Analyses of the behaviour of fuel rods in UJV Rez, a.s

As part of the support for the operation of nuclear units of CEZ a.s., UJV Rez a.s. works on analyses of the behavior of fuel rods in normal operation conditions and design accidents. Analyses are carried out both as part of the licensing process (introduction of new fuel types, performance increases) and as support for the entire fuel cycle (analysis of experimental results of innovative fuel types, calculations within the safety evaluation of campaigns, development of fuel degradation models under dry storage conditions). This article presents the computational tools, methodologies, experimental base, and selected results. As part of the licensing process, the TRANSURANUS code developed by JRC ITU is used, which has been adapted and validated at UJV Rez for the analysis of VVER fuel produced by TVEL. For advanced analyses, 2D and 3D thermomechanical models are developed and applied in the ABAQUS code. Licensing analyses are carried out according to methodologies that also take into account modern Best Estimate approaches. Thanks to its membership in the OECD Halden Reactor Project and the OECD Studsvik Cladding Integrity Project, UJV Rez has access to unique experimental data on testing advanced types of nuclear fuel, which are systematically evaluated in terms of impact on economy, reliability and operational safety. Last but not least, the UJV Group participates in the implementation of fuel inspections at the Temelin NPP and provides their independent evaluation of the results, including placing the results in the context of a comprehensive assessment of the condition of the core. (author)