Cameron Tracy and colleagues argue that the US Department of Energy (DOE) should conduct a new safety assessment of its nuclear Waste Isolation Pilot Plant (WIPP) before loading it with 34 tonnes of plutonium from dismantled nuclear weapons (Nature 529, 149–151; 2016). We contend that the long-term risk of disposal in WIPP should be balanced against the benefits.

The reanalysis that the authors propose would take several years. During this time, Congress could well abandon the disposal programme. Leaving the plutonium above ground indefinitely would pose a much greater environmental threat than disposing of it in WIPP.

Disposal in WIPP would also offer a cheaper, simpler and more secure alternative (see to the unaffordable plan to convert the plutonium to mixed oxide with uranium and burn it in nuclear-power plants.

There is a way to keep the disposal programme moving. The DOE proposes to put 6 tonnes of excess weapons-usable plutonium in WIPP from its Savannah River site. This will not markedly affect the WIPP inventory. Packaging that plutonium for disposal will take about 6 years (see Meanwhile, the DOE could redo the WIPP safety analysis and evaluate other disposal options for the 34 tonnes of plutonium (see, for example,, which will remain in bunkers at Savannah River and in Texas until a solution is found.