Orificed fuel support

In BWR/2 plants the fuel support casting is welded to the guide tube. The fuel orifice is attached to the fuel support by a bayonet connection. 

Structurally, the core shroud provides support for the top guide, core plate, and core support structure. The core shroud also supplies lateral restraint to hold the reactor core in place. The top guide and core plate are fastened to support ledges, which are part of the core shroud. Typically, peak end of life fluence levels for the middle of core shroud are on the 

Typically, the core shroud head is a dome-shaped stainless steel structure, which is attached to the core shroud top flange. The shroud head and steam separator assembly, which is welded to the shroud head, form the cover of the core discharge plenum region. The shroud head is bolted to the core shroud flange by the shroud head bolts. The steam separator standpipes are welded to openings in the shroud head which serve as the path for flow exiting the core region. 

The shroud head bolts fasten the shroud head and steam separator assembly to the core shroud flange. The bolts are manufactured from Alloy 600 and stainless steel material. The bolts are spread equally about the shroud head flange. The purpose of the shroud head bolts is to secure the shroud head and steam separator assembly. The number of shroud head bolts varies with plant size. 

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Each fuel assembly that makes up the core rests on an orificed fuel support mounted on top of the control rod guide tubes. Each guide tube, with its fuel support piece, bears the weight of fuur assemblies and is supported by a control rod drive penetration nozzle in the bottom head of the reactor vessel. The core plate provides lateral guidance at the top of each control rod guide tube. The top guide provides lateral support for the top of each fuel assembly. 

The core plate consists of a circular plate with round openings. The core plate provides horizontal support and guidance for the control rod guide tubes, incore flux monitor tubes, peripheral fuel supports, and startup neutron source holders. The last two items are also supported vertically by the core plate. The entire assembly is bolted to a support ledge in the core shroud. The core plate also forms a portion within the core shroud, which causes the recirculation flow to pass into the orificed fuel support and through the fuel assemblies. 

Each housing transmits loads to the bottom head. These loads include the weights of a control rod, a control rod drive, a control guide tube, an orificed fuel support, and the four fuel assemblies that rest on the fuel support. The lower portion of CRD housings are primary pressure boundaries. 

The orificed fuel supports (OFS) are stainless steel castings which rest on the top of a control rod guide tube as shown in Figure 2-10. Each OFS supports the weight of four (4) fuel bundles. 

The orificed fuel support is made of cast stainless steel. Cracking of the supports has not been observed. Based on the material composition, the low stress state of the support, fluences, which remain below the threshold level for lASCC and field experience, neither IGSCC nor LASCC are of concern for the orificed fuel supports. 

Orificed Fuel Support No incidents of cracking reported... 

There have been no reported cracks in the orificed fuel supports. 

IAEA) Nuclear Safety Standards normal water chemistry orificed fuel support post weld heat treatment reactor pressure vessel reactor pressure vessel internals reactor water clean up (system) stress corrosion cracking stand-by liquid control (system) shot peening safety relief valve... 

Core orificing Fixed orifices accomplish control of core flow distribution among the fuel assemblies. These orifices are located in the fuel support pieces and are not affected by fuel assembly removal and replacement. 

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