Abstract
The Proton Power Upgrade (PPU) project [1] at Spallation Neutron Source (SNS) is aiming at increasing the neutron beam intensities at the First Target Station (FTS) and advancing accelerator capability to additionally power a future Second Target Station (STS) [2]. PPU will involve upgrading the SNS accelerator complex to double the currently available proton beam power from 1.4 to 2.8 MW, by increasing the proton beam energy from 1 GeV to 1.3 GeV and by increasing the proton beam current.
PPU will enable new science capabilities enhancing the experiment throughput of the 19 existing FTS instruments, which are heavily oversubscribed. STS will include 22 additional neutron scattering instruments.
Numerous neutronics analyses are performed to support PPU evaluating the FTS systems for higher beam power and for system upgrades. Part of the PPU scope is an extension of the Ring to Target Beam Transport (RTBT) line, a stub out of the accelerator tunnel for the future Ring to STS Transport (RTST) line[3]. As the RTST tunnel will not be built within the PPU project, the stub will be shielded by a plug, which is planned to be made from regular concrete.
In order to provide radiation protection safety, analyses are required to design adequate plug thickness for the stub. The thickness of the stub is driven by the criterion that the area downstream of the plug is “unrestricted access area”, demanding the dose rate downstream the stub be below 0.25 mrem/h at 30 cm from the surface at normal operation and below 20 Rem/hr for accident cases. Additionally, analyses verifying the amount of soil for shielding the accelerator tunnel to the above stated requirements are performed.
