Chernobyl Nuclear Accident Congressional Hearings Transcript

19
The temperatures, however, were so high that what happened was
the sand and other stuff Hke limestone, that was in the material
dropped on the reactor melted and formed a lava-like material.
This lava-like material contains the bulk of the fuel that remained
in what is now covered by the sarcophagus.
The RBMK reactor had a pressure relief system. In case a pressure
tube breaks, there would be a pressure pulse in the core, and
to prevent an overpressure situation, there were pipes that took
this overpressure into suppression pools under the reactor, where it
bubbled through water to attend to the pressure. The molten fuel
suspended in this lava-like mass ran through these pipes. The temperature
of the lava was less than the melting point of the pipes.
So it ran through these pipes and coated the bottom of the suppression
pools. It formed a big mass under the reactor.
There was a 6.6-foot thick concrete floor under the reactor core.
After the accident, in some places, measurements show that there
are eight to 20 inches of good concrete left, and the area above that
is remaining of the now solidified, molten core mass. The floor of
the suppression pools are coated with this lava-like substance. A lot
of it's still in the pipes. There are a couple of pictures I provided
you showing what looks like spaghetti coming out of one of the
valves, which is the molten material.
Now, this molten mass immediately after the accident was putting
out radiation dose rates on the order of 20,000 r/hour. The socalled
elephant's foot, which I provided you a picture of, is probably
down to about 2,000 r/hour now. There are certain hot spots
there which contain lots of fuel that are still on the order of 2,000
or 3,000 r/hour. There are other areas there where it's down quite
low, one r/hour or less. It depends on how much fuel dissolved in
that particular mass of lava.
Above the core on what used to be the operating floor of the reactor,
you have the fuel and graphite that was thrown in from the
roof, you have the fuel and graphite that was left laying on the
floor from the explosion, you have the fragments which settled
back in there. The vaporized fuel condensed and formed aerosols
and fine particulate matter which is in there.
Now, with that situation, after the accident they took actions to
prevent and to mitigate the releases of radionuclides. They very
rapidly designed the sarcophagus, which you've seen pictures of.
This was not what you would call a sophisticated design project
taking lots and lots of time. It was something that was worked out
really quick that could be done really quick. They scooped up the
dirt around there so they could get the radiation levels down so
that people could work. They made prefabricated frameworks near
the site which they moved into the site and pumped concrete into.
In the process of doing this, one of the things they did not do was
compact the dirt under the sarcophagus so that it could hold this
large mass of concrete and structure that they had put on top of it.
The work was done such that the normal quality control that
would be done to a massive concrete structure like that could not
be done, so you're not really assured that the concrete will be good,
strong concrete like you would find in a normal construction
project.