During a severe accident in a nuclear power plant, the degradation of
fuel rods and melting of materials lead to the accumulation of core
materials, which are commonly, called “debris beds”. To stop core
degradation and avoid the reactor vessel rupture, the main accident
management procedure consists in injecting water. In the case of debris
bed, the reflooding models used for Loss of Coolant Accident are not
applicable. The IRSN has launched an experimental program on debris bed
reflooding to develop new models and to validate severe accident codes.
The PEARL facility has been designed to perform, for the first time, the
reflooding of large scale debris bed (Ø540mm, h=500mm and 500kg of
steel debris) in a pressurized containment. The bed is heated by means
of an induction system. A specific instrumentation has been developed to
measure the debris bed temperature, pressure drop inside the bed and
the steam flow rate during the reflooding. In this paper, the results of
the first integral reflooding tests performed in the PEARL facility at
atmospheric pressure up to 700°C are presented. Focus is made on the
quench front propagation and on the steam flow rate during reflooding.
The effect of water injection flow rate, debris initial temperature and
residual power are also discussed. Finally, an analytical model
providing the steam flow rate and the quench front velocity is proposed
to interpret these results.