CNIC: Fukushima 1 had world’s first Loss of Coolant accident (LOCA)

CNIC Press Conference re Fukushima  Daiichi Nuclear Power Plant

At CNIC’s press conference on Saturday night (March 26) an important new perspective on the course of events at the Fukushima Daiichi Nuclear Power Station was presented by Mitsuhiko Tanaka. Tanaka is a science writer and former nuclear engineer at Babcock Hitachi who helped design the reactor pressure vessel of Fukushima Daiichi Unit 4.

Tanaka concluded from official data showing parameters for Fukushima Daiichi Unit 1 that a loss of coolant accident (LOCA) had already begun by very early in the morning of March 12, about 12 hours after the earthquake struck. He found the evidence supporting this analysis amongst data published on the Prime Minister and Cabinet web site. The data does not begin until 2:45 am on March 12. There is no data for March 11, the day when the earthquake occurred.

The key factors are a marked drop in pressure in the reactor pressure vessel, accompanied by a marked fall in the water level and a rise in pressure in the containment vessel. This suggests that coolant leaked from the pressure vessel into the containment vessel. If so, it would be the first “classic LOCA” in the world (given that Three Mile Island was not a “classic” LOCA case).

At about 2:45 am on March 12 the figures for these parameters were as follows:

– Pressure in the reactor pressure vessel: 0.8 mega pascal, compared to the usual 7 mega pascal operating pressure and about 5 mega pascal for Units 2 and 3.

– Pressure in the containment vessel: 0.8 mega pascal, compared to the usual 0.1 mega pascal (ie atmospheric pressure, because the containment vessel is not normally subject to pressure).

– Water level: figures not given in the presentation, but the drop was shown on a graph.

The likely cause of this was a pipe rupture. This probably happened immediately after the reactor before the data that has been disclosed. Apparently there was an attempt to use Emergency Core Cooling System (ECCS) at 16:36 on March 11, two hours after the earthquake took place, but power was lost so it did not work.

If the above is true, a LOCA occurred immediately after the earthquake and ECCS failed, TEPCO gambled with the safety of the people in the surrounding areas by not informing the public immediately of the situation. The population should have been evacuated immediately because the consequences of this most feared type of nuclear accident could readily be predicted. Presumably the Nuclear Industrial and Safety Agency knew what was happening. Was the Nuclear Safety Commission also been involved in concealing the true situation.

Tanaka presented the theory of a LOCA as the logical explanation of the above data, but acknowledged that some key data needed to confirm this was missing.

Please note that the above summary is not an official record. It may be used as a guide for people wishing to follow up this issue, but it should not be quoted as a record of Tanaka’s words. Please watch the video to confirm what Tanaka actually said. Ideally you should translate directly from Tanaka’s Japanese explanation, only using the English interpretation to identify the location of the key issues on the video.

At the time of writing the final complete archive version was not available. Until the complete version is ready you can find the press conference in three parts on the left side below the blank screen on the URL below. The central analysis is on the second of the videos.

Philip White

International Liaison Officer

Citizens’ Nuclear Information Center

On 26/03/2011, at 4:09 PM, Philip White wrote:

A press conference will be held from 19:00 pm tonight (March 26 Japan time) at CNIC’s Tokyo office (Akebonobashi Co-op 2F-B, 8-5 Sumiyoshi-cho, Shinjuku). Analysis of the latest developments will be provided by nuclear engineers Masashi Goto and Mitsuhiko Tanaka.


There is very limited space, so please contact CNIC in advance if you wish to attend (phone: 03-3357-3800). As usual the press conference will be broadcast live on Ustream.

Below is the link to the archive video of CNIC’s press conference held at the Foreign Correspondents’ Club of Japan on March 25 with analysis by Dr Masashi Goto (former Toshiba engineer) and Dr Hisako Sakiyama (medical doctor and radiation expert) and comments by CNIC’s Chihiro Kamisawa.

Philip White
International Liaison Officer
Citizens’ Nuclear Information Center

Leave a Reply