European Nuclear Thermodynamic Database validated and applicable in Severe Accidents “ENTHALPY”

1998-2002, rapport final février 2003FIS5-CT1999-00001info:eu-repo/semantics/publishe

Fuel and fission product behaviour in early phases of a severe accident. Part I Experimental results of the PHEBUS FPT2 test

International audienceOne objective of the FPT2 test of the PHEBUS FP Program was to study the degradation of an irradiated UO2 fuel test section and the fission product behaviour under conditions of low steam flow. The results of the post-irradiation examinations (PIE) at the upper levels (823 and 900 mm) of the 1-m long test section are presented in this paper. Material interactions leading to local corium formation were identified firstly between fuel and Zircaloy-4 cladding, notably at 823 mm, where the cladding melting temperature was reached, and secondly between fuel and stainless steel oxides. Regarding fission products, molybdenum left so-called metallic precipitates mainly composed of ruthenium. Xenon and caesium behave similarly whereas barium and molybdenum often seems to be associated in precipitates. © 2014 Elsevier B.V. All rights reserved

Fuel and fission product behaviour in early phases of a severe accident. Part II Interpretation of the experimental results of the PHEBUS FPT2 test

International audienceOne objective of the FPT2 test of the PHEBUS FP Program was to study the degradation of an irradiated UO2 fuel bundle and the fission product behaviour under conditions of low steam flow. The results of the post-irradiation examinations (PIE) at the upper levels (823 mm and 900 mm) of the test section previously reported are interpreted in the present paper. Solid state interactions between fuel and cladding have been compared with the characteristics of interaction identified in the previous separate-effect tests. Corium resulting from the interaction between fuel and cladding was formed. The uranium concentration in the corium is compared to analytical tests and a scenario for the corium formation is proposed. The analysis showed that, despite the rather low fuel burn up, the conditions of temperature and oxygen potential reached during the starvation phase are able to give an early very significant release fraction of caesium. A significant part (but not all) of the molybdenum was segregated at grain boundaries and trapped in metallic inclusions from which they were totally removed in the final part of the experiment. During the steam starvation phase, the conditions of oxygen potential were favourable for the formation of simple Ba and BaO chemical forms but the temperature was too low to provoke their volatility. This is one important difference with out-of-pile experiments such as VERCORS for which only a combination of high temperature and low oxygen potential induced a significant barium release. Finally another significant difference with analytical out-of-pile experiments comes from the formation of foamy zones due to the fission gas presence in FPT2-type experiments which give an additional possibility for the formation of stable fission product compounds. © 2014 Elsevier B.V. All rights reserved

Post-irradiation Examination of the Lower Part of the Phébus FPT2 Degraded Bundle

The Phébus PF project is an international programme examining the release behaviour of fission products from irradiated fuel. It is led and being carried out by the French Institut de Radioprotection et de Sûreté Nucléaire (IRSN) at Cadarache in collaboration with the European Commission, EU national research institutes as well as USA, Canada, Korea, Japan and Switzerland. The FPT1 test examined bundle degradation and release under steam atmosphere while FPT2 was carried out under steam-limited conditions. After an initial campaign of macrophotography and examination of the major features of the degraded bundle at ITU, the PIE (Post Irradiation Examinations) continued with the extraction of six selected sites from different levels to perform microscopic examination and analysis of the structures found there. This paper reports on the initial findings in the lower part of the bundle. The macroscopy confirmed the state of the bundle determined by the immediate post-test X-ray and ¿ tomographies carried out at Cadarache. The bundle, as in previous tests, had a characteristic central cavity and a corium pool at one-third height of the bundle, while the upper part showed substantial oxidation, damage and distortion. The corium pool extended the full width of the bundle and appeared to be deeper than that of FPT1. The corium appears to be fully oxidic and has similar amounts of uranium and zirconium with traces of fission products, structural materials and shroud material. Beneath the pool, the cladding was still substantially oxidized and distorted with some fuel-cladding interaction. There was considerable debris beneath the bundle including zones of corium as well as melted metallic structures that probably originated from cladding and reactor structural materials. The extent of damage indicated that the most extreme temperatures were not achieved at this level.JRC.E.2-Hot cell

Bundle Degradation Behaviour in the Phebus FP Tests Derived from their Post Irradiation Examination (PIE)

The Phébus FP project is an international project examining the release and behaviour of fission products from irradiated fuel. It is led and being carried out by the Institut de Radioprotection et de Sûreté Nuclèaire (IRSN) at Cadarache in collaboration with the European Commission and the EU national research institutes as well as USA, Canada, Korea, Japan and Switzerland [1,2]. ITU & PSI have undertaken the post irradiation examination (PIE) of the bundles. The first test FPT0 used trace irradiated fuel and acted as a reference. FPTI examined bundle degradation and release under steam atmospheres while FPT2 was carried out under steamlimited conditions. FPT3 was carried out with reduced steam flow conditions but also using a B4C absorber rod. The latter test is still undergoing examination.JRC.E.2-Hot cell