Shielding activities

12 DECEMBER,2020 | By Markus Brugger

When strolling through our experimental areas you certainly got used to the hundreds of shielding blocks, surrounding the experiments, delimiting the beamlines, and ensuring the required radiation protection. They tend coming (with few exceptions) in three ‘flavours’: concrete, iron and marble, and aim at optimizing the attenuation of prompt, as well as the reduction of residual radiation. For pragmatic reasons, many of them have standard sizes (multiples of 40cm), but easily weigh several tons and often must be moved when beamline configurations change in our user areas. They have also aged over time, thus whenever possible (throughout consolidation activities such as the East Area Renovation project, or the preparation of a new experiment, we aim at refurbishing them, thus involving severe cleaning and painting activities. In this context, our group manages the entire shielding stock for the accelerator sector, thousands of blocks in total. For the production of shielding blocks in standard sizes, we have established two frame contracts (one for concrete, the other for iron blocks) and for special requirements (e.g., recently in the EAR, nToF upgrade or SPS dump project context), dedicated design studies are made, detailed specifications established, and productions followed upon, until the final installation. Let us have a look together at a few recent examples, starting with the production of large concrete beams for the East Area shielding of the primary and mixed beam areas. For the primary zone we face a particular challenge as this area, thanks to a dedicated ventilation system, must be kept at under-pressure, thus also requiring a particular air tightness of the surrounding shielding structure. Having a closer look on how these heavy blocks are stacked one on top of the others, you easily realize the corresponding challenge. Nevertheless, a technical solution was developed, and we are now looking forward to the corresponding commissioning tests early 2021. In addition to the air tightness, the East Area also required several new shielding blocks of particular size and shape. One block of 1.2m x 0.6m x 9m adds already up to about 15 tons and required a dedicated manufacturing process to be closely followed. The total number of shielding blocks placed and stacked on top of each other in the in the East Area even required a detailed analysis of the underlying civil engineering structure. As a second example, the SPS dump installation got recently finalized and required quite a few large new shielding blocks with a special marble surrounding to minimize future residual dose rate levels. These are impressive shielding structures which were first pre-assembled and tested, prior the recent successful final installation in the SPS. Finally, some of you might also remember the mobile shielding endeavour for the CHARM irradiation facility in the East Area. A similar challenge was now also successfully addressed for the nToF facility where we designed and implemented a dedicated mobile shielding wall to allow for later easy access to the target area, as well as enabling an additional irradiation station. Furthermore, the design is also compatible for a possible later implementation of a remote irradiation station. All in all, not only figuratively quite a heavy activity, acting often in the shadow but literally a critical building block for many of our areas.