A negligible amount of radioactive steam released at a nuclear plant in northern Japan escaped outside the compound, but there is no fear of damage to environment, operator Tokyo Electric Power Co. said Friday.

An increase in the level of tritium was detected during an air sampling outside the plant on Sunday, and the operator later found out that radioactive material was leaking in steam from the Fukushima Daiichi Nuclear Power Station, about 240 kilometers (150 miles) northeast of Tokyo, the company said.

The amount of the leak, however, was negligible and left no damage to the environment outside the plant, it said.