Melt cooling by bottom flooding: the experiment CometPC-H4 and -H5 Ex-vessel core melt stabilization research
- Authors
- Publication Date
- Jan 01, 2004
- Source
- OpenGrey Repository
- Keywords
- Language
- English
- License
- Unknown
Abstract
The large-scale experiments CometPC-H4 and -H5 investigate cooling of simulated corium melts by flooding the melt from the bottom through layers of porous, water filled concrete. Both experiments use 800 kg of oxidic and metallic melts, initial temperature from 1800 to 1900 C, with simulation of nuclear decay heat by inductive heating with 300 KW typical. The experiments are performed in a cylindrical geometry to allow flooding from the bottom or/and from the sidewalls after erosion of the layers of sacrificial concrete, which cover the porous concrete. In the experiment CometPC-H4, lateral erosion was faster than expected with the consequence that passive flooding started from the sidewalls. Sideward erosion was safely stopped by the lateral water inflow, but the surface of the melt was flooded and a permanent surface crust formed before onset of flooding from the bottom. This resulted in a typical top flooding situation, in that the surface crust prevented efficient melt fragmentation. Therefore, upward heat removal was not sufficient and downward erosion of the bottom concrete continued. After further erosion of the sacrificial concrete layer at the bottom, the melt contacted the porous, water filled concrete layer. Passive injection of coolant water into the bottom of the melt increased the steam pressure and broke up the surface crust, through which part of the residual liquid melt was ejected into the overlaying coolant water. Although coolability was improved, parts of the melt locally continued downward erosion, which finally interrupted the internal heating of the melt after 3000 s. With this experience, the subsequent experiment CometPC-H5 was designed with adequate thickness of the sacrificial concrete layers to start melt flooding from the bottom. The experiment showed the typical bottom-flooding situation with fast melt cooling and formation of a porous melt structure. However, during the further course of the test, some residual liquid melt fraction impeded the water inflow. Subsequent increase of the water pressure by the operator broke up the blockage and generated a coolable situation. Successful cooling was then demonstrated until 1 hour, when heating of the melt was terminated. With the background of all relevant CometPC tests it is concluded, that this cooling concept has a high potential and that the water filled porous concrete layer is a reliable barrier. However, porosity of the melt during flooding and solidification should be improved by conceptual modifications, which inject the coolant water more homogeneously. (orig.) / Contract number FIKS-CT1999-00003 / Available from TIB Hannover: ZA 5141(6945) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische Informationsbibliothek / SIGLE / European Commission (CEC), Brussels (Belgium) / DE / Germany
