Tepco failed to repair broken seismometers at Fukushima NPP

25 February 2021

Since last year, Tokyo Electric Power Company Holdings (Tepco) had failed to repair two broken seismometers at unit 3 of the Fukushima Daiichi NPP, company officials said on 22 February during a meeting of the Nuclear Regulation Authority. The instruments therefore did not record the tremors caused by the magnitude 7.3 quake earthquake that shook the Tohoku region on 13 February.

Tepco said the seismometers at units 1-4 at the plant had broken down during the March 2011 earthquake and tsunami that triggered the triple meltdown at the NPP. The company subsequently measured the strength of earthquakes using seismometers at the unit 5&6 reactors. However, in March 2020, NRA had indicated the need to assess the seismic adequacy of the unit 3 reactor building, which was damaged in a hydrogen explosion during the 2011 nuclear crisis. Tepco had then set up seismometers on the first and fifth floors of the building. The one on the first floor had broken down after being submerged due to heavy rain in July 2020, while the one on the fifth floor malfunctioned in October.

A Tepco official told a press conference that the company had planned to install new seismometers after identifying the causes of the malfunctions and implementing preventive measures. However, a government official said Tepco should have introduced substitutes immediately, before considering replacing them with upgraded seismometers.

Tepco had admitted on 19 February that cooling water levels had fallen in the unit 1 and unit 3 reactors at the Fukushima. Although the company had initially reported that there was no abnormality at the plant as a result of the recent quake, Tepco spokesman Keisuke Matsuo said the drop in water levels indicated that damage to the unit 1 and 3 primary containment chambers had been worsened, allowing more water to leak.

Matsuo said the cooling water level fell as much as 70 centimetres in the primary containment chamber of the unit 1 reactor and about 30 centimetres in unit 3. However, Tepco was unable to determine any fall in unit 2 water levels because indicators had been taken out to prepare for the removal of melted debris.

The leaked water is believed to have remained inside the reactor buildings and there is no sign of any outside impact, he said. Tepco will monitor the water and temperatures at the bottom of the containment vessels, Matsuo said.

Increased leakage could require more cooling water to be pumped into the reactors, which would result in more contaminated water having to be treated and stored in huge tanks at the plant. Tepco says its storage capacity of 1.37 million tons will be full by summer. A government panel’s recommendation that it be gradually released into the sea has faced fierce opposition from local residents and a decision is still pending.

Meanwhile, the Tokyo High Court on 19 February held the government as well as Tepco accountable for the 2011 nuclear disaster, ordering both to pay about 280 million yen ($2.6 million) in compensation to more than 40 plaintiffs forced to evacuate to Chiba, near Tokyo, for their lost livelihoods and homes.

This decision reverses an earlier ruling by the Chiba district court that excluded the government from responsibility. Judge Yukio Shirai said the government could have foreseen the risk of a massive tsunami and taken measures after a long-term assessment in 2002 of seismic activities.

Of the 14 rulings already handed down in district courts, there is an even split in whether the central government was liable or not. The latest ruling was the third by a high court. The Sendai High Court in September 2020 found the central government liable, but another presiding judge in the Tokyo High Court handed down a ruling in January that did not recognise responsibility on the part of the central government. The Supreme Court is expected to eventually make a ruling covering all the high court cases.

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