Studies of Mercury in High Level Waste Systems

Historically, mercury was added to the nuclear weapons processing as a catalyst for the dissolution of aluminum metal. After neutralization the mercury was disposed to the High Level Waste tanks where its speciation led to mercuric oxides/hydroxides in the sludge and a small soluble mercuric ion concentration in the alkaline supernate. This report in its original revision described a three-pronged approach for studying possible sources of elevated mercury vapor in and around the Tank Farm evaporator systems. This approach examined the engineering differences between the evaporator designs, the chemistry of mercury and its concentrations, and the potential for organomercury species.During the course of this work, the presence of dimethylmercury in the High Level Waste system was established. Vapor and liquid samples were analyzed from the three evaporator systems (2H, 2F, and 3H) along with the transfer lines leading to the Effluent Treatment Facility and tanks within the ETF. The magnitude of the dimethylmercury concentrations led to ventilation modifications at the 3H Evaporator and design for modifications at the 2H evaporator. Continued sampling efforts are aimed at understanding the boundaries of where dimethylmercury vapors exist