Tokyo Electric Power Co. (TEPCO) began constructing a temporary airtight structure to cover the exposed roof of Unit 1 at the Fukushima Daiichi nuclear power plant. A buildup of hydrogen caused an explosion that blew the roof off of the unit in March, sending radioactive material into the air.

The roof is expected to be complete by August and last two or three years, according to news reports. It is designed to prevent rainwater from entering, and potentially leaking out from, the building. TEPCO reportedly said the covering is not radiation-proof, but will stop some radiation from being carried out.

Reports said the cover is made of a polyester fabric with a vinyl chloride resin coating supported by a steel frame 154 feet wide and 177 feet tall. A pair of 750-ton cranes with lead-lined cabins to protect the operators from radiation that still is being emitted from the reactor will install the cover.

Unit 1 was given priority because most of the building’s original roof collapsed into the structure. That makes it easier to maneuver cranes around its perimeter, news reports said.

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