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Our research

Learn about our research on the second and third generation reactors here.​​​​

Learn about our research on the second and third generation reactors here. Within the scope of research on second and third generation reactors at IRESNE, the objectives are to extend the service life of nuclear power plants currently operating in France (2nd generation), to support the start-up of the EPR (3rd generation), and to develop new components for current and future reactors.

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IRESNE helps find solutions to the technical needs expressed by its industry partners, mainly EDF and Framatome. IRESNE is involved in the fields in which it has built up expertise and capitalised on its knowledge and experience, i.e.: behaviour of nuclear fuel and fuel assemblies, reactor core physics, behaviour of components and systems, and nuclear safety which includes severe accidents.​

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Research on nuclear structures and components

The researchers at IRESNE work on improving reactor structures and components. Their research focuses more specifically on:

• Contamination in the primary system:
  It is essential that we understand contamination in the primary system of pressurised water reactors (PWR) when designing, operating and dismantling such facilities. Our research targets how we can control primary system contamination using the computer code called OSCAR, which was jointly developed with EDF and Framatome. We use this computer code to simulate the PWR primary system contamination by corrosion products, fission products and actinides.
  

• Steam generators:
  Steam generators are key components in nuclear power plants. A steam generator is made up of a large number of tubes housed in a shell. These tubes act as heat exchangers to generate steam that is fed into turbines to produce electricity. Oxide deposits can accumulate and eventually clog the steam generator tubes after several years of operation. This is known as fouling and it can seriously affect the overall performance of the nuclear power plant.
  IRESNE has a test facility called COLENTEC that it built to specifically study this phenomenon. This test loop is used to reproduce deposits under representative conditions that are likely to accumulate in steam generator tubes. The studies already completed have allowed us to identify the contribution of precipitation and how the initiation of material passivation affects the fouling process.
  

• Effects of irradiation on the reactor vessel:
  A nuclear reactor comprises a steel vessel in which the reactor core is housed. Immersed in a hostile environment, the materials are put to the test. They are not only subjected to thermomechanical and chemical loads, but also to neutron irradiation. The microstructure and properties of the reactor vessel steel are modified by irradiation. During operation, it has been observed that the steel’s ductility reduces over time. This is why the reactor core is the subject of studies and specific monitoring developed to manage material ageing and ensure the resistance of the vessel steel until the end of its service life. The operating experience (OPEX) built up over the years guarantees that this component meets the strict safety requirements. We nevertheless continue to investigate the effect of neutron fluence. The MATADOR computer code was developed for this purpose; it is capable of describing the intensity of particle fluxes or ionising radiation travelling through a material.
  The mechanical strength of the reactor vessel determines the service life of the facility because it cannot be replaced. The reactor vessel also provides the second containment barrier against radioactive elements, which means it plays a key role in the facility’s nuclear safety.
  

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Nuclear fuels and fuel assemblies

A nuclear reactor requires fuel to produce the nuclear fission reactions that generate heat and then electricity. We run studies on a range of nuclear fuels and their fuel assemblies.

• Fuel behaviour studies:
  Research on fuels is used to elaborate physical behaviour models which are then integrated into numerical simulation software developed within the framework of the our PLEIADES platform which brings together the latest online digital tools. This platform is therefore used to study the behaviour of fuel (UOx and Mox) under irradiation in normal, incident and accident conditions, as well as post-irradiation studies on the same fuels.
  

• Analysis of fluid-structure interactions:
  Teams at IRESNE are tasked with studying the dynamic interactions between a structure and a fluid. These interactions lead to the exchange of energy between the flow and the structure. In some cases, this non-conservative process has a positive stabilising effect. Yet more than often it has a negative effect, causing fluid elastic instabilities that provoke excessive vibration. Using our hydraulic test platform, we can characterise, model and simulate fluid/structure interactions of fuel assemblies to be able to predict the different possible interactions during reactor operation.
  

• Behaviour of fuel assemblies in accident conditions:
  A loss-of-cooling accident occurs when the reactor core is not cooled correctly. Dubbed LOCA, this type of accident occurs when a pipe in the primary cooling system breaks or fails. This failures causes the system to depressurise during which the water vaporises. Though the fission reactions have stopped, the fuel in the reactor core continues to heat due to the residual power from the accumulation of fission products. This is why IRESNE analyses the behaviour of fuel assemblies during different reactor cooling accidents, not only to design and develop solutions and measures to prevent this type of scenario, but also to further refine our expertise in the field.
  

• Innovation in the fuel sector:
  The key issue in R&D is to constantly strive to make nuclear energy safer, cheaper and more sustainable. IRESNE is focusing its attention on developing innovative technical building blocks to rise to this challenge. Some of these building blocks are driving innovations in fuel.​​​
  ​​ We design and develop industrial fabrication processes, such as additive manufacturing (3D printing), with the goal of simplifying the overall process, reducing costs, and improving both the quality and versatility of the design.​​​
  ​​ We also study the fabrication of experimental fuel rods - equipped with or without instruments - that are used to conduct separate effects and integral tests. ​​​
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Nuclear safety

All stakeholders in the field of nuclear safety actively work to develop solutions that make nuclear energy increasingly safer. Our teams are committed to developing and improving the tools and systems of second and third generation reactors designed to provide maximum safety levels in all conditions.

