Conference Agenda

Accurate modelling of plate heat exchangers (PHEs) is essential for the thermal-hydraulic analysis and safety assessment of Small Modular Reactor (SMR) designs. This work presents a validation and uncertainty quantification study of the PHE model implemented in the system code ATHLET. The model is evaluated against experimental data from the ELSMOR test facility. The analysis demonstrates consistent overprediction under certain operating conditions and consistent underprediction under others, indicating that the current model formulation does not provide consistently conservative results for safety-related applications. The sources of these deviations are investigated by combining Monte Carlo analysis with Sobol variance decomposition analysis to identify the main variables contributing to the deviations and to assess model uncertainties. A new model is implemented in ATHLET and compared with the previous one using the ELSMOR test facility as a benchmark. The comparison between the new and the old model shows a reduction in the deviation between model predictions and experimental data, while also reducing the tendency toward systematic over- or underprediction across the investigated operating range. Overall, this study contributes to the refinement of ATHLET, which will be critical for future thermal-hydraulic analyses of SMRs employing PHEs.

The growing importance of low-carbon energy sources in addressing rapid climate change has reinforced the role of nuclear energy as a key component of a sustainable and resilient energy mix. While conventional water-cooled reactors have benefited from decades of operational experience and continuous improvement, there remains significant potential for further advances. In particular, next-generation reactor technologies offer the possibility to enhance intrinsic safety and significantly reduce the volume and long-term radiotoxicity of nuclear waste. Among these advanced concepts, heavy liquid metal (HLM) cooled systems—especially the lead fast reactor (LFR)—stand out as promising solutions. LFRs combine the advantages of fast neutron systems, which enable efficient use of fuel resources and waste minimisation, with inherent safety features such as the high boiling point of the coolant, its chemical inertness, and excellent heat transfer properties.

ANSELMUS, is a 54-month research and innovation action funded by the European Union under the Horizon Euratom programme, launched in 2022. Over the course of the project, substantial progress has been made in advancing the safety assessment framework for HLM reactor systems. At the beginning of the project, two advanced European reactor designs—ALFRED (Advanced Lead Fast Reactor European Demonstrator) and MYRRHA (Multi-purpose hYbrid Research Reactor for High-tech Applications)—were selected as reference systems. These designs represent key milestones in Europe’s strategic roadmap for the deployment of advanced nuclear technologies. Their relative maturity has provided a strong foundation for the detailed analyses carried out within ANSELMUS.

A central achievement of the project has been the development of two comprehensive Phenomena Identification and Ranking Tables (PIRTs). These PIRTs systematically identify and prioritise the key physical phenomena relevant to the safety performance of HLM reactors under normal operation as well as accident conditions. By doing so, they provide a structured basis for identifying verification and validation needs, guiding both experimental campaigns and modelling efforts. The PIRTs have played a crucial role in supporting more robust and transparent safety evaluations of both ALFRED and MYRRHA, and they are expected to serve as valuable reference tools for future HLM reactor development.

In parallel with these analytical activities, ANSELMUS has made significant progress in the experimental validation of several critical safety-related sub-systems. These include the performance and reliability of safety rods, which are essential for rapid reactor shutdown, as well as systems for detecting failed fuel pins, an important aspect of maintaining fuel integrity. In addition, the project has investigated coolant chemistry control systems, which are vital for ensuring long-term material compatibility and preventing corrosion within HLM environments. The results of these experiments have provided important data for validating models and improving the understanding of system behaviour under realistic operating conditions.

Significant progress has also been achieved in the development and validation of numerical models used to simulate fuel assembly behaviour. Through a coordinated programme of experimental testing and advanced simulations, the project has improved the predictive capability of these models, thereby enhancing confidence in their use for safety assessment and design optimisation. Furthermore, ANSELMUS has contributed to advances in reactor safety monitoring and inspection techniques, with particular emphasis on the challenges posed by high-temperature HLM environments. This includes the development and assessment of methods for in-service inspection of reactor vessels, which are critical for ensuring structural integrity over the reactor’s lifetime.

Beyond its technical scope, ANSELMUS has also addressed the broader context of deploying HLM reactor technology. The project has explored how LFR systems could be integrated into a diversified and low-carbon energy landscape, considering factors such as flexibility, grid compatibility, and complementarity with renewable energy sources. Economic aspects have also been examined, providing insights into the potential competitiveness and cost structures of advanced nuclear systems. In addition, the project has considered the social and ethical dimensions of advanced nuclear technologies, recognising that public acceptance and responsible innovation are essential for their successful implementation.

Finally, ANSELMUS has placed strong emphasis on education, training, and dissemination activities. Throughout the project, dedicated efforts have been made to engage a wide range of stakeholders, including researchers, industry representatives, policymakers, and the general public. Workshops, publications, and outreach initiatives have contributed to increasing awareness and understanding of HLM technologies and their potential role in achieving climate goals. As the project approaches its conclusion, these activities ensure that its results are effectively shared and can support future research, development, and policy decisions.

The financial viability of lead-cooled fast reactors is subject to significant uncertainty, stemming from the first-of-a-kind nature of the technology and from market volatility. Previous deterministic analyses of the ALFRED reactor using the INCAS code identified construction duration and cost of capital as dominant financial risk drivers but could not quantify the probability of achieving bankability. This paper extends ALFRED’s financial analysis to a Monte Carlo stochastic framework in which key project risk variables (construction delays, capital cost overruns, and capacity underperformance) are sampled from probability distributions derived from ALFRED’s risk register. The framework is applied twice: 1. baseline conditions, to quantify the inherent financial risk of ALFRED; and 2. with modified policy inputs (including reduced cost of debt/equity and alternative tax assumptions) held fixed in each run. By isolating the stochastic component from the policy component, this second part quantifies the benefits in terms of probability of achieving bankability due to specific public support mechanisms.