Project description

In the following sections a brief description of the project (Mitigating Environmentally-Assisted Cracking Through Optimisation of Surface Condition – MEACTOS) is given. The project consortium is presented on a separate site.

Objectives

The goal of the MEACTOS project is to improve the safety and reliability of Generation II and III nuclear power plants (NPPs) by improving the resistance of critical locations, including welds, to environmentally-assisted cracking (EAC) through the application of optimized surface machining and improved surface treatments. This project will quantify the effect of various surface machining and treatment techniques on the EAC behavior of specific structural materials in the primary circuit of NPPs. The gained knowledge will be summarized in practical guidelines, which can be used for incorporation into key nuclear design and manufacturing codes. Furthermore, a tailored roadmap for harmonization of guidelines and codes will be produced.  In these ways, MEACTOS will improve safe and reliable economic nuclear energy production in Europe.

MEACTOS will contribute to tackling the obsolescence of the machining practices used in the nuclear field with direct application to the construction of the new plants. Finland, France, United Kingdom, Slovakia, Bulgaria, Belarus, Poland and also Russia are building or planning to build new plants to start its first operation in in the coming years.

Concept & methodology

The effect of the surface machining and treatment technique on the material’s EAC initation behavior will be quantified using accelerated testing methods developed in NUGENIA+ projects MICRIN+ and ASATAR, e.g., constant extension rate tensile (CERT) testing using tapered specimens and multiple factor acceleration testing using notched tensile specimens. The link between laboratory testing and component behaviour will be examined in terms of EAC models.

The MEACTOS project will contain two phases: (1) qualitative screening phase, and (2) a verification phase to demonstrate quantitatively improved EAC initiation performance. As illiustrated in the figure below, the link between surface machining/treatment parameters and EAC initiation performance is the characterisation of the material surface and near-surface regions in terms of properties (hardness), residual stress and microstructure.

Finally, both the screening and verification phase will produce technically-relevant information on mitigation of EAC initiation. This information will be incorporated into guidelines for modern surface machining and treatment techniques.

Ambition

The anticipated results of this project, will lead to a proactive approach for dealing with materials degradation, greater reliability for the existing plants as they age, and reliability for plants that will be built. Some of direct expected benefits are:

  • Improving the service lifetime of the austenitic weld alloys by reducing microstructural and stress-related factors that contribute to EAC.
  • Reducing the scheduled in-service inspections and maintenance costs through the use of more EAC-resistant components.
  • Ecological benefits, due to the reduction or possible elimination of lubricating fluids based on petroleum products.
  • Other additional benefits include (i) potential reduction in machining cost by reducing machining time and increasing the cutting tool lifetime and (ii) cross-cutting benefits, as these improvements in manufacturing processes can be applied to other industries such as food, petrochemical and pharmaceutical.
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Dissemination & knowledge transfer

Dissemination and exploitation activities will be implemented from the beginning of the project and continuously throughout its duration to maximize the impact of project results. Dissemination efforts will be progressively increased as project results are obtained, in order to assure a wide exposure of MEACTOS project and to facilitate exploitation of its outcomes after the end of the project. The MEACTOS data sharing policy will extend to the consortium (i) considering all data access requests with a view to making data sets available in the circumstance that it would add value to the overall objectives of the project and related activities and (ii) reviewing the ‘Open Access’ option at midterm.

Some of the actions planned are:

  • Communication (project website, social media presence, newsletter, etc.)
  • Relevant scientific publications
  • Fully citable reference database (Online Data and Information Network, ODIN)
  • Contact with potential end users
  • Workshops & summer school
  • Possibility of establishing networks and clusters
  • Participation in conferences/workshops/exhibitions

Management structure & WP description

WP1 - Ethics requirements

WP2 - Project management

WP2 will carry our management activities in order to coordinate goals and requirements of the overall project to ensure the project plan. It will provide the overall financial, administrativeand consortium management for the project. It will ensure that the contractual obligations towards the Commission are properly fulfilled. It is responsible for the organization and participation in the project meetings and for the quality assurance of the progress and results of the project. An initial risk management plan will also be implemented to identify potential mishaps during the entire project execution and to prepare an action plan that will deal with them when they emerge. Technical coordination of the activities and tasks included in the work plan will be managed by CIEMAT.

WP3 - Review of the latest knowledge on EAC initiation

The objective of WP3 is to develop and produce a state-of-the-art (SOTA) report, incorporating knowledge gained in the relevant NUGENIA+ projects MICRIN+, MCSCAMP and ASATAR (as well as from the NULIFE White Paper), on the role of surface conditions on EAC initiation susceptibility. This will ensure that the MEACTOS project will advance the current knowledge and experience regarding the effect of machining and surface treatment on EAC initiation susceptibility. Existing in-house data and experience on initiation research will be co-ordinated and shared among the partners so that the latest information on the effect of surface treatment available for initiation mitigation, including advanced surface machining methods, is reviewed. WP3 will also form the technical basis and joint forum for the decisions on the surface conditions to be selected for WP4 – WP6.

