[morning_gelato]

With modern reactor designs the inherent safety mechanisms mean that humans are not in the loop to reduce reactivity or remove decay heat.

Here's an example from Argonne National Laboratory:

> In the first test, with the normal safety systems intentionally disabled and the reactor operating at full power, Planchon's team cut all electricity to the pumps that drive coolant through the core, the heart of the reactor where the nuclear chain reaction takes place. In the second test, they cut the power to the secondary coolant pump, so no heat was removed from the primary system.

"In both tests," Planchon says, "the temperature went up briefly, then the passive safety mechanisms kicked in, and it began to cool naturally. Within ten minutes, the temperature had stabilized near normal operating levels, and the reactor had shut itself down without intervention by human operators or emergency safety systems."

https://www.ne.anl.gov/About/hn/logos-winter02-psr.shtml

[stormbrew]

There is obviously a difference between:

- There are many passive systems that work in concert to prevent the fission material from having a runaway chain reaction that continues on its own,

and

- It is literally impossible within our understanding of physics for the reaction to continue without the continued application of power to the reaction chamber.

No matter how 'safe' the former gets, it's just asymptotically approaching the latter. There will always be more assumptions and caveats involved in preventing a self-sustaining reaction from continuing.

In particular, re. that article, a lot seems to be resting on the sodium cooling pool being present while there's something else going wrong. So what if an earthquake breaks it open and dumps it out. Or a bomb.