Saturday, June 09, 2018

The Nuclear Reactor that Makes Its Own Fuel

Nuclear cooling towers (Credit: Click to Enlarge.
To say that nuclear energy has a bad name would be an understatement.  To say that it has a future, however, would be to state the obvious.  Despite soaring solar and wind generation capacity additions globally, the world is still almost completely reliant on fossil fuels—and nuclear power is a much cleaner, cheap alternative to these.  Rather, it would be, were it not for the risk of a meltdown and the problem with radioactive waste.

One company, chaired by none other than Bill Gates, says it has found solutions to both these problems.

TerraPower came into existence in 2008 with the purpose of finding a reliable alternative to fossil fuels using a nuclear reactor concept first developed more than half a century ago.  The breed and burn reactor, so called by the Russian scientist who first conceived of it, Savely Feinberg, was supposed to be able to produce the fuel it needed to sustain the nuclear reaction within itself, as the reaction progressed.

Breed and burn reactors would require much less enriched uranium and could keep the reaction going for decades.  At the time, the concept proved too difficult and costly to implement, and the problem with nuclear waste as well as the Chernobyl and Fukushima disasters lay too far in the future for anyone to care.

Fast-forward about four decades and two researchers, one of them the father of the H-bomb Edward Teller and the other an astrophysicist, Lowell Wood, designed a new version of the breed and burn reactor that TerraPower chose as a starting point for its quest to find the nuclear reactor of the future.

In a recent story for IEEE Spectrum, Michael Koziol details how the TerraPower reactor works, noting its advantages over other reactors such as—primarily—the ability to use uranium waste as a fuel and need much less enriched uranium.  Also, a major advantage would be the eliminated need to dispose substantial amounts of radioactive waste as there would be very little waste:  most fuel will go towards keeping the chain reaction going with the help of fuel pins enclosed in the reactor.  And whatever waste there is—a fifth of the waste of current reactors—would be used to start new chain reactions in other traveling wave reactors.

Theoretically, such a reactor could operate for 50 years without interference and much more efficiently than the currently dominant light water reactors as it would use liquid sodium as a coolant and not water.  Liquid sodium is great at moving heat out of a reactor’s superheated core and transporting it to water-heating system that then produces heat to power the turbines.  Yet sodium is also great at another thing:  burning.

According to one prominent critic of traveling wave reactors using sodium as coolant, the President of the Institute for Energy and Environmental Research, these reactors carry a very high risk of explosion as the sodium is extremely flammable upon contact with oxygen.  This, combined with other challenges, make them unviable economically.

Arjun Makhijani detailed all the challenges of such reactors in a 2013 paper, where he noted the risk of sodium leaks resulting in fire, such as the one that led to the emergency shutdown of a TWR in Japan in 1995.  Sodium leaks also prevented a TWR in France from operating at above 7 percent of capacity for a decade before that reactor, too, was shut down.  Besides the leaks, Makhijani said, TWRs are simply not competitive on cost and will likely be obsolete before they are commercialized.

Indeed, it will be a couple of more decades before these reactors could begin being built on a large enough scale to make a difference in global emissions.  TerraPower, which has partnered with the China National Nuclear Corporation, plans to start building a test reactor using the traveling wave concept in China in 2019.  If all goes well, it would start operation in the mid-2020s.

Multiplying its success, if we assume the reactor is successful, will take twenty or more years, Koziol notes.  So far, everything is being done in the lab.  The test reactor will reveal whether the traveling wave reactor design as developed by Bill Gates’ TerraPower has a future as a reliable, economically viable alternative to coal, gas, and existing nuclear power technology.

Read original at The Nuclear Reactor that Makes Its Own Fuel

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