, boron carbide, and ferro-boron. However, the densities and/or maximum operating temperatures of such materials are often design limiting in radiation shielding applications.

[0008] A number of thermosetting polymer compositions have been proposed to address the combined demands for higher operating temperatures and lower density of the radiation shielding components. For example, U.S. Patent No. 7,524,438 discloses an unsaturated polyester-based material for neutron-shielding and for maintaining sub-criticality, the material comprising an unsaturated polyester resin, at least an inorganic boron compound, and at least a hydrogenated inorganic compound, in amounts such that the boron concentration is 4.10²¹ to 25.10²¹ atoms per cm³ and the hydrogen concentration is 3.10²² to 5.5xl0²² atoms per cm³. U.S. Patent No. 7,160,486 discloses a composite material based on vinylester resin and an inorganic filler capable of slowing and absorbing neutrons for neutron shielding and maintenance of sub-criticality. The vinylester resin may be an epoxymethacrylate resin and the inorganic filler may contain a zinc borate and an alumina hydrate or magnesium hydroxide. However, testing has revealed that these known materials are capable of operating at temperatures of only up to 160°C.

[0009] Accordingly, a need exists for more effective neutron shielding and radiation absorption compositions and methods, including new radiation absorbing compositions with improved properties that can be used to absorb and/or shield neutron radiation, including but not limited to, thermal stability at extreme operating temperatures, lower density (lightweight with same neutron shielding and absorption abilities), and improved gamma shielding and gamma resistance. One of the more recent developments in high performance thermoset polymers materials involves ring opening metathesis polymerization of the polymer, such as cyclic polyolefins, in order to provide compositions having outstanding mechanical and thermal properties over the range of extreme temperatures, while providing high hydrogen content useful in neutron shielding.

BRIEF SUMMARY OF THE INVENTION

[0010] Aspects of the disclosure relate to a neutron shielding and radiation absorbing composition comprising a thermoset polyolefin material obtained by ring opening metathesis polymerization and containing at least one neutron absorbing element such as, but not limited to, boron, gadolinium, samarium, lithium, iron or cadmium. The resulting composition provides for a lightweight, cured in-situ composite, for neutron shielding and absorption at extreme temperatures.

DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention is directed to neutron shielding and radiation shielding or absorbing compositions that provide comparable neutron shielding properties to known materials, with the added benefits of being low-density (< 2.5 g/cm³, preferably < 2.0 g/cm³), having the ability to operate at temperatures below -100°C or temperatures above 160°C, and being a thermoset material having the ability to be cured in-situ.

[0012] The composition according to the present invention contain at least three components, as follows. The first component is a thermoset olefin resin (base material), the second component is a compound containing at least one type of neutron absorbing additive, and the third component is a catalyst which serves to initiate ring opening metathesis polymerization (ROMP) and cross link with the thermoset olefin resin. Upon cure, the olefin forms a continuous matrix incorporating the neutron absorbing additive particles. Additional components may optionally be included in the composition. Such optional additional components include, but are not limited to, additives such as rheology modifiers, reinforcing fillers, low profile additives (LPAs), flame retardants, gamma retardants and thermally conductive components. Each of these components is described in more detail below.

[0013] In some embodiments, the components and/or the relative amounts thereof in the composition may be adjusted or controlled in order to tailor the properties of the composition. For example, the amount of the neutron absorbing elements may be adjusted to control the density or the macroscopic neutron cross section of the composition.

Olefin Resin Base Material

[0014] The base material contained in the neutron shielding material according to the present invention is preferably a thermoset olefin or polyolefin resin, and more preferably a high- temperature thermoset olefin or polyolefin resin, and most preferably a high-temperature thermoset olefin resin. In one embodiment, the base material is high-temperature thermoset olefin resin comprised of one or more monomers capable of ROMP, such as, but not limited to, polydicyclopentadiene (PDCPD) resin, dicyclopentadiene (DCPD), tricyclopentadiene (TCPD), norbomene (NB), ethylnorbornene (ENB), octylnorbomene (ONB), nadic anhydride (NA), as well as their derivatives functionalized with ester, amide, imide, ketal, ether, cyano, trifluoromethyl and halogen groups. It will be apparent to those skilled in the art that the above list is incomplete and other ROMP-capable monomers fall within the scope of the present invention. In a preferred embodiment, the base material is comprised of cyclic olefin polymers and copolymers. However, it is also within the scope of the present invention to include alternative thermoset olefin or polyolefin resins or other materials as the base material, provided they provide the desired cross- linking in the compositions, and/or have the desired hydrogen content, and/or have the desired extreme temperature properties.

