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Description
The ISOLDE (Isotope Separator On-Line DEvice) facility at CERN produces radioactive ion beams for research in nuclear, atomic and solid-state physics using thick targets irradiated with a 1.4 GeV / 2 microA (2.8 kW) proton beam. The facility comprises two target stations, each equipped with a dedicated beam dump located about two metres downstream of the target. The beam dumps are surrounded by concrete shielding blocks and buried beneath several metres of soil.
To support future operation with a proton beam of up to 2 GeV and 6 microA (12 kW), the ISOLDE target area is being upgraded as part of the IBDRS (ISOLDE Beam Dump Replacement & Sustainability) project. The project, which is being carried out during ISOLDE’s Long Shutdown 3 (LS3, 2026–2027), includes the excavation of the soil above the beam dumps, their replacement and the reinforcement of the surrounding shielding.
Since the shielding blocks and beam dumps had remained largely inaccessible throughout the last 30 years of operation, neither their physical condition, relevant for handling and transport, nor the residual dose rates could be assessed in advance. The expected high dose rates and the uncertainty regarding the condition of the components made the planning of the dismantling particularly challenging.
This work presents the residual dose rate calculations carried out with the FLUKA Monte Carlo code to support the radiological planning of the dismantling of the existing beam dumps. As direct radiation measurements were not possible before the start of the work because the radioactive components were inaccessible, the simulations formed the basis for the step-by-step dose planning and the optimisation of the work in accordance with of the ALARA principle. They were used to estimate the maximum individual and collective doses associated with each stage of the dismantling sequence, from the initial configuration to the complete removal of the shielding and beam dump blocks. Additionally, a photon skyshine analysis was performed to evaluate the contribution of photon scattering in air to dose rates at larger distances from the worksite.
Once the shielding became accessible at the end of the excavation phase, radiation measurements were performed. The FLUKA predictions were benchmarked against these measurements, demonstrating very good agreement and confirming the reliability of the calculations across the dismantling sequence.
| Topics | T4. Shielding and dosimetry |
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