Abstract
The introduction of NS-1 solvent into the entire primary system of Dresden Unit-1 nuclear power reactor on September 12, 1984, represented the culmination of several years of development, testing, planning, and construction. The solvent, NS-1, was newly developed to dissolve the highly radioactive deposits of nickel ferrite. An extensive metallurgical test program followed to document its compatibility with the construction materials of the Unit. To circulate the cleaning solvent throughout the primary system, temporary equipment was installed. Moreover, a completely new facility was constructed to process the spent complete cleaning solutions and rinses, because the older existing equipment was not suitable for handling this volume of radioactive waste.
The cleaning of Dresden-1 occurred during a 100 hour period at 250°F (124°C). The chemical condition of the circulating solvent was measured throughout the procedure. The oxides of iron, nickel, and radioactive cobalt all dissolved most rapidly in the first few hours, and much more slowly as the cleaning neared completion. Copper, on the other hand, decreased in concentration after the initial rapid dissolution of the oxide, indicating the probable plating out of metallic copper. A special rinse formulation was employed to redissolve and remove it.
After the cleaning was complete and the reactor had been refilled with pure water, it was possible to measure radiation levels to compare with those taken before the cleaning. The most accurate of these measurements gave decontamination factors ranging from 46 175, a significant removal of the radioactive deposits.
