Natural Circulation Experiments in the Borssele Nuclear Power Plant.

With respect to unsymmetric plant performance under natural circulation conditions in pressurized water reactor power plants only a limited experience is available. Most of the existing knowledge results from computer calculations. This was the reason for performing natural circulation tests in the Borssele nuclear power plant during cooldown of the plant for refueling. The results show that residual heat removal is assured under all boundary conditions taken into account. On the other hand, under certain circumstances stagnation of the natural circulation in one loop was demonstrated.