The Ergosphere
Tuesday, June 25, 2019
 

Deconstructing HBO's "Chernobyl"

Thunderf00t does a bang-up job:




Edit:  Thunderf00t is a good storyteller but weak on the nuclear stuff.  Here are my notes, addressed as an open letter to him:

First, you missed a completely obvious way to debunk the "5 megaton" garbage.  It only took 10 megatons to completely erase the island of Elugelab in the Ivy Mike test.  5 MT would have scoured Pripyat off the ground and turned the entire Chernobyl power plant to vapor.  Instead, most of the reactor building was still standing!  That wasn't a megaton or even kiloton-level explosion; it was worth, at most, a few hundred pounds of TNT.

Second, you've got a whole lot of your concepts about nuclear fission pretty badly wrong.

The reason that low-enriched uranium can't make a bomb is because you literally cannot sustain a chain reaction in pure LEU, or even LEU oxide, no matter how much of it you have.  The detail of "cross sections" comes to bite you; a fission neutron straight from a nucleus is about as likely to be absorbed by a U-238 nucleus that it goes near (and make no further neutrons) as it is to be absorbed in passing by a U-235 nucleus.  With U-238 being vastly more abundant, fission neutrons can't replace themselves and the "reaction" has no "chain"; the chain gets broken almost immediately.

So, how did the Chicago crew create a chain reaction in natural uranium (just 0.711% U-235)?  They had a MODERATOR, in the form of a big pile of relatively pure graphite bricks.  The graphite, almost pure carbon, only rarely tends to absorb neutrons but does a fairly good job of slowing them down as the neutrons bounce around.  And as the neutrons slow down, a funny thing happens:  U-235 atoms are HUGELY more successful in catching slow ("thermal") neutrons than U-238 atoms are.  When you get things slowed down JUST enough that each fissioning atom leaves neutrons that wind up splitting exactly one more atom, the chain goes unbroken:  you have a self-sustaining "chain reaction".  But for this to work, the moderator has to be between the fuel elements and slow neutrons down before they can get sucked up by U-238 or escape entirely.

What does this have to do with a reactor meltdown?  As soon as the fuel melts and runs together, it loses the moderation because the moderator is now outside the fuel mass, not between bits of it.  Ergo, the chain is broken and the reaction stops.  (In reactors using water as a moderator, losing the water also shuts down the chain reaction.  Chernobyl used graphite.)

But that doesn't stop the heat.  The OTHER thing you neglected is that the fission reaction itself is not the only source of heat in a reactor!  About 6.5% of the energy actually comes from the radioactive decay of the fission products, the daughter nuclei created by the splitting atoms.  This heat does not stop when the chain reaction stops; you have to wait for the material to "cool" as the "hottest" fission products decay away.  The stuff that decays the fastest releases heat the fastest, and goes away fastest.  Within an hour the "afterheat" is down to 1.5%, 0.4% after a day and 0.2% after a week.

Maybe you want to re-record some of your narration on your video to get those details right.  Just sayin'.

PS:  No I was not drunk when I wrote this, just fat-fingered.  All typos spotted have been corrected.



 
Comments:
The Atomic Insight blog author has suggested the timing of the release of "The China Syndrome" just before the TMI accident was not a mere coincidence given the conflicts of interests of the film backers.

I was curious what The Ergoshpere blog author thinks about the timing of the release of the last episode of the "Chernobyl" mini series, as it was just before the alleged Iranian attack on a US oil tanker?
 
I don't think about it.
 
Post a Comment



<< Home
Talk largely about energy and work, but also politics and other random thoughts


Mail Engineer-Poet

(If you're mailing a question, is it already in the FAQ?)

Important links

The FAQ
Glossary
The Reference Library

Blogchild of

Armed and Dangerous

Blogparent of

R-Squared




The best prospect for our energy future:
Flibe Energy

ARCHIVES
January 1990 / February 2004 / March 2004 / June 2004 / July 2004 / August 2004 / September 2004 / October 2004 / November 2004 / December 2004 / January 2005 / February 2005 / March 2005 / April 2005 / May 2005 / June 2005 / July 2005 / August 2005 / September 2005 / October 2005 / November 2005 / December 2005 / January 2006 / February 2006 / March 2006 / April 2006 / May 2006 / June 2006 / July 2006 / August 2006 / September 2006 / October 2006 / November 2006 / December 2006 / January 2007 / February 2007 / March 2007 / April 2007 / December 2007 / January 2008 / May 2008 / June 2008 / August 2008 / October 2008 / November 2008 / December 2008 / February 2009 / March 2009 / April 2009 / May 2009 / June 2009 / July 2009 / August 2009 / September 2009 / October 2009 / November 2009 / December 2009 / January 2010 / April 2010 / May 2010 / June 2010 / July 2010 / August 2010 / September 2010 / October 2010 / November 2010 / December 2010 / January 2011 / February 2011 / March 2011 / April 2011 / May 2011 / July 2011 / August 2011 / September 2011 / October 2011 / April 2013 / November 2013 / December 2013 / January 2014 / February 2014 / March 2014 / April 2014 / July 2014 / August 2014 / September 2014 / October 2014 / November 2014 / February 2015 / April 2015 / October 2015 / March 2016 / April 2016 / May 2016 / June 2016 / July 2016 / November 2016 / December 2016 / February 2017 / May 2017 / June 2017 / September 2017 / October 2017 / November 2017 / March 2018 / May 2018 / June 2018 / October 2018 / December 2018 / January 2019 / March 2019 / June 2019 /


Powered by Blogger

RSS feed

Visits since 2006/05/11: