Nuclear Fuel Operational Experience at Kozloduy NPP

Kozloduy NPP operates two WWER-1000 units. The TVSA type fuel assemblies have been used at Kozloduy NPP, reactors since 2004. Since 2008 the reactor cores of Unit 5 and 6 have been fully loaded with TVSA. The new assembly type TVSA-12 are in operation at Unit 6 from 2016. The new fuel type TVSA-12 contains increased content and enrichment (up to 4.7%) of uranium and also increased grain sized fuel in addition to the increased skeleton robustness. TVSA-12 allows thermal power up-rating up to 104% (3120 MW) using 42 fresh FAs. The paper discuss from practical point of view information about the experience of TVSA and TVSA-12 fuel implementation, fuel assemblies main design characteristics and KNPP reloading schemes, neutron-physics characteristics, relevant measurement data, fuel reliability statistics, I, Xe, Kr concentrations in the moderator and coolant specific activity data, as an indicator for fuel problem during cycle, our methods to prevent fuel failure, controlling the linear power of the fuel rod, burnup and reactor power changes limitations etc. (author)