In recent years, small modular reactors (SMRs) have gained significant momentum worldwide as a key component of next-generation nuclear energy systems, driven by their enhanced safety features, flexible deployment, and economic potential. However, SMR designs introduce significant challenges for deterministic, hence efficient reactor physics modeling, including complex geometric configurations, heterogeneous material compositions, and relatively smaller core sizes. These characteristics lead to stronger neutron leakage effects, higher flux gradients, and pronounced spectral and spatial heterogeneities, necessitating the application of multigroup and higher-order neutron transport methods beyond the traditional diffusion approximation. In parallel, the accurate coupled simulation of reactor physics and thermal-hydraulics processes is essential for SMR deployment. Such coupled analyses are a fundamental prerequisite for reactor design optimization, safety analyses, and regulatory licensing. Reliable prediction of core behavior under both steady-state and transient conditions is required to support safety evaluation, including reactivity feedbacks, power distribution evolution, and operational transients.

The Institute of Nuclear Techniques at the Budapest University of Technology and Economics (BME NTI) has developed an advanced deterministic reactor physics code, SPNDYN, based on the finite element solution of the SP3 neutron transport equations. The code is capable of high-fidelity core analysis and has been coupled with the Apros thermal-hydraulics system code, providing a framework for multiphysics simulations.

The aim of this PhD research is to further extend and enhance the capabilities of the Apros-SPNDYN code system for advanced SMR analysis. The candidate is expected to:

• Develop and implement an adjoint SP3 solution method for sensitivity analysis and advanced reactor physics applications;
• Extend the code to support pin-level SP3 modeling, enabling high-resolution core simulations;
• Develop an accurate transient SP3 solution method for efficient space-time reactor analysis (preferably based on an improved quasi-static method);
• Implement isotope concentration tracking and burnup calculation modules for fuel depletion analysis;
• Perform verification, validation, and benchmark calculations, with a focus on SMR-relevant configurations.

Given the existing Apros-SPNDYN coupling, a key objective of the research is to develop and implement advanced coupled reactor physics and thermal-hydraulics simulation methodologies for SMR applications, enabling high-fidelity analysis of steady-state and transient reactor behavior.

The outcome of the PhD project will contribute to the development of next-generation simulation tools for SMR design, safety assessment, and licensing support, thereby strengthening BME NTI's state-of-the-art capabilities in advanced reactor analysis.