Cement solidification of intermediate level radwaste with the moss system at the Rossendorf research center

At the Rossendorf Research Center (FZR) at Dresden, Germany, various radionuclides were produced using irradiated nuclear fuel. For preparation of molybdenum-99 (technetium-99m) sources for nuclear medicine from dissolved fuel, a process called AMOR-I was used. In a second process, AMOR-II, non-converted uranium was recovered for reuse in AMOR-I As part of the decommissioning of the AMOR-I plant, the residual solutions from the AMOR-II process will be treated and immobilized in a safe way. The AMOR-II solution contains about 1-1010 Bq/1 total β/γ-activity and a residual α-activity of about 2-105 Bq/1. The Westinghouse Atom MOSS system, because of its robust and reliable method for direct cement solidification in the final waste drums was chosen as the preferred method. The MOSS system is a complete, remotely controlled system for cement solidification of liquid radioactive waste. The system is compactly installed in a framework the size of a standard 20-ft transport container. The system uses the 'lost-stirrer' technique to immobilize different kinds of waste such as ion exchange resins, sludge and evaporator concentrate in standard drums. The container together with the separate control module can be transported from one site to another for different tasks. The Rossendorf MOSS solidification process is designed based on extensive tests giving suitable methods for handling the AMOR-II solution. The AMOR-II solution is strongly acidic. Therefore, prior to solidification, the waste solution is neutralized using sodium hydroxide. The neutralization is done in a separate tank close to the MOSS. Immediately after neutralization, the aluminum hydroxide waste precipitate is transferred to the waste drum and mixed with cement according to the qualified recipe. The actual solidification campaign will start at FZR in April 2000. (authors)