In the frame of the EU ECC-SMART project, the pre-conceptual design of a water-cooled small modular reactor operating at supercritical pressure (SCW-SMR) with seven heat-up stages is under development and assessment. BME is participating in this project as a consortium member and is developing several models and coupled code systems to investigate the features and characteristics of the proposed new concept. This first part of the two-part paper presents the concept design, and the models developed in the Apros thermal-hydraulics system code and the Serpent 2 Monte Carlo reactor physics code. The developed coupling methodology of these models is also described in detail. Finally, the first coupled calculation results, obtained using two different core enrichment maps, are presented and compared. The behaviour of the seven heat-up stages and the power and temperature distributions of the core are evaluated in detail.

In the frame of the EU ECC-SMART project, the pre-conceptual design of a water-cooled small modular reactor operating at supercritical pressure (SCW-SMR) with seven heat-up stages is under development and assessment. The first part of the two-part paper presented the concept design, the models developed at BME in the Apros thermal-hydraulics system code and in the Serpent 2 Monte Carlo reactor physics code, the developed coupling methodology of these models, and the results of the first coupled calculations. This second part of the paper outlines the approaches adopted by the BME research team to improve the original design, primarily to reduce the high cladding temperatures. The effects of the increased mass flow rate and the introduction of inhomogeneous inlet orifices are thoroughly investigated and presented. Finally, a comprehensive sensitivity analysis has also been performed to demonstrate the robustness of the proposed design.

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.

BME, as a consortium member, is participating in the ECC-SMART project, which has been awarded an EU/EURATOM/H2020 grant in 2020, and is researching the development of a supercritical water-cooled small modular reactor concept called SCW-SMR. This paper summarizes the research work carried out so far at BME within the framework of the project. Firstly, several international benchmarks were modelled by the APROS system code and the Ansys CFX CFD software package in order to demonstrate their applicability for the thermal hydraulics analysis of SCW. Later, a complete reactor vessel and a simplified primary circuit model were built with APROS, and a full-length fuel assembly model was developed in Ansys CFX. All the seven heat-up stages of the SCW-SMR pre-conceptual design were modelled and analyzed with these tools. The Serpent 2 Monte Carlo code and the inhouse SPNDYN finite element code were used for reactor physics benchmarking, for various stand-alone reactor physics calculations and in loosely coupled (with APROS and Ansys CFX) and tightly coupled (with APROS) code systems in order to design and optimize the fuel and the reactor core of the SCW-SMR concept. Many successful calculation series (e.g. the socalled SCWR-FQT benchmark) have been performed with these codes and code systems.

Most of the codes available for homogenized group constant generation for deterministic transport calculations apply the approximation of scalar flux weighting during energy group condensation of higher-order anisotropic scattering matrices. In this paper, we point out the bias caused by scalar flux weighting of linearly anisotropic scattering matrices in the result of SP3 and S-12 calculations. An infinite pin cell was homogenized with Serpent 2 and ERANOS ECCO to compare group constants with different energy group condensation options. Serpent 2 applies scalar flux while ERANOS ECCO performs current weighting of the linearly anisotropic scattering matrices. Three simple reactor models were built assuming different core sizes using standard rectangular assemblies with 15 x15 fuel pins to analyze the effect of the various weighting options. Diffusion, SP3, and S-12 calculations were performed for the three models using group constants generated with Serpent 2 and ERANOS ECCO. The effect of scalar flux weighting of linearly anisotropic scattering matrices in higher-order transport calculations is shown by comparing the decrease in reactivity due to the decreased reactor size and the assembly power distribution to reference results obtained with Serpent 2 Monte Carlo calculations. Analogous results were observed during the extension of our investigations to a VVER-440 benchmark and the Budapest University of Technology and Economics (BME) Training Reactor. We also studied the effect of increasing the number of groups in these examples. Neglecting higher than linearly anisotropic scattering and indirect application of diffusion coefficients in higher-order transport calculations is advised with few-group structures if angular flux-moment spectra-weighted higher-order scattering matrices cannot be generated. Although in few-group calculations, it can lead to more accurate higher-order transport solutions than applying scalar flux-weighted linearly anisotropic scattering matrices, by increasing the number of energy groups, the distorting effect of scalar flux weighting can also be decreased.

