RDS-112 Cyclotron Facility Decommissioning
Meghan Sanderson | McMaster UniversityEnoch ABC Ballroom
The RDS-112 cyclotron facility, consisting of an 11 MeV self-shielded cyclotron, was located in the McMaster University Medical Centre in Hamilton, ON. This facility was operated from 1990-2018, producing radioisotopes for medical imaging and research; primarily F-18 along with C-11, N-13 and O-15. The McMaster University Health Physics Department provided radiation safety support throughout the lifetime of the facility. By 2018, when all operations ceased, the cyclotron was owned by the Centre for Probe Development and Commercialization. All sealed and unsealed radioactive material was removed and it was determined that the facility would be decommissioned. However, the problem at hand was determining the process, as the option to remove the cyclotron as a whole was expensive and not feasible. The final decision was to dismantle the cyclotron and its related components, with the work being planned and led by McMaster Health Physics.
Methods: Samples and measurements of the internal components and the surrounding concrete shielding were taken to characterize and estimate the extent of activation. From this data, the decommissioning plan was created. In April 2023, researchers at King’s College London (KCL) identified 82 components of the RDS cyclotron which they could use for their own cyclotron. These components were removed, surveyed and cleared for release for shipment. All 82 components showed activation below exemption quantities or below minimum detection limits. In June 2023, an opening was created in the exterior wall of the building and the demolition commenced. Air sample measurements were taken during the demolition of the concrete shields to determine if this generated any airborne contamination. Daily contamination surveys were performed to ensure that no loose contamination was generated. The demolition began with the 6 surrounding concrete shields which contained majority of the total material, working towards the central components of the cyclotron. The shields were demolished in sections from which representative samples were taken and analyzed. All samples were surveyed for both loose and fixed contamination using contamination and dose rate meters prior to being removed from the building. Further analysis was performed using low-energy gamma spectroscopy along with liquid scintillation to characterize and quantize what, if any, activation products were present.
Results: The pre-demolition samples showed that the activation was mostly localized to the metal components around the ion source, extraction ports and target stations. The inner six inches of the concrete shields also showed low levels of activation. As demolition proceeded, the analysis confirmed that the activity levels of majority of the material were well below the exempt and unconditional clearance limits and was able to be unconditionally released. The lead shielding surrounding the targets also showed no activity above the minimum detectable limits. Approximately 56,600 kg of material was exempt or unconditionally cleared, and approximately 5,700 kg is considered to be potentially radioactive. The activated components not able to be unconditionally released were found to be parts of the more centralized components, consisting of a small section of the North and bottom steel shields surrounding the magnet, two floor tracks, I-beams and a localized portion of the upper and lower magnets near the targets. These remaining materials will be kept under McMaster’s consolidated licence until a plan for conditional release or radioactive waste disposal is finalized.
Conclusion: This project was the first of its kind in Canada completed under a Canadian Nuclear Safety Commission (CNSC) licence to decommission an isotope production accelerator facility. The decision to dismantle the cyclotron resulted in majority of materials being unconditionally released, in addition to many of the parts being reused in the RDS cyclotron at King’s College. This proves to be a viable alternative to the expensive option of removing the cyclotron as a whole.