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Under-Head Shield Assembly

Project Scope:

  • Design and build an under-head radiation shield (UHS) to shield the reactor head when stored on the head stand using a combination of carbon steel and lead wool blankets as shielding materials.
  • Total shield weight is 12,000 lbs. with no single item weighting more then 101 lbs.
  • Total time to assemble the shield was two hours.


  • The UHS was designed to meet site seismic and structural design requirements. The design ensured seismic and structural stability and demonstrated that critical interactions were acceptable.
  • The UHS is a self-supporting steel ring frame. It is used to support lead wool blankets that provide shielding from the reactor vessel head to protect personnel by reducing general area dose, O-ring groove cleaning and O-ring replacement operations. Three layers of lead blankets can be hung on the inside of the UHS frame during use.
  • The UHS is comprised of twelve similar pre-constructed segments that are pinned together. Pinned connections incorporate an innovative jacking method that allows the diameter of the shield assembly to be adjusted to best fit the head.
  • A retractable shield plate was incorporated into the design to attenuate radiation near the head bolt flange during O-ring inspections.
  • 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 the floor to complete the security barrier and meet the requirements of a “locked high radiation area”.

View the Under-Head Shield System Component-Storage Container

The video below illustrates a mock erection of the UHS before the lead blankets are hung.
This video has been compressed for time.

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