Final Interpretation Report of the PHEBUS test FPT0: Bundle Aspects

In this paper, the actual status of understanding of the dominant bundle degradation processes is presented. Here, mainly the results reported in the last years in the Bundle Interpretation Circles organised by JRC/IE and IRSN (Institut de Radioprotection et de Surete Nucleaire, Cadarache) are summarised. For the extensive and detailed computational analyses the commonly used severe accident codes such as ICARE, MELCOR, SCDAP/RELAP and ATHLET-CD are used. For the analysis of fission product release from the FPT0 bundle, specific codes such as SVECHA and XMPR were used as well.JRC.F.4-Nuclear design safet

Phébus FPT3 - Overview of Main Results concerning the Behaviour of Fission Products and Structural Materials in the Containment

FPT3 was the last of the five in-pile integral experiments in the Phébus FP programme, whose overall purpose was to investigate fuel rod degradation and behaviour of Fission Products (FPs) released via the primary coolant circuit into the containment building. The results contribute to validation of models and computer codes used to calculate the source term for a severe accident with core meltdown in light water reactors. Unlike the previous tests, FPT3 used B4C as absorber material in the pre-irradiated (24.5 GWd/tU) fuel bundle, while featuring a steam-poor period as in FPT2, that used Ag/In/Cd absorber. The main FPT3 containment results are summarised: the source term of FPs, fuel and structural materials from the experimental circuit into the containment; the composition, morphology and deposition processes of aerosols in the containment atmosphere; the specific behaviour of the radiologically-significant FP iodine; and finally the performance of Passive Autocatalytic Recombiners (PARs) exposed to the containment atmosphere just after the transient. The major elements contributing to the aerosol mass in the containment are the volatile FPs Cs and Mo, the control rod material B, the cladding material Sn, and the instrumentation materials Re and W (specific to Phébus tests). The fractional compositions, leaving aside the control rod materials, were very similar in FPT2 and FPT3. After reactor shutdown, homogenisation of the aerosol size in the containment led to only one aerosol population, similar to the previous tests. Long-term aerosol deposition in the containment is dominated by gravitational settling and diffusiophoresis, but also significant deposits were measured on the vertical wall, consisting of multi-component aerosols, again comparable with FPT2. A significant result of FPT3 is that iodine is mainly in gaseous form in the atmosphere up to containment isolation; the rest in aerosol form. Another important result is the fast decrease of the iodine concentration in the atmosphere, for total iodine (gas and aerosol), mainly due to deposition on the painted condensers; the depletion of the airborne aerosols Cs and Te was about a factor of 3 slower. As in FPT2, gaseous iodine is mainly in molecular form. Iodine collected in the sump is essentially in soluble form throughout, probably due to the replacement of Ag/In/Cd by B4C as the absorber material. Concerning the PARs, which were introduced in the vessel when the overall aerosol, FP and hydrogen releases in the containment atmosphere had ended, analysis of their surface temperature evolution indicated that, despite the very low oxygen concentration in the FPT3 containment, they worked quite well and were not poisoned by FPs during their 30 minute exposure time.JRC.F.5-Safety of present nuclear reactor