Novel designs for nuclear reactors, being drawn up by researchers at MIT and a new research institute in the United Arab Emirates (UAE), could decrease the risk that nuclear fuel could be diverted for use in nuclear weapons.
When nuclear materials are in use inside a nuclear reactor, they’re too hot to steal, says Youssef Shatilla, a professor at the Masdar Institute, in the UAE. The greatest danger comes when fuel is being manufactured, when enrichment facilities can be used to make weapons-grade materials, or when nuclear materials are in transit, during either delivery or waste removal. To lessen the first danger, the government of the UAE plans to lease its fuel from other countries rather than making its own fuel. As a result, it won’t have the technology to enrich uranium for making nuclear weapons.
The MIT and Masdar researchers are working on the second problem. They’re designing new reactors that would need to be refueled far less often than conventional ones–once every 15 to 30 years rather than every 5 years. This would decrease the frequency of deliveries and the chances that the materials could fall into the wrong hands. “If you look at how you can divert nuclear material so it can be used in a weapons program, it is when the nuclear fuel is outside of the reactor core, when it’s relatively cool and people can manipulate it,” Shatilla says. “Our strategy is to keep the fuel inside the core as long as we can.” The new reactors would have the added benefit of producing at least one-third of the waste of existing plants.
The new designs are part of an effort by the UAE to convince the international community to approve its plans to build nuclear reactors to generate electricity. The UAE and other Middle Eastern countries want to build nuclear power plants as a way to meet fast-growing domestic electricity demand. This would let them export oil and gas rather than burning it to generate electricity. “You cannot stay on course burning your own precious resources to generate electricity,” Shatilla says. “In 30 to 40 years, oil and gas will be very expensive commodities–too expensive to burn.”
To decrease the frequency of refueling, the researchers at MIT and Masdar are investigating ways to get more energy out of a given amount of fuel. One way to do this, says Mujid Kazimi, a professor of nuclear engineering at MIT, is to increase the concentration of uranium-235, the isotope of uranium that undergoes fission to create the heat that drives nuclear power plants. Currently, nuclear fuels contain less than 5 percent uranium-235, but this can be enriched to about 20 percent without making the material suitable for use in weapons. However, increasing the enrichment level poses a couple of challenges. Manufacturing plants that make fuel pellets from enriched uranium will require new safety precautions, Kazimi says. What’s more, the fuel will need to be modified to ensure that the reactions don’t proceed too quickly. The presence of so much “fissionable material,” Kazimi says, could lead to a relatively quick chain reaction that would use up fuel too quickly. By incorporating materials known as burnable poison that absorb neutrons emitted during fission to slow down the reactions, the fuel could slowly generate heat over 15 years or more, he says.