former Soviet Union built 17 nuclear units based on the RBMK design used
at the Chornobyl nuclear power plant. Today it is generally recognized
that there are three generations of RBMK nuclear power plants.
The low core power density of RBMKs
provides a unique ability to withstand station blackout and loss of
power events of up to an hour with no expected core damage.
Ability to be refueled while operating, permitting a high level of
The graphite moderator design allows the use of
fuel that is not suitable for use in conventional water-moderated
significant difference between the RBMK nuclear plant design and most of
the world's nuclear power plants is the RBMK's lack of a massive steel
and concrete containment structure as the final barrier against large
releases of radiation in an accident. The effectiveness of
American-style reactor containments was shown in the 1979 Three Mile
Island Unit 2 accident, when virtually all radiation was retained inside
the containment building, despite considerable melting of the fuel. In
the Chornobyl accident, the RBMK plant's accident localization system
(the RBMK's version of containment) could not withstand the force of the
Accident mitigation systems are limited and
Reactor control systems are unforgiving to many
potential system upsets, with a consequent potential difficulty of
Faster and less stable nuclear chain
reactions--and power increases--when cooling water is lost. In tech
nical terms, this characteristic is called a "positive void
coefficient." Soviet engineers sought to mitigate this tendency by
backfitting RBMKs with faster-acting control rods and other improvements.
U.S.- style light water moderated plants, however, are designed with
just the opposite characteristic--a "negative void coefficient"--so
that the nuclear chain reaction automatically stops when coolant is lost.
The design of the Kursk-5 RBMK has reportedly been modified, resulting
in a negative void coefficient.
Limited capability for steam suppression in the
Flawed separation and redundancy of electrical
and safety systems.