Since last year, Tokyo Electric Power Company Holdings Inc. (Tepco) left two broken seismometers unrepaired at the No. 3 reactor within its Fukushima No. 1 nuclear plant, officials said Monday.

The instruments at the plant in Fukushima Prefecture did not record the tremors caused by a powerful earthquake that rocked the Tohoku region on Feb. 13 because they were not functioning. In some locations in Tohoku the quake measured upper 6, the second-highest level on the Japanese seismic intensity scale.

The problem was reported during a meeting of the Nuclear Regulation Authority on Monday.

According to Tepco, seismometers for the No. 1 to No. 4 reactors at the plant broke down during the March 2011 earthquake and tsunami that hit the region and triggered a triple meltdown at the power plant.

The company currently measures the strength of earthquakes using seismometers at the No. 5 and No. 6 reactors.

In March last year, the NRA pointed to the need to assess the seismic adequacy of the No. 3 reactor building, which was damaged in a hydrogen explosion that occurred during the early stage of the 2011 nuclear crisis.

Within that month, Tepco set up seismometers on the first and fifth floors of the building.

The one on the first floor broke down after being submerged due to heavy rain last July, while the one on the fifth floor malfunctioned last October.

At a news conference Monday, a Tepco official said that the company had planned to install new seismometers after identifying the causes of the malfunctions and implementing preventive measures.

Tecpo should have introduced substitutes hastily, before considering replacing them with upgraded seismometers, the official added.

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