A reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has a generally cylindrical shape and is closed at both ends, e.g., by a bottom head and a removable top head.  A top guide typically is spaced above a core plate within the RPV.  A core shroud, or shroud, typically surrounds the core plate and is supported by a shroud support structure.  Particularly, the shroud has a generally cylindrical shape and surrounds both the core plate and the top guide.  The top guide includes several openings, and fuel bundles are inserted through the openings and are supported by the core plate. 
Known core plates are fabricated from several stainless steel plates and formed ring segments joined together by welding.  A typical core plate has over 200 welds.  Fabricating such a core plate is very labor intensive.  In addition, maintaining the required core plate geometry is difficult because of weld distortion and tolerance stack-ups between the several plates and ring segments. 
The core plate welds also, increase the susceptibility of the core plate material to a detrimental effect known as inter-granular stress corrosion cracking (IGSCC).  Although no cracking currently is known to be occurring in a core plate, cracking may occur in the heat affected zone of the welds.  Eliminating welds in the core plate therefore would eliminate the potential of cracks initiating in welds.