Two delayed critical uranium (93.2) metal cylindrical annuli with central Be moderation

Two cylindrical annuli of uranium metal were assembled to delayed criticality in 1963 with beryllium metal in the center to study the effects of beryllium to provide data for verification of neutron transport theory methods including cross section data for criticality safety calculations. These systems were assembled on a vertical assembly machine in the East cell of the Oak Ridge Critical Experiments Facility. The annuli was divided into two halves with the upper fixed half supported by a 0.010-in-thick, 30-in-diam stainless steel (type 304) diaphragm. The lower half which was hydraulically movable was supported on a very low mass tower consisting of mainly three 0.125-in-thick vertical pieces 120 degree apart. These systems, when assembled to delayed criticality, were located in 35 x 35 x 30 ft. high experimental room, 11.7 ft from the 5-ft-thick West wall, 12.7 ft. from the 2-ft-thick North wall and 9.2 ft. above the concrete floor. When assembled the positive reactor period measured was +403 sec for the nominal 15-in-OD assembly and +31 sec for nominal 13-in-OD assembly. The reactivity effects of nearby materials such as the support ring (+) for the diaphragm, the diaphragm (-) and the lower support stand(+) were evaluated. The total reactivity worths of the nearby support materials were 8.9 and 5.4 cents for the 15-in-OD and 13-in-OD assemblies, respectively. The reactivity effect of each of the components was measured for the nominal 13-in-OD assembly and they were -11.2 cents for the diaphragm, +4.4 cents for the support ring, and +12.2 cents for the support stand