b'P ROVING THE P RINCIPLEAt this power level, the fuel would have Compared to the EBR, the MTRs neu- waer, which could do double duty andtto be replaced fairly oftenabout every trons needed to be slowed down. T hecarry away heat as well. Neutrons wouldseventeen daysbecause fission prod- slower it traveled, the bigger a neutron strike the lightweight water molecules,ucts would build up in the fuel and looked to a target nucleus, and the easier bounce around, and lose energy withdampen the chain reaction. A spento grab. The MTR required a feature not each little bounce. 1 3 t fuel element would consume only five present in the EBRa moderator topercent of its U-235 atoms. 12slow the neutrons. The designers chose In 1946 the Clinton Lab, directed byAlvin We i n b e rg, proposed that theAEC build the MTR along with a com-panion chemical processing plant torecover the enriched uranium from ther e a c t o rs spent fuel. The A E Capproved, and by Christmas 1947 bothprojects were at an advanced stage ofdesign. Naturally, the Clinton scientistsexpected to build the entire complex atOak Ridge. When the AEC announcedthat it intended to centralize all reactordevelopment at Ar gonne, the angryOak Ridgers felt demoted and com-plained bitterly that the AEC stole allour reactors. 1 4The decision to centralize reactordevelopment at Argonne soon weak-ened. By 1949, the Reactor SafeguardsCommittee deemed it best that theMTR neither go to Argonne nor OakRidge. It was better suited to theremoteness of the Idaho provingground, chiefly because of its 30-megawatt operating level. Zinn was justas glad the complex didnt end up atArgonne because he didnt relish Above. Horizontal section of the MTR (birds eyeview). Beam holes provide access for test samplesnear the reactor core. Left. The MTR before it wentcritical and before experiments began. The coffin atcenter floor level is a shielded device for loading atest sample into the beam hole. It replaced the holesplug, which was stored during the experiment in aspecial building. The MTR had three working levels.Note control room at upper right.INEEL 61965 0'