Dynamic Strength of Structural Materials for Nuclear Reactors
Study of Dynamic Strength of Structural Materials Used as First Wall of Nuclear Reactors and for Protection of Constructions and Containers against Outside Impact Loading
Tech Area / Field
- MAN-MAT/Engineering Materials/Manufacturing Technology
- FIR-NSS/Nuclear Safety and Safeguarding/Fission Reactors
- INF-SOF/Software/Information and Communications
3 Approved without Funding
Russian Academy of Sciences / Institute of Mechanical Engineering Problems, Russia, St Petersburg
- VNIIEF, Russia, N. Novgorod reg., Sarov
- CNRS / Laboratoire de Physique et Mecanique des Materiaux, France, Metz\nSandia National Laboratories, USA, NM, Albuquerque\nLos Alamos National Laboratory / Materials Science and Technology Division, USA, NM, Los-Alamos\nNational Institute for Materials Science / Advanced Materials Laboratory, Japan, Tsukuba
Project summaryGoal of the project efforts is study of dynamic strength of structural materials of internal (first) wall of nuclear reactors in conditions of abnormal pulse (explosive) loading, as well as study of dynamic strength of materials used to protect constructions (nuclear reactors) and containers for storage of active materials against intensive external shock loadings.
Materials of the first wall should have a series of unique properties providing, from one hand, resistance against strong neutron and other radiations, and, from the other hand, to have high strength characteristics. Study in the area of creation of materials for the first wall of a reactor should comply with very strict and often contradictory mechanical requirements. The materials should be, from one hand, high-plastic materials with high values of extension strain characteristics, and, from the other hand, their quasi-static strength should provide safe operation of reactor at high pressures of explosion products. At the same time, special requirements are raised concerning to dynamic strengths of materials for the cases of irregular explosive and high-temperature regimes of loading. To provide safe operation of a reactor in conditions of explosive loading, it is necessary to perform independent testing of dynamic strengths of materials, since dynamic plasticities and strengths of materials don’t correlate with data of quasi-static tests.
Theoretical models used for calculation of shock-wave behavior of such materials should take into account dependence of mechanical properties on strain rate, as well as processes of dynamic structure formation at various scale levels. Constitutive equations for these calculations should be based on results of real tests of materials in the microsecond range of shock loading durations. Tests for face end spall are currently the only type of tests providing information on dynamic strength in this range of loading duration.
The other important and independent characteristic of dynamic strength of structural materials is threshold of dynamic resistance against shock compression. It is determined by tests with plane collision.
Experimental and calculated-theoretical information on the present direction of study has obtained in different laboratories of key institutes of the USA, Europe and Russia [1-10]. A lot of results have used for substantiation of models, used in the present Project and described behavior of matters under dynamic loading [11-16].
The experimental base of Institute of Engineering Science Problems of RAS satisfies currently the requirements of high-velocity tests of materials. The Institute experts developed a precision technique to record material response to shock loading. This technique is based on laser interferometry of loaded samples. The equipment for shock testing of materials includes:
1. Light-gas guns having calibers of 30 mm and 37 mm providing shock loading of plane targets in the range of impactor velocities from several tens meters per second up to thousand meters per second.
2. Laser interferometers allowing to record time profiles of free surface of shock-loaded targets.
3. Complex of devices for microstructural studies of samples after shock loading.
Within the framework of the project, it is proposed to perform a detailed studies of spall strength and dynamic resistance of materials to shock compression in the impactor velocity range of 50-500 m/s. As studied materials, it is planned to use two materials applied as first wall of a nuclear реактора: a) stainless steel 12Kh18N10T, b) nickel alloy KhN75 VMYu.
As a material for protection of constructions and containers against intensive shock loadings, it is planned to study armor steel 40KhSNMA.
Two types of copper, namely, M-2 and technically pure electrolytic copper M0 will be used as examples for study of shock-resistance of current conducting designs of nuclear power plants.
The additional characteristic, which is measured during shock loading of targets, is dispersion of particles velocity. This characteristic describes dynamics of internal structure of material under shock loading, as well as intensity of energy exchange between mesoscopic (0.1-10 m) and macroscopic scale levels of deformation and destruction. Knowledge on dispersion of particles velocity at shock deformation allows predicting optimal regimes of material application from the point of view of providing its dynamic durability.
In the project, it is planned to study structure formation processes at shock loading and association of these processes with kinetics of energy exchange between structural levels of deformation and destruction. With this purpose, it is planned to perform micro structural studies of samples by the methods of optical and scanning electronic microscopy. The criteria of dynamic fragmentation and spall strength of materials taking into account the processes of evolution of internal structure of material should be formulated.
To calculate characteristics of strength and plasticity of materials, it is planned to use four theoretical approaches in parallel. These theoretical approaches are the bases of numerical models developed in VNIIEF and IPMash to describe behavior of matters at dynamic pulse loadings. The approaches are:
– Elastic-plastic models of materials response to shock loading. They are based on dislocation dynamics.
– Self-coordinated local-hydrodynamical model for description of dynamics of shock-deformable matters with internal structures.
– Structural-analytical model of dynamic deformation of matters with internal impurities.
– Kinetic multistage model of spall destruction.
All these theoretical approaches are based on use of experimental data on dynamic durability and kinetics of material microstructure. For computation of shock profiles by the above-mentioned models, it is planned to use specially developed computer codes.
Data obtained during the project efforts can be used for justification of safety of presently functioning NPP and NPP under development.
The Project efforts will use potential of high-skilled scientists and engineers earlier involved in weapon development for improvement of safety of Russian atomic nuclear power plants. Thus, two basic objectives of the ISTC will be reached:
– reorientation of scientific potential of weapon scientists and engineers;
– improvement of safety of atomic nuclear power plants in Russia and other CIS countries.
Within the Project framework the following efforts will be performed:
– Review of current status of studies in materials dynamics.
– Verification of theoretical models and adjusting of numerical techniques using available experimental data.
– Experimental studies of shock-wave behavior of four types of structural materials in range of shock loading velocities of 50-500 m/s.
– Theoretical calculations basing on obtained experimental data.
– Analysis of results obtained during the Project efforts. Formulation of recommendations on optimum regimes of materials application.
The program of experimental studies will be discussed and coordinated with the foreign collaborators. It is planned to discuss results obtained during the Project efforts at workshops with participation of the foreign collaborators.
All the obtained results will be sent to the foreign collaborators for verification of their computer codes.
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