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Ceramic Fabrication Methods and Actuator Designs
Published in Kenji Uchino, Micro Mechatronics, 2019
Particle shape, particle size distribution, and compositional uniformity are key factors to control when producing ceramic powders in order to optimize the reproducibility of the electromechanical response. A conventional method for producing powders is the mixed-oxide method, which involves firing a mixture of oxide powders in a process called calcination. The calcined material is then mechanically crushed and milled into fine powders. One major disadvantage of the mixed-oxide method is that it tends to produce materials with pronounced microscale compositional fluctuations. Wet chemical methods (such as the co-precipitation and alkoxide methods) are thus generally preferred, as they produce more compositionally homogeneous ceramics. In this section, these processes for producing barium titanate, lead zirconate titanate, and lead magnesium niobate ceramics are reviewed.1
Nuclear and Hydropower
Published in Roy L. Nersesian, Energy Economics, 2016
Spent fuel can either be sent to permanent storage or reprocessed. Reprocessing plants, located in Europe, Russia, and Japan, separate uranium and plutonium. Recovered uranium is converted back to uranium fluoride and reenriched with U235. Plutonium can be blended with enriched uranium to produce a mixed oxide fuel called MOX. MOX has been used commercially since the 1980s with about 2,000 tons fabricated and loaded in power reactors. Europe has about 40 reactors in Belgium, Switzerland, Germany, and France licensed to use MOX, with 30 reactors loaded with MOX. Japan has about ten reactors licensed, with several loaded with MOX. MOX fuel assemblies generally make up about one-third of a core, but some may have as much as half. France and Japan (before Fukushima) planned to expand the role of MOX and some new advanced light water reactors are able to accept complete fuel loadings of MOX if desired. The US has done some development work in the past with MOX, but does not favor reprocessing of spent fuel assemblies as a result of a decision made early on. Considering the build-up of the number of spent fuel assemblies with no permanent facility for storing them, perhaps it is time to reconsider this decision.
Control and Shielding Materials
Published in C. K. Gupta, Materials in Nuclear Energy Applications, 1989
There exists considerable interest in increasing use of gadolinium as burnable poison in PWRs. One good reason is that it provides good reactivity hold-down at the beginning of fuel life. Another reason for the trend is that gadolinia, unlike boron compounds, can be readily mixed with uranium oxide and does not have to be lumped in separate rods. Its odd-mass number (A) isotopes, 155Gd and 157Gd, account for its high thermal cross section, which results in a more complete burnout toward the end of the cycle, which yields better neutron economy and hence a higher fuel utilization. As additional advantages of increased usage of gadolinium in PWRs, mention may be made of (1) no displacement of water, and practically no displacement of fuel, resulting in an easier lattice utilization; and (2) elimination of the problems of handling and disposal of the extra burnable poison rods at the end of cycle. Potential disadvantages include (1) a degraded thermal conductivity and lower melting point of the mixed oxide, which leads to a lower power generation; (2) a more complex configuration which is harder to analyze; and (3) an increased cost of fuel assembly fabrication. As it stands, the advantages outweigh the disadvantages, and the fuel manufacturers are moving toward enhanced use of gadolinia.
Scoping Studies for a Lead-Lithium-Cooled, Minor-Actinide-Burning, Fission-Fusion Hybrid Reactor Design
Published in Nuclear Science and Engineering, 2023
Joshua Ruegsegger, Connor Moreno, Matthew Nyberg, Tim Bohm, Paul P. H. Wilson, Ben Lindley
There are many different fuel cycle schemes that can be used for the recycling of plutonium and MAs, either separately or together, with associated advantages and disadvantages.5 A subset of possible schemes partition uranium and plutonium (and possibly neptunium), from MAs and FPs, allowing separate recycling of plutonium and MAs. An advantage of this scheme is that U/Pu-based fuels are suitable for a wide range of reactor applications, including as mixed-oxide fuel in thermal reactors. A disadvantage is that MAs must then be handled separately in a specialist system, such as an externally driven system. This is mitigated by the relatively low proportion of recycled fuel that must be handled in this manner. The fission-fusion hybrid (FFH) is one such system. While FFHs have been investigated previously, their use with pure MA fuel (i.e., not containing other transuranics) is a relatively unexplored area.
Best Estimate Plus Uncertainty (BEPU): Why It Is Still Not Widely Used
Published in Nuclear Technology, 2019
Evgeny Ivanov, Giovanni Bruna, Antonio Sargeni, Franck Dubois
This study has been intended to assess whether the last term would be reduced due to progress in modeling and knowledge of nuclear physics. It should be noted that there is no available mock-up experiment representative of mixed oxide (MOX)gMOX fuel is made of plutonium and uranium oxides.–loaded systems with epithermal spectra as it seems complicated to establish brand new ones for reasons of cost and safety. Indeed, an epithermal spectrum means the worst neutron economy and hence the biggest critical mass (i.e., increased costs) while any variations of moderation ratio—indifferently increasing or decreasing—insert positive reactivity (making a safety issue). Thus, we had to use available undermoderated and overmoderated IEs together with a few epithermal ones somehow “enveloping” the field of interest in order to transpose observations onto the applications.14