Results from phase 2 of the radioiodine test facility experimental program

A series of intermediate-scale experiments were conducted in the Radioiodine Test Facility (RTF) in a vinyl-painted, zinc-primer coated, carbon steel vessel in order to assess the effects of vinyl surfaces on iodine volatility in both the presence and absence of radiation. This test series, Phase 2 of a larger, comprehensive program assessing a variety of containment surfaces, also examined the effects of organic (i.e., methyl ethyl ketone) and inorganic (i.e., hydrazine) additives, pH, and venting on the aqueous chemistry and volatility of solutions initially containing cesium iodide. These tests have clearly demonstrated that organics are released to the aqueous phase from the vinyl coating and that, under radiation conditions, these organics can have a significant effect on the formation of volatile iodine species. In particular, the RTF results suggest that radiolytic decomposition of the released organics results in dramatic reductions in pH and dissolved oxygen concentration, which in turn are responsible for increased formation of molecular iodine and organic iodides. When the pH was maintained at 10 (Test 3), much lower iodine volatility was observed; low iodine volatility was also observed in the absence of radiation. This test series also demonstrated that vinyl surfaces, particularly those in contact with the gas phase, were a sink for iodine. (author) 4 figs., 6 tabs., 17 refs