A “trip” in the system at the Pickering Power Plant caused an unexpected shutdown earlier this week, leaving the province scrambling to find alternative sources of energy, CTV News has learned.

The shutdown, caused by a “trip” in the system that is designed to ensure safe operations, forced Ontario to import power to keep electricity flowing in the province. The “trip” was caused by a turbine valve problem in the non-nuclear side of the reactor.

The sudden shutdown had a serious impact on the Ontario power grid. At the time, four reactors at the facility in Darlington, Ont. were already down for planned maintenance, along with two units at another nuclear facility. 

Combined with the unexpected outage, the province was short 40 per cent of the nuclear supply. 

The reactor in Pickering has since come back online and has been reconnected with the power grid. 

With a report from CTV's Paul Bliss.