In her 2006 book, Uncertainty Underground, Macfarlane criticized plans to store spent nuclear fuel in a mountain near Las Vegas called Yucca Mountain. She said the seismic and volcanic activity as well as oxidizing in the environment would make the nuclear waste unstable. Macfarlane has supported storing nuclear waste at reactor sites in dry casks and the allocation of billions to find a suitable geologic repository for storage over the next few decades.