Application of best estimate methodology for Wendelstein 7-X experimental nuclear fusion device

Fusion is the energy production technology, which could potentially solve problems with growing energy demand of population in the future. Wendelstein 7-X (W7-X) is an experimental stellarator facility currently being built in Greifswald, Germany. Prior to start of the operation of the facility, its safety has to be demonstrated by the performance of the safety analyses. The rupture of a 40 mm target cooling pipe during plasma vessel structure heating regime is regarded as the most dangerous LOCA event. In case of pipe line rupture in side plasma vessel, the automatic valves close, preventing water discharge and pressure increase in the plasma vessel. A fast closure of the automatic valves means smaller amount of water discharged and lesser pressure in the plasma vessel. On the other hand, fast closure of the valve can lead to pressure pulse in targets cooling system and it may be the cause of W7-X cooling system pipeline failure. Thus, the consequences of such accident should be analyzed. They depend on many factors (initial conditions of the cooling system, activation logic of the safety system, valve closure time, etc...) in order to evaluate the safety of the device, the best estimate approach should be used in the accident analysis. This article presents the model of W7-X target modules cooling circuits developed with RELAP/SCDAPSIM/MOD4.0 code. The code contains a variety of member-developed computational packages. One of them is an integrated uncertainty analysis package. The pressure pulse in targets cooling system during fast closure of the automatic valve was performed using the developed model and uncertainty analysis was provided. The results of the analysis showed that pressure pulse in targets cooling system evaluating possible uncertainties does not reach the safety limit and the pipes remains intact.