堆工原理 UNIT 8.ppt

sdasdasd  PRINCIPLE OF REACTOR ENGINEERING核 反 应 堆 工 程 原 理PU SHENGDI 2007.08  UNIT 8  REACTOR MATERIALS UNIT 8 REACTOR MATERIALS A unique aspect of the reactor environment is the presence of intense nuclear radiation of various types. These radiations are capable of producing significant deleterious changes in the physical and mechanical properties of materials. The effects of radiation on structural and other materials intended for use in a nuclear reactor system must therefore be given consideration. UNIT 8 REACTOR MATERIALS The radiations in a nuclear reactor consist mainly of alpha and beta particles (from radioactive decay), gamma rays, neutrons, and fission products. As far as nonfuel materials, which are mainly metals, are concerned, neutrons are the most important in producing radiation effects. UNIT 8 REACTOR MATERIALS The effects of neutrons on materials arise largely from the transfer of kinetic energy to atomic nuclei in one way or another. Thus, highly energetic recoil nuclei may be produced as a result of (n,γ) and other neutron reactions or of elastic scattering. If the energy of the recoil nucleus is sufficient to permit it to be displaced from its normal (or equilibrium) position in the space lattice of a solid, physical changes of a disrupting (or damaging) the crystal lattice by the displacement of atoms is commonly referred to as “radiation damage”. UNIT 8 REACTOR MATERIALS A reactor system must include a containing vessel, e.g., the pressure vessel of a water-cooled reactor, mechanical support for the core components, piping for the coolant, and cladding for the fuel elements. Mechanical properties, such as tensile strength, ductility, impact strength, and creep, must be adequate for the operating conditions. The material must be capable of being fabricated or joined, e.g., by welding, into the required shape. UNIT 8 REACTOR MATERIALS Thermal conductivity should be high to minimize thermal st