Studies on iodine trapping by water systems at Studsvik

From large-scale experiments on the iodine removal efficiency of a water pool at 100°C as well as from supporting laboratory runs within the concentration range 10−8 to 10−5 M, it was observed that permanent trapping was achieved to a great extent even at neutral pH conditions. The efficiency was considerably higher at lower iodine concentration. The fraction permanently trapped approximately corresponded to the theoretically evaluated equilibrium amounts of hypoiodous acid and iodide. A mathematical model designed for the washout of molecular iodine in reactor containment atmosphere by sprays gives iodine concentration in containment versus spray time. The model takes the degree of hydrolysis of iodine at different pH values and concentrations into consideration. Initial results from spray experiments performed in a 2.5 m3 tank at pH = 6 to 7.5 and gas phase concentrations around 4 × 10−4, 5 × 10−5, and 1.5 × 10−6 kg/m3 gave half-times due to spraying of about 45, 5, and 2 min, respectively. They confirm the expected strong influence of iodine concentration on washout half-time.