MYRRHA Spallation target design

The position of the free surface is given by the exact balance between the nozzle inlet and outlet flow and needs to be kept within millimetres under all circumstances. This is particularly difficult to maintain under the thermo-hydraulic dynamics of beam trips and start-ups.

In order to cope with these dynamics, there is a second free surface in the spallation loop's main vessel about 2.3 m higher than the nozzle free surface. A mechanical pump lifts the Pb-Bi in the outflow line to the second free surface. The inlet flow line from the second free surface to the nozzle is drag limited to compensate for the hydrostatic pressure. An MHD pump in the inflow line provides fine-tuning in order to warrant a perfect balance between inlet and outlet flow. The free surface level is measured by a LIDAR (Light Detection And Ranging) in line with the proton beam. The LIDAR output is used to control the mechanical/MHD tandem pumps.