Re: Design of Nuclear Power Plants

[bflood@SLAC.Stanford.EDU (Bob Flood)]

>2)  The RBMK reactors are carbon moderated
>while the remaining operating US commercial
>power reactors are water moderated.  A basic
>explanation of the end result is that carbon
>moderation leads to situations in which the
>RBMK reactors can/will have an overall positive
>reactivity coefficient.
>

More important, from my point of view, is the fact that a moderator is
necessary to sustain the chain reaction, and a coolant is necessary to
remove the heat of the reaction. Use of water as both coolant and moderator
(in all US power reactors) means that loss of coolant carries with it loss
of the moderator, which reduces or stops the chain reaction. The RMBK design
allows for loss of coolant without losing the moderator, which can (and did)
result in an uncooled chain reaction.

Bob Flood
Unless otherwise noted, all opinions are mine alone.
(415) 926-3793
bflood@slac.stanford.edu