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The backup power source of a reactor-monitoring device at the Fukushima No. 1 Nuclear Power Plant ended up disconnected for four months until the March 2011 earthquake and tsunami triggered a disaster at the plant, Tokyo Electric Power Co. (TEPCO) said.

Failure to connect the backup source may have prevented data on the status of the plant from getting to the government for about two hours after the outbreak of the crisis. That could have affected the initial response to the disaster and the predictions on the spread of radioactive materials.

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The device left without backup power was a media converter, which monitors the state of the plant and sends data to the government’s Emergency Response Support System (ERSS). That data also goes to the System for Prediction of Environmental Emergency Dose Information (SPEEDI), which provides quick estimates on the effects of radiation in an emergency and it also can predict the spread of radioactive materials.

TEPCO officials said workers tried to connect the backup power supply to the media converter during renewal work in November 2010, but the cable was too short so they left it disconnected.

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As a result, when the earthquake struck and the nuclear power plant lost its external power supply at 2:47 p.m. on March 11, 2011, data transmissions stopped. Due to aftershocks from the quake, the communications network did not start back up until 4:43 p.m. Early data could have gone out to officials had the backup power source been connected.

The company believed the temporary loss of data did not greatly affect SPEEDI, said TEPCO official Junichi Matsumoto.

“What was unable to be transmitted was data from the early stages, and it is assumed that this had little effect on SPEEDI. We don’t believe there was great urgency,” he said.

ERSS devices monitor the reactor containment vessels at nuclear power plants across Japan, and predict how nuclear accidents will unfold. The government has spent 15.5 billion yen developing the system.

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