Page 120 - 79_04

Microalgae:
the
first
nuclear
engineers?

Palabras
clave:
Microalgas;
Biorremediación
de
uranio;
Reactor
nuclear.

1.
INTRODUCTION

When
on
2nd
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
235U
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
235U
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

235U/238U.

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.

635