Nuclear Industry

1.Nuclear Fuel Industry.
U²³⁵ that can generate fission reaction in the natural uranium minerals has ratio of only 0.7%, it can only be used for the reactor after various machining process to make it to the product with the concentration up to 2%-4%U²³⁵, after operation of the reactor, unburned U²³⁵ in spent  fuel and the new produced Pu²³⁹ will require recycling technique process to reclaim them. A complete system of nuclear fuel industry includes uranium mineral mining-hydrometallurgy-concentration-reactor- chemical treatment, etc. in the whole recycling process of nuclear fuel, stainless steel and corrosion resistant alloy material are widely used, without proper stainless steel material, there will not be modern nuclear fuel industry.

(1)Hydrometallurgy of Uranium
Uranium minerals should undergo working procedures including acid pickling/ alkali pickling-solvent lixiviating-solvent extracting-denitration, to form U₃O₈ in the end. The application of stainless steel in the above technique process is shown in the following table. For the reason of alkali lixiviating, corrodibility is comparatively weak, using the common steel can be acceptable, but at the liquid-gas interface position, the baffle plate should use  TP316L as the material, it can prevent the corrosive pitting caused by splashing of sulfide. When using nitric acid for lixiviating, the material should be 18-8 Type Austenite stainless steel with intercrystalline corrosion resistance. When using sulfoacid for lixiviating, material should be Cr-Ni Austenite stainless steel containing molybdenum or molybdenum-copper compound, under the corrosive conditions; it is required to use the deposit strengthening Austenite stainless steel.

Application conditions of stainless steel in the uranium Hydrometallurgy factory

(2)Refining of Uranium
Replacing U₃O₈ produced by hydrometallurgy with UF₄, and change UF₄ to UF₆，there are the wet method and dry method technique in the actual production.
The technique process for producing UF₄ with dry method, equipment material shall bear the corrosion by nitric acid, nitric acid steam, UO₂(NO₃)₂, , material shall vary according the working procedures, details see the table below:

Material of technique equipments for refining uranium

(3)Concentrating Uranium.
In using the gaseous diffusion to separate U²³⁵，the isolating cover of the compressor should use 0Cr35Ni65Al. The high speed rotating cylinder for centrifugal separation uses the Martensite aged steel.

(4)Retreatment of nuclear fuel.
Giving chemical treatment to spent fuel of the reactor and the radiant nuclear fuel of the production reactor, and separating U and Pu, the chemical treating process to the dangerous nuclear fission product is called nuclear fuel retreatment, or after treatment.

For nuclear fuel retreatment, presently mature technique is water method, the reclaiming process is constructed of three parts including the unshell of fuel components, fuel solving and the separating/ reclaiming of fuel. Material problem of the last part can refer to section of “Refining of Uranium”. For the two part at the front, the technique medium has strong corrodibility, so the equipments, pipes, pumps, valves of the nuclear fuel after treatment factory are all made of stainless steel and corrosion resistant alloy. The material will differ according to the technique medium condition, shown in the following table:

Corrosion resistant material in the unshell technique of nuclear fuel retreatment

Dissolving of fuel core　Normally solution similar or close to the unshell is used for dissolving. In dissolving the metal uranium, uranium oxide, and uranium-aluminum fuel, nitric acid is widely used, material of solving capsule commonly use 0Cr23Ni13Nb，TP304L and Carpenter20 alloy.

Treating equipment for high radioactive waste liquid　The high radioactive waste liquid is the compound medium containing various waste gas and various high radioactive liquids, it is highly corrosive, and often contains HNO₃, sulfate radical, iron ions, in treating this kind of waste liquid, leakage must be strictly prevented, in case the environment is polluted, material of the equipments should be 0 TP304 and 0 TP310SNb, the latter has excellent corrosion resistance, and operating all post- treatment factories use it as structure material of reactor (vaporizing and concentrating).

2.Nuclear power Industry.
(1)light-water reactor (LWR)
The reactor used to provide power for generating electricity, it is commonly cooled by water, and is generally called light-water reactor (LWR). Light-water reactor can be divided to as pressurized water reactor(PWR) and boiling-water reactor, PWR is the mainstream type.

The following table shows stainless steel application conditions for pressurized water reactor (PWR) nuclear power plant:

Conditions of stainless steel of pressurized water reactor (PWR)

(2)Sodium Cooling Reactor
The fuel jacket material is improved 316 stainless steel that contains Ti. 00Cr18Ni12Mo2 is used in the sodium capsule and thermal loop . According to the difference of temperature, the evaporator and super heater unit can use 2 1/4 Cr-1Mo,  TP321,  TP316L， TP304, Incology800, etc.