The Vermont Yankee nuclear plant has been shut down for at least a week to repair cracks in safety system.

A spokesman for Vermont Yankee Nuclear Power Corp. Lawrence Keyes, said the small cracks have not resulted in leakage of radioactivity and "pose no threat to the health and safety of the workers or the public."

Company officials said the cracks were discovered Wednesday in the torus, a steel-enclosed, doughnut-shaped pool designed to protect the reactor if its normal cooling system fails.

Keyes said the cracks apparently occurred during recent welding to reinforce the joints between the torus and its 32 support columns. Welders from General Electric, which manufactured the Yankee reactor, had done nine of the column when problems were discovered.

The plant was shut down late Saturday night after attempts at repair caused one crack to deepen and experts recommended that the cracked metal be replaced.

Keyes said the water level in the torus must be lowered to remove the flawed metal. It would violate federal safety requirements to operate the plant with the lower level or with the cracks in the torus, he said.

The torus is designed to absorb the powerful blasts of steam that would be released if the reactor's normal cooling system failed. Water in the torus quickly condenses the steam, relieving pressure on the reactor.