Reactor pressure vessel properties

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Sato I and Suzuki K, Manufacturing and material properties of forgings for the reactor pressure vessel of the high temperature engineering test reactor . Nuclear Engineering and Design, 1997,171,45-56. 

Abstract This chapter describes requirements for speciality WWER reactor pressure vessel materials in terms of their chemical composition and mechanical properties. The main principles of manufacturing technology for WWER pressure vessel fabrication are also discussed, including welding and cladding. 

Key words WWER reactor pressure vessel, chemical composition, mechanical properties, welding, cladding. 

It is widely known that radiation embrittlement behaviour of reactor pressure vessel (RPV) steels depends on various parameters such as material composition, neutron flux and irradiation temperature. Sound understanding and modelling of embrittlement mechanisms require systematic knowledge of effects of individual parameters and their synthesis on microstructural development and then mechanical properties. Most such knowledge has been obtained from single-parameter experiments using test reactor irradiation. This is because test reactor irradiation allows researchers to obtain mechanical property data together with microstructural data on materials with well-controlled chemical compositions under well-controlled irradiation conditions such as flux and temperature. Surveillance data in commercial power reactors are non-systematic in this context and relevant microstructural data are very scarce. 

J.K. Knott and C.A. English, Views of TAGSI on the principles underlying the assessment of the mechanical properties of irradiated ferritic steel reactor pressure vessels , Int. J. Press. Vessels Pip., 1999,76, 891-908. 

IAEA (2009), Effects of irradiation on mechanical properties, Chapter 3 in Integrity of Reactor Pressure Vessels in Nuclear Power Plants Assessment of Irradiation Embrittlement Effects in Reactor Pressure Vessel Steels, IAEA Nuclear Energy Series NP-T-3.11, International Atomic Energy Agency, "Vienna. 

Some of the radionuclides produced in the materials inside the reactor pressure vessel can be used as monitors of the neutron fluence the components (e. g. the wall of the reactor pressure vessel) are exposed to during reactor operation. The materials located within the neutron field, such as the reactor pressure vessel steels, are subjected to nuclear reactions induced by fast neutrons. This can affect their mechanical properties over the course of the reactor lifetime. This applies, in particular, to the ductility of the materials as a consequence of neutron irradiation, the ductility is reduced, leading to a shift of the Nil Ductility Transition (NDT) temperature towards higher values. 

Metals (e g., power reactor pressure vessel steel) to determine the service lifetime because of property changes (embrittlement, stress corrosion, ageing) ... 

One of the main tasks of nuclear-reactor safety research is assessing the integrity of the reactor pressure vessel (RPV). The properties of RPV steels and the influences of thermal and neutron treatments on them are routinely investigated by macroscopic methods such as Charpy V-notch and tensile tests. It turns out that the embrittlement of steel is a very complex process that depends on many factors (thermal and radiation treatment, chemical compositions, conditions during preparation, ageing, etc.). A number of semi-empirical laws based on macroscopic data have been established, but unfortunately these laws are never completely consistent with all data and do not yield the required accuracy. Therefore, many additional test methods are needed to unravel the complex microscopic mechanisms responsible for RPV steel embrittlement. Our study is based on experimental data obtained when positron annihilation spectroscopy (PAS) and Mdssbauer spectroscopy (MS) were applied to different RPV steel specimens, which are supported by results from transmission electron microscopy (TEM) and appropriate computer simulations. 

If advanced materials were to be used in the reactor pressure vessel or the RCSASs, samples of these materials should be subjected to a high fast neutron flux and exposed to the environment of the pressure vessel. They should be examined periodically throughout the plant lifetime to monitor changes in physical properties (in particular ductility and toughness) and to enable predictions to be made of the behaviour of the material. 

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