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Fukushima nuclear accident: Saturday 19 March summary

Last Saturday the the crisis level at the Fukushima Daiichi nuclear power station was rapidly on the rise. Hydrogen explosions, cracks in the wetwell torus and fires in a shutdown unit’s building — it seemed the sequence of new problems would never end. A week later, the situation remains troubling, but, over the last few days, it has not got any worse. Indeed, one could make a reasonable argument that it’s actually got better.

Yes, the IAEA has now formally listed the overall accident at an INES level 5 (see here for a description of the scales), up from the original estimate of 4. This is right and proper — but it doesn’t mean the situation has escalated further, as some have inferred. Here is a summary of the main site activities for today, followed by the latest JAIF and FEPC reports. You also might be interested in the following site map:

Another large cohort of 100 Tokyo fire fighters joined the spraying operation to cool down the reactors and keep the water in the spent fuel ponds. The ‘Hyper Rescue’ team have set up a special vehicle for firing a water cannon from 22 m high (in combination with a super pump truck), and today have been targeting the SNF pond in unit 3. About 60 tons of sea water successfully penetrated the building in the vicinity of the pool, at a flow rate of 3,000 litres per minute. Spraying with standard unmanned vehicles was also undertaken for 7 hours into other parts of the the unit 3 building (delivering more than 1,200 tons), to keep the general containment area cool. The temperature around the fuel rods is now reported by TEPCO (via NHK news) to be below 100C.

Conditions in unit 3 are stabilising but will need attention for many days to come. Promisingly, TEPCO has now connected AC cables to the unit 1 and 2 reactor buildings, with hopes that powered systems can be restored to these building by as early as tomorrow (including, it is hoped, the AC core cooling systems), once various safety and equipment condition checks are made.

Holes were made in the secondary containment buildings of Units 5 and 6 as a precautionary measure, to vent any hydrogen that might accumulate and so prevent explosions in these otherwise undamaged structures.  The residual heat removal system for these units has now been brought back on line and these pools maintain a tolerable steady temperature of 60C. More here. These buildings were operating on a single emergency diesel generator, but now have a second electricity supply via the external AC power cable.

Why are they concentrating on these activities? Let’s revisit a bit of the history of last week. The spent fuel pool still has decay heat (probably of the order of few MW in each pool) that requires active cooling. When power went out on Friday, the cooling stopped and the pool temperature has been rising slowly over the weekend, and probably started boiling off (and a large volume may have also been lost due to ‘sloshing’ during the seismic event). The pool is located on the 4th floor above the reactor vessel level. It remains unclear why they could not arrange fire trucks to deliver the sea water before the fuel rods got damaged and started releasing radioactivity. Now the effort is hampered by the high radiation level (primarily penetrating gamma rays). This is the inventory of those spent fuel ponds that have been causing so many headaches:

In order to remove the decay heat after the reactor shutdown, the cooling system should be operating. Following the loss of offsite power, the on-site diesel generators came on but the tsunami arrived an hour or so later and wiped out the diesel generators. Then the battery provided the power for 8 hours or so, during which time they brought in portable generators. However, the connectors were incompatible. As the steam pressure built up inside the pressure vessel, the relief valve was open and dumped the steam to the pressure suppression chamber, which in turn was filtered out to the confinement building and the hydrogen explosion took out the slabs.

The sea water was then pumped in by fire trucks and the reactor pressure vessels are now cooled down to near atmospheric pressure but the fuel assemblies are uncovered at the top quarter or third (the FEPC updates give the actual pressure and water levels). It appears that the pressure vessels and the reactor containment structures are intact, except the Unit 2, where the hydrogen explosion took place inside the containment and hence damaging the lower wetwell torus structure (but almost certainly not the reactor vessel, although the exact status is unclear). It appears that the radioactivity releases are mostly coming from the spent fuel storages than the reactor cores.

World Nuclear News has a really excellent extended article here entitled “Insight to Fukushima engineering challenges“. Read it! Further, you must watch this 8 minute reconstruction of the timeline of the accident done by NHK — brilliant, and really highlights the enormous stresses this poor station faced against a record-breaking force of nature. As I’d noted earlier, just about everything that could have went wrong, did. But valuable lessons must also be learned.

