18 research outputs found
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Fast Neutron Radioactivity and Damage Studies on Materials
Many materials and electronics need to be tested for the radiation environment expected at linear colliders (LC) to improve reliability and longevity since both accelerator and detectors will be subjected to large fluences of hadrons, leptons and gammas. Examples include NdFeB magnets, considered for the damping rings, injection and extraction lines and final focus, electronic and electro-optic devices to be utilized in detector readout, accelerator controls and the CCDs required for the vertex detector, as well as high and low temperature superconducting materials (LTSMs) because some magnets will be superconducting. Our first measurements of fast neutron, stepped doses at the UC Davis McClellan Nuclear Reactor Center (UCD MNRC) were presented for NdFeB materials at EPAC04 where the damage appeared proportional to the distances between the effective operating point and Hc. We have extended those doses, included other manufacturer's samples and measured induced radioactivities. We have also added L and HTSMs as well as a variety of relevant semiconductor and electro-optic materials including PBG fiber that we studied previously only with gamma rays
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Neutron-Absorbing Coatings for Safe Storage of Fissile Materials with Enhanced Shielding & Criticality Safety
Neutron-absorbing Fe-based amorphous-metal coatings have been developed that are more corrosion resistant than other criticality-control materials, including Al-B{sub 4}C composites, borated stainless steels, and Ni-Cr-Mo-Gd alloys. The presence of relatively high concentration of boron in these coatings not only enhances its neutron-absorption capability, but also enables these coatings to exist in the amorphous state. Exceptional corrosion resistance has been achieved with these Fe-based amorphous-metal alloys through additions of chromium, molybdenum, and tungsten. The addition of rare earth elements such as yttrium has lowered the critical cooling rate of these materials, thereby rendering them more easily processed. Containers used for the storage of nuclear materials, and protected from corrosion through the application of amorphous metal coatings, would have greatly enhanced service lives, and would therefore provide greater long-term safety. Amorphous alloy powders have been successfully produced in multi-ton quantities with gas atomization, and applied to several half-scale spent fuel storage containers and criticality control structures with the high-velocity oxy-fuel (HVOF) thermal spray process. Salt fog testing and neutron radiography of these prototypes indicates that such an approach is viable for the production of large-scale industrial-scale facilities and containers. The use of these durable neutron-absorbing materials to coat stainless steel containers and storage racks, as well as vaults, hot-cell facilities and glove boxes could substantially reduce the risk of criticality in the event of an accident. These materials are particularly attractive for shielding applications since they are fire proof. Additionally, layers of other cold and thermal sprayed materials that include carbon and/or carbides can be used in conjunction with the high-boron amorphous metal coatings for the purpose of moderation. For example, various carbides, including boron, tungsten, and chromium carbide, as well as graphite particles can be co-deposited with a metallic binder phase with either thermal spray or cold spray technology. These moderator layers would also be fire resistant. By coating the vessels and piping used for spent fuel reprocessing, including slab and pencil tanks, enhanced criticality safety and substantially better corrosion resistance can be achieved simultaneously. Since these alloys are Fe-based, any substitution of these for high-performance Ni-based alloys is expected to result in a cost savings. Ultimately, the cost of these materials should comparable to that of stainless steels
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Development of a Large-Field Cold Neutron Source at the University of California, Davis, McClellan Nuclear Radiation Center (UCD/ MNRC)
The project is to investigate, study, and develop a large-field, beryllium filtered cold neutron source for use in performing neutron radiography for a wide variety of basic research activities at the UC Davis/ McClellan Nuclear Radiation Center (MNRC). The UCD/ MNRC’s 2-MW TRIGA reactor which went online in 1990, and is the youngest research reactor in U.S. is renowned for its world-class facilities for performing thermal neutron radiography. It provides support for non-destructive inspection of materials and technology in the automotive, aerospace, and material science areas. The proposed research intends to study, design, modify, and transform one of the existing four thermal neutron radiography beams into a large-field, beryllium filtered cold neutron radiographic beam. When added to the extensive experiences in thermal neutron radiography, this additional capability will further enhance the existing thermal neutron radiography to support basic research activities in the automotive, aerospace, material, chemical, and biological sciences. It will also make investigating crucial dynamic (real-time) engineering problems such as flow restrictions across valves or two-phase flow situations feasible. The project is dedicated to advancing our existing technology of implementing neutron radiography and development of fundamental nuclear science and technology. Thermal neutron radiography is a well-known powerful tool for non-destructive inspection of materials, especially industrial materials, as a complementary technique to X-ray radiography. The capability of neutron radiography, as compared with X-ray radiography, is determined by the features of the neutron-matter interactions. X-rays interact mainly with the electron shells of the atoms, therefore the cross sections for X-rays increase with the atomic number making it very difficult to image low atomic number elements (i.e. hydrogen, carbon, etc.). In contrast, neutrons interact with atomic nuclei, so that