A joint European Canadian Chinese development of a supercritical water-cooled small modular reactor technology has been in progress since September 2020 in the framework of a Horizon 2020 project called ECC-SMART. A specific work package has been dedicated to studying the design- and safety-related neutronic parameters and reactor physics behavior of the SCW-SMR to support the pre-conceptual design process. Three Monte Carlo codes, viz., MCNP, OpenMC, and Serpent, were selected for pre-conceptual design applications and code-to-code comparison within the Gen-IV SCWR-FQT reactor physics computational benchmark. The effective multiplication factor, the axial power distribution within the fuel, the axial three-group neutron flux distribution, and the spatial distribution of the energy deposition due to neutron and photon interactions were determined. In this paper, results and lessons learned from this study are presented, and useful considerations are summarized to provide guidance in obtaining consistent results among the three Monte Carlo codes.

As a follow-up to the paper previously published by the authors detailing the hybrid finite element (HYBFEM) solution of the SP3 equations, in this paper, besides a semi-analytical solver verification with an analysis on the applied source fitting polynomial order, three-dimensional WER-440, and WER-1000 benchmarks are reproduced with the continuous Galerkin (CGFEM) and HYBFEM SP3 modules of the SPNDYN code. The effect of the applied axial nodalisation and radial element order on the calculation results is discussed. The HYBFEM solver extended with a discontinuity factor (DCF) calculation module based on Serpent 2 output parameters is verified on a two-dimensional WER-1000 benchmark. The SPNDYN CGFEM and HYBFEM results show very good agreement. We also verify that by introducing DCFs in SP3 calculations, the reference transport solution can be reproduced with high accuracy. We high-light the effect of using scalar flux weighted linearly anisotropic scattering matrices in higher-order transport calculations. (C) 2022 The Authors. Published by Elsevier Ltd.

The C-PORCA reactor physics code of the Paks Nuclear Power Plant performs three-dimensional, two-group diffusion calculations applying parametrized group constants generated by the HELIOS code. To improve the accuracy of the calculations, the C-PORCA code was extended with a simplified spherical harmonics module. This paper presents the applied finite-element-based solution algorithm of the SP3 equations in response matrix formalism. Radially primal mixed-hybrid finite element method is used for response matrix calculation with the inclusion of Lagrange multipliers to enforce nodal balance on each element. The axial solution is analytically performed connecting the axial and radial directions through radial leakage with transverse integration. Coupling between the adjacent volumetric elements is performed with node-to-node axial and radial partial current-like moment iterations, that enables the application of SP3 discontinuity factors and the parallelization of the calculation process. The accuracy of the SP3 solution algorithm is demonstrated on academic benchmark and VVER-440 core calculations. (C) 2021 The Author(s). Published by Elsevier Ltd.

This paper describes steady-state reactor physics measurements and calculations that were performed for the Training Reactor of Budapest University of Technology and Economics (BME TR) with the purpose of benchmarking. Based on the available geometry specifications and material compositions a model of BME TR was created with the well-validated, general-purpose Serpent 2 Monte Carlo code. Uncertain parameters (such as fuel density and control rod positions) were adjusted to related measurements. The Serpent 2 model was used for the generation of group constants, examining several homogenization schemes. Models were created in the PARCS diffusion code, the SPNDYN diffusion and SP3 code and the PARTISN discrete ordinates code. Various Monte Carlo and deterministic calculations were performed with the adjusted models and the results were then compared with actual measured data. The calculations and measurements show good agreement, this way the Serpent model was successfully validated, while the deterministic models make a good basis for more complex benchmarks in the future, such as transients with thermal–hydraulic feedback.

Az atomerőművek a fejlett, összetett villamosenergia-rendszerek fontos alapegységei: magas rendelkezésre állásuk, alacsony fajlagos működési költségük, folyamatos, időjárástól független működési módjuk és a szén-dioxid kibocsátásától mentes üzemük mind olyan tulajdonságok, amelyek különösen fontossá teszik őket napjainkban.A jelenleg működő erőművi flotta koreloszlása és a villamosenergia-igények bővülése szükségessé teszi új atomerőművi egységek létesítését.Ennek során a legkorszerűbb biztonsági követelményeket kell figyelembe venni

Although diffusion theory is still the most widely applied deterministic method in reactor physics calculations, due to the increasing complexity of material composition and geometric structures in today's reactor design, and as a result of rapid development of computational technologies, neutronics codes based on higher-order transport approximations and advanced numerical approaches are becoming widespread. One promising alternative of diffusion theory is the simplified spherical harmonics (SPN) method. Since Gelbard heuristically proposed an approximate form of the multidimensional spherical harmonics equations, firm theoretical substantiation and - quite recently - generalization of the theory have been elaborated, thus several neutron physics code are being developed based on its application. In this paper, semi-analytical solutions of the steady-state, one-group SP3 equations are presented for homogeneous slab, cylindrical and spherical geometries assuming up to third-order scattering anisotropy. The developed methods are applied for preliminary verification of a finite-element-based SP3 solver developed by the authors. (C) 2020 The Author(s). Published by Elsevier Ltd.

