Why are these Natural Fossil Reactors important?

Because they are rare and fascinating objects

Evidence of a reactor site at Oklo.

Natural fossil reactors have (so far) only been found in the country of Gabon in equatorial Africa.

They help us understand the ancient earth

The geological record.
[Source: Wikipedia CCL]

The geologic time scale is a chronologic schema (or idealized model) relating stratigraphy to time that is used by geologists, paleontologists and other earth scientists to describe the timing and relationships between events that have occurred during the history of the Earth.

They are the only natural example of radioactive waste containment

The Oklo mine site looking east

Oklo is the only very long full-scale natural analog for the geological disposal of radioactive waste.

Natural radioactive waste containment

Reactor Zone 2 on the west wall of the mine.

Mobile and retained radioactive elements at Oklo:

This is the state of the Oklo uranium ore pit today. The majority of the mined uranium existed as a layer of U ore which covered the right hand side of the pit.

Of the first 9 reactors only about one third of one reactor (reactor zone 2) remains and is now fixed in concrete into the side of the mine pit. This was done not because the reactor zone is dangerous to life but to stop it from sliding down the slope of the pit. The reactor zones themselves were centimetre to metre thick layers of highly enriched U, buried within the U ore.

Natural radioactive waste containment

Retention of Fission Products at Oklo

What are the criticial long term radioactive wastes?

Isotopic studies of Oklo fossil reactors show that the reactor parameters can be determined and that most of the fission product elements were retained within the reactor zones for 2000 Million years. There is evidence of mobile fission products being retained close to reactor zones in the iron and clays even in a highly porous environment.

Natural radioactive waste containment

Multiple barrier containment

Containing radioactive waste

The Oklo fossil demonstrates many of the features of what has become known as the ‘multiple barrier’ concept of radioactive waste disposal. This means building into the storage medium and repository as many barriers to the loss of radioactive wastes as possible. Eve if the the waste escapes from the immediate container an appropriate sequence of outer barriers and chemicals are arranged so as to ‘capture’ the radiactive waste in a chemical form that will retain the waste as much as possible within the containment site.