Main > Custom Projects > Custom Projects > Reactor Vessel Under-Head Shield

Reactor Vessel Under-Head Shield

Project Scope:

  • Design and build an under head radiation shield (UHS) used to shield the reactor head when stored in the head stand using a combination of carbon steel and lead wool blankets.
  • The support stand is designed to be lifted as a complete assembly when the lead blankets are removed.


  • UHS design basis included a II/I analysis for interaction with category I safety components.  The design requirements ensured seismic structural stability and determined critical interactions.
  • The UHS is a self-supporting steel ring frame.  It is used to support lead wool blankets that provide shielding from the reactor vessel heads during under head inspections, O-ring groove cleaning and O-ring replacement.  Three layers of lead blankets can be hung on the inside of the UHS frame during use.
  • An existing inventory of blankets already owned by the plant were modified for use with this stand, resulting in a significant cost savings.
  • The UHS is comprised of nine similar pre-constructed segments bolted together.  Bolted connections incorporated an innovative jacking method that allowed the diameter of the shield assembly to be adjusted to best fit the head.
  • Retractable shield plate incorporated into the design to attenuate radiation from the head bolt flange during O-ring inspections.
  • After assembly, shield can be hoisted into place using the polar crane system and be positioned inside of the head stands pedestals on the refueling floor.
  • A lockable shielded door is provided for under head access.  A vertical adjustable security barrier is located at the bottom of each shield support section.  The barrier is lowered to reach the floor to complete the security barrier and meet the requirements of a “locked high rad area”.