RE: Two questions on Japan accident

["Karam, Andrew" <Andrew_Karam@URMC.Rochester.edu>]

>1. Is 18% normal for power reactor fuel enrichment?

18% is high for "normal" power reactors.  They run from about 3-6%.  This
was for (I believe) a fast breeder reactor.

>2. Is 35 lbs @ 18% really likely to go critical?

According to Critical Dimensions of Systems Containing 235U, 239Pu, and 233U
(LANL, 1986) the minimum critical mass of a spherical, homogeneous,
water-reflected solution of uranium at 18% enrichment is a little over 1 kg,
or about 5 kg total uranium weight.  The minimum spherical critical volume
is about 13 liters.  Any more mass or any smaller volume will sustain
criticality.  Different geometries may or may not support criticality
because of neutron leakage.

Andy

Andrew Karam, CHP              (716) 275-1473 (voice)
Radiation Safety Officer          (716) 275-3781 (office)
University of Rochester           (716) 256-0365 (fax)
601 Elmwood Ave. Box HPH   Rochester, NY  14642

Andrew_Karam@URMC.Rochester.edu
http://Intranet.urmc.rochester.edu/RadiationSafety
Can a knowledgeable radsafer educate me a bit by clarifying two points
from the IAEA news release on the accident:
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