R & D on mercury target pitting issue

A technical issue in mercury spallation target development is pitting, which appears on the target vessel in conjunction with the pressure wave. Pitting has been found in off-beam line test by split Hopkinson pressure bar (SHPB) test as well as in the on-beam test of mercury target at WNR of LANSCE. In SHPB tests pressure in mercury was reduced from 80 to 40, 20 and 10 MPa. Specimens made of type 316 stainless steel were inspected before and after the impacting test at ×450 magnification. Results show that over 20 MPa pitting was generated. But at the lowest pressure in mercury, the number of pits was very limited and substantial damage was small. Substantial damage by pitting is characterized by holes where mass is removed from the wall. Depression itself may not be a substantial damage as long as it is not accompanied by holes.