Effects of pitting damage on fatigue limit and lifetime in mercury target M. Futakawa * , T. Naoe, H. Kogawa, M. Teshigawara, Y. Ikeda Quantum Beam Science Directorate, Japan Atomic Energy Agency, Tokai-mura, Ibaraki-ken, Naka-gun 319-1195, Japan Abstract High power spallation targets for neutron source are being developed in the world. Mercury target will be installed at the material and life science facility in J-PARC, which will promote innovative science. The moment the proton beams bombard the mercury target, pressure waves will be generated in mercury by thermally shocked heat deposition. Cavitation will be induced through the pressure wave propagation in the mercury and erode the vessel inner surface contacting with mercury, i.e. pitting damage. The eroded vessel wall is damaged by cyclic fatigue because pulsed proton beams strike the target repeatedly. It is, therefore, important to evaluate the fatigue strength of the eroded vessel wall from the viewpoint of target lifetime estimation. In the paper, we describe the effects of pitting damage, cyclic fatigue damage and mercury envi- ronment on the lifetime of the mercury target. Ó 2006 Elsevier B.V. All rights reserved. 1. Introduction A liquid-mercury target system for the MW-class target is being developed in the JAEA as taking into account the neutron yield and self-circulating heat removal efficiencies, and will be installed at the material and life science facility in J-PARC (Japan Proton Accelerator Research Complex) [1]. The proton beam with a 1 ls pulse duration is injected into the mercury through a beam window at 25 Hz. The moment the proton beams bombard the target, stress waves will be imposed on the beam window and pressure waves will be generated in the mercury by thermally shocked heat deposition [2,3]. Provided that the negative pressure generates through the pressure wave propagation in the mercury target, there is a possibility for the forma- tion of cavitation in mercury and the cavitation of micro-bubbles collapses to form pits on the inter- face between mercury and the target vessel under proton injection [4]. Off-line tests on the pressure waves without proton beam had been carried out to evaluate the dynamic response of mercury by using an SHPB (Split Hopkinson Pressure Bar) impact machine. We found the pitting damage on the interface between solid metals and mercury [5,6]. Following SHPB tests, on-beam tests using proton beam had been performed to confirm the pitting damage observed in the off-line tests [7]. After both the experimental results, the so-called pitting damage becomes as a crucial issue to the 0022-3115/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jnucmat.2006.05.018 * Corresponding author. Tel.: +81 29 282 5363; fax: +81 29 282 6712. E-mail address: futakawa.masatoshi@jaea.go.jp (M. Futaka- wa). Journal of Nuclear Materials 356 (2006) 168–177 www.elsevier.com/locate/jnucmat