The IAEA and Japanese government has reported the potential contamination of food products from the local Fukushima area via radioactive iodine (mostly vented as part of the pressure relief operations of units 1 to 3). This is a short-term risk due to the 8-day half-life of radioactive iodine (and a small risk, given the trace amounts recorded), but precautions are warranted, as discussed here. What does this mean?

In the case of the milk samples, even if consumed for one year, the radiation dose would be equivalent to that a person would receive in a single CT scan. The levels found in the spinach were much lower, equivalent to one-fifth of a single CT scan.

… and to further put this in context:

The UK government’s chief independent scientific advisor has told the British Embassy in Tokyo that radiation fears from the stricken Fukushima nuclear power plant are a “sideshow” compared with the general devastation caused by the massive earthquake and tsunami that struck on 11 March. Speaking from London in a teleconference on 15 March to the embassy, chief scientific officer John Beddington said that the only people likely to receive doses of radiation that could damage their health are the on-site workers at the Fukushima Daiichi plant. He said that the general population outside of the 20 kilometre evacuation zone should not be concerned about contamination.

As to the possibility of a zirconium fire in the SNF ponds, this seems unlikely. Zr has a very high combustion point, as illustrated in video produced by UC Berkeley nuclear engineers. They applied a blowtorch to a zirconium rod and it did not catch on fire. The demonstration is shown about 50 seconds into this video. The temperature was said to reach 2000C [incidentally, I visited that lab last year!].

The the Japan Atomic Industrial Forum has provided their 12th reactor-by-reactor status update (16:00 March 19).

Here is the latest FEPC status report:


  • Radiation Levels
    • At 7:30PM on March 18, radiation level outside main office building (approximately 1,640 feet from Unit 2 reactor building) of Fukushima Daiichi Nuclear Power Station: 3,699 micro Sv/h.
    • Measurement results of ambient dose rate around Fukushima Nuclear Power Station at 4:00PM and 7:00PM on March 18 are shown in the attached two PDF files respectively.
    • At 1:00PM on March 18, MEXT decided to carry out thorough radiation monitoring nationwide.
    • For comparison, a human receives 2,400 micro Sv per year from natural radiation in the form of sunlight, radon, and other sources. One chest CT scan generates 6,900 micro Sv per scan.
  • Fukushima Daiichi Unit 1 reactor
    • Since 10:30AM on March 14, the pressure within the primary containment vessel cannot be measured.
    • At 4:00PM on March 18, pressure inside the reactor core: 0.191MPa.
    • At 4:00PM on March 18, water level inside the reactor core: 1.7 meters below the top of the fuel rods.
    • As of 3:00PM on March 18, the injection of seawater continues into the reactor core.
    • Activities for connecting the commercial electricity grid are underway.
  • Fukushima Daiichi Unit 2 reactor
    • At 4:00PM on March 18, pressure inside the primary containment vessel: 0.139MPaabs.
    • At 4:00PM on March 18, pressure inside the reactor core: -0.002MPa.
    • At 4:00PM on March 18, water level inside the reactor core: 1.4 meters below the top of the fuel rods.
    • As of 3:00PM on March 18, the injection of seawater continues into the reactor core.
    • Activities for connecting the commercial electricity grid are underway.
  • Fukushima Daiichi Unit 3 reactor
    • At 2:00PM on March 18, six Self Defense emergency fire vehicles began to shoot water aimed at the spent fuel pool, until 2:38PM (39 tones of water in total).
    • At 2:42PM on March 18, TEPCO began to shoot water aimed at the spent fuel pool, until 2:45PM, by one US Army high pressure water cannon.
    • At 3:55PM on March 18, pressure inside the primary containment vessel: 0.160MPaabs.
    • At 3:55PM on March 18, pressure inside the reactor core: -0.016MPa.
    • At 3:55PM on March 18, water level inside the reactor core: 2.0 meters below the top of the fuel rods.
    • As of 3:00PM on March 18, the injection of seawater continues into the reactor core.
  • Fukushima Daiichi Unit 4 reactor
    • No official updates to the information in our March 18 update have been provided.
  • Fukushima Daiichi Unit 5 reactor
    • At 4:00PM on March 18, the temperature of the spent fuel pool was measured at 152.4 degrees Fahrenheit.
  • Fukushima Daiichi Unit 6 reactor
    • At 4:00PM on March 18, the temperature of the spent fuel pool was measured at 148.1 degrees Fahrenheit.
  • Fukushima Daiichi Common Spent Fuel Pool
    • At 10:00AM on March 18, it was confirmed that water level in the pool was secured.
  • Fukushima Daiichi Dry Cask Storage Building
    • At 10:00AM on March 18, it was confirmed that there was no damage by visual checking of external appearance.

