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Toughness Properties of Steels for Reactor Pressure Vessels

#3072


Modelling of Brittle and Ductile Fracture and Prediction of Irradiation Damage Effect on Fracture Toughness Properties of Steels for Reactor Pressure Vessels on the Basis of Local Approach

Tech Area / Field

  • FIR-MAT/Materials and Materials Conversion/Fission Reactors
  • FIR-NSS/Nuclear Safety and Safeguarding/Fission Reactors

Status
8 Project completed

Registration date
30.06.2004

Completion date
24.11.2008

Senior Project Manager
Tocheny L V

Leading Institute
TsNIIKM PROMETEY (Construction Materials), Russia, St Petersburg

Collaborators

  • Framatome ANP GmbH, Germany, Erlangen\nSerco Assurance, UK, Warrington

Project summary

Introduction and Overview. The reactor pressure vessel (RPV) is a major focus of nuclear power plant life management activities. The structural integrity of the RPV has to be maintained throughout the lifetime of a nuclear plant. The structural integrity of the RPV is estimated with the brittle strength criterion and a key input to calculation of brittle strength of the RPV is fracture toughness of a material. It is important to assess how fracture toughness varies as a function of temperature, and how the fracture toughness vs. temperature response changes with in-service material degradation due to irradiation. Therefore, the major task of mechanics and physics of RPV materials, in a framework of nuclear plant safety problem, is the prediction of the irradiation damage effects on brittle strength of RPV materials.

The most promising approach for fracture toughness prediction for RPV irradiated materials which is now intensively developed is based on the local approach to brittle and ductile fracture analysis. A worth-while model for fracture toughness prediction was proposed by the authors of the present ISTC proposal. This model is now known as “Prometey” model. Publications on this model are sufficiently fully represented on international journals and conference proceedings. It was shown that as distinct from other approaches, the Prometey probabilistic model provides adequate prediction of the fracture toughness temperature dependence for RPV materials in different conditions.

The purpose of the proposed ISTC project is to predict the irradiation damage effect on fracture toughness properties of RPV steels by means of multi-scale modelling on the basis of the Prometey model. This multiscale approach is fully compatible with the most advanced techniques which are being developed in the world, in particular those related to the prediction of irradiation damage effects in reactor components in the framework of the PERFECT project, which is being performed by the foreign collaborators.

The ISTC project will contribute to the main objectives of the PERFECT project:

- RPV-2 + “Toughness Module” , which will provide the tensile and fracture toughness properties of the irradiated RPV steel;


- to carry out a first European Collective Exercise of component analysis in which material behavior assessment will be done by numerical simulation with the proposed tools;
- to use the proposed simulation tools to complement previous or current international research programs (EURATOM, FUSION, TACIS, PHARE and others).

The ISTC project will contribute to the PEREFECT Sub-Project III "RPV: Mechanics Modelling": this Sub-Project will provide the codes, models and databases required to build the “Toughness Module” of RPV-2. Within the ISTC project, theoretical studies, calculations and experimental programs on irradiated WWER RPV steel will be carried out.

The proposed ISTC project will be executed by the specialists of CRISM “Prometey” in collaboration with European specialists actively involved in the development of leading-edge technologies as the PERFECT project is world-wide recognized. This close collaboration with the most relevant European specialists who are familiar with such techniques will contribute to enhance CRISM “Prometey” positioning into the global scientific community by guaranteeing that the results of the project can be easily integrated into international exercises of prediction of irradiation effects on RPV elements. Some part of the project studies are intended to be used for solving tasks on EC PERFECT project.

Expected Results and Their Application. In the framework of the project the following tasks will be solved.

Task 1. Model of brittle fracture behavior for irradiated RPV steel. The Task will provide the following expected results: (i) microcrack nucleation criterion for unirradiated and irradiated RPV steels; (ii) the physical-and-mechanical model of brittle fracture for irradiated RPV steels. Deliverable is foreseen as technical report R1 “The physical-and-mechanical model of cleavage microcrack nucleation and propagation for irradiated RPV steel”. This task will contribute to Work-Package (WP) III-1 and WPIII-2 of the PERFECT project, and the results may be used for deliverables M6 and M7.

Task 2. Prediction of brittle fracture toughness for irradiated steel. The Task will provide the following expected results: (i) procedure for prediction of the neutron fluence effect on the temperature dependence of cleavage fracture toughness for WWER RPV steels; (ii) the calculated curves for the temperature dependence of cleavage fracture toughness on the basis of the Prometey probabilistic model for different materials with various degree of embrittlement; (iii) an engineering method for determination of the temperature dependence of fracture toughness for materials with various degrees of embrittlement. Deliverable is foreseen as technical report R2 “Prediction of the temperature dependence of fracture toughness for RPV steels with various degrees of embrittlement on the basis of new engineering method”. This task will contribute to WPIII-3 of the PERFECT project, and the results may be used for deliverable M2 and M9.

