Beam Plug for Radiation Shielding Penetrations

A beam line plug has been designed to fill the cylindrical hole formed by beam lines which pass through radiation shielding walls. The plug consists of multiple steel discs held together along their cylindrical axis by a steel cable forming a flexible snake-like structure. Other disc materials including laminates may be used to solve a variety of radiation shielding problems. When the beam line is to be used, the plug is pneumatically withdrawn into a vertical extension of vacuum line that is connected through a 90° bend to the beam line. Upon release, the plug is reinserted by pneumatic action. The beam plugs being used at the Brookhaven Three-stage MP Tandem Van de Graaff Facility are 7.6 cm diameter and provide 80 cm equivalent thickness of steel to fill penetrations through a 120 cm thick concrete wall. Fast-neutron measurements at the shielding wall surface show that the beam plug is indistinguishable from concrete shielding. A description of the beam plug mechanism, failsafe features, test results, and performance data is presented.