FUKUSHIMA Report (2):
The actual reason why this accident could not have been avoided

Eiichi Yamaguchi (Doshisha Univ.),
Presented at the 3rd International Symposium on Innovation Strategy (ISIS2012), held on Sept. 11, 2012, at University of Cambridge, UK

Japanese page: 'Core problem in the TEPCO nuclear plant accident -- Similarity with the JR West train accident at Amagasaki',  by Eiichi Yamaguchi (Doshisha Univ.), Talk on Feb. 26, 2013
Posted on Oct. 3, 2013    
==> See:  FUKUSHIMA Report (1): Criminal error in TEPCO management of technology and damages given to "Brand Japan" by Eiichi Yamaguchi (Doshisha Univ.) and Morinosuke Kawaguchi (Arthur D. Little (Japan), Inc.) (Fukushima Project Committee), News Release, Nov.  2011  (Posted on Sept. 20,2013)

For going back to Japanese pages, press buttons.

Editor's Note (Toru Nakagawa, Sept. 29, 2013)

This page is Prof. Yamaguchi's Fukushima Report in English in a more readable form than the page posted a week ago.

On the Fukushima Report posted a week ago, Mr. Richard Platt asked us to translate Yamaguchi's Japanese article into English for better readability.  Prof. Yamaguchi sent me a PPT file of his English presentation at ISIS2012 held at University of Cambridge on Sept. 11, 2012.  This page posts the presentation slides with the narration note in the text.

For further reference, you will find the following Web sites and articles useful:

ISIS2012 Site (English):
     Special Session:
     Presentation by Prof. Yamaguchi:

Prof. Eiichi Yamaguchi's Lab. official site (English):

   Presentation Slides                PDF

  Good morning. My name is Eiichi Yamaguchi from Doshisha University. Now, we would like to begin with the Special Session "Essential Cause of the Fukushima Nuclear Plant Accident" in the 3rd International Symposium on Innovation Strategy (ISIS-2012).

First, I will give a lecture about "The actual reason why this accident could not have been avoided". Here, I will make it clearly understandable how the accident occurred. I am sure you never need technical background. You will find it so easy to understand the essential cause of the accident. Here I will show you only 16 slides, which are already uploaded to the server. So, if you go to the ISIS web site, you will get the pdf of each slide like this.

The next one is an invited talk entitled "The engineering ethics as the key to bind the business and scientific knowledge - Case of two nuclear power plants: Fukushima and Onagawa" written by Taku HIRANO and Professor FUJIMURA from Tokyo Inst. Technology.
We will have a coffee break after that, but please make sure that we will take the photo during the break. Please come to the outside and we will take your picture.

Finally, Professor Sabine ROESER from Delft University of Technology will give an invited talk about "Fukushima, risk and moral emotions". .


Now, I will start my talk entitled "The actual reason why this accident could not have been avoided".   This is an executive summary of FUKUSHIMA Report, and during the talk I will circulate this book.  

As shown in the photo, Destroyed part of Fukushima Daiichi Nuclear Power Station consists of four units.  Here, No.1, No. 3 and No.4 are destroyed at the top floor because of hydrogen explosion.  Since No. 4 was out of operation, the hydrogen is supposed to be leaked from No.3. 

From now on to the forth slide, I will use the same four slides as I used in the last year to make you understand clearly. 


This shows the location of commercial nuclear power stations in Japan.  As shown here, there are 17 nuclear power stations.  Each contain several plants so that there are 50 nuclear plants in Japan.
All the nuclear plants are now out of operation except for two, which is No.3 and No.4 at Oi nuclear plant station.


Fukushima Daiichi Station is located 200 km far from Tokyo, and 700 km far from Kyoto. 

On 15th of March, TEPCO wanted to evacuate all the employees of Fukushima Daiichi at the midnight of 14th of March, 2011, but Prime Minister Kan scolded the president of TEPCO as "Japan will be completely destroyed if you evacuate them. " at 3 am on 15th of March.  Actually, if they were evacuated on 15th of March, even Tokyo would be radioactivated. 


It is interesting that, near the Fukushima Daiichi Station, there are two nuclear stations.  One is TEPCO Fukushima Daini Nuclear Station within 20 km south.  The other is Tohoku EPCO Onagawa Nuclear Station. 

The reason why Onagawa Nuclear Station was saved will be discussed by Professor Fujimura at the second lecture of this special session. 

Fukushima Daini was located at the same sea level as Daiichi, it was damaged by 14 m Tsunami but it was finally saved because the external electricity was alive.


