b'C HAPTER E IGHTT H E R EA CT O R Z O O G O E S C R I T I C A LThen gradually construction workers were replaced by operations people.Idaho Department of Labor, 1951W alter Zinns The first criticality runs at a zero Zinn figured he needed seven and a halfpower state, meaning that the reaction more kilograms of enriched uraniumproduces just enough neutrons to keep and asked the AEC to release it fromestimate was too low. He thought the the chain reaction alive. This generates military supplies. The material went tobreeder reactor was ready for action in very little heat. In the early 1950s, the Argonne Laboratory in Chicagolate May 1951. He had ordered forty when every reactoralong with its where the engineers fabricated morekilograms of enriched uranium packed fuelwas a first of its kind, reactor fuel rods. These procedures cost himinto 179 fuel rods and some extras as a designers could only estimate how three months. 1margin for error. His crew placed them much uranium would form a criticalinto the core one after the other, mea- mass. The deed was done. Finally, on Augustsuring reactivity effects each time. As 24, 1951, the EBR went into history asthe supply of rods dwindled, dignified the first reactor to go critical at theguests and visitors waited expectantly NRTS, the first to use U-235 fuel, andin the control room, watching needles the first to use a liquid-metal coolant.trace ink on scrolls of data paper. The The physics measurements indicatedextra rods went into the reactor. With that the arrangement and shape of thethe last one inserted, the reactor fuel rods needed improvement beforeremained calm. the reactor could be connected to anelectrical generator. Two-thirds of theAny reactor has several milestone fuel rods were shipped back to Chicagomoments in its early life. The first is the where the fuel was removed from itsday and the hour it attains criticality for stainless-steel cladding, placed in athe first time. After that, the operators hydraulic press and die, and madepass mini-milestones as they gradually slightly shorter and fatter. Returned tostep up the power levels, calibrate Idaho, the rods were arranged in a beltinstruments, and run safety tests. A final around the original rods. The new mass-moment of truth arrives when it runs ing of uranium allowed the reactor tounder perfect control at its maximum- produce the core temperatures requiredrated power level. INEEL 4053 to power the generator. 2The four famous lightbulbs at EBR-I were strung upGoing critical for the first time is signif- between the generator (out of picture) and the On December 20 the reactor was con-icant because it shows that the physi- handrail.nected via the generator to a string ofcists have loaded the reactor with four lightbulbs. At 1:23 p.m. the bulbsenough fuel and arranged it suitably. glowed brightly, and Zinn wrote in the6 4'