New methods development for SCORPIO-VVER core monitoring systems to address advanced VVER 440 fuel types

With introduction of advanced design fuel with Gd burnable absorber to Czech and Slovak VVER 440 reactors SCORPIO-VVER CMS faces new requirements and challenges. New methodology and tools had to be developed in the area of core design (neutron physics, core thermal hydraulics and fuel thermal mechanics) to properly model and address new design features of Gadolinium bearing fuel of Gd 1 and Gd 2 type. These methods have to be adapted for implementation in SCORPIO-VVER CMS. The paper provides comprehensive list of requirements and open questions, which need to be properly addressed and clearly defined prior to major innovation of the system commence. All related fields are being step by step re-evaluated (neutron physics, thermal-hydraulics and fuel thermal-mechanics). Pin power determination methodology had to be improved. Higher geometrical complexity on upper and lower core ends, particularly for transition cores with different fuel types, led to change in axial nodalization. More stringent fuel related limits (design criteria, lover margins) with higher burn-up and required unit (fuel) maneuverability require new calculation strategy in fuel conditioning/de-conditioning PCI supervising module PES. Validation of simplified simulator for HiBu domain is under development using FEMAXI code and new 2D-3D tool development for CEZ utility. Conclusions of the paper concentrate on mid term and long term innovation plans for core and fuel operation reliability crucial systems. (Author)