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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - SOTERIA (Safe long term operation of light water reactors based on improved understanding of radiation effects in nuclear structural materials)

Teaser

Summary

SOTERIA â€“ Safe long-term operation of light water reactors based on improved understanding of radiation effects in nuclear structural materials â€“ is a 4-year European research project in the field of nuclear safety, concentrating on safe long-term operation (LTO) of existing nuclear power plants (NPPs). The project, launched in September 2015, gathers a total of 24 partners from 10 European countries, amongst them the most important players in the European nuclear field.
The safety of nuclear energy has come back to the frontline of public debate through recent events such as the tragic accident in the Japanese Fukushima Daiichi nuclear plant in 2011, or the shutdown of the Doel nuclear reactor in Belgium in early 2015. Moreover, it is one of todayâ€™s major priorities of regulators and nuclear power providers to continue operating existing NPPs beyond the originally anticipated time frame. As a matter of fact, upgrading an existing plant for lifetime extension is less cost intensive than building a new one, and it can also result in increased power output and improved operational performance.
In order to guarantee a continuous safe LTO of existing power plants, it is crucial to understand the role of ageing phenomena of the materials used in NPPs and to translate this knowledge in reliable tools and methods for industrial end-users, as well as in guidelines for political stakeholders and future nuclear safety policies on national and European level.
The multi-disciplinary SOTERIA consortium takes up this challenge and aims at improving the understanding and the prediction of ageing phenomena in reactor pressure vessels (RPVs) and internal steels (internals) caused by neutron irradiation. By combining advanced modelling tools with experimental data, the project partners focus on four technical objectives:
1. Carry out experiments assessing neutron flux and fluence effects on RPVs and internals in pressurised water reactors
2. Evaluate the residual lifetime of RPVs by taking into account metallurgical heterogeneities
3. Assess the effect of the chemical and radiation environment on embrittlement in internals
4. Develop models for the assessment of ageing mechanisms in RPVs and internals, as well as an integrated computer-based platform including the developed modelling tools
Finally, SOTERIA also has an educational objective which is to communicate on the project results towards the nuclear engineering and research community to improve and harmonise the knowledge of ageing phenomena in NPPs.

Work performed

SOTERIA is divided into six Work Packages (WP), see figure below:
WP1 is dedicated to the project strategic and operational management. During the first reporting period, WP1 focused on the establishment of an efficient management infrastructure, including work procedures, management and collaboration tools, and strategic decision-making bodies. An independent Technical Review Committee (TRC) has also been created, and first meetings were held.
WP6 groups the activities around training, end-user involvement/assessment, and the dissemination and the exploitation of the project results. During the first 18 months, a detailed dissemination strategy was established, a public project website launched, and various dissemination material created, including a first Press Release, a public presentation, a project flyer, as well as a periodic newsletter.
WPs 2 to 5 are dealing with technical aspects of the project:
WP2 sets up experiments to improve the microstructural and mechanical models for RPV and internals, taking into account flux and fluence effects for a better estimation of embrittlement, hardening and swelling. During the first reporting period, suitable irradiated materials to study neutron flux effect on RPV and internals have been identified, mechanised and transported to the labs.
WP3 sets up experiments to assess the effect of initial microstructural heterogeneities on RPV fracture behaviour, providing information for improving fracture models developed in WP5. During the first reporting period of the project, the most significant uncertainties for RPV embrittlement were identified, a comprehensive experimental material test matrix was created, possible material heterogeneities in terms of chemical composition were analysed, the experimental needs for multi-scale modelling in WP5 were identified, and material specimens have been manufactured and transported to various European labs.
WP4 sets up experiments to better describe IASCC and evaluate environmental effects on internals failure. Experimental data will be used to improve IASCC models developed in WP5. During the first reporting period, most of the tasks focused on the preparation, characterisation and transport of the base-material specimens to the different partners. Additional work involved the demonstration of several testing methodologies.
WP5 develops models and algorithms based on the outputs from these experiments made in WP2 to WP4. WP5 will also integrate all models on a platform. Over the first 18 months, WP5 defined several reference cases for upcoming model validation. To date, this information has been used to validate a new Kinetic Monte-Carlo (OKMC) code, with improved computational capacities. Modified/improved crystal plasticity laws have been developed to be used to generate input data for fracture models. These models will be integrated in the SOTERIA calculation platform.
The platform and its models developed in WP5 will be continuously assessed by the SOTERIA End-User Group (WP6). Recommendations for adjustments will be made to WP5 to guarantee the acceptability of the models by the industrial stakeholders.

Final results

Thanks to the tools developed in SOTERIA, it will become possible for NPP operators to move from a reactive to a proactive management of material ageing in nuclear plants. Although previous European projects, such as LONGLIFE and PERFORM 60, have already developed tools to better understand the ageing phenomena in NPPs, these tools were mainly used as a support for observations. By taking into account the main challenges faced by the industry; SOTERIA will be able to bring these tools a step forward, to account for the actual life-limiting mechanisms of NPPs. Progress beyond the state-of-the-art aim at facilitating NPP ageing management and supplement data obtained from existing surveillance programs. Further, SOTERIA tools could also help plant operators to better plan activity suspension for maintenance.
The improved understanding of ageing phenomena, as well the developed tools within SOTERIA are expected to have the following impact:
1. Scientific impact by answering questions related to metallic materials, condensed matter physics, corrosion, metallurgy, modelling, the improvement of modelling approaches and tools from nano- to microscale
2. Regulatory impact by contributing to the development of European nuclear safety policies via clear guidelines
3. Public safety-related impact by improving the safety of nuclear power plants in Europe and worldwide
4. Competitiveness-related impact by reinforcing the EU leadership in reactor design and operation
5. Knowledge-related impact by improving the innovation capacity and knowledge integration of the industrial stakeholders
6. Economic impact by helping to reduce the time of reactor unit outage by improving maintenance procedures
7. Environmental impact thanks to a zero CO2 emission level guaranteed by NPPs