Abstract
Design of the Target Service Cell (TSC) of the Spallation Neutron Source (SNS) requires computing detailed profiles of the gamma-ray dose rate outside its structure in order to abide by exposure limits and plan access control for the facility's personnel. Three-dimensional spatial distributions of the dose rate inside the TSC are also necessary to optimize the locations of electronic instruments and verify their design criteria at selected sites. For these reasons, in addition to the deep penetration feature typical of shielding calculations, a deterministic transport method solution, namely discrete ordinates, is preferred over Monte Carlo. Even then, the computation is complicated by the large size of the structure, large volume of air (internal void), optical thickness of the enclosing walls, and multiplicity of radiation sources. Furthermore, severe ray effects observed in preliminary calculations throughout the TSC internal cavity that persist in the transport through the concrete walls require special treatment. The computational model for conducting this complex calculation using Oak Ridge National Laboratory's TORT code, with support from peripheral codes in the Discrete Ordinates Oak Ridge System (DOORS), is presented. Successful elimination of primary ray effects via the newly developed three-dimensional uncollided flux and first collision source code GRTUNCL3D is also illustrated.
Published Version
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