[0015] The base material is present in the composition in an amount of 70 wt% to 99 wt% based on weight of the composition, and more preferably in an amount of 90 wt% to 98 wt% based on the total weight of the composition.

Neutron Absorbing Additive [0016] The terms neutron absorbing additive, neutron absorbing isotope, neutron absorbing material, neutron absorbing particles, neutron absorbing compound and neutron absorbing element are used interchangeably herein and refer to any element having a high neutron cross-section for incoming neutron energy levels (i.e., an element which absorbs neutrons). The neutron absorbing additives for inclusion in the composition according to the present invention may be, for example, boron, gadolinium, samarium, cadmium, bismuth, iron, lithium, compounds thereof, or isotopes thereof. It is also within the scope of the present invention to include more than one type of neutron absorbing additive in the composition.

[0017] The neutron absorbing additive(s) may be included in the composition in an amount of 0.5 wt% to 70 wt% based on the total weight of the composition, more preferably 0.5 wt% to 30 wt% based on the total weight of the composition. In some embodiments, the neutron absorbing additive(s) is/are present in the composition in an amount of 0.5 wt% to 2.5 wt% based on the total weight of the composition.

[0018] In one embodiment, the neutron absorbing additive contains an isotope having a microscopic thermal neutron cross section greater than about 500 bams or a microscopic fast neutron cross-section greater than about 10²⁴ cm ¹.

[0019] The neutron absorbing additives of the present invention may be in various forms. More preferably, the additives are in the form of microparticles and/or nanoparticles. In some embodiments, the nanoparticles have sizes that range from about 1 nm to about 1 cm in diameter. In some embodiments, the nanoparticles have sizes that range from about 1 nm to about 250 nm in diameter. In some embodiments, the nanoparticles have sizes that range from about 1 nm to about 100 nm in diameter. In some embodiments, the nanoparticles have sizes that are less than about 100 nm in diameter. Boron carbide nanoparticles are presently preferred. In some embodiments, for example, the neutron absorbing additive is boron carbide and is added to achieve a natural boron density of 10¹⁷ boron atoms/cm³.

[0020] Neutron absorbing additives may be associated with base materials in various manners. For instance, in some embodiments, neutron absorbing particles are uniformly dispersed throughout the base material, are intertwined with the base material, and/or are positioned within the surface of a base material. In some embodiments, the neutron absorbing particles are positioned within internal cavities of a base material. In some embodiments, the neutron absorbing particles are evenly distributed throughout the base material. In some embodiments, the neutron absorbing particles can be dispersed throughout a compound, element, composition, material, or combinations thereof, which are utilized to form the base material.

[0021] In some embodiments, the neutron absorbing additives are layered compounds. In some embodiments, the neutron absorbing additive is layered within compounds, elements, compositions, materials, or combinations thereof, which are used to form the base material. In some embodiments, the neutron absorbing additive is included through compounds, elements, compositions, materials, or combinations thereof, which are used to form the base material.

Catalyst

[0022] The presently preferred catalysts for inclusion in the compositions are ROMP catalysts, and more particularly Grubbs catalysts, including a first-generation Grubbs-ROMP catalyst, a second-generation Grubbs catalysts and Hoveyda-Grubbs catalysts. Ruthenium-based Grubbs catalysts are well known in the art and are commercially available. The catalyst enables the cross- linking of the olefin or polyolefin base material so that the final composition product is a thermoset, high-temperature, high-strength material. Thus, upon curing, the base material cross-links and solidifies around the neutron absorbing material, such as neutron absorbing particles, or any other functional additives included in the formulation. It will be apparent to those skilled in the art that other types of catalysts suitable for ROMP may be utilized within the scope of the present invention. Examples of such catalysts include, but are not limited to, titanium, tantalum, tungsten and molybdenum-based complexes, with the latter two categories being known as Schrock catalysts.

