Officials at an experimental Japanese nuclear fuel reprocessing plant are investigating the leakage of a small amount of radioactive material earlier this week, the operator said Friday.

No radioactive material leaked into the atmosphere and no one was exposed to radiation, said Yukio Takahashi, spokesman for Japan Nuclear Fuel Ltd.

Plant officials are investigating why about seven liters (1.8 gallons) of radioactive chemical leaked from a pipe joint onto the floor of a refining building at the plant in Rokkasho, 580 kilometers (360 miles) northeast of Tokyo, Takahashi said.

The leak was discovered by a worker late Wednesday and stopped after the chemical process was shut down, he said.