Experience of HELHEX code package validation at Kozloduy NPP

Aleksandar Kamenov, Krasimir Kamenov (Kozloduy NPP)

28th Symposium of AER on VVER Reactor Physics and Reactor Safety (2018, Olomouc, Czechia)
Reactor physics experiments and code validation (benchmarks)


The HELHEX code package for WWER-1000 reactor core steady state neutron physics calculations has been developed at the University of Sofia in 2013. HELHEX consists of a 3D two-group nodal diffusion code HEX3DA and a 3D two-group pin-by-pin diffusion code HEX3DP. HEX3DA employs a newly developed nodal method HEXNEM3 [Christoskov, Petkov, 2012] which is an extension to the HEXNEM2 method [Grundmann, Hollstein, 1999] implemented in DYN3D code. The method HEXNEM3 is based on transverse integration and a specific two-dimensional expansion of the intranodal fluxes in the hexagonal plane. The nodal and pin-by-pin XS-libraries are generated using the Helios-1.5 lattice code. The albedo coefficients for the radial and axial boundaries are calculated with the Helios-Mariko system. A visualization module HEX3VI coupled with the thermo-hydraulic module COBRA-4I is also developed as a part of the code package.
The experience of HELHEX code packages validation and TVSA and TVSA-12 fuel implementation at Kozloduy NPP units 5 and 6 were presented at the 8th, 9th, 10th, 11th and 12th International Conference on WWER Fuel Performance, Modelling and Experimental Support in 2009, 2011, 2013, 2015 and 2017. Neutron-physics characteristics for Unit 6, cycle 23rd calculated by HELHEX and KASKAD have been compared with relevant measured data.
This paper contains information about start up physics tests program for Unit 6, cycle 23rd. The base construction of TVSA fuel assemblies has been in operation at Kozloduy NPP VVER-1000 reactors since 2004. The improved TVSA-12 assembly distinguishes itself with increased uranium content, enrichment up to 4.7wt% and increased skeleton stiffness. First loading was done at 2016.

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