Task 3. Simulation of ductile crack growth on the basis of original ductile fracture model. Investigation, modeling and prediction of the phenomenon of cleavage fracture after ductile crack growth. The Task will provide the following expected results: (i) a calculation-and-experimental method for prediction of the ductile crack growth resistance curves (JR-curves) for steels in initial and irradiated conditions; (ii) the ductile crack growth resistance curves for RPV steels with various degree of embrittlement; (iii) procedure for prediction of the temperature dependence of cleavage fracture toughness with regard of the ductile crack growth for RPV steels with various degree of embrittlement. Deliverable is foreseen as technical report R3 “Prediction of JR-curves and the effect of ductile crack growth on cleavage fracture toughness for RPV steels with various degrees of embrittlement”. This task will contribute to WPIII-2, WPIII-5 and RPV-2 “Toughness Module” of the PERFECT project, and the results may be used for deliverable M2, M9 and others.

Task 4. Verification of fracture toughness prediction methods. The Task will provide the following expected results: (i) database on available and original experimental results on fracture toughness for various RPV steels in different condition; (ii) comparison of experimental data and results predicted with the proposed methods. Deliverable is foreseen as technical report R4 “Prediction of the neutron fluence effect on the temperature dependence of fracture toughness for RPV steels”. This task will contribute to WPIII-4, WPIII-5 and RPV-2 “Toughness Module” of the PERFECT project, and the results may be used for deliverable M2, M14, M15 and others.

The scientific significance of the project consists in development of the cleavage and ductile fracture models taking into account irradiation damage and elaboration of methods for analysis of crack behaviour in solids.

The practical significance of the project is to provide advanced methods and procedures for assessment of structural integrity of the irradiated RPV on the brittle fracture criterion. On the basis of the above results, more adequate predictions of fracture toughness for irradiated RPV materials and the corrected assessment of RPV service life may be obtained. In future, approaches elaborated in a frame of the project are foreseen to be incorporated in Standards for determination of fracture toughness of RPV steels. One of the derived outcomes of the project will be to place CRISM “Prometey” in a better position to valorize and commercialize its knowledge and technology capacities before utilities, nuclear safety regulators, nuclear engineering companies and manufacturers of capital goods for the nuclear industry all around the world.

Meeting ISTC Goals and Objectives. The Project completely meets ISTC aims. It provides scientists and personnel formerly engaged in weapons development an opportunity to conduct research aimed at peaceful activity because the RPV elements involved are only applied to NPPs. It promotes real integration of Russian scientists into the international scientific community and reinforces their adaptation to market economy for future subcontracting of services in the field of nuclear technology; it supports basic and applied research for peaceful purposes, especially in fields of energy production and nuclear safety. Besides, to solve international technical problems, via interaction with of EC PERFECT project.

Scope of Activities. The proposed project is a complex of theoretical, calculated and experimental investigations aimed for development of the cleavage and ductile fracture models with regard for irradiation damage, and elaboration of methods for analysis of crack behaviour in solids in order to predict the irradiation damage effect on fracture toughness properties of reactor pressure vessel steels. Main outputs of the expected results are the assessment methods of the RPV structural integrity on the brittle strength criterion on the basis of modern advanced physical, mechanical and engineering approaches. In the framework of the project four tasks are foreseen to be solved. Publications, presentations on conferences and technical reports are foreseen to be provided as deliveries. The project results will contribute to the European PERFECT Sub-Project III “RPV: Mechanics modeling”.

Role of Foreign Collaborators/Partners. During performing the project the researchers from CRISM “Prometey” will continue close collaboration with the participants of the project from France, Germany, United Kingdom and other European specialists. The followings tasks will be discussed: theoretical models and calculation methods; program and work schedule of common researches; main results of investigation; preparation of common publications and presentation on conferences. As a result of common activity of Russian and European scientists a decisive contribution will be made to solving the problem being of interest from the point of view applications to the safety of nuclear power plants.

Technical Approach and Methodology. Approaches and methods of solid mechanics, fracture mechanics (local and global approaches), physics of strength, plasticity and fracture will be used. Calculation studies will be performed by analytical and numerical methods with finite elements method by using special PC programmes. Experimental studies will be carried out according to native and international standards and normative documents as well as original procedures.


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