Alternative Linear Accelerator Vault Construction
We are seeing more and more applications of high-density block and lead plate in the construction of linear accelerator vaults in lieu of the traditional concrete walls and ceiling. There are a number of advantages to this approach: less depth of structure, greater ease of construction for additions and renovations, plus the opportunity for cost savings in a renovation application due to the minimized impact to add a new vault.
With all of this said, there are a number of boxes to check if you choose to pursue this approach. You must carefully select the block vendor. Take your time reviewing the requirements for the project. Early on in the process agree to terms—contract language, bonding requirements, payment terms (prior to shipment, at delivery, or progressively based on the completion of work), and insurance requirements including errors and omissions due to the design-build nature of the application. And very importantly, if there are seismic requirements make sure the vendor understands the seismic zone, as well as any special project structural considerations. These are free-standing structures and therefore they must perform and be treated as a building structure.
Selection of the block vendor early in the design process allows for coordination with the other design elements, and will determine from the beginning who will perform the physics on the vault. Vendor products vary, and therefore their radiation physics characteristics are unique to their block dimensions and shape. If you change vendors midstream, it will require a complete recalculation of the vault.
Another option to consider is purchasing the vault turnkey. However, you need to make sure this aligns with the project delivery. We must emphasize that whatever direction is chosen, close supervision is needed to make sure you secure the correct insurance coverage, receive properly stamped and approved structural design and documentation, and that the physicist’s calculations and analysis are in hand before work begins.
This alternative approach for vault shielding is a great option; just make sure you understand the level of attention and focus needed to deliver it correctly.