TOKYO - STEAM leaked from part of a pump carrying water to the No. 7 nuclear reactor in the quake-hit Kashiwazaki-Kariwa nuclear plant in northern Japan on Saturday, but the leak was soon fixed, Kyodo news agency said.

Though the steam contained a minuscule amount of radioactive material, there was no impact on the outside environment, Tokyo Electric Power Co (TEPCO), which runs the plant - the world's biggest - was quoted by Kyodo as saying.

TEPCO officials were not available for comment.

TEPCO restarted the 1,356 megawatt No. 7 unit on May 9 for the first time since the plant was forced to shut nearly two years ago following a magnitude 6.8 quake.

On Friday, it raised output to 100 percent as part of a test run.

Restart of the No. 7 unit could cut TEPCO's annual fuel purchases by more than 70 billion yen (S$1.03 Billion) and reduced carbon dioxide emissions by more than 5 million tonnes, according to company and Reuters calculations. -- REUTERS