Vapor Suppression Tank of ITER Nuclear Fusion Reactor: Stress and Strain State Of The Steel Anchors Imbedded In The Concrete Foundation due to a Hydrogen Detonation

This paper illustrates dynamic analyses of the support system of Vapor Suppression Tanks (VST’s) under loads caused by a hydrogen detonation event. The VST are components of a safety system of the nuclear fusion reactor ITER (International Thermonuclear Experimental Reactor), for the managing of a Loss of Coolant Accident (LOCA) in the Vacuum Vessel (VV). During a LOCA, non-condensable gases, containing H2, could accumulate in the volume of the suppression tanks. Several hydrogen ignitors are located in the Vapor Suppression Tank (VST) in order to trig the hydrogen combustion. Therefore, hydrogen deflagration and detonation have an extremely low probability to occur. This event is considered ‘beyond the design basis loading’ and the correspondent limits are defined in terms of collapse load and accumulated plastic strain. The paper illustrates several scenarios of hydrogen detonation and the numerical analyses for calculating the pressure histories on the VST components. The lower flange of the VTS, the concrete plinth and the metallic anchors are analysed under the pressure impulses due to hydrogen detonations. A model correspondent to a sector of 45° of the VTS support system has been implemented by means of 3D elements using the FEM computer code MSC-MARC. The stress and strain state have been determined by means an elastic –plastic dynamic transient analysis. The accumulated plastic strain at the final instant of the transient verify the limit established by the Code Case 2564-4 of ASME Section VII – div-3.