What Is Chernobyl's Elephant's Foot Made Of?

The Chernobyl nuclear accident caused a lava-like flow of radioactive fuel and other materials that hardened into a giant mass now known as the Elephant's Foot. Learn how corium like this forms in today's episode of BrainStuff, based on this article: https://science.howstuffworks.com/chernobyl-elephants-foot.htm

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Episode Transcript

Speaker 1 (00:01):
Welcome to Brainstuff, a production of iHeartRadio, Hey brain Stuff
Lauren Vogelbaum here. April of nineteen eighty six saw the
accident at the Chernobyl nuclear power plant in Ukraine. Eight
months later, workers who entered a corridor beneath the damaged
Number four reactor discovered a startling phenomenon. Some sort of

(00:25):
black lava had flowed out from the reactor core, as
if it had been some kind of human made volcano.
One of the hardened masses was particularly startling, and the
crew nicknamed it the elephant's foot because it had flowed
into a massive, wrinkled shape resembling an elephant's foot. Sensors
told the workers that the lava formation was so highly

(00:48):
radioactive that it would take just five minutes for a
person to get a lethal amount of exposure from it.
A decade later, the US Department of Energy's International Nuclear
Safety Project, which elected hundreds of pictures of Chernobyl, obtained
several images of the elephant's foot, which was estimated to
weigh about two tons. Since then, the elephant's foot, which

(01:10):
is known as a lava like fuel containing material or LFCM,
has remained macabre object of fascination, but what is it?
Because the elephant's foot was so radioactive, scientists at the
time used a camera on a wheel to photograph it.
A few researchers got close enough to take samples for analysis.

(01:32):
What they found was that the elephant's foot was not
the remnants of nuclear fuel, or not nuclear fuel alone.
Experts explained that the elephant's foot is composed of a
rare substance called korium, which is produced in a nuclear
accident when the nuclear fuel and parts of the reactor
core structures overheat and melt together, forming a mixture. A

(01:55):
Quorium has only formed on its own five times in history,
a once during a three mile island accident in Pennsylvania
in nineteen seventy nine, once at Chernobyl, and three times
at the Fukushima plant disaster in Japan in twenty eleven.
For the article this episode is based on How Stuff Works,
spoke by email with Edwin Lyman, director of Nuclear power

(02:16):
Safety for the Union of Concerned Scientists. He said, if
a core melt cannot be terminated, then eventually the molten
mass will flow downward to the bottom of the reactor
vessel and melt through with a contribution of additional molten
materials dropping to the floor of the containment. The hot
molten mass will then react with the concrete floor of
the containment if there is one, again changing the composition

(02:40):
of the melt. Depending on the type of reactor, the
melt can spread and melt through the containment walls, or
continue to melt through the floor, eventually infiltrating groundwater. This
is what happened at Fukushima. When the melt cools sufficiently,
it will harden into a hard rock like material. How

(03:00):
stuff works also spoke by email with Mitchell T. Farmer,
a veteran nuclear engineer and program manager at the Argonne
National Laboratory. He explained the quorium looks quote a lot
like lava, a blackish oxide material that gets very viscous
as it cools down, flowing like sticky molten glass. The

(03:22):
composition of a particular quorium flow and thus its appearance,
will vary based on what materials melt together to make it.
For example, the elephant's foot has a brownish hue that
comes from concrete made with a lot of silica, basically glass.
A part of it is always going to be uranium oxide. Fuel.
Other ingredients include the fuel's coating, typically an alloy of

(03:45):
zirconium called circuloi, and structural materials, which are mostly stainless
steel composed of iron. A farmer said, depending on when
water is resupplied to cool the quorium, the quorium composition
can evolve in time As steam boils off. The steam
can react with metals in the quorium, azirconium and steel

(04:07):
to produce hydrogen gas, the effects of which you saw
during the reactor accidents at Houkshima. The oxidized materials in
the quorium are converted to oxides, causing the composition to change.
But if the quorium isn't cooled, it will move down
through the reactor vessel, melting more structural steel along the way,
which causes even more changes in its composition. A farmer said.

(04:31):
If still under cooled, the quorium can eventually melt through
the steel reactor vessel and drop down onto the concrete
floor of containment. This happened all three reactors of Fukushima.
The concrete that comes in contact with the quorium will
eventually heat up and begin to melt. Once the concrete melts, concrete,

(04:52):
oxides typically known as slag, are introduced into the melt,
which causes the composition to evolve even further. The melting
the concrete also releases steam and carbon dioxide, which continue
to react with metals in the melt to produce hydrogen
and carbon monoxide, causing still more changes in the quorium's composition.

(05:13):
The resulting mess that created Elephant's Foot is extremely dangerous. Generally,
quorium is much more hazardous than undamaged spent fuel because
it's in a potentially unstable state that's more difficult to handle, package,
and store. A lineman said to the extent that quorium
retains highly radioactive fission products plutonium and core materials that

(05:37):
have become radioactive a quorium will have a high dose
rate and remain extremely hazardous many decades or even centuries
to come, and although it should be contained, doing so
could be hazardous in itself. That's because very hard, solidified
quorium like that of the elephant's foot would have to

(05:58):
be broken up to remove it from damaged reactors. Lyman
said that will generate radioactive dust and increase hazards to
workers and possibly the environment, but what's even more worrisome
is that scientists don't know how quorium might behave over
the long term, of like when it's stored at a
nuclear waste repository. What they do know is the quorium

(06:21):
of the elephant's foot is likely not as active as
it was, and that is cooling down on its own
and will continue to cool but it is still melting
down and remains highly radioactive. In twenty sixteen, the new
safe confinement shield, a giant structure of steel and concrete,

(06:42):
was slid over Chernobyl to prevent any more radiation leaks
from the nuclear power plant. Another steel structure was built
within this containment shield to support the decaying concrete sarcophagus
in Chernobyl's reactor number four. The new safe confinement would
ideally help prevent a massive cloud of uranium dust from
dispersing into the air in the case of an explosion

(07:04):
in room three oh five to two. Room three oh
five to two was directly under the number four reactor
core and has been showing signs of increased neutron emissions
since twenty sixteen. It's totally inaccessible to humans because of
the deadly radiation levels and as fascinating as it is,
nobody wants to see another elephant's foot. A farmer has

(07:28):
spent most of his career studying nuclear accidents and working
with quorium in an effort to develop ways for plant
operators to terminate an accident, how much water to inject
and where to inject it, and how fast water can
cool the quorium and stabilize it. He said, we do
large experiments in which we produce quorium with the real materials,

(07:49):
but we use electrical heating to simulate decay heat instead
of decay heating itself. We focused most of our work
on studying the efficiency of water addition in quenching and
cooling quorum for various quoreum compositions. Thus, we are doing
research on accident mitigation. The other end of it is
accident prevention, and this is a principal focus area for

(08:12):
the nuclear industry. Today's episode is based on the article
Chernobyl's Elephant's foot is a toxic massive quorum on HowStuffWorks
dot Com, written by Patrick J. Kiger. Brainstuff is production
of My Heart Radio in partnership with how stuffworks dot Com,
and it is produced by Tyler Klang. For more podcasts

(08:32):
from my heart Radio, visit the iHeartRadio app, Apple Podcasts,
or wherever you listen to your favorite shows.