Speaker
Description
The Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL) is an accelerator-based neutron source facility that provides the most intense pulsed neutron beams in the world for scientific research and industrial development. SNS converts a 1.8 MW proton beam of 1.3 GeV energy and sub-micro-second pulse width incident on a mercury target into a neutron source at 60 Hz repetition rate. The neutron production occurs when a horizontally injected proton beam strikes the liquid mercury target contained by vessel, which is placed in the center of the target monolith.
The central components of the SNS target monolith are the Proton Beam Window (PBW), the Inner Reflector Plug (IRP), and the target vessel. During operation, these components are exposed to intense radiation fields and therefore become highly radioactive. The incoming proton beam passes through the PBW before striking the liquid-mercury target vessel, which is located within the IRP.
The IRP is replaced on regular basis because neutron poisons in certain moderators gradually burn out, reducing their ability to produce the narrow neutron pulses required for neutron-scattering applications. The replacement of IRP is a complex task due to its location in the area receiving high irradiation, being under significant amount of shielding, and its size requiring removal in segments. For planning the replacement workflow to help to reduce radiation exposure to workers dose rates for each stage of extraction/replacement operation are predicted. Residual dose rates are evaluated through detailed analyses using the MCNP particle-transport code and the Cinder2009 transmutation code. While the replacement was taking place, measurements were performed and later were compared to the calculations.
| Topics | T5. Induced radioactivity and decommissioning |
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