The process of removing unused nuclear fuel from the No. 3 reactor building at the Fukushima Daiichi plant will start today, said officials with Tokyo Electric Power. TEPCO says it expects work to wrap up before April 2021.

Tokyo Electric Power said workers at the Fukushima Daiichi nuclear power plant in Japan short-circuited one of the two thermometers used to monitor temperatures at the bottom of a reactor vessel that contains nuclear fuel. The error caused about 100 tons of highly radioactive water to leak from a storage tank, TEPCO said. Company officials said a new thermometer would need to be installed through a pipe, but the company has no immediate plans to replace the equipment because of high radiation levels surrounding the reactor building.

Nearly 2,000 workers involved in Fukushima Daiichi cleanup operations who were exposed to at least 100 millisieverts of radiation are more susceptible to develop thyroid cancer, according to Tokyo Electric Power. The figure represents an increase in TEPCO's estimates.

Temperatures at all three damaged Fukushima Daiichi reactors have dropped below the boiling point, allowing Tokyo Electric Power to proceed with efforts to bring the units to cold shutdown. "We have cleared the temperature issue and taken a step forward towards achieving cold shutdown by the end of this year," said Takeo Iwamoto, a spokesman for the company. But TEPCO won't declare a cold shutdown until it fulfills other conditions, such as bringing down radiation emissions.

Tokyo Electric Power is linking a flawed exhaust system to the March 12 hydrogen blast that rocked the Unit 1 reactor of the Fukushima Daiichi nuclear plant in Japan. Venting the containment structure at the reactor could have pushed the hydrogen gas back inside instead of outside, leading to the explosion. "We did not sufficiently consider the possibility that hydrogen gas might flow back into the reactor building when power sources were lost," a TEPCO executive said.