The Joint European Torus is currently the largest operating tokamak in the world. JET was established with a long-term objective to contribute to the creation of safe, environmentally sound prototype fusion reactors. To meet this objective, JET operates using deuterium as a fuel but also in D-T mode where the fusion reaction is fuelled by deuterium and tritium. To justify the safety of D-T experiments, safety reports have been produced at stages to obtain approval for the past experimental campaigns. The Safety Case is currently under review in preparation of the next tritium campaign in 2014/ 2015.

In this prospect, the hazard assessments have been reviewed and when possible, the calculations in support of these assessments have been updated. For the in vessel loss of coolant accident, the state of the art CEA developed thermal hydraulics code CATHARE 2 V2.5_2, has been adapted down to pressure relevant to fusion applications. The complexity of the heat transfer mechanisms involved in the vacuum vessel has been represented with different elements available in the code to improve the 0D model. Modeling parameters have been studied and any compromise in modeling was done by increasing conservatism of the peak pressure in the VV. Some physical parametric studies have also been run especially on the failure of safety equipment designed to minimize the in vessel consequences on the LOCA. One major result of the analysis is that the initial calculations were conservative in their assumptions and that some break size initially considered as beyond design could lead to pressure peak in the vessel which could be limited by the safety systems below the bursting disk pressure.

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