Roll-on Shield Assembly consists of a mobile Roll-on Shield structure assembly and stationary Fixed Shield assembly. The Roll-on Shield structure assembly covers the hatch opening in the FM vault floor when it is in the fully advanced condition.
The Roll-on Shield structure assembly together with stationary Fixed Shield assembly provides the necessary Shielding over the hatch opening to reduce the radiation fields beneath the hatch opening. This facilitates access into the FM Service Area for maintenance of fueling machines and other auxiliary systems even when the reactor is operating. Rails are provided for movement of the shield, along with guide legs, front rollers, drive actuators and stopping and safety mechanisms