The Pressurized Water Reactor
consists of internal and external components.
The internal component
consists from fuel pellets, fuel rods, fuel assemblies, cladding, the coolant, moderator
and control rods.
The external components consists from
pressurizer, reactor coolant pumps, steam generator and turbine.
We will discuss some of
internal components in this article and follow in future articles.
- fuel pellets
The basic component of the
core is the cylindrical fuel pellet. It is composed of slightly enriched
uranium dioxide powered that is compacted by cold pressing & then sintered
to attain the required density the sintered uranium dioxide is chemically inert
at reactor temperatures and pressures with respect to the cladding and enclosed
gases. The slightly dished ends of each pellet permit axial expansion at the
center of the pellets. The consequences of any accidental branch of the
cladding are minimized by the ability of the uranium dioxide lattice to retain
fission products and to resist deterioration caused by high temperature water.
- Fuel rods
Uranium dioxide pellets are
inserted into zircalloy-4 tube, and each end of the tube is sealed by welding
an end plug to form a fuel rod. The pellets are prevented from shifting during handling
and shipment by compression spring between the top end plug of the fuel pellet
stack.
3.
Fuel assemblies
A square array of fuel rods
structurally bound together constitutes a fuel assembly. Control rod guide
thimbles replace fuel rods at selected spaces in the array and fastened to the
top and the bottom nozzles of the assembly spring clip grid assemblies are
fastened to the guide thimbles along the height of the fuel assembly to provide
support for the fuel rods. The fuel rods are contained and supported, and the
rod to rod center line spacing is maintained within this skeletal frame work.
The bottom nozzle of the fuel
assembly controls the coolant flow distribution and also serves as the bottom
structural element.
The top nozzle of the fuel
assembly function as the fuel assembly upper structural element and forms a
plenum space where the heated reactor coolant is mixed and directed toward the
flow holes in the upper core plate. The spring clip grids provide support for
the fuel rods in two perpendicular directions.
