Phebus-FP is an international integrai experimental programme initiated the French Institute de Radioprotection et de Suretè Nucléaire (IRSN), the European Commission and 'Electricité de France'. Its objective is to investigate the main phenomena involved in Light Water Reactors severe accidents through six in-pile tests. The test facility simulates cure, primary circuit and reactor containment of a PWR, with a scaling factor of about 5000. The programme is also sponsored by USA (NRC), Japan (NUPEC and JAERI), Canada (COG), Korea (KAERI) and Switzerland (PSI and HSK). The first two experiments (Phebus-FPT10 and Phebus-FPTl) were performed on December 2, 1993 and three years later, on July 26, 1996, respectively. Afterwards, Phebus-FPT4 (on July 22, 1999)and Phebus-FPT2 (on October 12, 2000) were carried out. The Phebus-FPT1 test bundle was constituted by 18 fuel rods with a fission length of 1 m previously irradiated in light water reactor BR3, 2 fresh fuel rods and 1 silver-indium-cadmium control rod. The bundle has been then irradiated for 7 days in the Phebus reactor in order to produce the short lived fission product. During the transient it was heated progressively up to a large fraction or the fuel was liquefied. The chemical environment created during the Phebus-FPT1 transient contained a large number of species, generated at variable temperature by fission product, structural material, fuel and steam, and this produced a very complex chemistry. To date, the presence of a gaseous species of iodine in the hot leg of the primary circuit during the zircaloy oxidation phase has not been completely interpreted, even though a number of possible and different explanations have been widely discussed. For certain, it would seen quite confirmed that the fraction of gaseous iodine arriving to containment (supposed to be HI) is not correlated with the increase of the hydrogen concentration. This paper reports the results of a study carried out in order to contribute solving this problem. It is based on the determination by the HSC 5.1 Computer Program of the fission product and structural material speciation in the Phebus-FPT1 core during the transient. In addition, this could consent the introduction of some simplification for the relative kinetics calculation. The results have indicated mainly that: - At temperatures higher than 1000°K, CsI, InI, Hi, and I are the dominant gaseous iodine species. Other estimated important species, such as CdI, CdI2, AgI, are nearly absent far all conditions. ' - The percentage of HI formed increases when the percentage of H2 and the Cs/In ratio decrease. The formation of HI would seem linked to the competing equilibria of the species of indium. - The transport of gaseous iodine to containment should occur, at least partially, by m and perhaps a Utile fraction of the initial InI(g). The significant formation of InI(g) justifies the gaseous iodine fraction that was found in the hot leg of the primary circuit.
|Titolo:||Fission Product and Structural Material Speciation during the Phebus-FPT1 Transient|
|Data di pubblicazione:||20-apr-2004|
|Appare nelle tipologie:||5.2 Documento in Garanzia della Qualità|