The element in question, thorium, has been portrayed as a potential nuclear fuel source that could not be used to make nuclear weapons.
"We think that the public debate regarding its proliferation-resistance so far has been too one-sided," said lead author Steve Ashley of the University of Cambridge.
"Small-scale chemical reprocessing of irradiated thorium can create an isotope of uranium - uranium-233 - that could be used in nuclear weapons. If nothing else, this raises a serious proliferation concern."
Thorium has been promoted as a uranium alternative for nuclear power generation, in large part because it is three to four times more abundant, and deposits are found in many parts of the world. In addition, many scientists have noted that the most common form, thorium-232, cannot actually be used to produce nuclear fission. To be used for nuclear power, thorium-232 must be bombarded with neutrons until it radioactively decays into uranium-233, also producing the highly dangerous and radioactive isotope uranium-232 i as a result. All of this means, thorium advocates say, that the production of weapons-grade uranium from thorium would require the use of large, high-tech facilities that could be easily monitored by nuclear regulators.
During its natural process of radioactive decay, thorium-232 breaks down into thorium-233. Just 22 minutes later, much of the thorium-233 decays into an element known as protactinium-233. At this stage, it is possible to separate the protactinium-233 out from the protactinium-thorium mix. Twenty-seven days later, the protactinium-233 will have naturally decayed into uranium-233, without producing any uranium-232 that would need to be handled by large facilities. This natural process could be accelerated, the scientists note, by bombarding the elements with neutrons at each stage.
"The problem is that the neutron irradiation of thorium-232 could take place in a small facility," Ashley said. "It could happen in a research reactor, of which there are about 500 worldwide, which may make it difficult to monitor."
Based on prior experiments, the authors conclude that it would take only 1.6 metric tons of thorium to produce the eight kg of uranium-233 required to make a nuclear weapon. It would be possible to refine this much uranium-233 "in less than a year," they said.
"The most important thing is to recognize that thorium is not a route to a nuclear future free from proliferation risks, as some people seem to believe," Ashley said.
"We need more debate on the associated risks, if we want a safer nuclear future."