dependence on atomic number is not observed. This major difference enables thermal neutron radiography to significantly outperform X-ray radiography in detecting elements such as H, Li, O, N, B, Cd, Gd in structural metals such as Al, Fe, Zr, Sn, W, Pb. In comparison to thermal neutrons (Eavg = 0.0253 eV), beryllium filtered cold neutrons (energies < 0.005 eV) are attenuated to an even greater extent by the elements listed above and to a lesser extent by those structural metals listed above. As a consequence, imaging contrast and sensitivity are significantly enhanced for detecting minute quantities of hydrogen in thick layers of metal. On the other hand, all existing cold neutron sources are confined to < 6 cm in diameter in the U.S., which potential applications are thus limited. Based on the existing experiences and facilities of thermal neutron radiography at the UCD/ MNRC, we investigate and study such a large-field, beryllium filtered cold neutron source to expand our understanding of cold neutron nuclear characteristics and support basic research applications in other scientific fields
Recommended from our members
Development of a Large-Field Cold Neutron Source at the University of California, Davis, McClellan Nuclear Radiation Center (UCD/ MNRC)
The project is to investigate, study, and develop a large-field, beryllium filtered cold neutron source for use in performing neutron radiography for a wide variety of basic research activities at the UC Davis/ McClellan Nuclear Radiation Center (MNRC). The UCD/ MNRC’s 2-MW TRIGA reactor which went online in 1990, and is the youngest research reactor in U.S. is renowned for its world-class facilities for performing thermal neutron radiography. It provides support for non-destructive inspection of materials and technology in the automotive, aerospace, and material science areas. The proposed research intends to study, design, modify, and transform one of the existing four thermal neutron radiography beams into a large-field, beryllium filtered cold neutron radiographic beam. When added to the extensive experiences in thermal neutron radiography, this additional capability will further enhance the existing thermal neutron radiography to support basic research activities in the automotive, aerospace, material, chemical, and biological sciences. It will also make investigating crucial dynamic (real-time) engineering problems such as flow restrictions across valves or two-phase flow situations feasible. The project is dedicated to advancing our existing technology of implementing neutron radiography and development of fundamental nuclear science and technology. Thermal neutron radiography is a well-known powerful tool for non-destructive inspection of materials, especially industrial materials, as a complementary technique to X-ray radiography. The capability of neutron radiography, as compared with X-ray radiography, is determined by the features of the neutron-matter interactions. X-rays interact mainly with the electron shells of the atoms, therefore the cross sections for X-rays increase with the atomic number making it very difficult to image low atomic number elements (i.e. hydrogen, carbon, etc.). In contrast, neutrons interact with atomic nuclei, so that dependence on atomic number is not observed. This major difference enables thermal neutron radiography to significantly outperform X-ray radiography in detecting elements such as H, Li, O, N, B, Cd, Gd in structural metals such as Al, Fe, Zr, Sn, W, Pb. In comparison to thermal neutrons (Eavg = 0.0253 eV), beryllium filtered cold neutrons (energies < 0.005 eV) are attenuated to an even greater extent by the elements listed above and to a lesser extent by those structural metals listed above. As a consequence, imaging contrast and sensitivity are significantly enhanced for detecting minute quantities of hydrogen in thick layers of metal. On the other hand, all existing cold neutron sources are confined to < 6 cm in diameter in the U.S., which potential applications are thus limited. Based on the existing experiences and facilities of thermal neutron radiography at the UCD/ MNRC, we investigate and study such a large-field, beryllium filtered cold neutron source to expand our understanding of cold neutron nuclear characteristics and support basic research applications in other scientific fields
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Radiation Hardness Testing of Materials at the UC Davis/ McClellan Nuclear Radiation Center
The UCD/ MNRC research reactor of the TRIGA type is designed to be operated at a nominal 2 .0 MW steady state power as well as pulse and square wave operation. It is cooled and moderated by light water and reflected by graphite. The reactor core is located near the bottom of a water-filled aluminum vessel 7.0 ft in diameter and 24.5 ft in height. It went first critical in 1990 and has since become the highest power TRIGA reactor in the U.S. Radiation hardness testing of materials is made possible through the so-called “neutron irradiator” which provides fast neutron exposure to samples with minimal contamination from thermal neutrons and gamma rays. This neutron irradiator has three primary components; conditioning well, exposure vessel, and detachable upper shield for the exposure vessel. The conditioning well is installed adjacent to the annular graphite reflector inside the reactor tank. It is held vertically in place and rests at the bottom of the tank. The well-structure is shielded with sufficient boron nitride and lead encased in aluminum to remove thermal neutrons and gamma rays, respectively. The removable and water-tight exposure vessel has a usable inner space of approximately 7” in diameter and 9” in height. There are six removable titanium plates with holes arranged in a hexagonal shape which can hold the components to be irradiated. It also contains a valve at the bottom to purge and pressurize an assembled unit with helium in order to reduce Argon-41 production during irradiation. The exposure vessel is lined with boral and gadolinium paint to insure minimal leakage of thermal neutrons. The detachable upper shield contains boron nitride and lead encased in aluminum to complete the upper shield for the exposure vessel before it is lowered into the conditioning well for irradiation. Monte Carlo code simulation is benchmarked with multiple threshold neutron flux measurements. The converted 1 MeV equivalent silicon neutron flux at 1.5 MW operating power is 2.3 x 10^10 n/cm2.sec. Among others, materials such as silicon based devices, coatings for metals, superconducting magnets which are susceptible to fast neutron exposure and damage in their working environments are examined. This unique irradiation facility enables us to provide credible information regarding fast neutron radiation tolerance of materials used in crucial applications
