I base it on common sense and several known examples. The common sense part is that we know that we have to keep managing the waste after the plants no longer produce any energy, or money. Managing the waste costs money, and since we can't make estimates for even a decade into the future it's self-evident that we don't know what 500 years of storage will cost.
Secondly from known examples where the logic has already proven itself in practice.
One example is France, where the taxpayers have recently had to pay over 50 bn euros in costs that were never planned or paid for by the operator.
Another example is the cleanup costs for the German Asse II storage site. Several billion Euros for the cleanup alone, and the things you extract from that site will have to be stored someplace else at high cost as well, so the costs will keep ticking. Operators don't pay that either, taxpayers do.
Another example is Sweden, where they have a storage facility for second-rate waste, (i.e. low-intensity waste), which is mandated to operate for at least 500 years. It is currently employing over 100 highly qualified people and is going to grow over the next few decades.
This facility is currently underfunded for its planned operations, and please note that this is not even accounting for the costs of handling high-intensity waste. This site will only manage secondary waste, like contaminated pipes, pumps, filters and such - so the actual total costs are severely underestimated. Taxpayers in Sweden will have to pay these costs in the years to come.
Secondly from known examples where the logic has already proven itself in practice.
One example is France, where the taxpayers have recently had to pay over 50 bn euros in costs that were never planned or paid for by the operator.
Another example is the cleanup costs for the German Asse II storage site. Several billion Euros for the cleanup alone, and the things you extract from that site will have to be stored someplace else at high cost as well, so the costs will keep ticking. Operators don't pay that either, taxpayers do.
Another example is Sweden, where they have a storage facility for second-rate waste, (i.e. low-intensity waste), which is mandated to operate for at least 500 years. It is currently employing over 100 highly qualified people and is going to grow over the next few decades.
This facility is currently underfunded for its planned operations, and please note that this is not even accounting for the costs of handling high-intensity waste. This site will only manage secondary waste, like contaminated pipes, pumps, filters and such - so the actual total costs are severely underestimated. Taxpayers in Sweden will have to pay these costs in the years to come.