Chernobyl Nuclear Accident Congressional Hearings Transcript

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• Third, the Soviet graphite reactors are very large in
physical size. We have had favorable experience with
the more compact LWR systems.
• Fourth, they are very complex when compared to U.S.
LWRs. About 1700 individual pressure tubes are embedded
in the 1800 tons of graphite, each with its individual
inlet and outlet piping.
• Fifth, the advantages of graphite moderation in a watercooled
reactor are associated with production of
material for weapons: use of very low enrichment or
natural uranium and on-line refueling. Co-production of
commercial power and weapons materials was not supported
by our government or scientific experts; and graphite
moderation was not attractive to U.S. utilities, who had
no interest in providing materials for the U.S. weapons
program.
My discussion of the significant differences between
graphite and water moderation is not meant to say that
graphite is dangerous inherently. The U.S. technical community
has made important improvements in graphite safety,
and defense-in-depth can be designed into graphite reactors.
The next major difference between U.S. and Soviet reactor
designs is in the defense-in-depth barriers. These are
provided to ensure that nuclear fuel and fission products
cannot escape the core. Both Soviet RBMK reactors and U.S.
LWRs use UO2 fuel pellets surrounded by a zirconium cladding
or 'can' of about 0.02 inches to 0.03 inches wall thickness.
These fuel elements are similar, but the next barrier
of defense against release is radically different. The
Soviets use about 1700 individual zirconium alloy pressure
tubes, 23 feet high, and 3 1/2 inches in diameter to contain
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