The removal and replacement of legacy site research reactor vessels has been conducted by AECL three times, once following a severe reactor accident. CNSC REGDOC-2.11.2 Section 5.1 may consider in situ decommissioning for legacy nuclear sites where decommissioning was not planned as part of the design. Although decommissioning of AECL's WR-1 reactor at Pinawa Manitoba may not have been planned as part of design, it was likely a design consideration as reversal of installation is evident as a possible and practicable reactor vessel removal method.
WR-1 was designed with facilities and equipment to replace fuel channel pressure tubes; a standard operating procedure safely conducted on numerous occasions. Fuel channel replacement, including fuel handling, required about 12 hours per channel . Extending removal of currently defueled pressure tubes to include volume reduction is practicable. A Bruce Power video  demonstrates volume reduction for CANDU pressure tubes. WR-1 fuel channel volume reduction is straightforward due to existing handling equipment and the vertical orientation of the fuel channels. Following removal of a fuel channel, the fuel channel transfer flask could be positioned over a repurposed room under the main floor of the reactor building where the fuel channel is lowered for volume reduction. The compacted volume of all WR-1 fuel channels is ~ 1 cubic meter and fuel channel removal provides ~ 47% reduction  in overall reactor core activation radionuclide activity. Removal of the reactor main floor rotating deck plates provides additional direct access to the top of the reactor for use of advanced technologies to dismantle and remove the remaining 53% of core activation radionuclide activity found largely in the reactor vessel.
During the history of WR‐1 operations there were about 150 documented nuclear fuel failures, each contributing a small portion to the 1 kg upper bound estimate  of high-level radioactive particles deposited in reactor systems. Manitoba’s High-Level Radioactive Waste Act does not permit disposal of high-level waste in Manitoba, making removal of the irradiated fuel deposits in WR-1 systems necessary, also required by Section 8.10 of IAEA General Safety Requirement Part 6. WR-1 removal followed by waste consolidation at a larger disposal site eliminates creating another legacy liability in the form of a near-surface intermediate-level waste disposal site.
The Government of Canada should reduce the number of long-term legacy liability sites by dismantling and removing nuclear facilities where possible and practicable, regardless of whether decommissioning was planned as part of design.
1) IAEA-SM-99/33 (1967), Current Status of Canadian Organic Cooled Reactor Technology; https://www.osti.gov/biblio/4557804
2) Bruce Power (2009), YouTube Video; https://www.youtube.com/watch?v=L-HgGjzswAk
3) CNL (2016), WR-1 Reactor Radiological Characterization Summary, WLDP-26100-041-000-001