U-Mo Monolithic Fuel for Nuclear Research and Test Reactors

JOM, Nov 2017

Ramprashad Prabhakaran

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U-Mo Monolithic Fuel for Nuclear Research and Test Reactors

JOM U-Mo Monolithic Fuel for Nuclear Research and Test Reactors RAMPRASHAD PRABHAKARAN 0 0 1.-Pacific Northwest National Laboratory , Richland, WA, USA. 2.- , USA - 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 per the International Atomic Energy Agency (IAEA) database dated April 2016, there are 243 operational research reactors, 7 under construction, 11 being planned, 134 reactors have been permanently shut down and 352 reactors have been decommissioned. About half of the operational research reactors are over 40 years old.3 The U.S. Nuclear Regulatory Commission (NRC) regulates 42 research and test reactors of which 31 are currently operating. Most research and test reactors are at universities or colleges in the United States.2 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) Ramprashad Prabhakaran is the JOM advisor for the Nuclear Materials Committee of the TMS Structural Materials Division, and guest editor for the topic U-Mo Monolithic Fuel for Nuclear Research and Test Reactors in this issue. 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 Eighty-seven of the targeted 106 research and test reactors have been or can be converted from the HEU to LEU fuel, using the RERTR qualified dispersion fuels (fuel consists of fuel kernels surrounded by aluminum matrix material; density: 8 g/cm3).9 The remaining 19 reactors have an exotic geometry and/or are highpower/high-flux reactors. A majority of the This has led to a new pursuit of developing a high uranium density monolithic fuel that possesses the greatest possible uranium density in the fuel region. Based upon the density requirements and irradiation performance, metallic uranium alloy was chosen as a superior candidate for fuel materials.5 Uranium has some material drawbacks, such as poor oxidation and corrosion resistance, low hardness and yield strength, and lack of dimensional stability of the room-temperature alpha phase. Dimensional stability of the fuel during reactor operation is extremely important.12 Therefore, the high-temperature gamma (c) phase is desired, based on the is (...truncated)


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Ramprashad Prabhakaran. U-Mo Monolithic Fuel for Nuclear Research and Test Reactors, JOM, 2017, pp. 2529-2531, Volume 69, Issue 12, DOI: 10.1007/s11837-017-2612-3