On the other hand, at the Fukushima Daiichi Nuclear Station, external electricity as well as the emergency power generator were destroyed, so that these No.1, 2, 3 and 4 plants confronted severe accident.



As shown in this photo, the facilities at the sea coast was completely destroyed.  Since the emergency power generator was situated at the basement floor, all became out of control after tsunami.

Here I must note one essential point.  All the mass media have reported that, after the tsunami, all the station became black-out, and that these nuclear plant immediately lost their control.  However, it is not true.  As a matter of fact, there is the last fortification which keep cooling the reactor core for eight hours or more than 20 hours.


This figure illustrates the piping configuration of No. 1 reactor for Fukushima Daiichi Nuclear Station.  In this Reactor Pressure Vessel (RPV), steam generated by nuclear fission in this nuclear fuel goes to the turbine and generates the electric power.  Then, the steam is made water by tremendous amount of sea water at the condenser, and come back to RPV.  If this water current is stopped due to some reason, the control rod would be inserted into the fuel rod and stop the nuclear fission.  Nevertheless, decay heat would continuously be generated, and boil the water in RPV.  In order not to prevent the explosion of RPV due to the generated steam, you have to inject the fresh water from this water tank by HPCI (High Pressure Core Injection) pump as well as by CS (Core Spray) pump.  Simultaneously, this Safety Relief Valve (SRV) will be open to decrease the pressure in RPV.  This set of HPCI, CS and SRV is called ECCS (Emergency Core Cooling System). However, these pumps are operated by the external power. so that ECCS would not work  without any external power. 

In such sever cases, there is the last fortification for No.1 reactor.  This is isolation condenser, IC.  The IC can passively work without external power, in which generated steam is automatically delivered to the pool and cool down to the water.  This IC can work for about 8 hours.

I explained this last fortification of No.1 last year, so this year I would like to explain the last fortification of No. 2 and No.3 reactors.

As shown in this figure, No. 2 and 3 reactors have the evolved last fortification as shown in this figure.  Instead of IC, there is RCIC, Reactor Core Injection Cooling Systems.  Namely, the steam from RPV can rotate this pump.  Then, this pump can draw up the water in the suppression chamber.  The RCIC, the last fortification for No.2 and 3 reactors is designed to work for more than 20 hours.

At this opportunity, I would like to show the investigation of No.2 and 3 reactors, so please focus of this type of the last fortification, the RCIC. 


To make the following explanation clearly understandable, please remember these three physical quantities.

The first quantity is the water level in RPV which is measured from the top of active fuel. 

If the water level is positive, the fuel is completely immersed in the water and in the controllable state.  On the other hand, the water level is negative, a part of the fuel is exposed in the steam, and then generates tremendous amounts of decay heat.  Once the water level is negative, the melt-down process will start to produce radio-isotopes, Iodine 131, Cesium 134 and 137 etc., and the core is in the uncontrollable state.  So, human-being MUST try to keep the water level positive.  In other words, this quantity clearly shows the border of physics limit. 

The second quantity is the pressure in RPV.  The RPV is designed to resist high pressures at most 83 atmosphere.  To prevent the explosion of RPV, this safety relief valve (SRV) is designed to automatically open when the pressure in RPV exceeds 65 atmosphere. 

The third quantity is the pressure in Primary Containment Vessel (PCV).  The PCV is designed to resist the pressure up to 3.8 atm at maximum for No.2 and N. 3 reactors. 


Here, I have to note that, if the water level is decreased toward zero, you MUST inject the sea water from this fire pump line.  To do so, you have to decrease the pressure in RPV below 6 or 8 atmosphere by opening the SRV.  But if you open the SRV, the pressure in PCV will be increased to result in the explosion of PCV.  This will be the hell like Chernobyl.  Therefore, to avoid it, you have to open the vent as soon as possible.  However,  if you open the vent after the uncontrollable state, radioactive cesium and iodine will be emitted out to the atmosphere.  Therefore, the vent MUST be opened by hand within the controllable state with positive water level.

Now you are the professionals of atomic nuclear plant.  It is not nuclear science but just high pressure technology.  It is quite easy to understand.



First, let us analyze the time evolution of water level for No.3 reactors. 

The RCIC for No.3 manually turned on just after the earthquake at 1505.  That is why the RCIC kept cooling the core even when the ECCS was turned off due to the Tsunami at 1527.  However, the RCIC was off at 1136 on 12th of March, due to some human error. But very fortunately the HPCI, which is a part of ECCS, was automatically turned on 1 hour later at 1235 on 12th.  The HPCI kept working until 244 on 13th of March. 

