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Development of the MFPR model for fission gas release in irradiated UO2 under transient conditions

The fission gas release microscopic model of the mechanistic code MFPR is further developed for modelling of enhanced release from irradiated UO2 fuel under transient conditions of the power ramp tests, along with the microstructure evolution characterised by the formation of a new population of large intragranular bubbles with a rather wide size distribution (from 30 to 500 nm), observed in transient-tested UO2 fuel samples. | Development of the MFPR model for fission gas release in irradiated UO2 under transient conditions EPJ Nuclear Sci. Technol. 3 4 2017 Nuclear Sciences M.S. Veshchunov and V.I. Tarasov published by EDP Sciences 2017 amp Technologies DOI 10.1051 epjn 2016041 Available online at http www.epj-n.org REGULAR ARTICLE Development of the MFPR model for fission gas release in irradiated UO2 under transient conditions Michael S. Veshchunov and Vladimir I. Tarasov Nuclear Safety Institute IBRAE Russian Academy of Sciences 52 B. Tulskaya 115191 Moscow Russia Received 3 October 2015 Received in final form 29 June 2016 Accepted 6 December 2016 Abstract. The fission gas release microscopic model of the mechanistic code MFPR is further developed for modelling of enhanced release from irradiated UO2 fuel under transient conditions of the power ramp tests along with the microstructure evolution characterised by the formation of a new population of large intragranular bubbles with a rather wide size distribution from 30 to 500 nm observed in transient-tested UO2 fuel samples. Implementation of the additional microscopic mechanisms results in a notable improvement of the code predictions in comparison with the previous code version for the fractional gas release in the Risø ramp tests with three different hold times of 3 40 and 62 h at the terminal linear power of 40 kW m. 1 Introduction 3 4 and is currently the constituent part of the advanced fuel performance and safety code SFPR 5 the refined code For realistic description of fission-gas release and fuel MFPR was applied in 2 to the self-consistent consider- swelling as a function of fuel-fabrication variables and in a ation of the fuel microstructure evolution and fission gas wide range of reactor operating conditions mechanistic release under conditions of ramp tests 1 6 . Despite a models must treat them as coupled phenomena and must significant improvement of the code predictions after include various microscopic mechanisms influencing