TOKYO (Reuters) – The owner of the Fukushima nuclear plant, destroyed by an earthquake and tsunami nearly eight years ago, said on Friday it planned tests early next year to see how much melted uranium fuel has cooled in the damaged reactors.

The tests planned for January to March will stop water cooling in the reactors to analyze how the melted uranium core reacts and heats up after cooling has stopped, said owner Tokyo Electric Power Co.

All reactors need to be cooled to limit the radioactive reactions that produce heat to generate electricity. At Fukushima, Tepco jury-rigged cooling systems after the quake and tsunami wrecked the plant in March 2011.

The natural disaster triggered meltdowns at three of the Fukushima Daiichi plant’s six reactors, spewing radiation into the air, soil and ocean and forcing 160,000 residents to flee, many of whom have not returned.

From January, Tepco will begin to gradually reduce the amount of water being pumped over the melted fuel in reactor No. 2 at the site to half the amount over a week, a company spokesman said.

Then Tepco will resume full pumping, but in March the company will stop all cooling for a seven-hour period to test analytical models which have shown that the reactors will not overheat, he said.

Tepco said it would use the test results to better understand radioactive reactions during an emergency cooling halt. It will also help manage other water issues at the site.

Tepco has for years struggled to control the amount of water in the basements of the damaged reactors.

Groundwater flowing from hills above the plant enters the reactors, where it mixes with highly radioactive debris. The contaminated material is pumped out and treated before being stored in tanks that are quickly filling up.

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