As part of a national research project RUB PSS investigates the cooling process of degraded core sections like debris beds and melt pools. Focus of these works is the simulation of the DEBRIS test facility located at IKE in Stuttgart with both the integral code ASTEC V2.1, developed by IRSN in France, and the system code COCOMO, developed by IKE. The development process of the latter was largely influenced by the DEBRIS experiments and hence is very suitable for comparative calculations.Besides to the reflooding of dry and overheated particle bed configurations boiling and dryout phenomena are investigated within the DEBRIS test facility. The test setup allows enhanced test conditions regarding the overall temperature (up to 1,273&nbsp;K) and pressure level (0.1, 0.3 and 0.5 MPa). Furthermore, the experiments are conducted using two different particle types and varying flow conditions (bottom- and top-flooding).In this work, the simulation of two bottom flooding experiments with similar temperature and pressure conditions but different particle types will be presented. The first bed consists of 3.0x5.75&nbsp;mm cylindrical stainless steel particles. The second debris bed is a mixture of irregular shaped AL2O3 particles originating from the PREMIX experiments and spherical stainless steel particles in order to improve the heat-up process. The selected tests will be simulated with both a fixed input signal and a gravity-driven quench water flow similar to the actual test conditions. Focus of the analysis is on a comparison of the calculated and experimental results to validate the code capabilities to simulate the most relevant phenomena which occur while quenching dry and overheated particle formations under varying thermohydraulic conditions. ASTEC is validated using numerous experiments like the PEARL tests that are comparable to those conducted within the DEBRIS test facility and disposes a well-developed model basis for the simulation of late phase phenomena. The resulting temperature evolutions are in good accordance with the experimental results. This is also reflected by the evolution of the quench front and also applies to the conducted COCOMO simulations. The released amount of steam is overestimated by both codes and leaves room for improvement.

Analysis of the Reflooding Process in Degraded Particle Beds by Simulations of the Debris Test Facility With the Severe Accident Analysis Code ASTEC V2.1 and COCOMO Code

Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE28/volume/85246

2021 28th International Conference on Nuclear Engineering (ICONE28)

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