CRITICALITY EFFECTS OF CENTRALLY LOCATED TUBES AND RODS OF ALUMINUM, IRON, AND TUNGSTEN IN A HOMOGENEOUS REACTOR

摘要

The NASA zero-power reactor, consisting of an unreflected cylinder containing a solution of uranyl fluoride salt in water, was used to study simple heterogeneous effects. This heterogeneity was introduced into the reactor as tubes or rods of aluminum, iron, and tungsten located on the axis of the reactor and extending the full height of the core. For a given hydrogen- to uranium-235-atom ratio R of the fuel solution, criticality was achieved by varying the height of the fuel solution.. In addition, radial thermal-flux traverses for individual tubes of aluminum, iron, and tungsten were obtained. Some criticality measurements of cy¬lindrical void regions located on the axis of the reactor were also made.nOne-dimensional calculations with 19 energy groups were performed by using a diffusion-theory program written for the IBM 704 electronic computer-. Some three-group, two-dimensional transport-theory calculations using the Los Alamos two-dimensional transport (TDC) code were also made.nSeveral results, were established from the experiments and calcula¬tions. Cylindrical void regions and solid aluminum rods of the same diameter located at the center of the reactor with R of 300 gave nearly identical critical solution heights. The criticality of a number of in¬serts was adequately predicted by the Los Alamos TDC code by using three energy groups. Radial calculations using a one-dimensional diffusion-theory model can be made to agree with the experimental criticality data if the axial leakage of neutrons is properly accounted for within the insert regions.