A coupled thermal-hydraulics and reactor physics code system is being developed at the Institute of Nuclear Techniques of the Budapest University of Technology and Economics based on a higher-order transport approximation, the simplified spherical harmonics theory. The advantage of this method is that with a small increase in computational demand, it provides additional accuracy compared to diffusion theory. Besides due to the fact that the multi-group SP3 and diffusion equations have a mathematically similar form - it requires minimal effort to implement an SP3 solution algorithm to an existing diffusion code. This paper focuses on an algorithm developed by the authors which applies Galerkin weighted residual method for spatial and theta method for time discretization. Results of two-group kinetic SP3 calculations performed with the SPNDYN code are also presented for various one-dimensional perturbations taking into account the delayed neutron precursor balance equations as well. The flexible nature of the SP3 equations makes the developed code a good starting point for more realistic dynamic calculations in the future.

Abstract ATHLET-CD is the severe accident module of the code system AC2 that is designed to simulate the core degradation phenomena including fission product release and transport in the reactor circuit, as well as the late phase processes in the lower plenum. In case of a severe accident degradation of the reactor core occurs, the fuel assemblies start to melt. The evolution of such processes is usually accompanied with the failure of the core support plate and relocation of the molten core to the lower plenum. Currently, the criterion for the failure of the support plate applied by ATHLET-CD is a user-defined signal which can be a specific time or process variable like mass, temperature, etc. A new method, based on FEM approach, was developed that could lead in the future to a more realistic criterion for the failure of the core support plate. This paper presents the basic idea and theory of this new method as well as preliminary verification calculations and an outlook on the planned future development.

The reliable operation of the emergency coolant pumps and passive gravitational injection systems are an important safety issue during accident scenarios with coolant loss in pressurized water reactors. Because of the pressure drop and flow disturbances surface vortices develops at the pump intakes if the water level decreasing below a critical value. The induced swirling flow and gas entrainment lead to flow limitation and to pump failures and damages. The prediction of the critical submergence to avoid surface vortex building is difficult because it depends on many geometrical and fluid dynamical parameters. An alternative and new method has been developed for the investigation of surface vortices. The method based on the combination of CFD results with the analytical vortex model of Burgers and Rott. For further investigation the small scale experiments from the Institute of Nuclear Techniques of the Budapest University of Technology and Economics are used which were inspired from flow limitation problems during the draining of the bubble condenser trays at a VVER type nuclear power plants.

Activation calculations for two nuclear power plants of WWER-440 type have been performed by the authors in order to assist the decommissioning planning by assessing the radioactive inventory present at the time of and at different times after the final shutdown. According to related international literature and studies performed earlier by the authors, considering the activity more than 99% of this inventory is concentrated in the materials directly surrounding the reactor core, where the predominant evolution of radionuclides is generated by neutron induced nuclear reactions. In order to obtain the highest possible accuracy in modelling, three-dimensional Monte Carlo neutron transport calculations were performed. Besides the methods and models applied to these analyses, the paper also summarizes the results that can be generally applied to such nuclear power plant types. At the time of shutdown, the total activity of the stainless steel components is about 6 x 10(16) Bq and 1.3 x 10(17) Bq for the two NPPs considered. The biological shielding concrete constitutes approximately 7 x 10(13) Bq and -1.1 x 10(14) Bq. (C) 2014 Elsevier B.V. All rights reserved.

In this paper, the new German energy policy is analyzed. The main objective of this analysis is to find an answer to the question mentioned in the title of the paper by conducting a multidimensional investigation concerning the sustainability of the current energy policy of the German government. This document also contains information about the evolution of the previously released energy policies of Germany, the reason why the Government has decided about the so called Energiewende (energy turn), however this paper is especially devoted to examine the short- and long-term consequences of this political declaration. The reflections are principally based on statistics, relevant German laws, regulations, decisions and directives of the European Union. What is undoubtedly foreseeable that Germany has started a demanding but at the same time challenging struggle and if they win, their resounding triumph will set for the others an example to follow.