How long is nuclear waste around for before it is considered safe?

Answer 1

There are different ways of looking at this. And one should be warned that the idea of a half life is not immediately applicable to safety. Knowing the half life, you still have to do a lot of calculating, more than ordinary people can do in their heads.

The government of the United States has said high level waste from nuclear power plants will be safe in about 1,000,000 years. Unfortunately, there is no easily understood explanation of how they came to that number.

A much more easily understood number is used in Europe. The standard is that the material is safe when its radioactivity is no more than what comes from naturally occurring ores of uranium. This is easier because it can be calculated with some degree of precision, and the idea of safety is understandable. The number arrived at is 6,000,000 years.

To understand this fully, we have to keep in mind what 1,000,000 or 6,000,000 years means. Human history is only 5500 years old. But that history only applies to the places where it existed. Recorded history of most parts the world, including most of Africa, all of North and South America, and much of northern Europe and Asia is less than 1000 years old. It is really hard for anyone to imagine 1,000,000 years or what will happen in that time.