Re: RADSAFE digest 760

[Dick King <king@ukulele.reasoning.com>]

>> 
>> Date: Wed, 13 Dec 95 15:21:20 EST
>> From: "William Kolb" <William_Kolb_at_SETA@mail.hq.faa.gov>
>> Subject: Re: Repository analogues -Reply
>> 
>> >Forgive the following but some radsafers might be unfamiliar with the
>> >"fossil reactor" at Oklo:  Oklo is a uranium deposit in Gabon. Around 1800
>> >million years ago, it went critical and "operated" for approximately
>> >700,000 years releasing about 15,000 megawatt years of energy. This
>> >was possible because the U-235 levels were higher then, than they are
>> >today. Water in the ground served as the moderator. The fission
>> >products seem to have migrated only very small distances,  say less
>> >than 100 m. There are a ton of references, all of mine are old though.
>> 
>> To put this in perspective, the average output was about 2.5 watt-hours, 
>> sufficient for a night-light.

On these numbers the power output is more like 21 kilowatts, sufficient for a
small automobile.  It's not up there with a modern nuclear power plant, but
it's no night light.  And even a small reacter generates a lot of waste when it
runs for a long time.

15,000 megawatt-years worth of waste is what a 1000 megawatt [electric] power
plant produces every 5-6 years or so.

>>			  In reality, however, the reactor zones (there 
>> were about 6) would have surged as ground water started it up then boiled away. 
>> Still, it's a remarkable phenomenon and is likely to have occurred in other 
>> places but migration of the reaction products has long since oblitered the 
>> evidence.
>> 

It could only have happened a billion or so years ago because natural uranium
ain't what it used to be.  The substance we used to call "natural uranium"
would now be called "enriched uranium".

The point of noting the Oklo reactor is that even in a region that evidently
has ground water contact, and there is no care in packaging, it's possible to
not have migration ofr literally billions of years; it's tough to argue that
immobilizing the material by vitrification and burial in a desert region with
no ground water is doomed to failure.

-dk