[0023] The catalyst may be present in the composition in an amount of 0.025 wt% to 10 wt% based on the total weight of the base material. In some embodiments, the catalyst is preferably present in the composition in an amount of about 0.025 wt% to 1.25 wt% based on the total weight of the base material. In other embodiments, the catalyst is preferably present in the composition in an amount of 1.25 wt% to 5 wt% based on the total weight of the base material. In other embodiments, the catalyst is present in the composition in an amount of 5 wt% to 10 wt% based on the total weight of the base material. Additional Additives

Rheology Modifiers

[0024] It is within the scope of the present invention to include one or more rheology modifiers, for example, in order to control sedimentation of other formula components and to adjust the rheological characteristics of the composition during the manufacturing process. Non limiting examples of the rheology modifiers are bentonite or montmorillonite organo-modified clays, treated colloidal silica, modified urea, modified castor oil, synthetic or natural wax dispersions and other materials which are known in the art or to be developed. One or more rheology modifiers may be included in the composition in the amount of 0.5 wt% to 15 wt% based on the total weight of the composition.

Reinforcing Fillers

[0025] It is within the scope of the present invention to include one or more reinforcing fillers, such as, but not limited to, chopped glass strands, carbon fiber, wollastonite, mica, ceramic or glass beads, woven or nonwoven elements and other materials which are known in the art or to be developed. One or more types of reinforcing fillers may be included in the composition in the amount of 1 wt% to 60 wt% based on the total weight of the composition.

[0026] In one embodiment, the reinforcing fillers are layered compounds. In one embodiment, the reinforcing filler is layered within compounds, elements, compositions, materials, or combinations thereof. In one embodiment, the reinforcing fillers are woven or dispersed throughout compounds, elements, compositions, materials, or combinations thereof.

Low Profile Additives

[0027] It is within the scope of the present invention to include one or more low profile additives, for example, in order to control shrinkage and improve surface properties of the neutron shielding components. Non-limiting examples of the low profile additives include thermoplastic resins, such as polyvinyl acetate, (meth) acrylate copolymers, polystyrene, polyesters, and other low profile additive materials that are known in the art or to be developed. One or more low profile additives may be included in the composition in the amount of 1 wt% to 50 wt% based on the total weight of the composition. Flame Retardants

[0028] It is within the scope of the present invention to include one or more flame retardants, such as, but not limited to, bismuth oxide, aluminum trihydrate, colemanite, graphene, carbon fibers, or magnesium oxide. However, it will be understood by those skilled in the art that other flame retardants that are known in the art or to be developed would also be appropriate. One or more flame retardants may be included in the composition in an amount of 1 wt% to 60 wt% based on the total weight of the composition.

Gamma Retardant Additive

[0029] It is within the scope of the present invention to include one or more gamma retardant additives in the composition, such as, without limitation, lead, tungsten, colemanite, titanium, iron, gadolinium, samarium, bismuth, ruthenium, molybdenum, or magnesium. One or more gamma retardants may be present in the composition in the amount of 0 wt% to 30 wt% based on the total weight of the composition.

Thermally Conductive Additive

[0030] It is within the scope of the disclosure to include one or more additives to improve the thermal conductivity of the composition. Examples of such additives include, but are not limited to, iron, carbon fiber, graphene, graphene oxide, copper, aluminum, steel, silver, brass, bronze, and boron allotropes. These additives may be present in the composition in the amount of 0 wt% to 30 wt% based on the total weight of the composition.

Neutron Slowing Additive

[0031] Some light-elements, such as hydrogen or carbon, may be added to the composition in order to enhance the neutron slowing power of the neutron shielding material. Such additives may be incorporated separately or in combinations thereof, and include but are not limited to aluminum trihydrate, boric acid, polyethylene, and/or carbon allotropes. These additives may be present in the composition in the amount of 0 wt% to 50 wt% based on the total weight of the composition. Alternative Additives

[0032] In some embodiments, the radiation absorbing compositions of the present disclosure can include various types of alternative additives. For instance, in some embodiments, the additives that may be included in the composition include, without limitation, fullerenes, copper nanomaterials, silver nanomaterials, aluminum nanomaterials, metal hydride, hydrogen-absorbing alloys, carbon allotropes, silicon carbides, conductive metals, iron, silicon, carbon, and oxygen, or combinations thereof.

[0033] The additives of the present invention may have various effects on the composition. For instance, in some embodiments, the additives facilitate the attenuation of gamma radiation from the radiation absorbing compositions. In some embodiments, the additives protect the radiation absorbing compositions from gamma radiation. In some embodiments, the additives mitigate secondary gamma radiation and secondary gamma radiation generation resulting from neutron absorption by the radiation absorbing compositions. In some embodiments, the additives provide for a high coefficient of thermal conductivity. In some embodiments, the additives provide for control of electrical conductivity. In some embodiments, the additives can be utilized to control electromagnetic frequency (EMF) shielding.

