By Shinichi Saoshiro
TOKYO (Reuters) - Japan is set to declare on Friday that its tsunami-stricken Fukushima nuclear power plant has reached cold shutdown, passing a key milestone in efforts to bring under control the world's worst nuclear accident since Chernobyl 25 years ago.
The Fukushima Daiichi plant, 240 km (150 miles) northeast of Tokyo, was wrecked on March 11 by a huge earthquake and a 10-metre-high (33-ft-high) tsunami, which knocked out its cooling systems, triggering meltdowns and radiation leaks.
Prime Minister Yoshihiko Noda is expected to announce the accomplishment of one of the government's top goals at a news conference at 0900 GMT, though he may also warn that it will take decades to fully dismantle Fukushima's six reactors.
A cold shutdown is when water used to cool nuclear fuel rods remains below its boiling point, preventing the fuel from reheating. One of the chief aims of the plant's operator, Tokyo Electric Power (Tepco), had been to bring the reactors to cold shutdown by the year-end.
After months of efforts, the water temperature in all three of the affected reactors fell below boiling point by September, but Tepco has been cautious of declaring a cold shutdown, saying it had to see if temperatures and the amount of radiation emitted from the plant remained stable.
Declaring a cold shutdown will have repercussions well beyond the plant: it is a government pre-condition before it allows about 80,000 residents evacuated from within a 20 km (12 mile) radius of the plant to return home.
Tepco said early in the crisis that it did not plan to entomb the damaged Daiichi reactors in concrete, the option chosen at Ukraine's Chernobyl where reactors caught fire and burned for days. Instead, it favored the gradual removal of the nuclear fuel for storage elsewhere.
The government and Tepco will aim to begin removing the undamaged nuclear rods from Daiichi's spent fuel pools as early as next year. However, retrieval of fuel that melted down in their reactors may not begin for another decade, with the complete dismantling of the plant expected to take up to 40 years, domestic media reported on Thursday.
The enormous cost of the cleanup and compensating the victims of the disaster has drained Tepco financially. The government may inject about $13 billion into the company as early as next summer in a de facto nationalization, sources told Reuters last week.
Japan also faces a massive cleanup task outside the plant if residents are to be allowed to go home. The environment ministry says about 2,400 square km (930 square miles) of land around the plant may need to be decontaminated, an area roughly the size of Luxembourg.
The crisis shook the public's faith in nuclear energy and Japan is now reviewing its earlier plan to raise the proportion of electricity generated from nuclear power to 50 percent by 2030 from 30 percent in 2010.
Japan may not immediately walk away from nuclear power, but few doubt that nuclear power would play a lesser role in future.
Living in fear of radiation is part of life for residents both near and far from the plant. Cases of excessive radiation in vegetables, tea, milk, seafood and water have stoked anxiety despite assurances from public officials that the levels detected are not dangerous.
Chernobyl's experience shows that anxiety is likely to persist for years to come, with residents living near the former Soviet plant still regularly checking local produce for radiation before consuming them 25 years after the disaster.
The announcement may not dramatically improve Noda's support ratings, eroded by his steadfast commitment to a sales tax hike to cope with a public debt burden twice the size of Japan's economy. Noda is also faced with a formidable list of other tasks, such as helping a stagnant economy deal with the yen's rise to historic highs.
(Editing by Tomasz Janowski and Mark Bendeich)