Short‐term solubility of eight alloys circulating in mercury at room temperature

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Because mercury is a dense liquid at room temperature, it has found application in particle-accelerator targets with high energy-deposition rates such as proton spallation targets. Such targets usually require an active heat-removal system to remove the energy deposited by the particle beam, energy deposition rates that can be as much as several megawatts Ž. Weeks, 1996 . Solid targets generally require a water-cooling system that can introduce significant complexities into the system. However, a mercury target has several advantages over a solid target, one of which is that the mercury itself can be circulated to remove the deposited heat. Although the service lifetime of a mercury target container may be limited by corrosion or erosion caused by the flowing mercury, the present authors found it difficult to retrieve clear guidance from the literature for our application on the compatibility of various alloys with circulating mercury and even less guidance on the effects of radiation. Although one approach to a potential mercury incompatibility problem could be to schedule periodic removal of a target assembly for examination and possible replacement, it would be useful to have experimental evidence of the performance of a material under representative conditions prior to actual service. In order to be useful for application in a mercury-wetted environment, a material should form no solid alloys with Ž. mercury Weeks, 1967 . Since nickel is known to form intermetallic compounds with mercury as well as with lead and bismuth, it has been recommended that austenitic steels or other alloys with more than a trace of nickel be avoided for Ž. use with mercury Weeks, 1997 . Also, chromium is soluble in heavy liquid metals. Therefore, chromium depletion at surface grain boundaries of seasoned steels can be a concern when in contact with mercury. In spite of these concerns, the Spallation Neutron Source project under construction at the Oak Ridge National Laboratory is using 316L Stainless Steel for the mercury target container, and no such difficulties have been observed in laboratory and proton irradiation experiments with 316L Stainless Steel vessels containing mercury Ž. National Spallation Neutron Source, 1997; Haines, 2002 . The muon collider project is also proposing to use mercury Correspondence concerning this article should be addressed to G. A. Greene. for their production target in the configuration of a free jet; in very limited tests conducted to date, no mercury incompatŽ. ibility issues have been encountered Simos et al., 2001 . Although the potential exists for the mercury to become saturated with an alloying constituent, it has been suggested that the soluble components could precipitate or plate out in the cold sections of a flowing loop, thereby promoting the continued dissolution process. It has been suggested that molybdenum, tantalum, or carbide coatings may protect underlying Ž. alloys from corrosion by mercury Weeks, 1997 ; however, the subject of coatings is beyond the present scope.