Environmental Engineering Reference
In-Depth Information
.
Safety
There have been three serious reactor accidents, one
in
at Three Mile Island (TMI) in the United States,
one in
at Chernobyl in the Ukraine (then part of
the Soviet Union), and the Fukushima accident in
in
Japan. The worst in its effects was Chernobyl. All power
reactors outside the old Soviet Union (almost all are light
water reactors designated as LWRs
-
see Technical Note
) are built with containment buildings that can hold
radioactive materials inside in the event of an accident.
The Russian RBMK reactors, the type used at Chernobyl,
are built differently from LWRs, and have no contain-
ment buildings.
Three Mile Island: When operations resumed after a
regular maintenance shutdown, a series of start-up errors
occurred, mainly related to the settings of the valves that
controlled the
.
flow of cooling water to the reactor core.
Compounding the problem, the control system design
did not give operators much information about exactly
what was happening. The operators could not tell that
certain valves that should have been open were closed
and some that should have been closed were open. As
operations began, the level of cooling water in the
reactor vessel slowly dropped, exposing part of the core
which then melted,
releasing a
large amount of
highly radioactive material. It took
hours to bring
the situation under control. The containment building
kept almost all of the radioactive material inside, but
some radioactive gases did escape. The subsequent inves-
tigation determined that the average exposure to the
