3 ms·

You're absolutely right. The idea that bringing a few bars of plutonium next to each other for a photo could result in a criticality event is completely bogus.

You're absolutely right. The idea that bringing a few bars of plutonium next to each other for a photo could result in a criticality event is completely bogus. The real issue of course, is that you want people at a facility that handles plutonium to adhere very strictly to procedures. If you don't freak out when they take some selfies, next day they'll do something else. And one day, one of these things will be stupid and lots of people will get hurt.

joshuamorton 4y ago
I mean no, it's completely correct. Criticality happens when there's enough plutonium in a small enough space (or not enough plutonium, but in a space with a high density of neutron reflectors). The demon core incident(s), the Cecil Kelley criticality incident, and others don't involve explosives. Just read through the wikipedia list[0], and you'll see that causes included dropping a tungsten brick, an unexpected pool of water, and a human torso all acting as neutron reflectors and causing unexpected criticality. Like, dissolved plutonium solutions have to be one of the most wickedly, unexpectedly dangerous things out there, because pouring them from one container into another, stirring them vigorously, or standing too close to them can all cause them to go from "safe" to "deadly". [0]: https://en.wikipedia.org/wiki/Criticality_accident#Known_incidents https://en.wikipedia.org/wiki/Criticality_accident#Known_inc...
- credit_guy 4y ago
  Those examples, especially the Demon Core, had much higher quantities of plutonium. The Demon Core [1] was a sphere of 6.2 kg of plutonium surrounded by neutron reflecting tungsten carbide. The photo in this article shows a few small sticks of plutonium. They are not in contact with each other. They are not surrounded by neutron reflecting materials. The chance of criticality in that configuration was insignificant. Of course, any journalist worth his salt will make it look like we very nearly avoided an Armageddon. I stand by my statement: the danger in that situation was not the plutonium configuration itself, but the attitude towards safety of the workers. In that immediate instance the chance of a criticality excursion was close to nil, but if not reprimanded, those workers could have done something much more dangerous next time. [1] https://en.wikipedia.org/wiki/Demon_core https://en.wikipedia.org/wiki/Demon_core
  - anonu 4y ago
    I like your thoughts here. Not sure why your parent comment is getting downvoted. There are probably multiple facets to this story as the article alludes to: a government funded private lab raking in the big bucks and government trying to rein them in a bit with this violation in an overly punitive way. Rendering then useless so production goes elsewhere...
  - bombcar 4y ago
    Somewhere between known incidents with 6.2 kg of plutonium and nothing happened incidents with some sticks there’s a point at which something could happen. And modeling exactly where that point is is difficult, hence the rules and restrictions. The reaction of those involved lends much more credence to the “stop being idiots and clean this up Homer” reading.
    - credit_guy 4y ago
      > Somewhere between known incidents with 6.2 kg of plutonium and nothing happened incidents with some sticks there’s a point at which something could happen. Yes, but that somewhere is an epsilon below the demon core. How do I know? All nuclear bombs have a core, that's more or less the size of the Demon Core. They don't go critical until they need to. Here [1] is a photo of scientist holding a plutonium pit with nothing but gloved hands. He is smiling. He does not look like someone thinking that the likelihood of a criticality event is all that high. Now take another look at the few sticks of plutonium in the photo. Draw your own conclusions. [1] https://lajicarita.wordpress.com/2012/10/16/cmrr-is-no-more-but-the-pits-go-marching-on/ https://lajicarita.wordpress.com/2012/10/16/cmrr-is-no-more-...
      - aledalgrande 4y ago
        I was curious so I went to check, it seems that the minimum size (as a sphere) for a critical mass of Pu-239 would be around 10cm. https://en.wikipedia.org/wiki/Critical_mass#Critical_mass_of_a_bare_sphere https://en.wikipedia.org/wiki/Critical_mass#Critical_mass_of...
iab 4y ago
History is replete with examples of this

joshuamorton 4y ago

I mean no, it's completely correct. Criticality happens when there's enough plutonium in a small enough space (or not enough plutonium, but in a space with a high density of neutron reflectors). The demon core incident(s), the Cecil Kelley criticality incident, and others don't involve explosives. Just read through the wikipedia list[0], and you'll see that causes included dropping a tungsten brick, an unexpected pool of water, and a human torso all acting as neutron reflectors and causing unexpected criticality. Like, dissolved plutonium solutions have to be one of the most wickedly, unexpectedly dangerous things out there, because pouring them from one container into another, stirring them vigorously, or standing too close to them can all cause them to go from "safe" to "deadly". [0]: https://en.wikipedia.org/wiki/Criticality_accident#Known_incidents https://en.wikipedia.org/wiki/Criticality_accident#Known_inc...

credit_guy 4y ago
Those examples, especially the Demon Core, had much higher quantities of plutonium. The Demon Core [1] was a sphere of 6.2 kg of plutonium surrounded by neutron reflecting tungsten carbide. The photo in this article shows a few small sticks of plutonium. They are not in contact with each other. They are not surrounded by neutron reflecting materials. The chance of criticality in that configuration was insignificant. Of course, any journalist worth his salt will make it look like we very nearly avoided an Armageddon. I stand by my statement: the danger in that situation was not the plutonium configuration itself, but the attitude towards safety of the workers. In that immediate instance the chance of a criticality excursion was close to nil, but if not reprimanded, those workers could have done something much more dangerous next time. [1] https://en.wikipedia.org/wiki/Demon_core https://en.wikipedia.org/wiki/Demon_core
- anonu 4y ago
  I like your thoughts here. Not sure why your parent comment is getting downvoted. There are probably multiple facets to this story as the article alludes to: a government funded private lab raking in the big bucks and government trying to rein them in a bit with this violation in an overly punitive way. Rendering then useless so production goes elsewhere...
- bombcar 4y ago
  Somewhere between known incidents with 6.2 kg of plutonium and nothing happened incidents with some sticks there’s a point at which something could happen. And modeling exactly where that point is is difficult, hence the rules and restrictions. The reaction of those involved lends much more credence to the “stop being idiots and clean this up Homer” reading.
  - credit_guy 4y ago
    > Somewhere between known incidents with 6.2 kg of plutonium and nothing happened incidents with some sticks there’s a point at which something could happen. Yes, but that somewhere is an epsilon below the demon core. How do I know? All nuclear bombs have a core, that's more or less the size of the Demon Core. They don't go critical until they need to. Here [1] is a photo of scientist holding a plutonium pit with nothing but gloved hands. He is smiling. He does not look like someone thinking that the likelihood of a criticality event is all that high. Now take another look at the few sticks of plutonium in the photo. Draw your own conclusions. [1] https://lajicarita.wordpress.com/2012/10/16/cmrr-is-no-more-but-the-pits-go-marching-on/ https://lajicarita.wordpress.com/2012/10/16/cmrr-is-no-more-...
    - aledalgrande 4y ago
      I was curious so I went to check, it seems that the minimum size (as a sphere) for a critical mass of Pu-239 would be around 10cm. https://en.wikipedia.org/wiki/Critical_mass#Critical_mass_of_a_bare_sphere https://en.wikipedia.org/wiki/Critical_mass#Critical_mass_of...

iab 4y ago

History is replete with examples of this