Hydrogen Detonation In A Vapor Suppression Tank Of The Nuclear Fusion Reactor Iter: Determination Of Pressure Impulses And Vessel Stress And Strain State

The nuclear fusion reactor ITER (International Thermonuclear Experimental Reactor) foresees a Pressure Suppression System (PSS) for managing a Loss of Coolant Accident (LOCA) or other over pressurization accidents in the Vacuum Vessel (VV). This PSS is made of 4 tanks 100 m3 of volume partially filled by water with a cover gas maintained at sub atmospheric pressure (about 10 kPa absolute). Differently by the applications in the nuclear fission reactors, the steam condensation occurs in ITER at sub-atmospheric pressure conditions. During LOCA, hydrogen can be produced by different processes (interaction of the water steam with the Beryllium first wall, radiolysis or thermolysis) and it can be entrained in the suppression tanks with the steam. In the cover gas several hydrogen ignitors are located in order to trig the hydrogen combustion when an appropriate mixture of oxygen-hydrogen occurs. Hydrogen detonation was analysed in order to determine the stress and strain state if these accidents occurred in the cover gas. The pressure transients on the different parts of the VSTs has been determined by means MSC-Dytran FEM computer code. On the basis of which structural analyses of two VST tanks have been carried out by means of the FEM code MSC.Marc© (2016). 1D and 2D axisymmetric models, 3D shell model and 3D solid were analysed, considering two scenarios of hydrogen detonation (axial symmetric and non-symmetric wave propagation). The VST material has been modelled as elastic plastic – work hardening rate sensitive material. Allowable values of plastic strains are derived by the ASME VIII-div.3-Code Case 2564-4. The performed analyses have verified that the plastic collapse load, that is the ‘load that causes overall structural instability’ is not reached under the transient loads simulating a hydrogen detonation in the lower and upper tanks.