WP4 - Surface machining and treatment

The purpose of this WP is to develop improved, EAC-resistant surfaces on machined components, with particular attention to Alloy 182 and austenitic stainless steels. It is envisioned that this WP will include examinations of advanced machining procedures, MQL, cryogenic machining and the combination of both. Assessment of the specimens produced using these advanced machining and surface treatment processes will include measurements of residual stress, hardness, as well as microstructural examinations. WP3 will identify surface modification treatments which may be used separately or in combination with advanced machining processes. The experimental plans for both machining operations and the surface modification treatment will begin following the work of WP3. This WP will explore the effect of a surface modification treatment (mainly peening based) in order to provide a knowledge base for future advanced surface treatments. WP4 will generate the materials for other WPs as WP5 and WP6. Frequent interaction with WP5 will ensure that we obtain maximum effectiveness of this research.

WP5 - Surface and sub-surface materials characterisation

The purpose of WP5 is to characterise the physical effects of optimised machining/grinding and surface treatment processes on the alloy microstructure, with particular emphasis on the surface/near-surface microstructure as this is the critical region for localised environmental interactions (oxidation, corrosion, etc.). This WP will also include the assessment of residual stress induced by the machining process and will document the  hardness of the near-surface/sub-surface region as a function of machining operations. The importance of the surface and near-surface microstructure will be determined via the detailed characterization of selected post-test specimens from WP6. Thus, WP5 will provide the microstructural data to link WP4 and WP6 test results by utilising correlative analytical techniques to characterise and understand the microstructural and residual stress effects of advanced machining processes on EAC. Some data will used in WP7.

WP6 - Testing for EAC resistance under LWR conditions

The work focuses on the investigation of the EAC resistance of the studied materials as schematically shown in the figure below. Furthermore, since testing time would be impractical under true plant operational condition, the project addresses accelerated testing to enable results to be achieved within the time scale of the project. Considering very high EAC resistance of the surface treated materials two accelerated EAC testing techniques will be apllied, constant extension rate tensile (CERT) and accelerated constant load (CL) testing. Slow CERT testing with tapered flat tensile (TFT) specimens is performed to screen the effectiveness of different surface treatment methods against EAC initiation. Each test results in observation wheather yes/no EAC crack initiation happened; serie of the tests of various strain rates will result in determination of the threshold stress for EAC initiation.

It is possible that some of the surface treatments will improve the material resistance such that no EAC crack will initiate during CERT in nominal BWR/PWR environments and that additional acceleration with temperature and higher aggresivity of environment will be necessary to stimulate EAC. Therefore, other environments, i.e., high temperature BWR and PWR or oxygenated PWR, or more advanced ones, i.e., super critical water (SCW) and hydrogenated steam vapours (HSV) might need to be applied. Stimulation of EAC with these environments is a part of the investigation as the practicality of such approaches needs to be proven.

WP7 - Development of predictive tools

The state-of-the-art of WP3, the characterization of WP5 and the testing in WP6 will address the effect of various surface conditions on EAC and, hence, will underpin our understanding and create an outlook for mitigation. The current work package aims at capturing the gained knowledge in order to develop predictive tools that aid in the evaluation of the effect of surface conditions on EAC for plant components in primary water. The eventual objective is to use these tools to support inspection, repair or replacement strategies.

Some envisaged predictive tools are of an empirical nature, i.e., they make use of experimentalresults to fit model parameters (EngInit, SCK•CEN) or acceleration factors (ACETMA, CVR). Then, the parameters or factors are not necessarily physical properties that could be determined independently. Of special interest is to cover the effect of surface conditions with the model parameters. However, in view of accelerated testing, the effect of any accelerating factor also has to be captured by the model parameters. The response variables of value to the development of predictive tools include threshold stress, time-to-initiation, time-to-failure, surface crack density distribution. Other predictive tools are local approaches which take into account some physics of the underlying processes. One starts from a polycrystalline structure of the material, attaching physical properties to grains and grain boundaries. The polycrystal is subsequently mechanically loaded, according to actual testing procedures. The evolution of cracking will be modelled based on a number of distinct periods in the development of EAC; incubation,
initiation, subcritical crack advance and macroscopic crack growth. The local approach relies on modelling efforts made during a previous EU FP7 project, PERFORM60, and subsequent developments at EdF.

WP8 - Guidance and harmonisation

The purpose of WP8 is basically to summarize the work performed in MEACTOS. It joins the results of the testing campaign (WP6) taking into account the available machining procedures (WP3) as well as the complexity of the surface finishes of the selected components and repair procedures (WP4 and WP5).

WP9 - Dissemination of results and knowledge transfer

To efficiently disseminate the results and transfer the knowledge, generated and gathered in the framework of this project, inside the project consortium as well as to the whole European (nuclear) community (e.g., NUGENIA End Users, other nuclear industry, nuclear authorities, nuclear research organisations, etc.). The dissemination strategy takes into account the report published by the EC DG Research “Guide to successful communications”. A special focus will also be directed to young nuclear engineers and scientists and also to engineers, officers and companies applying the technologies investigated in the current project. Furthermore, the education and mobility of (young) engineers/scientists and exchange of knowledge between the project partners will be promoted (e.g., several PhD thesises will be started in the framework of this project). A carefully considered data management strategy will be implemented (e.g., by participation in the Horizon 2020 Open Data pilot) whereby data are collected in a timely manner and shared between the project partners. To facilitate efficient data transfer and systems integration, data formats will be developed in accordance with the methodology developed in the scope of an ongoing series of CEN Workshops on engineering materials data. Having served the data management needs of MEACTOS partners during the course of the project, beyond the term oth e project an Open Access reference database will be made available in perpetutity for the nuclear energy community. All aspects of the MEACTOS data management strategy will be implemented in accordance with its data management plan, which will be a living document that is reviewed and revised on a regular basis.