Site Characterization and Adaptation - Lessons Learned from the Port Granby LLRW Project in Canada-19255

摘要

The Port Hope Area Initiative (PHAI) is a community-based solution for the long-term management of historic low level radioactive waste (LLRW) resulting from 60 years of uranium and radium processing operations in the Town of Port Hope, Ontario. The Eldorado refinery, on the shores of Lake Ontario, began refining radium-226 from pitchblende ore, later transitioning to the refining of uranium ore. Process residues were deposited at the Welcome Waste Management Facility in the Town of Port Hope until the mid-1950s switching to the Port Granby Waste Management Facility (PGWMF), which continued to accept waste until the late 1980s. The Port Granby Project is part of the broader PHAI being completed by Canadian Nuclear Laboratories (CNL). The scope of remediation activities at Port Granby includes: 1) constructing a new, secure long-term waste management facility (LTWMF) and supporting infrastructure, and 2) excavating and relocating LLRW and marginally contaminated soil from the Port Granby Waste Management Facility (PGWMF) to the newly constructed LTWMF. Remediation design required extensive site investigations of waste buried in unmarked and unlined trenches across the PGWMF area. Investigations included reviews of historical records, interviews with past staff of Eldorado and Atomic Energy Canada Limited (the entity managing the PHAI cleanup prior to CNL), radiological surveys, and the advancement of boreholes across the site to facilitate the physical sampling of soil and groundwater contaminants indicative of the presence of LLRW. This paper describes the challenges associated with characterizing and quantifying waste prior to remediation and lessons-learned to adjust procedural adaptations during the characterization phase of a project to better anticipate the unanticipated nature and growth of the contamination profile that often occurs during remediation. Despite substantial pre-remediation investigative efforts, current PGWMF remediation activities have resulted in growth of both the areal and vertical extent of contamination. The contamination profile was shown to be dramatically influenced by leaching of contaminants deeper into native soils. In addition, remedial excavation discovered specific waste types such as unidentified compressed gas cylinders outside of the location indicated by historical records, as well as a quantity of unknown liquids and unmarked drums. These discoveries have resulted in higher waste quantity estimates and have required a partial redesign of the LTWMF mound (a higher final elevation and steeper slopes) to accommodate the increased waste volume. In addition, the means and methods necessary to execute the remedial construction had to be modified to account for the new conceptual model developed from the new contamination data. Despite extensive historical review and site characterization to define the nature and extent of LLRW buried at the PGWMF, actual conditions encountered during remediation efforts necessitated taking an adaptive approach to both the design of the LTWMF and the means and methods used for excavation and transport of waste.