Since the construction of the first commercial light water nuclear power plants (LWR) the design of their fuel rods hasn’t changed significantly. Mechanically robust and corrosion-resistant zirconium alloy (zircalloy) tubes are filled with ceramic fuel pellets, which get assembled into fuel assemblies for loading into the reactor.
Now it seems that silicon carbide (SiC) may soon replace the traditional zirconium alloy with General Atomics’ SiGa fuel cladding, which has been tested over the past 120 days in the Advanced Test Reactor at Idaho National Laboratory (INL). This completes the first of a series of tests before SiGa is approved for commercial use.
One of the main advantages of SiC over zircalloy is better resistance to high temperatures — during testing with temperatures well above those experienced with normal operating conditions, the zircalloy rods would burst while the SiC ones remained intact (as in the embedded video). Although normally SiC is quite brittle and unsuitable for such structures, SiGa uses a SiC fiber composite, which allows it to be used in this structural fashion.
Although this development is primarily part of the Department of Energy’s Accident Tolerant Fuel Program and its focus on melt-down proof fuel, the switch to SiC could also solve a major issue with zirconium, being its use as a catalyst with hydrogen formation when exposed to steam. Although with e.g. Fukushima Daiichi’s triple meltdown the zircalloy fuel rods were partially destroyed, it was the formation of hydrogen gas inside the reactor vessels and the hydrogen explosions during venting which worsened what should have been a simple meltdown into something significantly worse.
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