Characteristics and Properties of the Composition

[0034] The radiation absorbing composition according to the present invention may have various advantageous characteristics and properties. For example, in some embodiments, the radiation absorbing compositions exhibit flame resistance at flame temperatures greater than 400°C.

[0035] The radiation absorbing composition can be utilized at a wide range of operating temperatures between -273°C to 350°C. In some embodiments, the radiation absorbing composition can be utilized at sub-zero operating temperatures of less than -100°C, and more particularly sub-zero operating temperatures up to -273°C. In some embodiments, the radiation absorbing composition can be utilized at operating temperatures ranging from room temperature to 350°C. Preferably, the radiation absorbing composition can be utilized at operating temperatures above 160°C, more particularly from 160°C to 350°C, and even more particularly from 160°C to 300°C.

[0036] Preferably, the radiation absorbing composition has a low density in the range of 0.94 g/cm³ to 3 g/cm³, and more particularly in the range of 1 g/cm³ to 2 g/cm³. Most preferably, the radiation absorbing composition has a density of about 1.05 g/cm³.

[0037] The radiation absorbing composition of the present disclosure can have various neutron cross sections depending on the incoming neutron spectrum. For instance, in some embodiments, the radiation absorbing compositions have an effective fast macroscopic neutron cross section of from about 0.019 cm ¹ to about 0.31 cm ¹. In some embodiments, the radiation absorbing compositions have effective fast macroscopic neutron cross sections of from about 0.019 cm ¹ to about 0.03 cm ¹. In some embodiments, the radiation absorbing compositions have an effective fast macroscopic neutron cross section of from about 0.02 cm ¹ to about 0.03 cm ¹.

[0038] The radiation absorbing composition of the present invention may also have various neutron resistance values. For instance, in some embodiments, the radiation absorbing composition has a neutron resistance greater than about l.OxlO¹⁴ n/cm². In some embodiments, the radiation absorbing composition has a neutron resistance greater than about l.OxlO¹⁵ n/cm². In some embodiments, the radiation absorbing composition has a neutron resistance greater than about l.OxlO¹⁶ n/cm². In some embodiments, the radiation absorbing composition has a neutron resistance greater than about l.OxlO¹⁷ n/cm². In some embodiments, the radiation absorbing composition has a neutron resistance greater than about l.OxlO¹⁸ n/cm². In some embodiments, the radiation absorbing composition has a neutron resistance greater than about l.OxlO¹⁹ n/cm². In some embodiments, the radiation absorbing composition has a neutron resistance greater than l.OxlO²⁰ n/cm².

[0039] In some embodiments, the radiation absorbing compositions of the present invention mitigate secondary gamma radiation emitted from the compositions after neutron absorption. For instance, in some embodiments, the radiation absorbing compositions mitigate secondary gamma radiation emitted from the compositions after neutron absorption. In some embodiments, the radiation absorbing compositions of the present invention mitigate negative effects of neutron absorption, such as, but not limited to, secondary gamma production by the radiation absorbing composition after neutron absorption, alpha production by the radiation absorbing composition after neutron absorption, secondary x-ray production by the radiation absorbing composition after neutron absorption, and combinations thereof.

Methods of Preparing Radiation Absorbing Compositions

[0040] Additional embodiments of the present invention pertain to methods of preparing the radiation absorbing compositions of the present invention. Such methods generally include mixing the olefin or polyolefin base material, neutron absorbing additive(s), and optional additives, and then adding the catalyst. The resulting mixture is then allowed to cure in-situ upon mixing with the catalyst, to produce the composition as the catalyst cross-links with the olefin or polyolefin base material and solidifies around the neutron absorbing additive. In some embodiments, heat is applied to the mixture to accelerate cross-linking of the olefin or polyolefin base material.

[0041] The radiation absorbing compositions of the present invention can be prepared by various types of mixing techniques. For instance, in some embodiments, the mixing is acoustic mixing. In some embodiments, acoustic mixing allows for the application of low frequency, high- amplitude sound waves facilitating the movement of solids to induce mixing. In some embodiments, the mixing is high-speed shear mixing. In some embodiments, the mixing is a combination of high-speed shear mixing and acoustic mixing.

