Effects of pitting damage and repeated stresses on lifetime of mercury target

Pitting damage influences the lifetime of Japan Spallation Neutron Source (JSNS) mercury target. The lifetime estimation was carried out taking into account the fatigue crack growth from the bottom of pits. Material crack propagation coefficients in the equation of Paris law were obtained based on the results of 3-point bending fatigue tests on the specimens with various pitting damages. Based on the estimated crack growth rate and the relationship between pitting damage and the number of impact pulses, the relationship between the total crack length and the number of pulses was estimated. The crack length increased rapidly over the crack length of 430 μm and the fatigue failure occurred at 8.4×107 pulses. The lifetime of the JSNS mercury target that suffers the pitting damage and repeated stress simultaneously with failure probability of 10% was 270 h at 1 MW operation.