[en] A study of critical heat flux (CHF) in a close-packed bundle of electrically heated rods which simulated the closely spaced nuclear fuel rods of the Power Burst Facility (PBF) was performed. The study examined the effects that close rod spacing and rod bowing would have on CHF at low, near-atmospheric, pressure conditions similar to PBF conditions. The PBF nuclear reactor, which is used in the Nuclear Regulatory Thermal Fuels Behavior Program, has an open vessel and a driver core with forced upward flow through the close-packed rods. The core design power is 40 MW. An effort was undertaken to design a reload core with a steady state power level of 50 MW