A question of my own (ahem, Elder): whenever you see pictures of fuel ponds or reactor cores, you always see a guy handling a rod or standing over the pool wearing a gown and a surgical mask. Obviously not concerned about radiation. Are they only handling fuel rods prior to insertion into the reactor? Is there some unseen transport mechanism for transferring spent rods to containment? Is the water in the containment pool shielding that well, particularly since some of the uranium series are gamma emitters? Or is there extra shielding around the fuel rods I don't know about?
Bill, EH handled the whole criticality question pretty well...though I do have a few things to add.
Slotin, according to many who knew him, was a death-obsessed tool who courted the very disaster he so heroically and cooly averted. This event was not "critical" but sub-critical....once an assembly like the one he was playing with achieves criticality, well, it's
critical, as in sustaining fissions, in this case, in what would have been a decidedly uncontrolled manner. In a reactor, criticality is sustained and controlled.
Now, on to a pet peeve: you don't need a "Critical mass" to sustain criticality. I'm going to illustrate with something that I have to add a few preambles to: this information is entirely available on the internet, and mostly in the public domain.
When we speak of the assembly of a weapon, the actual object that is the core, it's often referred to as acheiving "critical mass" in that two pieces of material are rapidly introduced to each other, or an object is imploded to a certain density, but what we're really talking about with criticality is the propagation of fissions, that is to say, neutrons. If we have a smaller object, say a somewhat spherical (I can say "somewhat spherical," can't draw a picture or get more specific) mass of plutonium of less than the often quoted 10 kg of Pu-239, but it were surrounded by a neutron reflector, like beryllium, and made denser by dynamic detonation (I've always hated the use of the term "implosion" for this, though it is the standard) we can acheive criticality with less than the so-called "critical mass," whic is, after all, dependent upon a variety of factors such as purity and
surroundings. Thus it is that the French and Israelis have built wonderfully efficient thermonuclear devices using as little as
I can't reall say how many but it's less than 22 lbs of plutonium for the primary.....so I'm told, anyway.....:lol:
As far as nuclear fuel goes, it's important to point out that zirconium, uranium and plutonium are all pyrophoric metals. They make very, very, pretty, and very, very, very, hot fires-this is what should be most feared in japan's situation, and there's some pretrty rampant speculation that that's exactly what's happening at Unit #4.....
bad.
The people you see pictured next to fuel assemblies are typically checking the receipt of a shipment of new fuel that hasn't been irradiated. We used to say that if you drove over an assembly that was removed from the reactor at 60 mph you'd be dead before you hit it, as those fuel rods are emitting in excess of 1 million R-while there has been one instant death from fuel radiation in the industry, Chernobyl proved that it's not necessarily true, though that wasn't the same type of fuel at all.
Typically,EH, the refueling cavity is filled with 30 feet of water, as is the spent fuel pool, and the two are connected by a tunnel with a trolley. New fuel is loaded into the pool, into the trolley, sent through to the cavity, upended and placed in the core, all by remote manipulation from a moving bridge with long, water-filled tools. The same goes in reverse for "spent" fuel. THe water does provide shielding for these operations, this is why the tools have drilled holes so that they also are water filled. This is how the one death that I know of took place-a technician was using a boroscope to do fuel repairs (yes, they can do that) and failed to fill it with water, taking that dose directly to the eye and brain, and directly dropping dead....so I'm told....
I'm going to post my analysis of what I know of the events at Fukashima in the other thread. They're
bad-unprecedented really, and not quite to Chernobyl level-
yet, but well past Three Mile Island, no matter what the Japanese say. Damn things kept me on the phone and emailing for two days, now...
