The operator of Japan's crippled Fukushima nuclear plant said Tuesday it had shut down a key decontamination system used to clean radiation-tainted water, the same day local fishermen agreed to allow the release of uncontaminated groundwater around the facility into the ocean.

Tokyo Electric Power (TEPCO) switched off its Advanced Liquid Processing System (ALPS) after workers discovered leaks "seeping" from a tank late Monday.

About eight liters or 2.1 gallons of tainted water is believed to have leaked out, a TEPCO spokesman said. He added there was no immediate safety risk as the water had been recovered.

The suspension came just six hours after TEPCO switched back on two of three lines in the system, which cleans radiation-tainted water used to cool the reactors damaged by Japan's 2011 disaster.

The entire system had been shut down last Wednesday after TEPCO discovered a defect. The firm has repeatedly switched the system off over a series of glitches since trial operations began a year ago.

TEPCO is struggling to handle a huge — and growing — volume of contaminated water at Fukushima following the earthquake and tsunami, which lead to the worst atomic crisis in a generation.

There are about 1,200 purpose-built tanks at the site, filled with contaminated water. TEPCO has lobbied local fishermen to allow what it calls a "groundwater bypass" for nearly two years

Both Japan's Nuclear Regulation Authority and the International Atomic Energy Agency have said controlled release of low-level water should be considered to make storage space at the facility for irradiated water. And many experts say that at some point the water will have to be released into the sea after being scrubbed of the most harmful contaminants.

But local fishermen and their unions had been bitterly opposed to Tepco's proposed bypass after irradiated water leaked from tanks that were just uphill of the proposed groundwater drains last year.

The leaks sparked international alarm and led to a boycott of Fukushima fish by South Korea.

As part of its approval of the bypass, local media reported that fishermen requested that a third party organization check radiation levels of groundwater before it is released and any

released water to have less than 1 becquerels per litre of Cesium-134, a radioactive element that has a half life of around two years.

The legal limit of releasing Cesium-134 into the ocean is 60 becquerels per liter.

A fishing ban along the coast of Fukushima after the nuclear accident left most fishermen out of a job except for occasional work catching certain types of fish deemed safe.

Wire services