TOKYO (AFP) - Japanese nuclear power operator said on Friday (March 25) it would decommission an ageing reactor because of the cost of upgrading, the sixth to be scrapped due to tougher rules brought in after the Fukushima disaster.

Japan is pushing to restart its nuclear reactors, which were shuttered after a huge earthquake-triggered tsunami sent the Fukushima Daiichi nuclear plant into meltdown in 2011.

But safety regulations brought in after the disaster, which require companies to build structures to guard against huge waves and earthquakes, means it could cost billions to overhaul old reactors.

Only two are on line after passing the tests, while power companies have already announced plans to scrap at least five other old reactors.

Shikoku Electric Power had planned to restart the No. 1 reactor at Ikata nuclear complex in Ehime, western Japan, but said Friday it would decommission the 39-year-old technology instead.

The company said in a statement it took the decision after "comprehensively taking into account a possible operating term and construction costs" needed to pass the new safety measures.

The Nikkei business daily estimated safety upgrades needed to meet the new safety standards could cost 200 billion yen (S$2.43 billion).

Japan set up an independent watchdog, the Nuclear Regulation Authority, after the Fukushima disaster, replacing the previous arrangement where the industry ministry both oversaw the regulator and promoted nuclear power.

Prime Minister Shinzo Abe and utility companies have been pushing for a return to nuclear power as the disaster forced Japan to turn to pricey fossil fuels to plug the energy gap left by the shutdowns.