UK discounted provision for decommission costs: £100+ billion in 2013 https://www.theguardian.com/environment/2013/jun/23/britain-...
£161 billion in 2017 https://web.archive.org/web/20170516093449/https://www.gov.u...
£234 billion in 2018 https://www.gov.uk/government/publications/nuclear-provision...
... and counting.
UK: 15 reactors, ~10300 gross MWe. They analyzed and now think that decommissioning will cost £234 billion (309 billion USD).
USA: 98 reactors, 100350 gross MWe. 46 billion USD (Nuclear Waste Fund) are in provision.
One order of magnitude more power produced by the stuff to decommission in the US, and nearly 7 times less money to do so.
Decommissioning small and old reactors costs more, and entombing may, at least apparently (short-term), reduce the cost. In theory. Let's check a real and ongoing case: Oyster Creek. According to the EIA its construction costs were $488 million (2007 USD) ( https://www.eia.gov/nuclear/state/archive/2010/newjersey/ ). As soon as the decommission project started the Nuclear Regulatory Commission announced that it will cost "about $1.4 billion to shut down the plant". Not for an immediate and complete decommission, because the plant will stay in a “safe store” condition until 2075, with dismantling ((...)) set for a period between 2075 and 2078 ( https://www.powermag.com/oldest-u-s-nuclear-plant-shuts-down... ). Then new problems (costs!) may arise. Let's bet that, as usual, the taxpayer will pay.
Long-term waste management is another ticking bomb.
Moreover if there is a serious glitch (Chernobyl, Fukushima...), are bets are off. You can obtain an insurance policy for anything, AFAIK even for a space trip, but no insurance company covers such nuke risk.