[LAU] OT: metal, money, changes, bleg

[Jörn Nettingsmeier]

On 04/04/2011 08:42 AM, Patrick Shirkey wrote:
> On 04/04/2011 04:14 PM, Erik de Castro Lopo wrote:
>> Patrick Shirkey wrote:
>>
>>> So just to make sure I am correct here... All nuclear weapons require an
>>> assisted explosion?
>> Yes, you need both high heat and high pressure to force the fissile
>> material into the required chain reaction.
>>
>
> So, just having enough Pu-239 in one location is definitely,
> categorically not going to be able to cause a nuclear explosion? Not
> even a little one that might cause a rapid escalation?

no. and to see how hard it actually is: there were news of a botched 
nuclear test in north korea a while ago, where international observers 
found evidence of an explosion (by satellite or seismic measurements) 
that was vastly less than what was anticipated. such a situation is 
called a "fizzle", and what happens is that you bring the two halves of 
sub-critical material together too slowly or in the wrong way, and the 
chain reaction then heats it up and tears the material apart again 
before the entire mass has started to react.

when you pile up too much plutonium or uranium, criticality accidents 
can occur, but there is no possibility of an explosion even remotely 
comparable to a fission bomb. which is not necessarily a good thing: 
iiuc, a good clean atomic bomb test can be more "environmentally 
friendly" than a botched one, because a fizzle explosion distributes the 
material over a large area and could even lead to greater contamination 
than the fallout of a full explosion.

all this information can be found all over the web, in wikipedia, and 
various physics textbooks. for instance, there's a very interesting 
anecdote where richard feynman claims he had to show the uranium 
processing guys at oak ridge labs how to avoid criticalities (during the 
manhattan project) - they had been kept in the dark about this problem 
because some nuthead top-brass figured they had no "need to know". turns 
out they were keeping large cauldrons of enriched material lined up 
against a dry wall, and guess what a second team was doing on the other 
side of this wall? yup.


btw, there have been reports cropping up every now and then that 
re-criticality incidents have indeed happened in fukushima after the 
cold shutdown, either due to overcrowded spent fuel pools or the melting 
of one or more core.  this was substantiated by traces of very 
short-lived decay products that should not have been detectable anymore 
if no more chain reactions had occured after the cold shutdown.
this is of course reason to worry, because criticality would pose a 
great danger to the crew who has to mop up the mess, due to extremely 
high and uncalculable radiation peaks.
but it also shows that criticality != fission explosion.


i'm as pissed as you at the nuclear industry and current energy politics 
(and in fact, it looks like that at least in germany, the political 
climate will now finally allow us to retire nuclear energy for good and 
fully replace it with renewables).
but spreading vague fear and misinformation is really not helpful at all.

there is a very clear danger, but it's important to get the facts 
straight, otherwise it's too easy for proponents of nuclear energy to 
re-spin the current outcry into irrational fearmongering - which is 
going on alright, but the fact remains that fukushima is a huge 
environmental fuckup and the source of much human tragedy.

and if you continue to go on record with perpetuum mobile schemes and 
other easily refutable statements, you will not only be wasting your and 
other people's time, but also ultimately discredit your vote and work 
against your own political ends. (meta-conspiracy theory anyone?)