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Dynamic Neutronic and Mechanical Measurements with a Pulse Reactor of Uranium-Molybdenum Alloy

John T. Mihalczo, Jon A. Reuscher

Nuclear Technology / Volume 11 / Number 4 / August 1971 / Pages 563-577

Technical Paper / Symposium on Fuel Rod Failure and Its Effect / Reactor / dx.doi.org/10.13182/NT71-A30854

The time-dependent behavior of the neutron population in an unreflected, unmoderated cylindrical assembly of 90 wt% uranium (93.2 wt% 235U), 10 wt% molybdenum alloy following rapid establishment of a superprompt criticality with negligible initial neutron population has been studied. Reactivity increases up to 14¢ above prompt criticality resulted in pulses yielding as many as 3.72 X1017 fissions with reactor periods as short as 12.4 µsec and temperature increases as large as 880°C. In these experiments the reactor produced pulses of 2 x 1017 fissions without any damage. A pulse of 2.37 x 1017 fissions resulted in permanent elongation of the bolts holding the core together, and a pulse of 2.66 x1017 fissions caused cracks in some of the core parts. Stresses obtained from measurements of the mechanical vibration of the reactor parts were consistent with the observed damage.