Experience of WWER-1000 FA operation during 4-year fuel cycle

WWER-1000 reactor plant is initially designed for operation during a standard 2-year fuel cycle. At present 21 WWER-1000 power units are in operation in 3-year fuel cycle at 9 NPPs in Russia, Ukraine and Bulgaria. Operational experience and comprehensive tests of the fuel, discharged after 3-year operation confirmed a considerable margin of all parameters characterizing its reliability. This fact, together with new improvements in WWER-1000 fuel design, allows to starts the trial operation during 4-year fuel cycles. Analysis of WWER-1000 fuel assemblies (FAs) operational results and behavior of design parameters are described in the presented paper. Statistical data on operational results of WWER-1000 FAs, discharged after 4-year operation show that achieved average burnup for 1166 effective days is about 47.60 MWd/kgU and for 1016.9 effective days is about 44.20 MWd/kgU. On the other hand, for the whole period of FAs operation, there is no any FA discharged after 4-year operation in the core that is reached the design failure criteria corresponding to the leak-tightness control value. Analysis of the presented in that paper results confirms that WWER-1000 FAs operate successfully during 4-year fuel cycles