Ask An Engineer

Can nuclear waste be put to some positive use instead of just polluting the environment?

Technically yes, but we need to develop the technology to make it feasible…

By Elizabeth Dougherty

Technically yes, says Charles Forsberg, director of MIT’s Nuclear Fuel Cycle Study, a collaborative project between the Department of Nuclear Science and Engineering and the MIT Energy Initiative. “Some components of spent nuclear fuel can be recycled and used to make more energy. But it’s not economical to do so right now.”

Nuclear reactors typically use enriched uranium pellets for fuel. A starter device emits neutrons that split the atoms in the pellets. This atom splitting, called fission, releases more neutrons, which in turn split more atoms. This controlled chain reaction sustains itself until the fuel becomes “burned out” or “spent,” says Forsberg. “Like wet wood, it doesn’t burn well anymore.” Spent fuel can become high-level nuclear waste, or it can be recycled. Recycling the fuel, called reprocessing, involves removing the ash (fission products) and converting the uranium and plutonium into new fuel.

But according to MIT’s 2009 Future of Nuclear Power study (an update of one originally released in 2003), it is far cheaper to buy newly mined and enriched uranium than it is to recycle spent fuel. That’s not to say that nuclear waste might not have a higher value sometime in the future, when reprocessing techniques are better and costs come down, says Forsberg. Someday, he adds, “nuclear waste might be the world’s most valuable energy source.”

Pound for pound, uranium pellets are a million times more concentrated than fossil fuels. This means that nuclear reactors produce waste in much smaller volume than, say, coal plants. In one year, all nuclear reactors in the US (there are about 100 of them) produce only 2000 tons of waste. During the same year, coal plants produce 2 billion tons of carbon dioxide and 150 million tons of coal ash. And that ash stays ash forever; cadmium, arsenic and heavy metal toxicity does not decay over time the way nuclear waste decays.

Even though nuclear materials require special security and handling when they are transported and stored, all toxic materials carry the same environmental risks. “Whether it’s a municipal dump or a high-level nuclear waste repository, the basic principles are the same,” says Forsberg: “Don’t mess up the ground water.” Contaminated ground water causes human illness, whether it is contaminated by biological, chemical, or radioactive waste. The current solution for storing high-level nuclear waste is long-term burial deep underground—away from people and ground water—where the radioactivity decays away with time.

For now, MIT’s analyses point to a “once-through” fuel cycle as the best choice, but they are constantly looking for better fuel-cycle options because nuclear power is experiencing a resurgence brought on by concerns about climate change and declining oil reserves. “If we’re going to expand nuclear power, we need to rethink the fuel cycle,” says Forsberg. His team will be publishing an update on this topic in a new Future of Nuclear Fuel Cycle report due out in the spring of 2010.

Thanks to Jason Yujia Shen of Wuxi, Jiangsu Province, PRC, for this question.

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