Speakers
Description
The design of the Second Target Station (STS) at Oak Ridge National Laboratory’s (ORNL’s) Spallation Neutron Source (SNS) is currently underway [1]. STS will operate at a power of 700 kW with short pulses, less than 1 s, and a repetition rate of 15 Hz. The new target will be a rotating water-cooled tungsten target, which will have two coupled cryogenic moderators filled with liquid parahydrogen: one above and the other below the target. Sixteen neutron beamlines will view the moderator above the target and six neutron beamlines will view the moderator below the target, for a total of 22 new instruments.
The STS Neutronics Group is responsible for all neutronics analyses related to the design and construction of STS, which includes neutronics optimization of the target and moderator, heating and radiation damage of major components, and all aspects of STS shielding. This paper will present example shielding analyses typically performed for the design of STS. These include shielding along the proton beamline from the existing accelerator to the second target, activation of major components, energy deposition and radiation damage of the proton beam window, and shielding along the neutron beamlines from the target monolith through the bunker and beamline shielding to the instrument caves. The primary computational tool used by the STS Neutronics Group is MCNP6[2], but most of these analyses benefit from auxiliary codes that develop input for MCNP6 or process the output from MCNP6. These examples will highlight the cutting-edge computational methods the STS Neutronics group uses such as unstructured mesh geometries converted from CAD, activation simulations for charged and neutral particles in any energy regime, and advanced automated variance reduction techniques for deep penetration shielding and beamline shielding with long streaming gaps.
[1] ORNL, “Spallation Neutron Source Second Target Station Conceptual Design Report Volume 1: Overview, Technical and Experiment Systems,” S01010000-TR0001, R00, Oak Ridge National Laboratory (2020).
[2] C. J. WERNER, ed., “MCNP® User’s Manual, Code Version 6.2,” LA-UR-17-29981, Los Alamos National Laboratory (2017).