Scientific American: Safer Nuclear Reactors Are on the Way

Resilient fuels and innovative reactors could enable a resurgence of nuclear power

Controlling carbon in the atmosphere will require a mix of energy technologies—potentially including nuclear reactors, which emit no carbon but are seen as risky because of a few major accidents. That risk could be greatly reduced.

Commercial reactors have used the same fuel for decades: small pellets of uranium dioxide stacked inside long cylindrical rods made of a zirconium alloy. Zirconium allows the neutrons generated from fission in the pellets to readily pass among the many rods submerged in water inside a reactor core, supporting a self-sustaining, heat-producing nuclear reaction.

Trouble is, if the zirconium overheats, it can react with water and produce hydrogen, which can explode. That scenario fed two of the world’s worst reactor accidents: the 1979 potential explosion and partial meltdown at Three Mile Island in the U.S. and the 2011 explosions and radiation release at Fukushima Daiichi in Japan. (The 1986 Chernobyl accident was caused by faulty reactor design and operation.)

Manufacturers such as Westinghouse Electric Company and Framatome are hastening development of so-called accident-tolerant fuels that are less likely to overheat—and if they do, will produce very little or no hydrogen. In some of the variations, the zirconium cladding is coated to minimize reactions. In others, zirconium and even the uranium dioxide are replaced with different materials. The new configurations could be slipped into existing reactors with little modification, so they could be phased in during the 2020s. Thorough in-core testing, which has begun, would have to prove successful, and regulators would have to be satisfied. In a bonus, the new fuels could help plants run more efficiently, making nuclear power more cost-competitive—a significant motivation for manufacturers and electric utilities because natural gas, solar and wind energy are less expensive.

Although nuclear power has stalled in the U.S. and is being phased out in Germany and elsewhere, Russia and China are building aggressively. These markets could be lucrative for the manufacturers of these new fuels.

Russia is also deploying other safety measures; recent installations at home and abroad by the state-run company Rosatom have newer “passive” safety systems that can squelch overheating even if electrical power at the plant is lost and coolant cannot be actively circulated. Westinghouse and other companies have incorporated passive safety features into their updated designs as well.

Manufacturers are also experimenting with “fourth generation” models that use liquid sodium or molten salt instead of water to transfer heat from fission, removing the possibility of dangerous hydrogen production. China reportedly intends to connect a demonstration helium-cooled reactor to its grid this year.

In the U.S., lack of a permanent, deep geological repository for spent nuclear fuel has long put a brake on expanding the industry. Political sentiment may be changing. This spring, surprisingly, more than a dozen U.S. legislators proposed measures to restart licensing for the Yucca Mountain nuclear waste repository in Nevada, touted since 1987 as the country’s leading storage site. Meanwhile Senator Lisa Murkowski of Alaska is advocating for very small, modular reactors being developed at Idaho National Laboratory. (Rosatom is making small reactors, too.) And a group of Western states has entered a tentative deal with NuScale Power in Oregon for a dozen of its modular reactors. Improved fuels and growth in small reactors could be a big part of a nuclear power rebirth.

By:  Mark Fischetti
Source: Scientific American