Graphite flakes/UO2 fuel pellets with excellent thermal conductivity in radial direction

•Graphite flakes were used to improve the radial thermal conductivity of UO2.•Graphite flakes/UO2 presented highly-oriented structure and well-bonded interface.•The radial thermal conductivity of graphite flakes/UO2 was greatly improved by ~200%. In order to increase the radial thermal conductivity (TC) of UO2 pellets, highly-oriented graphite flakes (GFs) were first introduced to UO2 pellets by spark plasma sintering. The radial TC of GFs/UO2 agreed well with Hatta-Taya model, which was closely related to the well-bonded interface and highly-oriented structure. Compared with UO2, the radial TC of GFs/UO2 was greatly improved by about 200 % within a wide temperature range, higher than all the other reported value until now. Such enhancement in TC would significantly improve the safety of UO2 fuel pellets.