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In this paper, we integrate rupture criteria for two kinds of cavities with models that calculate the aforementioned parameters in UO2 LWR fuel for a given operating history. | Modelling of fine fragmentation and fission gas release of UO2 fuel in accident conditions EPJ Nuclear Sci. Technol. 5 11 2019 Nuclear Sciences c L.O. Jernkvist published by EDP Sciences 2019 amp Technologies https doi.org 10.1051 epjn 2019030 Available online at https www.epj-n.org REGULAR ARTICLE Modelling of fine fragmentation and fission gas release of UO2 fuel in accident conditions Lars O. Jernkvist Quantum Technologies AB Uppsala Science Park 75183 Uppsala Sweden Received 18 June 2019 Received in final form 23 August 2019 Accepted 6 September 2019 Abstract. In reactor accidents that involve rapid overheating of oxide fuel overpressurization of gas-filled bubbles and pores may lead to rupture of these cavities fine fragmentation of the fuel material and burst- type release of the cavity gas. Analytical rupture criteria for various types of cavities exist but application of these criteria requires that microstructural characteristics of the fuel such as cavity size shape and number density are known together with the gas content of the cavities. In this paper we integrate rupture criteria for two kinds of cavities with models that calculate the aforementioned parameters in UO2 LWR fuel for a given operating history. The models are intended for implementation in engineering type computer programs for thermal-mechanical analyses of LWR fuel rods. Here they have been implemented in the FRAPCON and FRAPTRAN programs and validated against experiments that simulate LOCA and RIA conditions. The capabilities and shortcomings of the proposed models are discussed in light of selected results from this validation. Calculated results suggest that the extent of fuel fragmentation and transient fission gas release depends strongly on the pre-accident fuel microstructure and fission gas distribution but also on rapid changes in the external pressure exerted on the fuel pellets during the accident. 1 Introduction under normal operating conditions are generally larger than 2
