25 Février 2016
February 24, 2016
A new finding on the 2011 Fukushima Daiichi nuclear accident has raised questions about the way the plant's operator initially explained the catastrophe taking place in the reactors.
Nuclear fuel in 3 of the plant's reactors melted down following the earthquake and tsunami on March 11th of that year.
Tokyo Electric Power Company did not admit there had been meltdowns for 2 more months.
The utility previously said it could find no grounds to conclude the reactors had melted down.
But it has been revealed that the firm's in-house manual noted that damage of more than 5 percent to a reactor core should be called a meltdown. A core houses nuclear fuel.
TEPCO found the description in the manual in a probe following a request from an investigative panel of the Niigata prefectural government.
If the utility had followed the manual, it should have assessed the damage was a meltdown 3 days after the accident, when the reactors' sensors were restored.
Engineers learned at that time that fuel in the No.1 reactor was 55 percent damaged, and 30 percent in the No.3 reactor. Both clearly meet the criteria of a meltdown.
TEPCO revised its manual after the accident. It now says it will assess and disclose when a meltdown has occurred before nuclear fuel is damaged 5 percent.
A new finding is raising questions about the explanation first offered for what was happening inside damaged reactors at the Fukushima Daiichi nuclear plant in 2011.
Nuclear fuel in 3 reactor cores melted following the earthquake and tsunami that March.
But Tokyo Electric Power Company officials failed to describe these as meltdowns.
They said there were no grounds for reaching that conclusion.
But 2 months later the utility formally admitted all 3 had melted down.
NHK has learned that the firm's own manual says a meltdown has occurred if at least 5 percent of a core has melted. Nuclear fuel is housed in the core.
The operator told NHK it discovered this definition in the course of responding to a request from a Niigata Prefectural Government panel investigating the accident.
An NHK reporter says this would suggest TEPCO did not understand the precise definition of a meltdown until nearly 5 years after the accident.
The utility says it will continue to investigate why it didn't use the word meltdown soon after the crisis began.
24.02.2016_No38 / News in Brief
Unplanned Events & Incidents
24 Feb (NucNet): Tokyo Electric Power Company (Tepco) said today its staff at the Fukushima-Daiichi nuclear station had guidelines on how to determine that a nuclear reactor is melting down, but that operators failed to use them properly as the accident unfolded in March 2011. Tepco said in a statement in Japanese on its website that operators did not thoroughly check the guidelines and failed to determine that core melt was a possibility. Tepco said laws, regulations and internal rules have been amended and retraining has been carried out, but admitted it needs to further improve its efforts to disseminate information about failures at the time of the accident.