U-Mo Monolithic Fuel for Nuclear Research and Test Reactors

Abstract

Research and test reactors consist of a wide range of civil and commercial nuclear reactors that are generally not used for power generation. The primary purpose of these reactors is to provide a neutron source for research and development purposes. These reactors are used for a number of applications, such as testing and analysis of materials, industrial processing and production of radioisotopes. In addition to the nuclear field, these reactors are also used in other areas, such as physics, chemistry, biology, geology, archeology, environmental science, and medicine. 1,2 As Research and test reactors are smaller in size and operate at lower temperature (typical coolant temperature is below 100°C) when compared to power reactors, but the operating conditions are more rigorous. The peak power density is about 5 kW/cc for a typical power reactor, whereas it could be about 17 kW/cc (in the fuel meat) for a typical research and test reactor. The burn-up is also very high in a research and test reactor. In a power reactor, burn-up is limited to less the 10% of the heavy metal while many research reactors will see complete depletion of heavy metal in peak locations. 4 The power of a typical power reactor is about 3000 MWt (sufficient to power about 200,000 households in the peak summer), whereas it is only in the range of 0.10 W (sufficient to power a night lamp) and 20 MWt (sufficient to power about 20 standard medical x-ray machines) for a typical research and test reactor. 2 These reactors are also covered by IAEA safety inspections and safeguards, similar to power reactors. These reactors employ a wider range of designs when compared to power reactors. 5 About 80% of the world's power plants are classified into two basic types (pressurized water reactors and boiling water reactors). 3 The first research and test reactors built around the 1940s which employed LEU (low enriched uranium: < 20 wt.% U-235) fuel were low-powered reactors, used mainly for studying reactor physics and reactor technology. However, due to the increased use of these reactors for a number of applications, the demand for higher specific power and the need to use greater U-235 concentrations increased, thus leading to the use of HEU (high enriched uranium: > 20 wt.% U-235; typically, 90% enriched) fuel, instead of LEU fuel. 4 The Reduced Enrichment for Research and Test Reactors (RERTR) Program was initiated by the United States Department of Energy in August 1978, in response to the increased concern about the potential diversion of HEU for use in nuclear weapons. 4,6 Since the 1980s, the United States policy has encouraged the use of LEU fuels for all new research and test reactor designs worldwide, and also for the conversion of the existing reactors from the HEU to LEU fuel. 7 The RERTR program (now called the Reactor Conversion Program under the National Nuclear Security Administration's Office of Material Management and Minimization) identified 106 research and test reactors in the United States and overseas for conversion to LEU fuel. 8...

Phonon dispersion of Mo-stabilized γ -U measured using inelastic x-ray scattering

“…2 Of the γ-U alloys, γ-UMo shows the best combination of high density and irradiation performance, which makes it a promising candidate as a replacement for High-Enriched Uranium fuel in nuclear reactors. 3 The α-, β-, and γ-U phases have been the focus of several experimental and theoretical efforts focusing on the temperature-dependence of the phonon spectrum and how it is influenced by electronic contributions. [4][5][6][7][8][9][10][11] The most detailed studies have been restricted to α-U, and indicate that electronic contributions may be responsible for (1) the unusually large thermal softening and (2) a large contribution to entropy that stabilizes the high temperature β-and γ-U structures.…”

Discovery, nuclear properties, synthesis and applications of technetium-101

“…Low enriched uranium (LEU)-Mo alloy dispersion and monolith fuels, i.e., LEU-10%Mo, have been implemented as an alternative to high enriched uranium (HEU) fuels for fission reactors. The desirable refractory behaviour of Mo combined with its high solid solubility in the gamma ( γ ) bcc phase of U makes it a viable candidate for generating a robust, high-temperature, higher-density alloy 130 , 131 . The isotopics of the Mo used in the fuel, however, are non-negligible, where the average neutron capture cross-section is σ c = 2.57 b for natural Mo, a value 13-times larger than that of zirconium (Zr), a common structural material used in the core of thermal reactors.…”