Periodic Reporting for period 3 - ECC-SMART (Joint European Canadian Chinese development of Small Modular Reactor Technology)
Periodo di rendicontazione: 2023-09-01 al 2025-02-28
Water plays a pivotal role in energy production, serving as a fundamental resource in various power generation processes. Fossil-fired power plants (FFPP)typically achieve thermal efficiencies of around 50% using supercritical water (SCW), whereas nuclear power plants (NPP) generally achieve efficiencies of about 35%. ECC-SMART aimed to assess the feasibility of a novel source of energy with efficiency above 40 %, combining extensive experience garnered from both FFPP operating under SC conditions and NPP employing water. In addition to larger nuclear units, interest in small modular reactors (SMRs) has resurged, successfully written into the project. Consequently, the European pre-concept of SCW-SMR was designed. While overcoming some preidentified knowledge gaps, the novel SCW-SMR pre-conceptual design arises from the previous EU´s project on supercritical water-cooled reactors. The project provided valuable insights into material behaviour under simulated SCW-SMR conditions, utilising advanced analytical tools to support the safety of future SCW-SMR systems. Improved models and methods for turbulent heat transfer and smooth and rough surfaces at SC conditions were provided and validated. The coupled analyses combining neutronics with thermal-hydraulic calculations were successfully conducted to optimize the core design of EU SCW-SMR. The project consortium has unified the strengths of European, Chinese, Canadian, and Ukrainian initiatives to develop safety criteria for the Small Modular Reactor (SCW-SMR) concept. This work builds on the science-based recommendations from the International Atomic Energy Agency and the Generation IV International Forum for Small Modular Reactors. Project approach includes the principle of defence-in-depth, which employs multiple safety layers, and a focus on physical protection, security, and non-proliferation to ensure responsible development. The guidelines for SCW-SMR safety demonstrations detail essential development stages, safety issues, specific requirements, and necessary experimental support. Additionally, these guidelines address the current legislative status regarding licensing, all of which are comprehensively outlined in the project Deliverables. Collaboration and resource sharing among partners across the world have advanced technology and accelerated project execution. Research under the ECC-SMART project, related to 4th generation reactors, supports the integration of nuclear energy into the energy mix by addressing safety, environmental, and economic factors, and builds on the natural evolution of light water reactors for future energy systems.
The successful collaboration under the ECC-SMART project resulted from numerous online and in-person meetings that fostered productive discussions and enhanced project execution. Our strong engagement of young researchers, alongside the close cooperation with the ENEN2plus project, significantly contributed to project activities. This collaborative approach has led to notable advancements in technical work packages. The material testing data were successfully used to optimise predictive corrosion models in SCW above its critical point. The use of advanced analytical tools deepened the knowledge of corrosion behaviour of the candidate materials and the developed alloy AFA. Stress corrosion cracking (SCC) studies indicated that 310S, 800H, and AFA alloys show no signs of SCC at 380 °C and only minor indications at 500 °C. Oxidation tests on irradiated 800H and 310S alloys showed no significant effect of 0.3 dpa on corrosion resistance, though mechanical properties were impacted. The radiolysis could be suppressed up to 500 °C using hydrogen injection. Electrochemical studies successfully validated weight gain measurements from the corrosion tests. Most of the data was stored in the MatDB database. A pre-conceptual EU SCW-SMR design with horizontal placement of fuel assemblies was proposed. Benchmarking of the system and CFD codes was conducted, leading to improvements in models and methods. A core layout and passive safety system for the novel design were also developed and evaluated. The optimized core layout contains fuel assemblies with an average enrichment of up to 10% that could operate up to two years without reshuffling. The reactivity control via B4C rods completed the pre-concept design. The safety and feasibility of the core were confirmed by negative temperature coefficients. Proper calculational tools have been developed in order to tackle complex neutronic and thermal-hydraulic problems. As a result, the developed UO2 core model is feasible in terms of power distribution and burnup cycle length, while providing acceptable fuel centerline and cladding temperatures. Guiding principles for applying Generic Safety Elements in ECC-SMART were established, alongside the PIRT (Phenomena Identification and Ranking Table) analysis covering material, thermal-hydraulic, and neutronic safety features. The work aligned safety challenges and phenomena of SCW-SMR with IAEA SSR-2/1 (Rev. 1) and OECD/NEA fuel safety criteria. Additionally, guidelines were developed for safety demonstration across the various phases of new reactor design development. Despite the challenges posed by experimental complexity and international coordination, the team successfully ensured steady progress toward a feasible pre-concept SCW-SMR. Key data were consistently published in open-access journals and presented at conferences, contributing to the project's transparency and impact. As a result, the participants are confident that all objectives set at the beginning of the project were fulfilled, providing a strong foundation for continued advancement.
The ECC-SMART project made important progress in developing SCW-SMR technology by addressing key technical, safety, and licensing challenges through international collaboration. Nearly 800 specimens (Incoloy 800H, stainless steel 310S, alumina forming alloy AFA) were tested under simulated SCW-SMR conditions. Unique long-term (≥7000 hours) exposures were conducted for the first time within the research community. The obtained results provided valuable insights into corrosion behaviour, testing and material selection for future designs. A new pre-conceptual reactor design was proposed, featuring horizontally oriented fuel assemblies and a core layout that allows two years of operation without fuel reshuffling. This concept improves operational flexibility and supports the use of passive safety systems, which were also developed and evaluated as part of the project. To support further the development, a set of design requirements was compiled based on earlier projects and current SCW-SMR concepts. Lessons learned were applied to define and refine key systems, such as the reactor core, fuel assembly, safety features, and control systems. This work helps identify research priorities and supports future design updates. Moreover, the project emphasized the importance of training and education, involving young researchers to develop their future career in nuclear energy field. Ongoing cooperation, supported by the advisory board, ensures that the results of ECC-SMART will continue to contribute to the evolution of advanced nuclear technologies.