The radiation environment for the change-out scenarios of the SNS Inner Plug and the Proton Beam Window Insert

The Inner Plug, and the Proton Beam Window Insert, central components of the SNS target monolith are exposed to high-level radiation fields during routine operation. The inner plug houses the SNS target, and the proton beam window insert contains the proton beam window located about 2 meters upstream from the target. Both the plug and the insert need to be replaced periodically due to radiation damage caused by high particle fluxes. In support of planning the replacement procedures, detailed information about residual radiation levels of the plug and insert components was requested as well as predictions of the radiation exposure to personnel during the change out. In addition shielding casks had to be designed for proper enclosure of the activated components. Analyses were performed to assess the dose rates for all steps of replacement. The analyses were performed in three steps. Firstly, transport calculations were performed to assess the isotope production rates in the zones. Secondly an activation analysis generated the resulting decay gamma sources for all cells of the complex 5 meters thick SNS target monolith structures. Third, decay gamma sources were used in subsequent transport analyses of the dose rates for all change out steps including the determination of the required shielding casks for the reusable plug components and the components which will be replace. This paper will present details of the analyses and the results.