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Behavior of Atomic Reactor Zirconium Cladding Fuel Rod Tubes

Zirconium alloy, for its excellent performance, is used as fuel cladding material of water-cooled nuclear reactor, and other core structural materials. Zirconium cladding tubes of fuel rods is the use of nuclear grade zirconium alloy material, with good sealing performance under operating conditions and long-term storage of fissile material produced, known as the first safety barrier nuclear power plant operation. Zirconium fuel cladding tube of small diameter, thin wall, under normal conditions, the cladding tube subjected to alternating stress and temperature effects, while subjected to intense neutron irradiation, therefore, high on the cladding material performance requirements.

Placed in a environment with the worst working conditions in a nuclear reactor, a cladding tube is faced with nuclear fuel, bearing the high temperature, high pressure and intense neutron irradiation, as well as severe tests to its resistance to high boron water corrosion, stress corrosion and iodine vapor corrosion of reaction products. In addition to being able to bear the high temperature, high pressure in the reactor and being corrosion-resistant and radiation-resistant and other requirements, nuclear-grade zirconium material must also have low hydrogen absorption and small neutron-absorbing cross-section and other properties. Because the fission reaction is carried out by the reactor through absorbing neutrons, if the nuclear fuel¡¯s cladding material absorbs too much neutrons, it will affect core reactions.
Zirconium material for a nuclear reactor must be strictly controlled its content of metal hafnium (Hf). As zirconium and hafnium are usually symbiotic, and hafnium has a particularly large cross-section of thermal neutron capture.  Therefore, in the production of nuclear-grade zirconium sponges, zirconium and hafnium should be separated and the content of hafnium in zirconium sponge should be lowered to 0.01% or less.
Since the zirconium alloy will be irradiated by neutrons in the reactor, making its overall performance worse by changing its mechanical properties, increasing its strength, weakening its ductility, bringing about distortion and longer irradiation, causing creep and internal stress and so on, so that a comprehensive performance deteriorated. Therefore, cladding material is a kind of product of high consumption. Periodic replacement is necessary. Its refueling cycle is generally 12 - 18 months.
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