One important issue in the evaluation of the radiological consequences of a severe nuclear accident is the determination of the amount of radioactive iodine in the environment, released from the damaged reactor core and transported through the reactor primary coolant system. IRSN has launched an experimental program to study the kinetic of the chemical reactions that take place in the circuits, as some of these reactions are supposed to lead to the existence of iodine under gaseous form, which has a great potential to be released in the environment. This program consists of tests performed in a horizontal line simulating the primary circuit with representative thermal hydraulic conditions and a simultaneous injection of gaseous iodine and several elements simulating the volatile fission products (Cs, Mo) and/or the control rod material (Ag, In, Cd, B) and/or the structure material released during the reactor core meltdown.
The results of two tests will be presented and discussed here. The first test studies the persistence of gaseous iodine at the circuit outlet in presence of caesium and boron in excess relative to iodine. The second test concerns the influence of molybdenum on the persistence of gaseous iodine – still in presence of a large excess of caesium compared to iodine.