Regular Article

Equilibrium state core calculations for an SCW-SMR concept using the Apros-SPNDYN coupled code system

¹ Department of Nuclear Energy, Institute of Nuclear Techniques, Budapest University of Technology and Economics, Műegyetem rkp. 3, Budapest, H-1111, Hungary
² Paks Nuclear Power Plant, PO Box 71, Paks, H-7031, Hungary

^* e-mail: boglarka.babcsany@reak.bme.hu

Received: 5 March 2025
Received in final form: 3 September 2025
Accepted: 22 October 2025
Published online: 2 December 2025

Abstract

The Institute of Nuclear Techniques of the Budapest University of Technology and Economics is actively involved in the development of a supercritical water-cooled small modular reactor concept as a consortium member within the ECC-SMART project, which received an EU/EURATOM/H2020 grant in 2020. For coupled thermal hydraulics and reactor physics analysis of this reactor concept, the SPNDYN in-house finite element reactor physics code has been coupled to the Apros thermal hydraulics system code, using a Transmission Control Protocol/Internet Protocol-based communication method within a Python environment. After introducing the supercritical water-cooled small modular reactor concept under development, this paper presents the methodology used for coupling Apros and SPNDYN, detailing the developed system code and reactor physics models, as well as sensitivity analyses related to the models. The results of coupled equilibrium state calculations performed with the Apros-SPNDYN code system for two different core layouts at the beginning of cycle reactor state are then presented. One of the core loading patterns suggested for the first cycle of the supercritical water-cooled small modular reactor consists of solely 5.0 at.% U²³⁵ enriched fuel assemblies, while the other is an optimised pattern with three differently enriched UO₂ assemblies. The obtained results are compared to reference Apros-Serpent 2 calculations for verification purposes. By coupling Apros and SPNDYN, coupled reactor physics and thermal hydraulics analyses of various transient scenarios of the core concept under development become possible with future contribution to a more thorough safety evaluation of this pre-conceptual design. This paper relates to the application of the SPNDYN finite element reactor physics code developed within the framework of the PhD research conducted by B. Babcsány and shortlisted for the PhD Award of the High Scientific Council of the European Nuclear Society in 2024.