The Radiological Situation in the Beam-Cleaning Sections of the CERN Large Hadron Collider (LHC)

This thesis contributes to radiological assessments of the design and operation of the Large Hadron Collider currently under construction at CERN. In particular, the scope of this thesis is to examine the beam cleaning insertions - two of the main loss regions of the LHC where beam particles which would otherwise cause unwanted losses at different places of the machine are purposely intercepted. Two critical issues with regard to the protection of personnel and environment are studied: remanent dose rates due to induced radioactivity and airborne radioactivity. Although a detailed estimate of remanent dose rates is important for an optimization of later maintenance interventions only very limited information on remanent dose rates to be expected around the collimators was available so far. This thesis is an attempt to extend the knowledge considerably, especially by applying a new calculational method. Since this new approach is used for the first time in the design of the LHC a careful benchmarking with experimental data is performed as part of this work. In addition, a revision of existing assessments of airborne radioactivity became necessary after various design changes of the collimation system and due to modifications in the ventilation scheme of the LHC. Therefore, an extensive parametric study is presented covering all possible design scenarious. The results of both studies will give important input to the design of the collimators and the beam cleaning insertions.