The significance of iodine for source term quantification has been studied by investigating its chemical behavior under the prototypical conditions of a hypothetical severe accident within the containment. As a result, some computer codes were developed and their validation is currently under way. The loss-of-fluid test (LOFT) program was one of the most relevant research projects in the area of nuclear safety. Its last experiment, LP-FP-2, simulated a V-sequence. A great deal of information was recorded on the fission product release, transport, and deposition. A theoretical approach to the chemical behavior of iodine in the blowdown suppression tank (BST) of the LOFT facility was attempted with the IODE and IMPAIR-2/M codes. The comparison of the predictions with the existing experimental data led to the conclusion that the BST system behaved as a low-volatility system, with most of the iodine in the form of the soluble nonvolatile species iodide. Only a partial conversion to volatile molecular iodine was observed due to the presence of radiation. However, the intensity of the γ field was so weak that this transformation was not quantitatively meaningful.