tailieunhanh - Mechanical Engineers Reference Book 12E Episode 7

Tham khảo tài liệu 'mechanical engineers reference book 12e episode 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 7 92 Materials properties and selection ducts a number of neutrons which serve to carry on the chain reaction other particles and energy including y-radiation. Fissile materials include U-235 a constituent of natural uranium U-233 a product of neutron capture by thorium and plutonium a product of neutron capture by U-238 the major constituent of natural uranium . They constitute the fuel in nuclear reactors. Fertile metals include U-238 and thorium. They are incorporated into nuclear reactor fuel or used separately in blankets to absorb neutrons and produce additional fissile material. Canning metals are used to contain nuclear fuel in a reactor maintain its integrity and dimensions protect it from attack by the coolant retain fission products so that they do not contaminate the coolant and through it the environment transfer the heat produced efficiently and absorb a minimum proportion of neutrons. Canning and core structural materials now in use include stainless steel for sodium-cooled and high-temperature gas-cooled reactors magnesium alloy for the original magnox reactors zirconium for pressurized water and boiling water-cooled power reactors and aluminium for water-cooled research reactors. Zirconium62 occurs naturally together with hafnium which has high neutron-absorbing properties. These must be separated by a complex chemical process before they can be used in water reactors zirconium as a core structural material hafnium as a control rod material. Both have excellent resistance to pressurized water attack if they are suitably alloyed and satisfactorily pure. Beryllium combines a very low nuclear capture cross section with good strength and hardness at moderately high temperatures. It appeared to have great promise as a canning and core structural material but the promise has not been fulfilled mainly because of its lack of ductility and resistance to environmental attack and partly because of doubts concerning the effect of helium which is produced when