Experimental Investigation of Liquid Tin Surface Property Safety Features for Potential Application as a Coolant in Direct Contact Liquid Metal Fast Reactors (DCLMFR) Heat Removal

Liquid tin (Sn) has several advantages as a coolant in Liquid Metal Fast Reactors (LMFR). The investigations for its potential applications were initiated during 1950s [R. E. Lyon, "LIQUID-METALS HANDBOOK," Atomic Energy Commission, Washington D. C., 1952]. One of the earliest proposals for liquid tin application as a coolant, was published by Weeks [Weeks, "Lead , Bismuth , Tin And Their Alloys as Nuclear Coolants," Nucl. Eng. Des., vol. 15, pp. 363-372, 1971], where he considered not only pure tin, but also some eutectic mixtures. Later, Khorasanov et. al. [G. L. Khorasanov, A. P. Ivanov and A. L. Shimkevich, Possibilities of using the liquid tin as a coolant in electronuclear plants, Russian Federation, 1999] mentioned several advantages of tin application in nuclear industry as a coolant. However, it aggressively interacts with the structural materials which complicates the usage. The concept of Direct Contact Liquid Metal Fast Reactors (DCLMFR) was originally proposed in [ J. Buongiorno, N. E. Todreas and M. S. Kazimi., "Thermal Design of a Lead-Bismuth Cooled Fast Reactor with In-Vessel Direct-Contact Steam Generation," in ICONE-9, Nice, April 8-12, 2001]. It is advantageous, because the design does not consider specific heat exchanging equipment: Liquid water is injected directly into the Pb-Bi coolant in reactor core and the generated steam is directed further to the turbine, assuring this way the natural circulation of the coolant. The concept that we propose is very similar: We intend to use liquid tin as a primary core coolant and for secondary direct heat removal coolant we consider the usage of non-condensing gases (or water/steam). However, we plan the secondary coolant injection to take place separately from the reactor core. It appears again to be the driven force for the primary coolant circulation. The liquid tin is suitable to become a coolant of this nuclear reactor design because non-condensable gases nitrogen, argon, helium carbon monoxide and carbon dioxide are practically insoluble. The current paper represents our pre-concept and pre-design studies that involve gas/tin surface interactions. We designed a simple device, based on Wilhelmy plate surface tension measuring approach, and studied the kinetics of formation of stannic and hydrated oxides while liquid tin was exposed to atmospheric air as well as liquid tin surface properties. We considered temperatures from the tin melting point up to below 600. We pay attention also to liquid tin dissolution properties regarding construction materials, some of which could be possibly used in the future design. The oxidation kinetics measuring plates were considered made from: copper, nickel, brass and various steels. In addition, we collected the accumulated at the liquid surface oxides and measured their composition to identify reliably the metal dissolution rates of the measuring plate. The results of these studies directly affect the selection of materials that could be possibly used in the future design. We also extended our study not only to pure liquid tin but also to its industrial grade alloys implemented as solders in electronic industry: Sn100, Sn60 and Sn40. (author)