POINT LEPREAU, N.B. - New Brunswick's public utility is investigating a spill of 300 litres of radioactive heavy water.

Officials say the spill occurred at the Point Lepreau nuclear power plant on Monday.

Spokesman Rod Eagles says the spill happened when a relief valve opened prematurely during a test.

He says it did not endanger workers, the public or the environment.

Eagles says workers left the area immediately and did not show any signs of radioactivity exposure in later testing.

This is the second spill at the plant in less than six months.

In December, four to six litres of radioactive heavy water spilled because of a leak at the plant.

Eagles says the test will resume when they know the cause of the spill.

Point Lepreau has been out of service since March 2008 for a major refurbishment and is scheduled to return to service this fall.