I did not know about that aspect of nuclear plants and in my non-expert view it would be a major point against nuclear plants in the discussion how to solve climate change (at least until we learn how to secure them in case of a war). Am I wrong?
EDIT: I would also like to ask if you can recommend some source where curious layman with no knowledge of physics could learn a bit more about this.
You are not wrong that it's a major point in the discussion, but even with that it can still be better than the alternatives for baseline production (the part that intermittent sources like solar and wind can't cover). Remember that coal power add insult to injury by continuously releasing radioactive pollution.
The new designs are built with the expectation that power can be cut off. The new design shut themselves off passively without any damage (that we know of) when the power is gone.
Seems to me like it should have been this way from this start. Catastrophic meltdown caused by power loss, no matter how many power backup systems there are should have been a non-starter. Basically requiring a 100% SLA, 6 nines not enough, with catastrophic consequences for failing to adhere to 100% uptime. That is scary as hell.
> I did not know about that aspect of nuclear plants and in my non-expert view it would be a major point against nuclear plants in the discussion how to solve climate change
It's a reasonable criticism to make, but I think it tends to be a bit overblown. Modern reactors have redundant layers of systems to prevent such a disaster from occurring. In the ~60 year history of nuclear reactors Fukashima is the only time this type of failure has happened (Three Mile Island and Chernobyl were very different), and even then it was due to a cascading series of problems:
* In hindsight it was a really poor idea to locate a nuclear plant by the ocean in a region known for strong earthquakes and tsunamis.
* The backup generators flooded because they were located in the basements, another poor decision for an area at risk of tsunamis.
* TEPCO had additional generators and batteries on site within 6 hours of the earthquake, which was in time to prevent a meltdown, but they were unable to connect them to the plant's electrical system (I don't recall the details of why).
It's also worth mentioning that this is only a problem with large reactors. Smaller designs like those used in ships and submarines still have decay heat, but the reactor core is physically smaller so that it doesn't contain enough isotopes to cause a meltdown. Many nuclear advocates believe that we should be building more nuclear plants with smaller reactors for this reason as well as smaller reactors being easier to operate without getting into a dangerous state.
As far as reading, I highly recommend Atomic Accidents by James Mahaffey [0]. It's very well written, aimed at a total layman, and covers basically everything that has gone wrong since we as a species started seriously messing with nuclear materials in the 19th century.
EDIT: I would also like to ask if you can recommend some source where curious layman with no knowledge of physics could learn a bit more about this.