THERMO-HYDRAULIC EFFECTS OF VVER-1000 MIXING GRIDS. POSSIBILITY TO INCREASE THE ALLOWABLE ENERGY RELEASES
24th Symposium of AER on VVER Reactor Physics and Reactor Safety (2014, Sochi, Russia)
Nuclear applications of computational fluid dynamics (CFD)
Abstract
THERMO-HYDRAULIC EFFECTS OF VVER-1000 MIXING GRIDS. POSSIBILITY TO INCREASE THE ALLOWABLE ENERGY RELEASES
Shipov D.L., Samoilov O.B., Falkov A.A., Lukyanov V.E. JSC “Afrikantov OKBM”, Nizhny Novgorod, Russia
ABSTRACT
To increase the effectiveness of operating VVER-1000 and new VVER modules as applied to TVSA fuel assemblies, the plate-type mixing grid (MG) with mixing vanes without fuel element spacing function was developed.
Based on the experimental investigations, the geometry of plate-type MG was optimized from the viewpoint of hydraulic characteristics, mixing properties and turbulising influence on critical heat flux.
For the first time for the Russian fuel, the plate-type MGs were installed in 2008 at Kalinin NPP unit 1. Similar MGs in TVSA-T fuel assemblies were used as a part of the total core loads in 2010 and 2011 at Temelin NPP units 1 and 2.
The MG optimized as for mixing vane deflection angle, layout through the cross-section and layout in the upper spans between main spacer grids (SG) will be loaded in 2014 as a part of 48 TVSA-12PLUS fuel assemblies at Kalinin NPP unit 1.
Three plate-type MG in TVSA-12PLUS will ensure:
- small hydraulic loss (pressure loss coefficient 0.4);
- mixing coefficient increase by 5 times;
- increase of critical heat fluxes by 30-40% due to coolant flow turbulence.
The effectiveness of optimized plate-type MG is confirmed by the results of
experimental investigations of hydraulic characteristics at full-scale TVSA-12PLUS mockup with three MG; of mixing properties using large-scale 94-rod aerodynamic model and 19-rod electrically heated model with high power peaking; of MG turbulising properties influence on critical heat flux using 10 models with uniform and non-uniform radial and axial power distributions and with different MG and SG spans.
The thermo-hydraulic calculations for increased power VVER-1000 core and advanced with increased efficiency 3300 MW VVER core with TVSA-12PLUS with three MG and improved thermo-hydraulic characteristics were carried out.
The results show that TVSA-12PLUS with three MG implements safety criterion preventing DNB in case of increased fuel element power (F∆H=1.63) and maximum linear power density 448 W/cm and 380 W/cm at relative core height of 0.5 and 0.8 respectively.
Using of effective plate-type MG in TVSA-12PLUS together with DNB margin increase improves fuel element operation conditions owing to coolant heating levelling and mass steam quality decrease.
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