Report issued by the Argonne National Laboratory discussing progress made by the Reactor Development Program during April 1963. Reactor physics, experiments, and safety studies are presented. This report includes tables, and illustrations.

From Introduction: "Interest in utilizing natural-circulation loops to obtain results that aid in the design of some boiler and nuclear reactor coolant systems has focused attention on the dynamic behavior of such loops. Much analytical and experimental work has been done so as to permit predictions of the transient behavior of both single-phase and two-phase neutral-circulation systems. The analytical portion of the study consisted of simulating the loop by utilizing a digital computer to predict the measured transients."