[0042] In some embodiments, the radiation absorbing compositions of the present invention can be prepared utilizing various mixing mechanisms. For example, in some embodiments, the mixing mechanism can include, but is not limited to: paddle-blending, shaking, blending, solid suspension, turbines, close-clearance mixers, single-phase blending, high shear dispersers, static mixing, hand mixing, or combinations thereof.

[0043] In some embodiments, the mixing is performed such that the base material, neutron absorbing additives and other additives, and the catalyst are uniformly dispersed throughout the radiation absorbing composition. In some embodiments, the mixing is performed such that the additives are uniformly dispersed throughout the radiation absorbing composition. In some embodiments, better dispersion of smaller micro-particles or nanoparticles improves attenuation.

Applications and Advantages

[0044] The composition according to the present invention has various advantages. For instance, the radiation absorbing composition according to the present invention has: (i) neutron absorbing capabilities at extreme (i.e., extremely low or extremely high) temperatures; (ii) a relatively low density; (iii) high neutron resistance; (iv) an effective fast macroscopic neutron cross section; and (v) low amounts of secondary gamma radiation.

[0045] As such, the radiation absorbing composition of the present inventio is suitable for use in various manners and for various purposes. Some purposes and applications include, but are not limited to, nuclear, aerospace, defense, military, space, medical and research applications. Examples in nuclear applications include spent nuclear fuel containers, protecting reactor systems and equipment, and temporary shielding around a nuclear power plant to shield workers.

[0046] The invention will now be described in connection with the following, non-limiting examples.

Example 1: Preparation of Radiation Absorbing Composition

[0047] 94 wt% polydicyclopentadiene (PDCPD) resin (base material), 2.5 wt% boron carbide particles (of 97% or greater purity) (neutron absorbing additive), 2.5 wt% B12O3 particles (of 97% or greater purity) (additional additive), and 0.20-1.5 wt % ruthenium-based Grubbs-catalyst (catalyst) were shear mixed together in a container and allowed to cure in-situ at room temperature and formed a radiation absorbing composition. The catalyst affected the ROMP of the PDCPD resin which, in turn, solidified around the boron carbide and B12O3 particles. The resulting radiation absorbing composition had a density of 1.02 g/cm³, a fast neutron resistance of 10¹⁸ n/cm², a hydrogen content of 10 wt% and a boron content of 10²⁰ atoms B/cm³. In an inert environment with the temperature rising at 10°C per minute, the radiation absorbing composition experienced 1% weight loss at 298.7°C, 5% weight loss at 410°C and 10% weight loss at 427.1°C. A 100-gram sample was continuously exposed to a 220°C air environment in a furnace for 50 days and the total weight loss was <1 wt%.

Example 2: Preparation of Radiation Absorbing Composition including Rheology Modifier [0048] A mixture of 5 wt% of self-activating clay (rheology modifier), specifically Claytone HY (BYK-Chemie), in PDCPD resin was placed in a paint shaker with 2 mm zirconia milling media and agitated for 60 minutes. The resulting pre-gel had a molasses-like consistency. The pre-gel was let down in a glass jar with the PDCPD resin to 1 wt.% clay. Next, 2.5 wt% of boron carbide particles of 0.5 micron average size were added to the pre-gel under low-shear agitation. The resulting suspension remained stable for 10 minutes, as was evidenced by an even and dark opaque appearance without signs of separation. The suspension was subsequently catalyzed with the 2 wt% of a ruthenium-based Grubbs catalyst, and allowed to cure in-situ to produce a radiation absorbing composition. The resulting radiation absorbing composition had a density of 1.02 g/cm³, a fast neutron resistance of 10¹⁸ n/cm², a hydrogen content of 9 wt% and a boron content of 10²⁰ atoms B/cm³. A 100-gram sample was continuously exposed to a 220°C air environment in a furnace for 50 days and the total weight loss was <1 wt%.

Comparative Example: Control Mixture Initially Lacking a Rheology Modifier [0049] 2.5 wt% of boron carbide particles of 0.5 micron average size were added under high- shear agitation to PDCPD resin and agitated for five minutes in a glass jar. Within three minutes of stopping agitation, a sediment layer of the boron carbide particles was clearly visible at the bottom of the jar. The composition was then remixed, and 2 wt% of a ruthenium-based Grubbs catalyst was added under agitation. The agitation was maintained until the onset of the polymerization to produce a uniform radiation absorbing composition.

