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#238February 2021

Taking Care of Old Plants

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In late December 2020, Rosenergoatom (part of Rosatom, Russian NPP operations subsidiary) signed an agreement with the French electric utility company Électricité de France (EDF) to extend its full membership in the Materials Aging Institute (MAI) for 2021–2024. The agreement enables Rosenergoatom to initiate research into the aging of nuclear structural materials and have unrestricted access to the results of research conducted by other MAI members.

Other Russian organizations participating in MAI research projects are the Russian Institute for Nuclear Power Plant Operation, Kurchatov Institute National Research Center and its subsidiary Prometey Central Research Institute of Structural Materials (all — ​Rosatom).

EDF and its partners — ​major industrial and utility companies — ​established the Materials Aging Institute in 2008. Its full members include KANSAI (Japan), EDF Energy (UK), CGNPC (China) and the Electric Power Research Institute (EPRI). The MAI aims to join efforts of the academic and engineering communities to study aging processes in structural materials applied in power engineering.

Rosatom takes part in several research projects led by the MAI. One of them is the RPV Integrity project dealing with integrity assessment issues underlying every feasibility study for the life extension of nuclear power plants. The project has three lines of research. First, a series of material studies intended to identify and clarify deterioration behaviors in VVER‑1000 reactor structural materials subjected to radiation and temperature aging during an extended (up to 80 years) service life. Second, researchers analyze whether it is possible to use small amounts of samples to correctly assess cracking resistance of the structural materials both in the initial state and after the thermal and irradiation-induced aging. The third line of research is assessment of heat-affected zones and metal condition around weld joints in reactor pressure vessels. The goal is to identify the most affected areas adjacent to the melt front to simulate and forecast the condition of metal in long-term operation.

The Vessel Internal Project is the second major initiative supported by Rosatom. Its purpose is to identify and estimate dependencies of stress corrosion embrittlement in reactor internals. The dependencies will help define optimal annealing conditions for reactor internals to prevent embrittlement.

The third project is dedicated to the management of concrete structure aging. The participants of the project analyze changes in structural behaviors of containment concrete under the influence of operating conditions, including temperature, humidity and radiation. The studies conducted by Rosatom as part of this project will help develop a formula to forecast concrete aging and calculate the service life of nuclear power plant containments.

The POLYAGE project studies the aging of polymer materials used at nuclear power plants, particularly new-generation cables, in operational conditions. Sheaths and jackets of these cables are made of halogen-free polymer composites. The studies will help monitor aging processes and estimate the service life of the cables.

Rosatom proposed a project on the increased reliability of Eddy current testing on scaled tubes of steam generators at VVER and PWR-based nuclear power plants. It is aimed at obtaining reliable data on the condition of heat-exchanging tubes with scale that distorts eddy current signals. The project provides for theoretical studies, numerical simulations and testing. The data to be obtained will improve the safety margin of steam generators installed at the VVER and PWR based nuclear power plants.

“Thanks to information sharing and joint research into material aging, the project participants gain knowledge in forecasting changes in material properties and improve their research methodology to timely prevent serious damage to NPP parts and components in long-term operation,” said Vladimir Potapov, First Deputy Director at the Russian Institute for Nuclear Power Plant Operation, who is in charge of research and development and new research projects and sits on the MAI Program Committee.

Joint efforts

As a rule, each MAI project lasts four years. If the project is of interest for MAI members, it is extended for another four years. This duration of projects is an explanation to the four-year extension of the full membership agreement.

Each foreign member of the Materials Aging Institute has the right to make research proposals to the Program Committee. If other MAI members show interest in the proposal and if EDF approves it and finance is sufficient, the new proposal will be included in one of the existing projects. There is a rule that at least two companies have to participate in the project. With this approach, tasks are solved more effectively as the parties share their expertise. For instance, it was researchers from France first and then from China who took interest in the project on the increased reliability of Eddy current testing on scaled tubes of steam generators at VVER and PWR-based nuclear power plants. Researchers from the three countries developed terms of reference and an action plan for the project and received approval from the Program Committee.

“Participation in MAI projects gives us an opportunity to present results of our research on the international scale. In 2013–2015, proposals made by Rosenergoatom were treated with distrust by other MAI members, but the situation has changed and we are regularly invited as research partners. This is a well-deserved appreciation of the work done by the Kurchatov Institute, Prometey Research Institute and Russian Institute for NPP Operation,” Yulia Rumyantseva, Head of International Scientific Cooperation at Rosenergoatom’s International Cooperation Department, said. She coordinates contacts between Rosenergoatom and the MAI.

Participants of each project share information in the workshops held at least twice a year. The workshops are organized by responsible project officers. Each project participant presents an intermediate report to be published on the website. All participants have access to the reports while full members have access even to reports on the projects they are not engaged in. “Cooperation on projects gives us access to the international database on material studies and community-approved results of research while saving time and money of the participants,” said Rosenergoatom Director for Technology Development Valery Bezzubtsev, Head of Cooperation and a member of the MAI Board of Governors.

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The results obtained jointly with other MAI members are put into practice and incorporated into industry regulations. For example, feasibility studies for the extension of service lives of VVER‑440 and VVER‑1000 reactors have become less conservative thanks to the data obtained in the cracking resistance assessment project. What is more, this data was included in Rosenergoatom’s internal documents and the Russian national standard “Water-Cooled Water-Moderated Power Reactor Pressure Vessel. Embrittlement Resistance Calculations.”

The results of the Concrete Structure Aging Management project will help update and harmonize concrete strength calculation formulas and be part of feasibility studies for buildings and structures of nuclear power plants.

Staff training is another focus area for the Materials Aging Institute. Each year, the MAI holds material deterioration courses for young engineers, researchers and post-graduate students. Rosenergoatom sent both students and lecturers for the training courses organized in 2018 (France) and 2019 (China). In 2020, the courses were to be held in Russia but, because of the pandemic, were rescheduled for 2021. The training courses are expected to take place in November both online and offline.

 

Photo: Rosatom signing an agreement with EDF to extend its membership in MAI