Core designing of the newly proposed (U+Gd)O2 FAs in the VVERs core and comparison with current UO2FAs

Abstract

This research is an independent study on the Russian newly proposed FAs (Fuel Assembly) called TVS-2M, contains (U+Gd)O2 for the future advanced VVERs. The TVS-2M FAs contain gadolinium-oxide which is mixed with UO2 (by different Gd density and U-235 enrichments which are given herein), but also the core does not contain BARs (Burnable Absorbers Rods). The new type TVS-2M FAs are modeled by the SARCS software package to find the PMAXS format for three states of CZP (Cold Zero Power) and HZP (Hot Zero Power) as well as HFP (Hot Full Power), and then the whole core is simulated by the PARCS (Shiraz-university Advanced Regenerator of Cross Section library) code to investigate transient conditions. In addition, the WIMS-D5 code is suggested for steady core modeling includes TVS-2M FAs and/or current TVS FAs. Several neutronics aspects such as the first cycle length (first cycle burnup in terms of MWth-day/kg-U), the critical concentration of boric-acid at the BOC (Beginning of Cycle) as well as the axial and radial power peaking factors, differential and integral worth of the most reactive CPS-CRs (Control Protection System-Control Rod), reactivity coefficients of the fuel, moderator, and boric-acid, and the core’s under-moderation estimation are carried out, and also benchmarked with the PWR Core Design Basis Limits. Moreover, thermal-hydraulics core design criteria such as MDNBR (Minimum Departure from Nucleate Boiling Ratio) (based on W3 correlation), and the maximum of fuel and clad temperatures (radially and axially) are investigated herein. The results show that all of the mentioned parameters are in acceptable safety margins and in some aspects the TVS-2M design has superiority on TVS design such as more discharge burnup (more cycle burnup) and more intrinsic safety margins. Keywords: Core Design Basis Limits, VVER-1000, Mixture of uranium-gadolinium oxides fuels, TVS-2M fuel assemblies, Thermal-hydraulics