in layman's terms how are atomic power plants able to control the
fission reaction to produce power
rather than explode like a bomb?

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Request for Question Clarification by pinkfreud-ga on 31 Oct 2005 11:57 PST

Does this help?

"Inside the reactor of an atomic power plant, uranium atoms are split
apart in a controlled chain reaction. In a chain reaction, particles
released by the splitting of the atom go off and strike other uranium
atoms splitting those. Those particles given off split still other
atoms in a chain reaction. In nuclear power plants, control rods are
used to keep the splitting regulated so it doesn't go too fast. If the
reaction is not controlled, you could have an atomic bomb. But in
atomic bombs, almost pure pieces of the element Uranium-235 or
Plutonium, of a precise mass and shape, must be brought together and
held together, with great force. These conditions are not present in a
nuclear reactor."

http://www.solcomhouse.com/nuclear.htm

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Clarification of Question by renoir-ga on 31 Oct 2005 17:27 PST

Pinkfreud:  I'm not sure how G/A works. hfshaw seems to have provided
me with a better answer.

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Request for Question Clarification by pinkfreud-ga on 31 Oct 2005 19:17 PST

renoir,

hfshaw cannot post an official answer, since he or she is not a Google
Answers Researcher. It looks as if you've gotten a nice freebie from a
helpful site user. If you're satisfied, and aren't seeking anything
further, you may want to cancel your question.

~pinkfreud

Both fission reactors and fission bombs involve self-sustaining chain
reactions.  When, for example, a uranium-235 nucleus absorbs an
additional neutron, the resulting uranium 236 nucleus is "excited" and
oscillates, sort of like a droplet of water, and eventually splits
apart into two subequal fragments and a bunch of energy.  This is
fission.  The two fragment nuclei have too many neutrons to be stable,
so they, in turn eject some neutrons.  On average, each fissioning
235-uranium nucleus releases 2.4 additional neutrons, each of which is
available to fission additional nuclei.  Those fission events then
release more neutrons, and so on.  Each fission "generation" results
in more and more neutrons and more and more energy release.  If
uncontrolled, this results in an explosion.

In a reactor, the number of neutrons available to induce fission is
controlled by a combination of reactor design (i.e., allowing some of
the neutrons to "leak out" of the reactor before encountering another
fissile nucleus), and, more importantly, by the incorporation of
moveable control elements containing of nonfissile materials that
absorb neutrons, such as cadmium, boron, hafnium, or gadolinium.  The
basic idea being to keep the number of neutrons produced by each
fission that are subsequently available to induce another fission
equal to one.  That way, each fission generates just one additional
fission, and the reaction just pokes along at steady state.


You can download a simple reactor simulator from
<http://www.kernenergie.net/datf/en/interactive/reactor.php?navid=23>,
and play around with control rods and see how a reactor core behaves.

This comment is for hfshaw.  Please post your comment as an answer so
that you can get paid.  Please clarify 2 items:  (1) "the leak-out
neutrons"....where do they go?  (2) how do the "moveable control
elements" work?