At 5:50PM on March 18, Japanese Safety Authority (NISA: Nuclear and Industrial Safety Agency) announced provisional INES (International Nuclear and Radiological Event Scale) rating to the incidents due to the earthquake.

Fukushima Daiichi Unit 1, 2 and 3 Unit = 5 (Accident with wider consequences)

Fukushima Daiichi Unit 4 = 3 (Serious incident)

Fukushima Daini Unit 1, 2 and 4 Unit = 3 (Serious incident)

(No official provisional rating for Fukushima Daini Unit 3 has been provided.)


By Barry Brook

Barry Brook is an ARC Laureate Fellow and Chair of Environmental Sustainability at the University of Tasmania. He researches global change, ecology and energy.

344 replies on “Fukushima nuclear accident: Saturday 19 March summary”


Yes I considered that, but from the information I’ve read that seems even less likely. There has been a debate and it actually might now been known that there was fresh fuel in SFP 4 waiting to go into the reactor. In this case it would be easier to get each fuel rod to criticallity, but they are noway as densely packed as in a reactor. Maybe if they all melted to the botton in a big lump and there was water above, recriticallity could occur. That would turn the water to steam above and stop the reaction, but there would be lots of radioactive material produced with no containment. Maybe that is what they were fearing. We will have to wait for a full report to find out what they were thinking and what actions good/bad/not necessary they were taking.


@Cornelius, on 20 March 2011 at 10:23 PM
The architectual static of the entire unit is quite rigid. This plant may not have been ready for the tsunami, but it is obviously earthquake resistant to an enormous extend.

You have to understand, an earthquake is not an explosion. It is ‘merely’ a violent movement of the underlying terrain. Try imagine you have an enormous hand an would try to pick the whole thing up in one go. According to the statics, that should be possible. It would not just fall apart like a cardhouse. A very bad earthquake might lift the whole thing up or sink it down, but it is not going to throw it up, or make it bounce down .

Stricktly speaking the containment structure is not ‘dependant’ on the underlying terrain to stay in one piece. This is something called ‘problem overkill’. Lets face it. Compared to the damage the tsunami caused, the damages to the structure due to a 9.0 quake are totally insignificant. That is quite an archievement.

The explosions may have corrupted the structures integrity in absolute terms, but short of that it is to my opinion not to be expected the structures will show signs of ‘fatigue’ any time soon.

(i would appreciate a second opinion or monitoring on this.)


Have you noticed the general news / media loop the last 24 hours? I would call it almost a blackout, but that could be mistaken. Now replaced by the side show of war. In any case, there seems to be a large drop off of updates and progress reports on the nuclear crisis to just general and vague reporting. That’s not to say it means anything sinister, but, as a communications professional, this is disconcerting. Does it mean things are touch and go? Or does it mean TEPCO just doesn’t care to inform the public about their ongoing crisis? Either way it is a blunder to keep the public in the dark, assuming the worst.


Actually, I don’t agree. Information is what the public deserves. Lack of information is what causes panic and misconceptions.


@ William Fairholm 5:47 AM

Thanks very much for your comforting and precise answer. It is the first time I read an explicit suggestion that there might be “fresh fuel” in the pond, and am suprised to the extent that I am not sure to have completely understood your sentence : “it actually might now been known that there was fresh fuel in SFP 4 waiting to go into the reactor”. Have you a link to somewhere on the web where this is developed in more detail ?