[0050] The neutron shielding and radiation absorbing composition according to the present invention can be used for a variety of applications, such as, but not limited to, serving as a neutron shield, a neutron absorber, a neutron moderator, a neutron attenuator, a neutron detector; nuclear reactor equipment, medical reactor equipment; and nuclear robotics. A neutron shield is a material that thermalizes and/or absorbs neutrons. A neutron absorber is a material that absorbs neutrons. A neutron moderator is a material that reduces the energy level of incoming neutrons. A neutron attenuator is a material that reduces the neutron flux passing through the material. A neutron detector is a device that detects neutrons. For the purposes of the present invention, the phrases “neutron shield” or “neutron shielding material” encompass the list of materials that interact with neutrons. The neutron shielding and radiation absorbing composition according to the present invention can be used for any application where a material is required that can interact with neutrons and withstand high neutron fluences.

[0051] It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concepts thereof. Also, based on this disclosure, a person of ordinary skill in the art would further recognize that the relative proportions of the components illustrated above could be varied without departing from the spirit and scope of the invention. It is understood, therefore, that this invention is not limited to that particular embodiment disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.

Claims

CLAIMS We claim:

1. A neutron shielding and radiation absorbing composition comprising a cyclic olefin polymer or copolymer base material, at least one neutron absorbing additive, and a catalyst.

2. The neutron shielding and radiation absorbing composition according to claim 1, wherein the catalyst is a ring opening metathesis polymerization catalyst.

3. The neutron shielding and radiation absorbing composition according to claim 2, wherein the catalyst is a first-generation Grubbs-ROMP catalyst, a second-generation Grubbs catalyst, or a Hoveyda-Grubbs catalyst.

4. The neutron shielding and radiation absorbing composition according to claim 1, wherein the at least one neutron absorbing additive comprises an element selected from the group consisting of boron, gadolinium, samarium, titanium, zinc, bismuth, lithium, iron, cadmium and isotopes thereof.

5. The neutron shielding and radiation absorbing composition according to claim 1, wherein the at least one neutron shielding additive comprises a material selected from the group consisting of a boron-containing compound, a cadmium-containing compound, a gadolinium- containing compound, a lithium-containing compound, a titanium-containing compound, a zinc- containing compound, a samarium-containing compound, a bismuth-containing compound, an iron-containing compound and mixtures thereof.

6. The neutron shielding and radiation absorbing composition according to claim 1, wherein the at least one neutron shielding additive comprises at least one isotope having a microscopic thermal neutron cross section greater than about 500 bams or a microscopic fast neutron cross-section greater than about 10²⁴ cm ¹.

7. The neutron shielding and radiation absorbing composition according to claim 6, wherein the at least one isotope is selected from the group consisting of boron, gadolinium, samarium, titanium, zinc, bismuth, lithium, iron and cadmium.

8. The neutron shielding and radiation absorbing composition according to claim 1, wherein the at least one neutron absorbing additive is present in the composition in an amount of 0.5 wt% to 30 wt% based on a total weight of the composition.

9. The neutron shielding and radiation absorbing composition according to claim 1, further comprising at least one flame retardant.

10. The neutron shielding and radiation absorbing composition according to claim 9, wherein the at least one flame retardant is selected from the group consisting of bismuth oxide, aluminum trihydrate and magnesium oxide.

11. The neutron shielding and radiation absorbing composition according to claim 1, further comprising at least one gamma retardant additive.

12. The neutron shielding and radiation absorbing composition according to claim 11, wherein the at least one gamma retardant additive is selected from the group consisting of lead, tungsten, colemanite, samarium, bismuth and magnesium.

13. The neutron shielding and radiation absorbing composition according to claim 1, wherein the composition has a density of about 1 g/m³ to about 2 g/m³.

14. The neutron shielding and radiation absorbing composition according to claim 13, wherein the composition has a density of about 1 g/m³.

15. The neutron shielding and radiation absorbing composition according to claim 1, wherein the composition has an operating temperature of from -273°C up to 350°C.

16. The neutron shielding and radiation absorbing composition according to claim 15, wherein the composition has an operating temperature of from 160°C up to 350°C.

17. A method of making a neutron shielding and radiation absorbing composition, the method comprising: mixing an olefin or polyolefin base material, at least one neutron absorbing additive, and a catalyst together to form a liquid mixture; and allowing the liquid mixture to cure in situ to produce the composition.