The SETH 2 project studies the thermal-hydraulic phenomena for the needs of accident management.
Context and objectives
Organized under the auspices of the OECD (Organization for Economic Cooperation and Development), SETH 2 is an international project in which the IRSN is actively participating by carrying out the pre-calculations and post-calculations for the tests using the ASTEC and TONUS codes.
Initiated in 2007 for a period of four years, SETH 2 continues the SESAR Thermal-hydraulics project - SETH) that began in 2001. It brings together international experts from twelve organizations in 9 countries of Europe and Asia.
In the context of the study of severe pressurized water reactor accidents, the hydrogen risk is defined as the possibility of loss of integrity of the reactor containment or its safety systems further to the combustion of hydrogen. The hydrogen comes mainly from the oxidation of zirconium in the cladding and structures of the fuel elements during core degradation and oxidation of the metals present in the corium (molten core) bath or in the raft foundation during the interaction between the corium and the concrete. The hydrogen thus produced is transferred then transported within the containment by the convection loops induced essentially by the condensation of the steam emitted through the primary circuit break or during the corium / concrete interaction. The uniformity of hydrogen distribution within the containment can vary depending on how the atmosphere is mixed. If the atmosphere is very heterogeneous, the hydrogen can reach high local concentrations that exceed the fire point of the gaseous mixture. Moreover, the distribution and concentration of hydrogen in the containment can be modified by the use of spray systems. This is because although spraying homogenizes the hydrogen distribution in the containment, it can - through condensation of the steam on the spray droplets - lead to deinerting of the mixture.
Devices such as recombiners and igniters can be installed in the containment to prevent hydrogen build-up in all or part of the containment. The dimensioning and assessment of the effectiveness of these prevention means requires the use of calculation codes that must be validated through comparison with well-instrumented experiments that reproduce the 3D phenomena governing gas flow in the containment in an accident situation.
The need for this type of experiment on large-scale facilities was emphasized in the OECD report concerning the state of the art in thermal-hydraulics and hydrogen distribution in the containment: this is the objective of the OECD-SETH2 project.
The purpose of the SETH 2 project is to conduct well-instrumented experiments to validate the multidimensional thermal-hydraulic codes (CFD, Computational Fluid Dynamics) and the multi-compartment codes (LP, Lumped Parameters) in the PANDA facility in Switzerland operated by the Paul Scherrer Institute, and in the MISTRA facility in Saclay, France, operated by the CEA (Atomic Energy Commission).
The test matrix planned for the two facilities comprises both separate and coupled effect tests and integral tests. The experimental programme thus defined concerns:
separate effect and coupled effect tests focusing on the rupture of a hydrogen stratification initially established through steam jets with different flow rates and positions, through the use of spraying, or from the plume produced by a recombiner,
overall tests focusing on the impact of the problems associated with the GEN III and GEN IV reactors (gaseous mixture resulting from sudden rupture of a rupture disk in the case of the EPR, or of the long-term cooling system for BWRs, etc.).
These tests will provide the comprehensive experimental data needed to validate the calculation codes on configurations representative of the atmosphere of reactor containments in severe accident situations.
Last update on 13th March 2012