Jean, I have also read a count of all 11k fuel rods at the plant and read that #4 pool including X number of fresh fuel rods to be loaded into the reactor. I’m sorry that I no longer have that link (I will try to find it in the hundreds of pages I’ve read the last few days) but I do recall it was from an “official” industry source not from a news article.


Shelby, on 21 March 2011 at 5:51 AM said:
“Have you noticed the general news / media loop the last 24 hours?”

I think that means they think this is not as much of a story anymore. Things serious, but improving, not getting worse each day as it was in the middle of last week. In Libya, you have the situation of a Dictator threatening to take revenge on his own people and the United National Security Council makes the strongest resolution ever: “All means necessary” to stop him. That is the new quickly changing news story. If you want to find stuff about Japan and even not nuclear disaster stuff, there is lots of it out there. You just have to go look instead of it being the top of the headlines for the mainstream media. Whether this good/bad/indifferent I’ll leave to each persons perspective. But not unexpected in my opinion and not sinister.


Jean-Luc R., on 21 March 2011 at 6:05 AM said:
“Thanks very much for your comforting and precise answer.”

Ok hear is a link with pesimistic projections of what will happen with the spent fuel in SFP 4. About half way down they mention fresh as well as used fuel. The only thing I can say about their pesimistic evaluation is it didn’t happen. They spayed water into SFP 4 and there was no huge release of radioactivity. Whether there ever was a realistic probability of release will take a very detailed analysis. The experiment has been done and in this case nothing major happened. I assume they were spraying boron in with the water. My main concern was not causing criticallity, but releasing a good portion of the radioactive fission products in the spent fuel. Again, this did not happen.


Aside — this may be helpful:

From the NOTES link (top of the main blog page)
To search BNC posts using Google:

Let’s say you want to search for “solar” and “capacity factor”. Then, enter your search term into Google as follows:

solar capacity factor


To search through BNC comments

What about if you want to search through comments on BNC, rather than the blog posts? You can’t do this through the BNC site’s standard search box, because this only accesses posts. However, you can do it here:

First, select the “comments” radio button. Then try typing in the following (for instance):

fission products

The default option will show you the Most relevant results, but you can also click on Show the most recent.


Jean-Luc R., on 21 March 2011 at 4:05 AM said:
“As far as I have experts at hand, a question which does not scare me but puzzles me, and whose answer must be obvious for the knowledgeable”

I should have looked at that link you provided earlier. If the translation you provided is accurate, I would assume this is fresh fuel and SFP 4 has the largest inventory of fresh as well as spent fuel. It is also near capacity, while the other ones are not. Why they then concentrated on SFP 3 first, I do not know. Maybe it had even less water than 4. If that was the case then water got out of there by some means besides evaporation. Sloshing or a leak. The only caveat is why would they have all this fresh fuel in all the SFPs, besides SFP 4 where they were going to load it into the reactor?


Here is an update by the IAEA. It answers some questions about the SFPs.

Unit 1

Unit 1 experienced an explosion on 12 March that destroyed the outer shell of the building’s upper floors. No precise information has been available on the status of the spent fuel pool.

Unit 2

No precise information has been available on the status of the spent fuel pool. Authorities began adding 40 tonnes of seawater to the spent fuel pool on 20 March.

Unit 3

Unit 3 experienced an explosion on 14 March that destroyed the outer shell of the building’s upper floors. The blast may have damaged the primary containment vessel and the spent fuel pool. Concerned by possible loss of water in the pool, authorities began spraying water into the building in an effort to replenish water levels. First, helicopters dropped seawater on 17 March, and every day since then, including today, emergency workers have sprayed water from fire trucks and other vehicles.

Unit 4

This reactor was shut down 30 November 2010 for routine maintenance, and all the fuel assemblies were transferred from the reactor to the spent fuel pool, before the 11 March earthquake. The heat load in this pool is therefore larger than the others.

On 14 March, the building’s upper floors were severely damaged, possibly causing a reduction of cooling capability in the spent fuel pool. Emergency workers began spraying water into the building today.

Unit 5 and 6

Instrumentation at these reactors began to indicate rising temperatures at their spent fuel pools starting on 14 March. Three days later, Japanese technicians successfully started an emergency diesel generator at Unit 6, which they used to provide power to basic cooling and fresh-water replenishment systems. Workers created holes in the rooftops of both buildings to prevent any hydrogen accumulation, which is suspected of causing earlier explosions at Units 1 and 3.

