Novel silicon carbide joining for new generation of accident-tolerantnuclear fuels

janfeb13

Novel silicon carbide joining for new generation of accident- tolerant nuclear fuels (Credit: MIT.) By Edward D. Herderick Figure 1. A joined assembly of two α-phase SiC blocks. Image was taken after irradiation at MIT research reactor. TFukushima, Japan, an extreme accident such as Fukushima readily absorbs neutrons. When theC, that4The control rods, in general, aremade of a material, such as BThere is a broad sense that SiC couldprovide additional margins of safety inhe disaster at the Daiichi nuclear power plant Daiichi, and there is significant activ- control rods are inserted fully, they presented a key question to ity in this area of research.1-4 However, absorb so many neutrons that the transitioning from the current state- chain reaction leading to heat genera- the materials community: of-the-art zirconium alloy nuclear fuel tion cannot take place. However, even “Are there materials inno- cladding to a SiC composite cladding after operators insert the control rods vations that can profoundly and it would represent the biggest shift amount of heat is generated by radioac-and stop the chain reaction, a certainis fundamentally a materials challenge, improve the safety of exist- in light water reactor materials tech- tive decay of atomic fragments gener- ing light-water reactors?” introduction. Therefore, the ceramic amount of decay heat is relatively smallated during the chain reaction. Thatnology since their original design and Fortunately, the answer is engineering community has a strong compared with the overall production “yes” on many fronts, but part to play in supporting and leading of the operating reactor. Nevertheless, development of enhanced, accident- it is substantial enough that it must be although there are many tolerant nuclear fuels. removed by circulating cooling water promising new materials and for several hours after the reactor is technologies, there are still ding and Fukushima Daiichi - shut down.The danger of this decay heat cameBackground on nuclear fuel clad many miles of development More than 90 percent of all the into focus when operators could not and implementation test- nuclear power plants operating glob- modulate heat generation in the Japan ally are of the light-water reactor incident. A narrative contained in the ing to travel on the road to (LWR) design, which produces heat Special Report on Fukushima published regulatory approval of any by controlled nuclear fission and is by the American Nuclear Society5 sets new reactor technologies. all 104 operating nuclear power plants the stage:“The Tohoku earthquake, whichcooled by water. In the United States, One example is a study of silicon are LWR designs.5 The main element occurred at 2:46 p.m. (Japan time) on carbide for a promising new approach of LWR fuel is an array of individual Friday, March 11, 2011, on the east to fuel rod safety underway at EWI fuel rods that are long (approximately coast of northern Japan, is believed (Columbus, Ohio; formerly known 4 meters) and thin (approximately to be one of the largest earthquakes as the Edison Welding Institute). 10 millimeters) composed of a high- in recorded history. Following the Although the research remains pre- performance zirconium base alloy in earthquake on Friday afternoon, the liminary, at least on the scale of typical the shape of a tube. Inside the fuel rods nuclear power plants at the Fukushima regulator hurdles and industry accep- are individual pellets of UO fuel that Daiichi, Fukushima Daini, Higashidori, tance, the facility’s work on SiC reactor can undergo a nuclear fission chain Onagawa, and Tokai Daini nuclear2 fuel rod applications has shown positive reaction, which, in turn, generates heat power stations (NPSs) were affected, results, including an evaluation after six that can be converted to electricity. and emergency systems were activated. months of exposure of an experimental Fuel rods are assembled into bundles The earthquake caused a tsunami, which assembly in a test reactor. with control rods, and operators place hit the east coast of Japan and caused a EWI is not alone in believing that these assemblies in the reactor core loss of all on-site and off-site power at SiC ceramic-matrix composites are where the reaction and energy genera- the Fukushima Daiichi NPS, leaving it a prime candidate for fuel cladding. tion takes place. without any emergency power.” 32 www.ceramics.org | American Ceramic Society Bulletin, Vol. 92, No. 1


janfeb13
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