Since no spent nuclear fuel has yet been stored for thousands of years, how can we be sure that it will be safe?
Actually, there is direct experience for millions of years with nuclear waste. It would appear that in the West African republic of Gabon, a uranium mine was discovered in 1972 that had up to 60% of uranium in the ore. The concentration was sufficient to sustain a nuclear chain reaction more than 200 million years ago. Scientists have determined that the chain reaction occurred intermittently over a period of 500,000 years! Despite being in a wet tropical region, the radioactive fission products remained locked in the natural repository and migrated only a few inches in millions of years. These radioactive fission products have long since decayed to stable isotopes.
