The reactor vessel assembly, shown below, consists of the reactor vessel and its internal components, including the core support structures, core shroud, moisture removal equipment, and jet pump assemblies. The purposes of the reactor vessel assembly are to:
• House the reactor core,• Serve as part of the reactor coolant pressure boundary,• Support and align the fuel and control rods,• Provide a flow path for circulation of coolant past the fuel,• Remove moisture from the steam exiting the core, and• Provide a refloodable volume for a loss of coolant accident.
The reactor vessel is vertically mounted within the drywell and consists of a cylindrical shell with an integral rounded bottom head. The top head is also rounded in shape but is removable via the stud and nut arrangement to facilitate refueling operations. The vessel assembly is supported by the vessel support skirt (20) which is mounted to the reactor vessel support pedestal.
The internal components of the reactor vessel are supported from the bottom head and/or vessel wall. The reactor core is made up of fuel assemblies (15), control rods (16), and neutron monitoring instruments (24). The structure surrounding the active core consists of a core shroud (14), core plate (17), and top guide (12). The components making up the remainder of the reactor vessel internals are the jet pump assemblies (13), steam separators (6), steam dryers (3), feedwater spargers (8), and core spray spargers (11). The jet pump assemblies are located in the region between the core shroud and the vessel wall, submerged in water. The jet pump assemblies are arranged in two semicircular groups of ten, with each group being supplied by a separate recirculation pump.
The emergency core cooling systems, penetrations number 5 and 9, and the reactor vessel designs are compatible to ensure that the core can be adequately cooled following a loss of reactor coolant. The worst case loss of coolant accident, with respect to core cooling, is a recirculation line break (penetrations number 18 and 19). In this event, reactor water level decreases rapidly, uncovering the core. However, several emergency core cooling systems automatically provide makeup water to the nuclear core within the shroud, providing core cooling.
The control cell assembly is representative for boiling water reactor 1 through 6. Each control cell consists of a control rod (7) and four fuel assemblies that surround it. Unlike the pressurized water reactor fuel assemblies, the boiling water reactor fuel bundle is enclosed in a fuel channel (6) to direct coolant up through the fuel assembly and act as a bearing surface for the control rod. In addition, the fuel channel protects the fuel during refueling operations. The power of the core is regulated by movement of bottom entry control rods.