Structural integrity of heavy liquid-metal target installed in spallation neutron facility. Pt. 3. Dynamic stress analyses of flat-type target container

To estimate the structural integrity of the heavy liquid-metal (Hg) target working as a spallation neutron source in a MW-class neutron scattering facility, dynamic stress behaviors after the incident of a 5 MW-pulsed proton beam were analyzed. In the analyses, a flat-type target container with a semi-cylindrical beam window, which is a simplified model of a cross-flow type target, was used as an analytical model of the dynamic structural analysis code LS-DYNA. Pressure waves leading to the dynamic stress were estimated by the LS-DYNA using analytical results of the volumetric heat generation obtained under the proton beam energy of 1.5 GeV, 3 GeV and 6 GeV with uniform cross-sectional power distribution in a rectangular beam profile. As the results, it became clear that the maximum dynamic stress of 636 MPa was appeared under the beam conditions of 1.5 GeV, 5 MW with 50 Hz of the beam pulse frequency, which exceeds the allowable strength of ordinary austenitic stainless steel such as type 316L stainless steel. In the case of the present proton beam condition of 3 GeV with 25 Hz, the target container made of high-yield strength alloy such as a ferritic steel F82H would be durable under the proton beam power up to 2 MW. The beam pulse intensity of 2 MW proton beam power with 25 Hz corresponds to that of 4 MW with 50 Hz. (author)