Studsvik’s pool facility for storage and inspection of SMILE materials, left: 29 tonnes transportation flask, three pools each about 8 meters deep; and right: pool-in-pool for cutting and inspections. Photo: Studsvik.
The Studsvik Material Integrity Life Extension Project (SMILE) was launched in 2021 with the aim of investigating metallic components and materials from nuclear power plants (BWR and PWR) under decommissioning, to better understand and predict ageing phenomena. The information obtained from the experimental investigations can be used to support plant ageing management activities, life extension programmes, and operating licence renewals. The five-year project (2021-2025) is supported by 20 organisations from 10 countries.
SMILE is conducted by Studsvik Nuclear AB, Sweden, based on experimental examinations and the testing of aged components and materials that are harvested from Swedish LWRs that are being decommissioned after more than 40 years of operation: Oskarshamn 1 and 2 (BWRs) and Ringhals 2 (PWR). Material replaced 30 years after operation is already available and is also investigated, e.g. the reactor pressure vessel (RPV) upper head and pressuriser from Ringhals 3 and 4.
The first task is to build a material library by retrieving the materials and documents to the greatest extent possible, with all the known information on the materials selected to be harvested from the three retired Swedish LWRs and the major replaced components from Ringhals 3 and 4. The task also includes calculations of irradiation doses and temperatures that the materials have experienced, based on operational information. All data collected and generated within SMILE will be organised and structured so that they can be easily transferred to a database should the necessary resources to create such a comprehensive database become available in the future.
The second task investigates irradiation and thermal embrittlement of low alloy steels used for reactor pressure vessels and other large vessels in the primary coolant circuits of LWRs. The third task is to address the stainless-steel alloys of core support structures and internals and is divided into two subtasks focusing on irradiation embrittlement, including welds and irradiation-assisted stress corrosion cracking, and corrosion fatigue susceptibility. The fourth task is to evaluate pressure boundary stainless steels, nickel base alloys and their welds, where irradiation effects do not play a significant role. The task is divided in two subtasks focusing on dissimilar metal welds and stainless-steel welds, stress corrosion cracking (SCC) resistance in BWRs and PWRs and alloy 690/152/52 primary water stress corrosion cracking resistance and thermal stability in PWRs.
In 2024, the documentation collection and calculations related to harvested materials were completed. Material harvesting at both the Oskarshamn and Ringhals plants had been delayed due to challenges related to decontamination and material accessibility but were fully completed in 2024.
Regarding experimental work, samples collection, preparation and characterisation before testing were mostly completed in all the tasks in 2024. The testing has also progressed significantly with plans to complete all the experimental work by the end of 2025. Side projects to extend the results database have also progressed significantly with work done as part of the European Commission H2020 FRACTESUS (Fracture mechanics testing of irradiated RPV steels by means of sub-sized specimens) project, as part of an in-kind SCK•CEN contribution and as part of MPA Stuttgart University’s in-kind contribution. VTT is also providing a large set of additional data through its national BRIGHT (Barsebäck RPV investigations through thickness) project, which started in 2023 under the auspices of the SAFER2028 national Finnish project.
Discussions continued in 2024 on a new project phase for 2026-2030. SMILE 2 would leverage the unique library of LWR materials aged for up to more than 40 years established with SMILE. The materials library would allow continued research on subjects addressed in SMILE, as well as studies on topics currently not included. Research topics are being prioritised with SMILE members.
Belgium, China, Czechia, Finland, France, Germany, Japan, Sweden, Switzerland and the United States.
January 2021 - December 2025