So, I conclude that the No.3 reactor was in a controllable state for 36 hours due to the RCIC and then HPCI.  However, from this point when HPCI was off, the reactor soon was entering into an uncontrollable state, and the negative water level gave the core melt down, producing tremendous amount of radioactive materials. 


This figure shows the time evolution of pressures in RPV by red circle, and pressures in PCV by blue circles.  You will find a strange phenomenon for pressures in RPV in the afternoon on 12th.  Do you understand why the strong drop of pressures up to almost about 8 atmosphere?

Yes, this is the period while HPCI was working from here to here.  The HPCI has the cooling capacity of 10 times more  than RCIC.  That is why the core was cooled very well in this time region.  This means that if TEPCO inject sea water during the time when pressures were below 10 atm, you do not have to even open the vent.  However TEPCO did not.  TEPCO even refused it.  Then several hours after the reactor is in the uncontrollable phase here at 847, they finally opened the vent.  Due to that, radioisotopes of cesium and iodine were emitted into the outside environment. 

They decided to inject sea water at 925, but it was too late.  Too ridiculous. 

So, now you completely understand that if CEO or CTO of TEPCO made a clear decision of sea water injection during this period in the afternoon on 12th of March,  Fukushima people and the people on the globe would never suffer from the radioactive pollution from No.3. 


This figure shows the time evolution of water level for No. 2 reactors.  As you can see from this figure, the RCIC kept working for 69 hours, which is almost 3 days.  During the RCIC working, the water level was maintained around 4m, which made the reactor within a controllable state. 

But finally the RCIC was shut off at 1322 on 14th, because it has finite life time,  Then, the reactor was in the uncontrollable phase around 5pm on 14th.  After the melt down of core,  TEPCO finally injected sea water, but again it was too late to recover the reactor from uncontrollable state. 

That is the nature.

This figure shows pressure in RPV by red and pressure in PCV by blue..  As you can see easily, the pressure in RPV was maintained below 65 atm, due to the SRV release.  That is why the pressure in PCV was increased gradually, and finally exceeded the maximal limit 3.8 atm.  Here, you can see abrupt increase of the pressure in RPV here after the runaway of the reactor, then sudden drop of pressure in RPV at here.  Do you understand what happened here.

Yes, the RPV had cracks and tremendous amount of radioactive materials came out here.  They finally injected sea water at 1954 but again too late. 

So, now you completely understand that if CEO or CTO of TEPCO made a clear decision of sea water injection during this period in the afternoon on 12th of March,  Fukushima people and the people on the globe would never suffer from the radioactive pollution from No.2.  As a matter of fact, the radioactive pollution from No.3 and No.2 are five times bigger than from No.1, which means that the damage from radioactive pollution would be one sixth.   

So, now we were trying our best to find out the reason why TEPCO management could not make any decision to inject sea water in the evening on 12th of March, 2011. 

Finally, we succeeded in happening to meet Lady Luck,  Dr. Hibino.  Hibino was a colleague when I worked for NTT Basic Research Labs as a physicist.  Dr. Hibino was a computer scientist, but originally a physicist.  He was a very good friend of Prime Minister Kan, and only trustable scientist for Kan.  On the other hand, all other nuclear technologist around Prime Minister Kan was the residents of the so-called nuclear village. 

After the accident, Kan called Hibino and asked Hibino to come to the Prime Minister's House immediately.  Then, Hibino saw everything what happened in the evening on 12th of March. 


And, Hibino finally testified as follows:

When I arrived at the Prime Minister's Official Residence (Kantei) at 21:00 on March 12, Prime Minister Kan had started to get the feeling that the same thing might possibly happen to reactors No.2 and No.3 as No.1. And, Kan has frequently instructed that TEPCO should forestall the situation.  However, TEPCO stalled the vents and sea water injection with the reason that the RCIC was still working.

 So, on the grounds that there was still working cooling system in place, they chose to delay opening the vent and  inject sea water into the reactor vessels.

Prime Minister Kan asserted that even if we were to say that the RCIC had indeed been functioning as intended, (as there was no heat coming out of the containment area), we can infer that the heat and pressure more than likely continued to gradually build up as it had nowhere to escape. Which is exactly why they should have quickly opened up the vents and inject sea water into the reactors immediately to cool down the out of control reactors. However,  Representative of TEPCO refused.




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