Project Details

This project consisted of the supply and installation of twenty-two stainless steel outfall risers that will discharge the water from OPG’s modular reactor in Darlington. The risers installed were 1.036m diameter, stainless steel pipes, approximately 19m long and located in a water depth of 12m.

Sacrificial steel casings were installed through through the overburden, down to the top of the bedrock. These casing kept the overburden from falling into the drilled holes before the permanent risers were installed. The bedrock was drilled in one pass using a down-the-hole cluster bit in a reverse-circulation configuration. The drill spoils were captured in dump-scows and transported for offsite, open-water disposal.

The risers were presuure tested onshore, prior to installation. Upon delivery to the site, they were flooded and lowered into their respective holes. Once placed, the annuli were filled with concrete, preventing water ingress during the risers’ future connection to the outfall tunnel. The concrete was transported to the outfall risers via barge and pumped in a tremie method, filling the annuli from bottom to top.

In the future, Aecon’s tunnel boring machine will pass beside and under the bottoms of the risers. Workers will then mine from the tunnel to the risers and remove the custom plug at the bottom of the riser, completing the tunnel-to-riser connections. After the tunnel is flooded, the caps on tops of the risers will be removed by divers. The outfall will then be functional.