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Non-Destructive Testing with Neutron Radiography at the UC Davis/ McClellan Nuclear Radiation Center
The UCD/ MNRC inherited NDT capabilities from the US Air Force and even though it is now mainly a research facility, it has kept this acquired asset performing at a production level. The UCD/MNRC facility is equipped with a hexagonal grid, natural convection water cooled TRIGA reactor designed to operate at a nominal 2 .0 MW steady state power as well as in pulse and square wave mode. The reactor utilizes a specially designed annular graphite reflector accommodating four removable units to accept four separate source ends of beam tubes. These tangential beam tubes lead to four large investigation bays with neutron radiography setting. The design basis for these beam tubes is to provide a path for primary thermal neutrons with minimum scattering and attenuation between the reflector inserts and radiography bays. Typical unperturbed beam parameters are summarized in the following: Each beam tube ends with a bulk shield as the primary beam stopper and a separate boron-included fast shutter to initiate and complete a neutron exposure. Traditional film system and more recently computed radiology system utilizing reusable storage phosphor imaging plate (SPIP) are extensively used as 2D imaging recording media. Bay 3 is designed with a charge coupled device (CCD) camera with system control hardware and software to perform 3D neutron tomography. Bay 4’s beam tube, different from the others, has an 11”-thick sapphire crystal filter to provide an even higher quality beam, i.e. much lower contamination from fast neutrons and gamma rays, for 2D neutron radiography. UCD/ MNRC is committed to offering state-of-the-art neutron imaging experiences for non-destructive testing projects. Our unique capabilities enable us to provide effective solutions to the customer’s needs. Providing quality assurance of complicated titanium castings for aircraft, inspecting metal loss of pressurized tanks for fighting forest fires, examining binding between corrosion-resistant coatings and base metal for spent fuel containers, are a few of many services rendered
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Fast neutron Damage Studies on NdFeB Materials
Many materials and electronics need to be tested for the radiation environment expected at linear colliders (LC) since both accelerator and detectors will be subjected to large fluences of hadrons, leptons and gamma’s over the life of the facility. While the linacs will be superconducting, there are still many uses for NdFeB in the damping rings, injection and extraction lines and final focus. Our understanding of the situation for rare earth, permanent magnet materials was presented at the Particle Accelerator Conference 2003. Our first measurements of fast neutron, stepped doses at the UC Davis McClellan Nuclear Reactor Center (UCD MNRC) were presented at the European Particle Accelerator Conference 2004. We have extended the doses, included other manufacturer’s samples, and measured induced radioactivities which are discussed in detail
Recommended from our members
Radiation Hardness Testing of Materials at the UC Davis/ McClellan Nuclear Radiation Center
The UCD/ MNRC research reactor of the TRIGA type is designed to be operated at a nominal 2 .0 MW steady state power as well as pulse and square wave operation. It is cooled and moderated by light water and reflected by graphite. The reactor core is located near the bottom of a water-filled aluminum vessel 7.0 ft in diameter and 24.5 ft in height. It went first critical in 1990 and has since become the highest power TRIGA reactor in the U.S. Radiation hardness testing of materials is made possible through the so-called “neutron irradiator” which provides fast neutron exposure to samples with minimal contamination from thermal neutrons and gamma rays. This neutron irradiator has three primary components; conditioning well, exposure vessel, and detachable upper shield for the exposure vessel. The conditioning well is installed adjacent to the annular graphite reflector inside the reactor tank. It is held vertically in place and rests at the bottom of the tank. The well-structure is shielded with sufficient boron nitride and lead encased in aluminum to remove thermal neutrons and gamma rays, respectively. The removable and water-tight exposure vessel has a usable inner space of approximately 7” in diameter and 9” in height. There are six removable titanium plates with holes arranged in a hexagonal shape which can hold the components to be irradiated. It also contains a valve at the bottom to purge and pressurize an assembled unit with helium in order to reduce Argon-41 production during irradiation. The exposure vessel is lined with boral and gadolinium paint to insure minimal leakage of thermal neutrons. The detachable upper shield contains boron nitride and lead encased in aluminum to complete the upper shield for the exposure vessel before it is lowered into the conditioning well for irradiation. Monte Carlo code simulation is benchmarked with multiple threshold neutron flux measurements. The converted 1 MeV equivalent silicon neutron flux at 1.5 MW operating power is 2.3 x 10^10 n/cm2.sec. Among others, materials such as silicon based devices, coatings for metals, superconducting magnets which are susceptible to fast neutron exposure and damage in their working environments are examined. This unique irradiation facility enables us to provide credible information regarding fast neutron radiation tolerance of materials used in crucial applications