b'C H A P T E R 6N E U T R O N S : F AS T F LU X , H I G H F LU X ,A N D R I C KO V E RS F LU Xdesign the reactor building and associat- its official name, the AEC community the container surrounding the reactor.ed buildings in the complex. Then a con- called it the fast flux, flux being the Obv i o u s ly , the materials of which these struction contractor, usually diffe r e ntword to describe the flow of neutrons. 4 items were made had to be chosen for than the A/E firm, built the project and their reluctance to absorb neutronsorhired local labor. The home-lab scien- Un or tutheir willingness to reflect them backfna t e l y, it was all too easy totists designed and often fabricated the waste or lose neutrons. The cladding into the core. The designers chose stain-reactor itself. Ty p i c a lly, they disassem- surrounding the fuel could absorb neu- less steel for the cladding. They sur-bled the reactor and shipped it in pieces trons. So could the coolant and the struc- rounded the core with a blanket madefor reassembly in Idaho. tural metal holding the rods in place. of natural uranium to catch the neutronsNeutrons could leak from the core into that would leak from the core. Any neu-The Argonne team had spent years con- trons that shot past the U-238 rods with-sidering every detail of the breeder in the core would have another chancereactor. Their main goal was to prove to hit U-238 atoms in the blanket.that the reactor could produce new fuelfrom the abundant isotope U-238. All With the fuel rods close together and thedesign decisions promoted this goal. A neutrons moving fast, the core wouldsecondary goal was to produce electri- generate a lot of heat. Acoolant wouldcal power, since that was the ultimate have to flow through the small spaceseconomic mission of the breeder. This between the rods and carry this heatwasnt expected to be hard to do,because conversion technology forreactor-generated power (turbines and Cutaway view of EBR-I power plant.generators) already existed.The reactor would have pencil-thin rodsof fuel enriched to more than 90 per-cent U-235. These would be arrangedclose together in the core of the reactor.Similarly shaped rods of U-238 wouldsurround them. Each neutron wouldhave to count; none could be wasted.Either the neutron fissioned another U-235 atom to keep the chain reactionalive or it penetrated a U-238 atom andchanged that into plutonium. 3By this time, physicists knew that ifnothing slowed down the neutrons dur-ing the chain reaction, each fissionedatom was a little more likely to producethree neutrons than two. The naturalspeed of the neutrons is almost beyondimagination. They sprint away at 44million miles per hour. Physicists callthem fast. Until the reactor acquired4 7'