A second generator came online on 18 March, and the next day, the higher-capability Residual Heat Removal system recovered full function. Temperatures in the spent fuel pools of Units 5 and 6 have gradually returned to significantly lower temperatures. (See graph at left.)

Common Use Spent Fuel Pool

In addition to pools in each of the plant’s reactor buildings, there is another facility — the Common Use Spent Fuel Pool — where spent fuel is stored after cooling at least 18 months in the reactor buildings. This fuel is much cooler than the assemblies stored in the reactor buildings. Japanese authorities have confirmed that fuel assemblies there are fully covered by water, and the temperature was 57 ˚C as of 20 March, 00:00 UTC.


I agree with Damen Matson’s comment.
I can buy a portable powersupply from Cat for about a million dollars. I am just a ordinary U.S. citizen. With a goverment that has connections to military equipment getting a generator onsite should be about as easy as getting media there. Onced dropped onsite the generator can be hooked up to their equipment (that is operable) using a temporary modification. We call it a temp-mod for short. If their equipment is not operable then get operating equipment in there and hook up to vents and drains on the piping system to get a flowpath. I would rather flood the place with borated water than overheat the core and spent fuel pool. I know the doserates are high but to get the situation under control as soon as possible is the desire.

When it comes to Nuclear don’t be afraid to ask for help from experts. Pride can be recovered later, if needed. If they can hook up power to the equipment now, don’t know why they did not buy a portable generator and drop it outside the door and run the cables inside to the bus or motors. Even if you have to bypass the breakers and control switches in the control room. Get the pumps up and running.

I agree with Damen Matson.
Give me some cutters, butt-splices, cable, radio and a portable generator. Call me on the radio and tell me when you want the pump on. I will power it up till you tell me to turn it off. Many valves have manual operators so controlling flowrate can be done locally.


William, becquerels are not really counts per second. They are a measure of atomic decays per second, whether or not they are detected – of course, mostly they are not. By contrast counts from a detector – often in “counts per minute” – depend on the protocol used, the nature of the sample, the type of detector, etc. To go beteen the two requires a great deal of careful figuring of what gets detected from any given sample.


If you want to avoid radiation, where should you go? Either of Tokyo’s International airports would be a good start. And I mean from almost anywhere in the world. From there moving to some spots closer to the nuclear plants would reduce the natural background even further and therefore your radiation exposure. Japan has lower natural background than most other places. In some cases much lower. Now getting there would increase your yearly dose, by quite a bit, if you fly there.

and here is radiological map of Japan by Prefecture. They don’t show readings for Fukushima and Miaygi where I know they have readings and they haven’t all week. Ibaraki has a high reading. 2040 nanoGrays/hr. This is about 10 times the world average background. They are using Grays instead of Sieverts and nano vs. the regularly used micro. Sieverts are just Grays converted by the type of radiation into an equivalent dose. At this level of general information, not important. Will be slightly higer in Sieverts.


Joffan, on 21 March 2011 at 8:10 AM said:
“William, becquerels are not really counts per second.”

Yeah, I new that. I was trying to keep it simple, and allude to the complexities by my comment on geometries and standard methodologies, but I stand corrected.



I con not find the link but the document you can probably be found by Looking for my posts on the 18th.

There is a report on loss of water accidents in spent fuel pools of decomissioned reactors. I think the date was Oct 2000.

Basically is said IF the fuel rods get crushed IF there is no boron IF non borated water is then put in the pool then the fuel MIGHT be in a configuration for new criticality. They also say that the only kind of pools where this might happen are low density storage pools. They also say that MOX has not been evaluated.

I believe that all of the pools at Fukushima I are high density storage pools with boron inserts in the racks and TEPCO has prieviously said they were borating the water, there might, at the begininning of the accident been a time where they were contiplating using non borated water if they ran out of boron.

So at one point the chance or recriticality might not have been zero but still vanishingly small.