• The Cabri International Programme (CIP):
  The Cabri International Programme (CIP) was initiated in 2000 in collaboration with the French Institute for Radiation Protection & Nuclear Safety (IRSN), EDF and twelve other global partners. It sets out to study the behaviour of nuclear fuel rods - especially the cladding - during a reactivity injection accident (RIA) in a pressurised water reactor (PWR) using the CABRI experimental facility. As operator of the CABRI reactor, our teams are involved in preparing, implementing and analysing the test results.
  

• Developing methodologies:​​
  Our collaborators explore all potential accident scenarios and then develop various methodologies to estimate and design any necessary improvements to continuously uphold nuclear reactor safety. We therefore work on: probabilistic safety assessments, the impact of uncertainty on margin estimates, risk-informing, and human & organisational factors. Quantifying and ranking the risks helps optimise reactor performance and ensure the nuclear safety of these reactors.
  

• Studying corium through experiments:
  Corium is a mixture of molten fuel and structural components in a nuclear reactor core; this mixture can form in the event of a loss-of-coolant accident. This is known as a severe accident or a core meltdown accident. The teams at IRESNE conduct experiments to study the physical characteristics of corium, its spread, solidification, and interaction with concrete or water, as well as its coolability and the behaviour of fission products. The experimental platform used to conduct these experiments is called PLINIUS; it can perform tests on prototypical corium between 2000 and 3500 K. This prototypical corium has the same chemical composition as the corium expected to be found in a severe accident, only with a different isotopic composition (use of depleted uranium).

• Studying corium through modelling and simulation:
  Other than carrying out experiments, the teams at IRESNE also develop tools to model and simulate the behaviour of corium in different accident scenarios. The data is used to refine our knowledge of phenomena likely to occur and to therefore predict and adapt our response to a severe accident scenario.

• Thermal and physical characteristics of corium:
  The thermophysical characteristics of corium are studied in great detail because they are used to model and simulate the behaviour of corium in severe accident conditions.

• Studying the release of radioactive material into the environment:
  At IRESNE, we conduct research on the source term and the potential impact of radioactive material released into the environment. These very in-depth, precise studies are used to define civil protection procedures to be deployed in the event of a severe accident.
  
  

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Pushing the boundaries

Our teams put their expertise and know-how to use by exploring and developing new models and new fuels for the second and third generation of reactors operating in France.

Our skills are capitalised in numerous cross-disciplinary subjects applicable in different fields of research.

• Computation to drive innovation:
  Our researchers are committed to designing and developing neutron and thermohydraulic calculation tools that can accurately model the interactions occurring in nuclear reactors and large components (e.g. heat exchangers). These calculations provide an increased level of accuracy with respect to our estimations and a refined understanding of the phenomena in play, and even of the design (e.g. heat exchangers).
  

• New materials and processes:
  The experts at IRESNE test new materials and processes, looking for ways to boost innovation to further nuclear safety and reactor performance. These materials are subjected to high constraints in an extreme environment, which is why our researchers develop increasingly innovative solutions, e.g. alloys that are stronger, more corrosion resistant, etc.
  

• Innovation for fuels:
  As part of optimising nuclear safety, our teams analyse fuel pellets, cladding materials, and fuel-cladding interactions. We are currently developing more robust fuels, known as accident-tolerant fuels (ATF). Research focuses on the risk of cladding failure under accident conditions. This failure is provoked by stress corrosion cracking due to the thermomechanical behaviour of the fuel rod on the one hand, and the presence of fission products corrosive to the cladding on the other hand. Our objective is to design and develop solutions that resolve the issue of pellet-cladding interactions affecting fuel rods in pressurised water reactors (PWR).
  

• Innovations for Generation III reactors:
  IRESNE has tasked teams with studying different concepts to optimise third generation reactors and to incorporate any innovative changes. Following on from the European pressurised reactor (EPR), a second version called EPR2 is being developed to take into account experience feedback that has already been collected. The EPR2 is based on the same technology as the EPR, but incorporating optimisations having been developed since, such as passive safety systems using back-up devices that exploit the laws of physics, the properties of the materials themselves, and the internal energy stored.

• Experiments to validate calculation tools:
  All the calculations tools we developed are experimentally validated and qualified in order to confirm their physical models. We conduct large experimental programmes to validate the scientific computing tools used to monitor core neutronics and the fuel cycle.

• Developing nuclear instrumentation
  Nuclear instrumentation is an essential aspect of nuclear R&D and more generally so for a range of other scientific fields. To accurately measure the phenomena occurring in a nuclear reactor or to collect data during experiments, we need specific instrumentation that can withstand the often extreme environments in which they must operate. The data collected is used to validate the computer models and concepts that are fed into our scientific computing tools and designed to simulate these interactions so they can then be exptrapolated.
  
  
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