More than 200 workers may have been exposed to nuclear radiation at the Bruce Power nuclear generating station near Owen Sound, Ont. (J.P. Moczulski/Canadian Press)

Up to 217 workers may have been exposed to nuclear radiation at a Bruce nuclear power plant near Owen Sound, Ont., says the Canadian Nuclear Safety Commission in a document released Tuesday.

The nuclear safety watchdog first confirmed last month that workers who were upgrading the Bruce A Unit 1 reactor may have been exposed to radiation.

A routine airborne sample taken on the morning of Nov. 26 at the plant threw up some red flags, according to a preliminary report by Bruce Power. Further testing of samples uncovered the presence of alpha particles, which can damage human tissue and cause cancer.

The number of workers who may have been affected by the incident was unknown until Tuesday, when the CNSC, the safety commission, filed a report with new details on the November incident. The report later appeared on Scribd.com, an online site for publishing and sharing documents.

The report states that regulatory limits on the levels of nuclear contaminants "are not likely to have been exceeded." But authorities aren't clear on exactly how much radiation the workers may have been exposed to.

Analysis of the possible exposure is ongoing, Tuesday's report said.

The plant has said that the workers who may have been affected were removed from duty. They described this as a "conservative" action given the amount of radiation that was detected.

The radiation has reportedly been contained to the Bruce A reactor, and the nearby communities of Tiverton and Inverhuron are said to be unaffected.

The CNSC will meet on Thursday to discuss the affair.

Bruce Power, a private nuclear utility that generates about a fifth of Ontario's electricity, operates six reactors at a former Ontario Hydro site on Lake Huron.