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dc.contributor.authorPASTORE Giovannien_GB
dc.contributor.authorPIZZOCRI Davideen_GB
dc.contributor.authorHALES Jasonen_GB
dc.contributor.authorNOVASCONE Stephenen_GB
dc.contributor.authorPEREZ Danielleen_GB
dc.contributor.authorSPENCER Benjaminen_GB
dc.contributor.authorWILLIAMSON Richarden_GB
dc.contributor.authorVAN UFFELEN Paulen_GB
dc.contributor.authorLUZZI Lelioen_GB
dc.identifier.citationProceedings of the Enlarged Halden Program Group Meeting p. Paper N° F7.4en_GB
dc.description.abstractExperimental observations relative to both in-reactor irradiation and post-irradiation annealing of oxide nuclear fuel indicate that substantial fission gas release (FGR) can occur on a small time scale during temperature transients (burst release). The rapid kinetics of the process cannot be interpreted as purely diffusion-controlled. Micrographs demonstrate the presence of patterns of grain boundary separations (micro-cracks) in transient-tested fuel, thus indicating micro-cracking as the basic mechanism of burst release. Representing such effect is essential for the proper analysis of fission gas behaviour and of the multiple related aspects of fuel performance during reactor operational transients and design-basis accidents. Models employed in fuel performance codes typically allow for gas release only following extensive grain-boundary gas bubble interlinkage (ductile behaviour of the grain boundaries). In this work, a new model for transient fission gas behaviour in oxide fuel is developed, which introduces the alternative mechanism of gas release from the grain boundaries following micro-cracking (brittle behaviour). As a preliminary approach, a relatively simple, semi-empirical description is adopted. The treatment extends an existing model for diffusion-controlled fission gas release and swelling. The effect of micro-cracking is interpreted as a reduction of the gas storing capacity of grain boundaries during transients, effectively leading to an increase of FGR and to a corresponding decrease of fission gas swelling. The fraction of cracked grain surface is described by a temperature-dependent sigmoid function, which reproduces the characteristics of transient gas release observed experimentally both during increasing as well as decreasing temperatures. Relative to existing transient release models, no discrete temperature threshold for burst release activation is involved, thus guaranteeing continuity of the calculated fission gas concentrations in both time and space. Thus, the model is compatible with a physically sound description of the coupled fission gas release and swelling. The model is implemented in the BISON fuel performance code and applied to the simulation of fuel rod irradiation experiments involving transients. The results are presented, pointing out an encouraging predictive accuracy and a consistent representation of the experimentally observed kinetics of FGR during transients.en_GB
dc.description.sponsorshipJRC.E.3-Materials researchen_GB
dc.publisherOECD Halden Reactor Projecten_GB
dc.titleModelling of transient fission gas behaviour in oxide fuel and application to the BISON codeen_GB
dc.typeArticles in periodicals and booksen_GB
JRC Directorate:Nuclear Safety and Security

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