Greens MLC Ian Cohen says it is not good enough that ANSTO has failed to discover how and why one of its workers was contaminated with radiation.

"We now need an independent inquiry to get to the bottom of this incident," Mr Cohen said.

"Residents and workers will be rightly concerned that a leak could occur without explanation.

"The Premier Morris Iemma must now intervene to protect Sydney residents. He should contact the Federal Minister responsible for ANSTO and demand an immediate independent inquiry.

"For a reactor to be operating in the heartland of suburban Sydney is crazy. Sydney-siders deserve a safe, clean, healthy city not one with a high-risk terrorist target on the edge of their backyard.

"Under the circumstances a new reactor at Lucas heights should not go ahead," Mr Cohen said.