Yes, that jogs my memory and I remember basically the same thing. Thought it odd that low density pools had a greater risk, but the lack of a neutron absorber explains that. High density pools could become critical under normal operation, so they have to have a neutron absorber.


It has been night here in Australia so I have only just read comments earlier worrying about the levels of radiocativity found in milk and spinach. It was dealt with yesterday in some detail, with references, if you scroll back through the thread.
In precis, the Japanesestated that the levels found meant you would have to drink a regular amount of milk 9500ml?0 per day for a year to get the same dose as from a CAT scan and that the health risks to humans were negligible.
“Edano said the level of radiation from the average yearly consumption of the milk in question would be the equivalent of a single CT scan, and around a fifth of this amount in the case of the spinach.”

Saturday, March 19, 2011 17:39 +0900 (JST)


Back, it seems they are claiming the hydrogen explosion on unit 4 was due to spent fuel alone. Thats the story and it sticks until all the facts come out I guess.


Mrs. Perps, I have to ask a question. Did anything I posted offend you last night? I was trying very hard since I started posting here to not cause a mass hysteria problem….


Just to correct my previous comment, I don’t think high density spent fuel ponds without a neutron absorber would become critical. They would become subcritical. I don’t think the density would support criticallity, but I haven’t read anything to support or disprove this view, so it is just my best guess.


we have a ten minutes interval reading of radiation in two (actually three, but the data for the third one, Daigo, is now suspended) towns in Ibaraki prefecture
if you look at the table in the central part of the document, you can see on the first column the time, on the second the readings for Kitaibaraki, on the third the ones for Takahagi, both about a hundered kilometers SW from Fukushima plant (see the map here )

the readings for daigo are missing, and I don’t know enough japanese to understand the reason.

I cannot find any abnormal reading, or anything less than very far from threatening human health.

I found those data on a blog mended by an italian living in Tokyo, I’ll watch sometimes to find more data.


There is a new IAEA report out. They have added stable iodide doseages for evacuees depending on age. None for those over 40. They have added a table that seems derived from the JAIF reactor status reports, but has some slight inconsistances with them. The main one I could see is the JAIF report says they are injecting water into the SFP of unit 2 and IAEA says they are spraying like they are for units 3 and 4.

Click to access ENGNEWS01_1300624909P.pdf


here an address for the environmental readings for several different places in Japan, and for different fields (air, drinking water and fallout).

it’s late here, going to sleep. have you alla a good rest, or a good work, depends on where you live…


@ Chris Warren
You neglect to ment ion that the report also said this:
“The Health Ministry said that radioactive iodine three times the normal level was detected in Iitate, a town of about 6,000 people 19 miles northwest of the Fukushima Daiichi nuclear plant, the Associated Press reported. That is one-twenty-sixth of the level of a chest X-ray and poses no danger to humans, a ministry official told the AP.”
Are you deliberately trying to make people more fearful than they need to be? If so what is your agenda here?


Has anyone ever modeled the mechanical effect of hydrogen explosions on spent fuel pool depth?

In other words, how much water would be lost from the spent fuel pool simply by the explosive effects of a hydrodgen explosion at the top of the pool?


The chart you refer to indicates readings under 100micro sieverts and this is less than you would get(600 micro sieverts) from a stomach x-ray.(Check the chart on the “Why I stay in Tokyo” post)
Are you tyring to frighten people here? If so what is your agenda?


Ms. Perps

I don’t think that just refering to data can be seen as trying to scare people. Unwarrented extraplolation, yes. Lots of people refering to information here, to reasure people. The data is to be used in an arguement. Those numbers are per hr, so if long enough in that field, then a legitament arguement could be made for health effects. Not likely they are letting anyone stay there. Question is if this is a general level for the area or a high spot. Remaining indoors if those are the readings outside would definitely be advisable.


@Ms. Perps
Definitely not trying to scare anyone. Was interested in any explanations as to why those sites were such an anomaly, and if people had been evacuated from there (you would hope so). The associated map shows the exclusion zone as a pure circle, with that area falling outside even the ‘stay inside’ zone. I’m familiar with what a 100 uSv/hr dose means, but it adds up to a bit over time if people in that area have not been given the ‘stay inside’ notice


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