The way I understand it, water is a also a neutron absorber, so a light water reactor require higher enriched fuel than a graphite reactor.
Since enriching uranium is expensive, using graphite ends up being cheaper (as long your reactor doesn’t explode).
Do you have a cite for that? It’s not that I don’t believe you but I have read elsewhere that the graphite tips were either removed or changed (depending on whose article you read). I poked around on google for a bit but didn’t find anything definitive, and I’d like to read the actual details of what they really did from a more reliable cite than what I have seen so far.
also IIRC the RBMK design could be used to produce weapons-grade plutonium.
Reading the accounts of what led up to the disaster, I find myself wondering what options they would have had, had they realized they put the reactor in such an unstable state.
INSAG-7, page 128, Figure II-13. See also the text summarizing safety improvements beginning on page 124.
There must be certain pros to graphite moderation since they are still proposed for Russian MKER reactors (though Wikipedia notes none have yet been completed) alongside other projects like pressurized water reactors and sodium-cooled reactors. The aforementioned dual-use potential (power as well as weapons-grade plutonium) might have been a factor?
Isn’t it true that even if the graphite rods had been inserted in the reactor as is, if the water had not boiled off and or Xe-135 had not been burned away, the accident would not have happened.
One thing that a lot of people don’t get (and the same misunderstandings were rampant after Fukushima) is that anything that is put into the atmosphere (or oceans) will be diluted more and more the further you get from the source of the incident, to the point that the affects become negligible at great distances. The danger of radioactivity in the ocean (or in the case of Chernobyl, in the air) hundreds or more miles away tends to be overstated, because any increase in radiation will be incredibly less than that of normal background radiation. I know that after Fukushima, people were blaming mutant fish found off the coast of California on Fukushima. But there was no credibility to any of that.
Chernobyl was ‘a perfect storm’ of incompetency, everything from the poor reactor design up to the failure of those in charge to follow proper safety procedures and lots of stuff in between, all were partly to blame. Note that the miniseries was fictionalized so you are better off not using it as if it was a documentary.
The water flashed to steam as a result of the massive power surge, though. Similarly, most of the control rods were pulled out because of the xenon poisoning; if the reactor had been operating normally they wouldn’t have overridden safety instructions and reduced the margin of control like that.
The final flash to steam that blew up the reactor was a result of the power surge, but was the power surge not started because the lower water flow through the reactor, caused by the test, resulted in more boiling and thus the positive void coefficient rearing its head? At that point more boiling led to higher reactivity which burned off more xenon which led to higher reactivity, and then it ran away and flashed all the water to steam and exploded.
There apparently is disagreement over whether the operators pressed the SCRAM/AZ-5 button simply to end the test before the power surge happened, as a response to increasing but still manageable power levels (as depicted in the show), or during/after the final major power spike. Of course we’re talking a difference of maybe five seconds between these three possibilities, so we’ll probably never know for sure. Anyway, only in the first scenario would AZ-5 have actually caused the explosion. That said, most literature seems suggests that the reactor began surging as a result of the lower water flow from the test, so AZ-5 in those scenarios either did nothing or perhaps accelerated the destruction of the reactor (that was going to happen anyway) by a few seconds.