Yes, nuclear accidents have occurred at Chalk River. There was one in 1952 in which the reactor blew its lid off. The core of the reactor had to be buried off-site. Fortunately, it was a very tiny reactor. It was the NRX reactor. There was also a smaller accident in 1958 involving the NRU reactor.
There have been accidents in Canada, not involving commercial power reactors on a major scale, but we've had some pretty close calls. In fact, we've had a close call, if you remember, with the accident that shut down the Pickering unit 2 reactor as a result of a pressure tube breaking in the core of the reactor—something that the engineers and scientists had promised officials could never happen.