Open vs. Closed Fuel Cycle

France gets about 75% of its plutonium fuel from material that the United States classifies as high-level nuclear waste.

An open fuel cycle uses reactor fuel once and stores spent assemblies permanently. A closed fuel cycle reprocesses spent fuel to extract usable plutonium and uranium, fabricates them into new fuel, and sends them back through the reactor. The two approaches produce nearly identical electricity but differ sharply on cost, waste volume, and the risk that separated plutonium could be diverted for weapons.

Spent fuel leaving a light-water reactor still contains about 95% uranium and roughly 1% plutonium. The remaining 4% is genuinely problematic high-level waste: fission products and minor actinides with half-lives ranging from decades to millennia.

The closed cycle (France). Chemical reprocessing separates plutonium and residual uranium. That plutonium gets blended with uranium to make mixed-oxide (MOX) fuel, which goes back into reactors. Waste volume drops substantially, though the remaining waste is more concentrated.

So why doesn't every country with nuclear power do this?

Two problems. Reprocessing is expensive: France's cycle costs more per kWh than buying fresh uranium. And separated plutonium is weapons-usable. The US banned commercial reprocessing in 1977 under President Carter precisely because civilian plutonium stockpiles create a proliferation pathway that geologic storage does not. The US currently holds roughly 90,000 metric tons of spent fuel at reactor sites with no permanent repository in operation.

The fuel cycle choice is a policy bet about whether proliferation risk outweighs the waste management benefit of reprocessing, a tradeoff the US and France resolved in opposite directions.

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