LMFBR Prompt Burst Excursion (PBE) experiments in the Annular Core Pulse Reactor (ACPR)

A series of in-pile experiments has been initiated to provide information on the energetics of LMFBR cores subjected to hypothetical superprompt-critical excursions. In these experiments, a single fuel pin in an instrumented piston-loaded autoclave is pulse heated into partial vaporization by the ACPR with initial reactor periods as low as 1.4 msec. Nine experiments have been performed with fresh unrestructured UO2 fuel pins. The first three were conducted without sodium coolant. In the dry experiments, energy depositions up to 3200 J/gm were obtained resulting in low pressure histories, negligible energy conversion ratios, and large upward axial fuel motions within the cladding. With sodium, the energy depositions also ranged up to 3200 J/gm resulting in large sharp pressure events (60 MPa), very low energy conversion ratios (2.1 x 10-4), and within-cladding axial fuel motions comparable to the dry capsule experiments