Austenitic stainless steel cladding

The electrochemical examination of fusion joints between nine pairs of dissimilar metal couples in seawater showed that in most cases the HAZ was anodic to the weld metals" . Prasad Rao and Prasanna Kumarundertook electrochemical studies of austenitic stainless steel claddings to find that heat input and 5Fe content significantly affected the anodic polarisation behaviour under active corrosion conditions whilst Herbsleb and Stoffelo found that two-phased weld claddings of the 24Cr-13Ni type were susceptible to inter-granular attack (IGA) as a result of sensitisation after heat treatment at 600°C /pa was unaffected by heat input. 

The fuel subassembly with CEA austenitic stainless steel cladding tubes has also been irradiated in MK-II core since 1988 and reached the final stage at 125GWd/t. 

The interior surfaces of the vessel are typically cladded with austenitic stainless steel. Cladding is used to prevent general corrosion by coolant and to minimize the build-up of corrosion products in the reactor coolant system. The cladding is applied in one or two layers by single-wire, multiwire or strip-cladding techniques. 

Hardness, Impact Strength. Microhardness profiles on sections from explosion-bonded materials show the effect of strain hardening on the metals in the composite (see Hardness). Figure 8 Ulustrates the effect of cladding a strain-hardening austenitic stainless steel to a carbon steel. The austenitic stainless steel is hardened adjacent to the weld interface by explosion welding, whereas the carbon steel is not hardened to a great extent. 

There have been a few instances of high temperature hydrogen attack of base metal which was clad or overlayed with austenitic stainless steel. All of the reported instances involved C-0.5Mo steel base metal. In one case,34 high tem-... 

Because of the size and the pressure of the vessel, austenitic stainless steel could not be used throughout, but must be applied on the inner surfaces of the ferritic material. This has been done by explosion plating of a 4 mm cladding on the base material prior to rolling the cylinder and forming the hemispherical head. For the flat cover and the sealing faces weldcladding was applied. 

Austenitic stainless steels are by far the most common and contain 18% chromium and 8% nickel, hence the term 18/8 stainless steel. The austenitic structure, which is the soHd solution of iron carbide and all the metal additives in iron, is stabilized at all temperatures, producing a soft and flexible product. It is used for fume hoods, decorative cladding, and architectural features. 

The stabilised austenitic stainless steels for cladding contain an alloying element (niobium), which forms stable grain boundary carbides. This prevents chromium depletion along the grain boundaries and makes the material immune to stress corrosion cracking. Non-stabilised material was used for the first layer because the thermal expansion coefficient of the material is closer to that of the low-alloy pressure vessel material. The presence of niobium in the second layer allows performance of so-called retrospective dosimetry in the RPV inner surface by machining out some scraps for further chemical separation and activity measurement to determine real neutron fluence on the RPV inner surface. 

The body of the vessel is of low-alloy steel. To minimize corrosion, the inside surfaces in contact with the coolant are cladded with a minimum of some 3-lOmm of austenitic stainless steel. The major characteristics of the RPVs used for four-loop plants are listed in Table 4.1 (IAEA, 2009). The PWR RPV design pressure is about 17 MPa and the operating pressure is about 15.5 MPa. The design temperature is 343 °C where the operating temperature is typically 280-325 °C (IAEA, 2009). 

The reactor vessel is a vertically mounted cylindrical vessel with a hemispherical lower head welded to the vessel and a removable hemispherical upper closure head. The construction is basically that of forged rings, forged hemispherical heads, forged flanges on the closure head and vessel, and forged nozzles. The internal surfaces that are in contact with the reactor coolant are clad with austenitic stainless steel. 

Clad material Improved Austenitic stainless steel... 

Stmctural materials Cladding of fuel elements lCrl3Mo2NbVB (EP-450) steel. Reactor stmctures Crl8Ni9 austenitic stainless steel. 

WWER NPPs are equipped with horizontal steam generators (SG). Two cylindrical collectors (hot leg and cold leg collector) form part of the boundary between the primary and secondary circuit in a SG. Tubes are attached to these collectors. The WWER-440 SG collectors are made of austenitic stainless steel, the WWER-1000 SG collectors are made of clad carbon steel. There is a bolted cover on the top of the collector (primary pressure boundaiy) and on the shell above the collector cover (secondary side). 

Russia. Conventional austenitic stainless steels have been optimized by addition of B, Ti and Mg. Extensive experience involving more than 100 000 fuel pins, has been gained on the 20% CW TchS-68 steel irradiated in BN-600 with oxide and MOX fuels at peak temperatures up to 700°C [Refs. 7.12,7.13]. More than 2500 fuel pins reached doses more than 80 dpa, with a maximum dose of 94 dpa. This steel has been used successfully as the standard cladding material since the beginning of 1991. Post-irradiation profilometry has... 

In Europe, especially, the use of austenitic stainless steel 304L (clad or solid) for batch digesters is normal practice solid duplex stainless steel is another option (Canavan, 1974). 

The nuclear fuel must be clad with a corrosion-resistant material to prevent the release of radioactive gases and fission products to the primary water. The fuel itself is usually uranium oxide, which is quite resistant to the primary water. The fuel is clad with austenitic stainless steel or Zircaloy-2 (R60802) or the extra-low nickel Zircaloy-4 (R60804). 

The piping, steam generator, and pressure vessel comprise much of the total exposed area in the primary section of a pressurized water reactor. The internal surface of the pressure vessel is clad with austenitic stainless steel. The piping and steam-generator components are primarily austenitic stainless steel or Alloy 600 (N06600). Carbon steel has been used in a few systems. 

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