Investigations on the Retention of Elemental Radioiodine by Activated Carbons at High Temperatures

At a 130°C temperature, which can be regarded as conservatively representing the temperature in the annulus of a pressurized water reactor (PWR) during the first phase of a design basis loss-of-coolant accident (LOCA), no significant difference was found in the retention of ¹³¹I loaded as elemental iodine by various fresh and aged commercial activated carbons (at the same aging time). In all cases, the ¹³¹I passing through deep beds of carbon (25 cm equivalent to a residence time of 0.5 s) was in a nonelemental form. At 180°C, which can be excluded in a LOCA, similar results were obtained. With aged carbons, however, elemental ¹³¹I also passed through equivalent carbon beds at this temperature. It is concluded that a minimum retention of 99.99% for elemental radioiodine, as required by new guidelines in the Federal Republic of Germany for PWR annulus exhaust air filters in a LOCA, can be achieved as well with various commercial activated carbons.