The "cost" of decommissioning is in the destruction of production capacity. If you decommission a plant that has 20 years at 800MW lifetime yet, it's not the fi

The "cost" of decommissioning is in the destruction of production capacity. If you decommission a plant that has 20 years at 800MW lifetime yet, it's not the fixed amount to actually demolish the plant that's the problem (this money is, as you correctly say, already set aside for this purpose), it's the cost of getting those 20y x 800MW from somewhere else, both in purely financial terms, but also environmental: The only way Germany can replace their nuclear capacity is with coal and gas.