NPP involve numerous concrete structures with embedded steel reinforcement, barrier and containment systems. Although concrete environment is particularly suitable for steel due to the alkaline nature that enables passivation of the steel surface, many corrosion processes take place in concrete structures, depending on the environmental conditions and geometry of the structure. This WP will concentrate on the parts of Nuclear Power Plants (NPP) where safety is the major concern, i.e. special conditions leading to chloride-induced corrosion of steel cylinder concrete pipes (SCCP) and to crevice corrosion of steel liner embedded in concrete of containment building. The aim is to provide background information for the modelling and non-destructive inspection as well as to facilitate proper prevention measures. The objectives include:

• Analysis and identification of the key factors that contribute to corrosion of liners at the steel/concrete interface in Nuclear Power Plants, definition and formulation of the phenomenological processes and suitable probabilistic analysis approaches.
• Recognition of strengths and limitations of available non-destructing diagnosis tools (NDT) to detect the occurrence and location of corrosion attack of liners in concrete.
• Selection and demonstration of the most promising NDT for the use with robotic platform in key operational environments.
• The improvement of recommendations on methodology for ageing management of NPP based on the WP2 findings.

Internal Swellings Reactions (ISR) are pathologies that can degrade concrete by causing swelling, cracking and major disorders in the affected structures. ISR include the delayed ettringite formation (DEF), the alkali-silicate reaction (ASR) and the occurrence of both simultaneously. In nuclear facilities, the possibility of these phenomena cannot be ruled out. Matter of fact, they include massive reinforced concrete elements for which a significant heating could have occurred at the early age. Moreover, reactive aggregates may have been used during the construction phase. Therefore, those risks ought to be studied and quantified especially if the extension of the lifespan of these installations is envisaged. The aim is to contribute to the assessment of lifetime extension of NPP structures whose concrete is affected by ISR and to provide background information for the modelling and non-destructive inspection. The main objective include:

• Increasing the knowledge on the development of ISR in the NPP structural environment by considering the following factors: the confinement developed in massive structures, the complex bi-axial loading due to post-tensioning, the scale effect and the coupling between creep shrinkage and expansion due to ISR.
• Developing a technical basis for regulatory guidance to evaluate ISR affected NPP through service life based on monitoring results and on coring’s residual expansion testing. The purpose is to help NPP owners manage structures affected by ISR.
• Providing recommendations on the detection of ISR in massive concrete structures using non-destructive techniques.
• Predicting the long-term expansion of NPP structures affected by ISR. The output of this part is a numerical benchmark where various modelling technics can be tested using extensive experimental data from representative massive concrete mock-ups.
• Proposing recommendations that would allow the End-Users properly account for the ISR impacts in the engineering calculations of the NPP structures (containment), in particular, in the LTO justifications

The aim of actions related to creep and shrinkage is to improve the modelling capability for drying and delayed strains of containment buildings:

• For operational phases, efficient and well validated empirical models for finite element computations are available. However, these models need to be calibrated on laboratory data (which is almost never available for existing containment buildings), on monitoring data (which is often available for containment buildings), or on predictions of the material behaviour of concrete (for which some models exist but are insufficiently validated). Hence, concerning the prediction of the behaviour of the containment during operation, the project will focus on the two latter options by:
• Benchmarking models for the prediction of the containment strains using the VERCORS experiment performed at EDF. A 3rd benchmark will be organized, and it will be proposed to participants to calibrate their models using only a selection of monitoring data which will have to be representative of monitoring of real CCBs
• Benchmarking models for the prediction of creep and shrinkage of concrete at a material scale at ambient temperature using two kind of models: regulatory or pre-regulatory codes (EC2, FIB Code Model) and micromechanics models.
• For operational phases also, it would be convenient to be able to use regulatory codes to predict the containment strains, but these codes (EC2, FIB Code Model, …) insufficiently take into account the temperature behaviour of concrete close to ambient temperature. Therefore, propositions will be performed to improve the Code Model 2010 related to the temperature behaviour of concrete

For accidental phases and particular operational situations involving exposition of concrete to temperatures higher than 70°C, the material modelling is less mature. Hence, the project will focus on improving the understanding and modelling of the material behaviour. An ambitious experimental program has already started on VERCORS concrete at high temperatures. This experimental program will be completed and material modelling will be performed and shared between the project partners

The general objective of WP5 is to develop a comprehensive methodology to assess the effects of prolonged irradiation of LWRs CBSs using a holistic approach combining operating conditions, materials degradation and structural significance. This WP includes both gamma and neutron irradiation experiments in accelerated conditions; and materials (meso-scale) and structural modelling activities. The objective of the experimental activities is to address specific knowledge gaps identified in the open literature: (i) The effects of gamma irradiation of the reinforced concrete, and the risk of radiolysis-induced corrosion; and, (ii) The effects of neutron-irradiation of concrete-aggregate made of igneous and metamorphic rocks, common in Europe, and not or insufficiently characterized in previous research works. These experimental studies will provide input data to the (materials) meso-scale models which are to be benchmarked by different partners in coordination, with the International Committee on Irradiated Concrete (ICIC) activities, using open-literature data from Russia and Japan during the first stage of the project. The validation of the varied meso-scale models will provide the necessary inputs to develop a sound structural analysis of a prototypical water-cooled water-moderated reactor (VVER) CBS. The final output of this research will be the creation of methodological guidelines applicable to varied LWRs establishing the long-term operation conditions assessment of the CBS.

WP6 comprises the dissemination, training, innovation management and End-User activities within the ACES project. This WP supports the technical tasks carried out as part of WP2 to WP5 by the incorporation of tools designed to both enhance the progress of work and communicate the obtained results. The main goals of WP6 are to:

• Disseminate the project results among the nuclear community, with special aim at relevant data for utilities facing LTO,
• Improve communication and facilitate information exchange between the project partners,
• Manage the innovation generated in the project,
• Involve End-Users and learn about their needs and perspective in order to help focus the results of the project to best meet their interests.

Work package 7 consists of the overall management, administration, and coordination of the consortium, meetings and communication actions to ensure a timely execution of the project in accordance with the proposal and its objectives. Additional gorals include:

• Comprehensive holistic approach to management of the project
• Productive communication with the EC, within the Consortium and with external bodies
• Financial, legal and administrative management
• Data Management Plan in accordance with the Pilot on Open Research Data
• Communication to and with external stakeholders