UPDATE 1-Canadian parliament orders isotope reactor restart

(Updates with order from Parliament)

By David Ljunggren

OTTAWA, Dec 12 (Reuters) - The Canadian Parliament on Wednesday overruled the country's nuclear watchdog and ordered a reactor that makes crucial radioisotopes for cancer tests be restarted immediately.

The Chalk River reactor -- which makes more than two-thirds of global supply of the medical isotopes -- was shut down in November, quickly triggering shortages.

The Conservative government, under heavy political pressure to solve the problem, pushed through legislation allowing the reactor to resume operations for 120 days.

This will involve using backup safety systems, an action that the Canadian Nuclear Safety Commission says is unsafe.

The House of Commons approved the legislation on Tuesday and the Senate upper chamber followed suit on Wednesday.

Once the reactor is restarted it will take three or four days before operator, Atomic Energy of Canada Ltd, can begin delivering isotopes. When injected into the body, the isotopes give off radiation that can be seen by a camera to diagnose cancer, heart disease and other medical conditions.

Government ministers insist there is no danger in restarting the reactor now and say that what they believe is the minuscule risk of an accident is heavily outweighed by the need to start producing radioisotopes again.