SPERT I: The characteristics of the boiling process and its relatin to moderator expulsion in Spert I were investigated in a series of capsule type experiments. A fuel-bearing oapsule, instrumented to provide pressure, volume, and temperature data during transient power excursions, was placed in a high flux region of the Spert I P core. Five step-induced transients initiated from boiling indicate that the kinetic behavior of the stainless steel clad P-18/19 core is dependent on initial temperature in a manner similar to that of previously tested aluminum clad spert cores. Reactivity oscillator techniques were used in the P-18/19 core to determine the phase and magnitude of the reactivity-to-power transfer function from 0.01 to 18.4 cps at low power and at temperatures below boiling. Criticality data on relatively simple lattices, both rod-free and containing a single poison rod, were obtained from a series of clean critical experiments performed on a number of light water-moderated and - reflected slab configurations of Spert III fuel elements. Changes in water height during the critical water height experiment were measured to plus or minus 0.0013 inches by means of a simple remoteindicating system designed and built for this purpose. SPERT III: The operational loading was …