Analysis of Debris Bed Formation, Spreading, Coolability, and Steam Explosion in Nordic BWRs
Pavel Kudinov, Alexander Konovalenko, Dmitry Grishchenko, Sergey Yakush, Simone Basso, Nazar Lubchenko, Aram Karbojian,
The work is motivated by the need to assess effectiveness of severe accident management strategy adopted in Nordic type BWRs with melt ejection from the vessel into a deep water pool below the vessel. In this work we address phenomena relevant to the debris bed formation, coolability and steam explosion experimentally and analytically.
A new series of DEFOR-A (Agglomeration) tests have been carried out in order to clarify the effect of the melt jet velocity on the particle size distribution and fraction of agglomeration. Ablation and plugging of the melt release nozzle is also addressed in this work.
DECOSIM code was further developed to address debris bed coolability in post-dryout regime. An analytical model is proposed based on the analysis of DECOSIM calculations for prediction of the maximum temperature of the debris if the size of the dry zone is known. A model for prediction of particulate debris spreading has been implemented in the DECOSIM code. The code has been further validated against latest COOLOCE data for multidimensional debris bed configurations.
A scaling approach for prediction of particulate debris spreading has been proposed in this work based on the PDS-C experimental data. A universal semi-empirical closure has been developed for prediction of debris spreading mass flux.
An approach to steam explosion sensitivity analysis using TEXAS code has been developed. Obtained database of the impulse and maximum pressure as a function of TEXAS input parameters is used for development of the computationally efficient surrogate model.
Nordic BWR, severe accident, debris bed formation, coolability, steam explosion