Analysis of Rostov-II Benchmark Using Conventional Two-Step Code Systems

Abstract

This paper presents the steady state analysis of the Rostov-II benchmark using the conventional two-step approach. It involves the STREAM/RAST-K and CASMO-5/PARCS code systems. This paper documents a comprehensive code-to-code comparison between Serpent 2, CASMO-5, and STREAM at the lattice level for the different fuel assemblies (FAs) loaded in the Rostov-II core; and between Serpent 2, PARCS, and RAST-K at the core level in 2D. Finally, the 3D results of both deterministic models are compared to the steady state measurements of the Rostov-II benchmark. With respect to the measurements available in the Rostov-II benchmark, comparable accuracy (30 ppm difference in boron concentration, 2% assembly power) with an industrial calculation scheme (BIPR8) are reported up to 36.73 EFPDs. The calculations reported in the paper showed that the modeling of the resonance self-shielding in the lattice code as well as the geometrical modeling of the reflector are key for an accurate solution (reducing the in-out power tilt). At the core simulator level, a fairly crude 1D reflector model appears to be enough. Overall, this paper provides the detailed models and conditions used in STREAM/RAST-K and CASMO-5/PARCS, and accurate calculation solution for the Rostov-II benchmark with STREAM/RAST-K and CASMO-5/PARCS compared with measurement.

Verification and validation of the high-resolution code nTF with VVER-1000 hot zero power monte carlo calculations and experimental data

“…For both cases nTF presents a tendency to flatten the power profile, overestimating the power at the edge and underestimating it in the center of the assembly. This is a common occurrence with MOC codes (Jang, 2021) and is studied further in this work for the full core. It is clear that the flux dip of the Gd pins has an effect on the nTF pin power prediction, however there is still very good agreement with Serpent2.…”

“…The code can simulate cylindrical fuel rod bundles of varying composition in a hexagonal pitch array with allowance for water gaps and corner stiffeners in the regions separating fuel assemblies. The heavy reflector can be simulated with homogeneous pins of water and steel, mapping the corresponding complex geometric structures in the 2D full core model (Jang, 2021). Nuclear data for CASMO5 is collected in a library containing microscopic cross-sections in 586 energy groups, based on the ENDF/B-VII.0 nuclear data evaluation, which are collapsed to 19 or 35 groups.…”

“…CASMO5-VVER employs a similar approach for the modeling of heavy reflectors in full core models. In the framework of the LRT VVER project, CASMO5-VVER was used to simulate a VVER-1000 2D full core (Rostov-2 (OECD/NEA), which was compared with a Serpent2 reference solution (Jang, 2021).…”

“…Fig. 8 presents the CASMO5-VVER model of Rostov-2 and the pin power comparison of CASMO5-VVER vs Serpent2 which results also in power tilts (Jang, 2021). nTF uses one spectrum for the condensation of cross-sections that corresponds to the fuel region and not the reflector material.…”

“…In order to study the effect of the scattering treatment with another MOC code, CASMO5-VVER is used to simulate Rostov-2 in 2D, based on the model developed in LRT in the framework of (Jang, 2021), with P0, P3 and P5 approximations for the anisotropic scattering. As it was mentioned already in this Section, the geometry of the Rostov-2 2D core is identical to the X2 reference model, except the groove region in the heavy reflector (see Fig.…”