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During the 2022 maintenance outage, we are installing a new generation of spallation target-moderator-reflector-shield (TMRS), known as Mark-IV for Manuel Lujan Jr. Neutron Scattering Center (Lujan Center) at the Los Alamos Neutron Science Center (LANSCE). This paper discusses the activation anal-ysis of the previous target Mark III, in service 2010-2021. The TMRS employs a split target geometry consisting of two cylindrical W targets positioned on the axis of the proton beam. The upper target has a cylindrical inconel shell filled with seven W discs, with thicknesses increasing downstream. The tungsten discs have Ta cladding and are surrounded by cooling water flowing through the spaces between them. The lower target is a single W-cylinder cladded with Ta surrounded by an inconel shell. These two targets are expected to be the hotspots from an activation perspective, including its cladding and the shell. Another significant activation contribution is expected to be from the proton beam window located above the upper target. The area around the targets is mostly filled with beryllium. However, there is stainless steel (SS) at the bottom of the lower target. Around the proton beam window, there is mainly SS as well. These materials act in part as self-shielding. However, to ensure radiation safety, Mark III was placed in a steel-lead shielding cask.
Activation of designated hotspots was calculated by combining MCNPX 2.7.0 [1] with CINDER 1.05 [2] codes. The final dose simulation was carried out by MCNPX using a gamma dose mesh tally and a set of point detectors (PD). The Mark III target was operated for 12 years with approximately half-year run cycles delivering 800 MeV proton beam. Simulations were compared with the Radiation Control Technician (RCT) measurement on the day Mark-III was taken out and placed into a shielding cask.
[1] Mckinney, Gregg. (2011). MCNPX User’s Manual, Version 2.7.0.
[2] S. T. Holloway, W. B. Wilson et al., A Manual for cinder2008 Codes and Data (LA-UR 11-00006), Los Alamos National Laboratory, March 1, 2011.