Design of the Spallation Neutron Source Target

research contact: Mark Wendel

The liquid mercury flow through the Spallation Neutron Source target has been simulated using Computational Fluid Dynamics (CFD). These simulated results provide important thermal and hydraulic information necessary in the design of the target. The temperature, pressure, and velocity fields have been computed in the target for a highly turbulent flow characterized by separated regions and high streamline curvature. Symmetry was assumed to reduce the computational effort.

SNS target design (0.5m long, 0.4m wide, 0.15m high)

The target design includes a main flow region inside a stainless steel structure where mercury enters from the sides, flows around a baffle into the proton beam path, and exits out the center. A cooling jacket that wraps from bottom to top around the target is used to cool the target window through which the proton beam enters. The stainless steel target structure is about 0.5m long, 0.4m wide, and 0.15m high.

Heat deposition into the target due to neutronic heating

The heat deposited into the target due to neutronic heating by the spallation process is a strong function of position in the beam tube. This heat load is accurately represented in the CFD analysis. The peak heat load occurs about 5 cm into the target on the target centerline.

Computed velocity and temperature fields

The computed velocity and temperature fields are shown in this figure using colored streamlines. Separated regions behind the flow baffle and near the central symmetry plane are evident. The flow is strongly three-dimensional with a swirl component added as the mercury is turned past the flow baffle.

Computed speed for three vertical planes and the horizontal midplane

The computed speed is given here for three vertical planes and the horizontal midplane. The low flow regions behind the flow baffle and near the window are evident.

Resulting temperatures in the target

The resulting temperatures in the target are shown for the same three vertical planes and horizontal midplane. Here the effect of the velocity field in combination with the beam heat deposition results in elevated temperatures near the beam window and behind the flow baffle.

Looking into the proton beam down the target with the mercury removed

Looking into the proton beam down the target with the mercury removed, the temperatures on the stainless steel target structure are shown. Also the cooling jacket channels can be observed. The elevated temperature at the beam window (red in color) represent a threat to the strength of the target structure.