Microalgae: the first nuclear engineers?
635
Palabras clave:
Microalgas; Biorremediación de uranio; Reactor nuclear.
1. INTRODUCTION
When on 2
nd
December of 1942 Enrico Fermi started the nuclear reactor
Chicago Pile-‐1 (CP-‐1) as part of the Manhattan Project at the Metallurgical
Laboratory of the Chicago University, he was convinced that CP-‐1 was the first
nuclear fission reactor running on Earth, he was far removed from reality. 1.7
billion years ago, at Oklo in Gabon, Africa, 16 natural nuclear fission reactors (i.e. a
uranium-‐rich deposit where self-‐sustaining nuclear chain reactions have occurred)
took place and ran approximately for hundred thousand years (1-‐2). Oklo was
discovered in 1972 by the French physicist Francis Perrin while he was analysing
isotope ratios, a possibility previously predicted by Kuroda (3).
A nuclear chain reaction took place in a uranium-‐rich deposit inundated
with water (that acted as a neutron moderator) at Oklo originating a natural
nuclear reactor (1, 4-‐5). The key factor for this event to happen was that the fissile
isotope
235
U reaches around 3.1% of the total uranium amount, a similar amount as
the used in some of human manufactured reactors.
Lovelock (6) proposed that the microalgae could have concentrated
235
U in
Oklo. But to date no experimental evidences were provided in this regard.
For become able to build a natural nuclear reactor microalgae need to meet
three characteristics:
i) being able to survive in an environment contaminated by uranium,
ii) being able to concentrate uranium,
iii) being able to produce isotopic fractionation enriching the relationship
235
U/
238
U. It seems unlikely that these three characteristics take place simultaneously
in microalgae. First, surviving under uranium contamination environment is not
straightforward. Uranium is a hazardous element owing to its toxicity as heavy
metal as well as its radioactivity (7). Second, neither seems simple that microalgae
bio-‐accumulate uranium because it is a material that has no biological utility. But
the hardest challenge to meet is that microalgae could get isotopic fractionation of
uranium. How microalgae could acquire these 3 qualities?
Astonishingly, there are experimental evidences that some microalgae
species were able to do this in a pond extremely contaminated by uranium at the
Saelices U-‐mine (Salamanca province, Spain). And they have recently started: since
the sixties of past century.
