[08-15]

Can you explain what that's supposed to mean?

An intentional nuclear explosion is air exploding because it's heated by a nuclear reaction. Chernobyl was water exploding because it was heated by a nuclear reaction. It's the same thing, but it's also a steam explosion. Is that paper saying "Chernobyl was not an ordinary boiler failure"? Of course it wasn't.

[mhh__]

As in, the conditions in a few of the fuel channels were sufficiently extreme as to cause an actual critical explosion (is the hypothesis)

[08-15]

Yeah, and that phrase has no meaning. Especially "critical explosion" is nonsense, because "critical" in the context of a nuclear chain reaction means "steady state".

What happened, as commonly understood, is that the reactor was in a state where it had a positive temperature coefficient. The insertion of the graphite-tipped control rods added reactivity, it became super-critical, and thanks to feedback, the power spiked to an order of magnitude more than the design power. All that heat flashed the water in the pressure channels to steam, which blew the top off the reactor. A steam explosion caused by heat from a nuclear reaction.

Now what the hell is a "critical explosion", what is "a nuclear jet", and how is a "nuclear explosion" not the sudden expansion of water or air?

[mhh__]

As in nuclear bomb goes bang.

I don't know much about nuclear physics (particle yes, nuclear engineering no).

[08-15]

See, that's exactly the problem. They tack on "nuclear" and "critical" to empty phrases so they sound scary to people who know nothing about nuclear fission. Thanks for confirming.