Q: Given a scientific passage and an answer, generate a question for the given answer.
Passage: Nuclear power is a controversial subject in California and most other places. Nuclear power has no pollutants including no carbon emissions. However, power plants are not always safe. The long-term disposal of wastes is a problem that has not yet been solved. The future of nuclear power is murky. Find out more at: http://science. kqed. org/quest/audio/new-nuclear/. Answer: nuclear
A:
What kind of power does not produce any pollutants, but produces waste that can be difficult to dispose of?