First refurbished Darlington unit starts up

The refurbishment of Darlington 2, the first of the plant's four units to undergo refurbishment in a CAD12.8 billion (USD9 billion) project that will enable the station to operate for an additional 30 years, began in October 2016. Its reassembly, which started in June 2018, was completed last month.

First criticality is the point at which a nuclear reactor maintains a sustained fission chain reaction, creating the heat needed to produce electricity. Achieving first criticality has required increased focus and flexibility in the face of additional requirements and potential distractions resulting from the COVID-19 pandemic, the company said.

"This is a historic moment for our station, at a time when essential services like ours are needed more than ever," Chief Project Officer Dietmar Reiner said.

A series of 'heat up' and low-pressure testing will now be carried out over the coming weeks before the reactor is brought to gradually higher levels of power and then reconnected to Ontario's grid, OPG said.

The Canadian Nuclear Safety Commission (CNSC) last week authorised the removal of a regulatory hold point allowing the reactor to leave the 'guaranteed shutdown' state and move to 1% of full power. Two further regulatory hold points will require CNSC authorisation as the reactor ramps up towards full power.

OPG has previously announced it is delaying the start of refurbishment at Darlington 3, which had been planned for May, until later this year in order to help ensure stable electricity supplies during the COVID-19 pandemic.