Problems related to use of Erbium as burnable poison for VVER are discussed. Comparison is made between neutronics characteristics of Uranium-Gadolinium and Uranium-Erbium fuel cycles. The study shows that use of Erbium as burnable poison allows decreasing the peaking factor in the core. Meanwhile residual Erbium at the end of the fuel cycle makes it necessary to increase fuel enrichment. There is made the conclusion of prospects of using Erbium as burnable poison for VVER.
This work deals with “Full-Core” VVER-440 extended calculation benchmark which was proposed on the 24th Symposium of AER in October 2014 [2]. This benchmark is based on calculation benchmark defined by ŠKODA JS a.s. on the 21st Symposium of AER in 2011 [1]. This benchmark differs from the first “Full-Core” VVER-440 benchmark in use of control rods from group No. 6. Reason why these benchmarks exist is problematic validation of power distribution predicted by macro-code on the pin by pin level against experimental data. This new benchmark is also a 2D calculation benchmark based on the VVER-440 reactor core cold state geometry with taking into account the geometry of explicit radial reflector. Loading pattern for this core is very similar to the first pattern of the Mochovce NPP. This core is filled with fuel assemblies with enrichment of 1.6%w 235U, 2.4%w 235U and 4.25%w 235U. The main task of this benchmark is to test the pin by pin power distribution in fuel assemblies predicted by macro-codes that are used for neutron-physics calculations especially for VVER reactors. The reference solution has been calculated by MCNP6 code using Monte Carlo method and the results have been published in the AER community. The results of reference calculation were presented on the 27th Symposium of AER in 2017 [3]. In this paper is presented comparison of available macro-codes results for this calculation benchmark.
This paper deals with the development of an approximation method to evaluate the isotopic composition of burnt VVER fuel rods (with U-Gd) by engineering codes (TVS-M, PERMAK-A) and taking into account fuel rods depletion conditions. Burn-up conditions for fuel rods differ from each other during operation due to the presence of water cavities, absorber and other within FA. Therefore, the isotopes evolution during burn-up in different fuel rods goes on in different manner even with identical values of fuel burn-up (MW · day/kg U). The isotopic content evolution can be described in detail by spectral codes. However, a full-size core calculation takes much running time. The approximation method, which takes into account fuel rods spectral differences during operation, was considered. The method is based on spectral functionality (a non asymptotic factor) usage, which allows to take into account the spectral conditions and history of exposure.
A burn-up calculation of VVER's cores by Monte-Carlo code is complex process and requires large computational costs. This fact makes Monte-Carlo codes usage complicated for project and operating calculations. Previously prepared isotopic compositions are proposed to use for the Monte-Carlo code (MCU) calculations of different states of VVER's core with burnt fuel. Isotopic compositions are proposed to calculate by an approximation method. The approximation method is based on usage of a spectral functionality and reference isotopic compositions, that are calculated by engineering codes (TVS-M, PERMAK-A). The multiplication factors and power distributions of FA and VVER with infinite height are calculated in this work by the Monte-Carlo code MCU using earlier prepared isotopic compositions. The MCU calculation data were compared with the data which were obtained by engineering codes.
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