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Fukushima Nuclear Accident – Monday 21 March update

It’s not yet time for the period of reflection and introspection on the Fukushima Daiichi crisis, but we’re getting there. Even the U.S. says the worst seems to be over. The IAEA and World Nuclear News have both released new updates on the situation (the IAEA report being particularly comprehensive this time, unlike some of their earlier sparse prose). Steve Darden at Seeker Blog has done an excellent job at extracting the key snippets of information, and so I reproduce his efforts below:

Offsite grid power has been brought to the Daiichi site, and is in the process of connection to each reactors equipment.

Restoration of Grid

Progress has been achieved in restoring external power to the nuclear power plant, although it remains uncertain when full power will be available to all reactors. Off-site electrical power has been connected to an auxiliary transformer and distribution panels at Unit 2. Work continues toward energizing specific equipment within Unit 2.

Here’s an excerpt on radiation measurements:

Radiation levels near Fukushima Daiichi and beyond have elevated since the reactor damage began. However, dose rates in Tokyo and other areas outside the 30-kilometre zone remain below levels which would require any protective action. In other words they are not dangerous to human health.

At the MIT Nuclear Science and Engineering site, the 20 March status update is encouraging. Included in the report was a note on the actual tsunami heights at the reactor sites:

The Fukushima power plants were required by regulators to withstand a certain height of tsunami. At the Daiichi plant the design basis was 5.7 metres and at Daini this was 5.2 metres.

Tepco has now released tentative assessments of the scale of the tsunami putting it at over 10 metres at Daiichi and over 12 metres at Dainii.

In the associated WNN report, is the following IAEA graph of unit 5, 6 fuel pond temperatures.

At units 1 and 2, external power has been restored. Tokyo Electric Power Company (Tepco) said it would restore functions in the central control room shared by the units so that accurate readings could again be taken from the reactor system. Next, workers will check the condition of the water supply systems to the reactor and the used fuel pond. With luck these will be able to go back into operation as they had been immediately after the earthquake on 11 March.

External power for units 3 and 4 should be in place ‘in a few days’ time’, said Tepco.

(…) Despite contradictory comments by the US Nuclear Regulatory Commission to US politicians and media, most observers in nuclear industry and regulation consider the measures taken by Japanese authorities to be prudent and appropriate.

Some other points, from NHK news reports:

・TEPCO planned an operation to release air containing radioactive nuclidesinside the containment vessel at unit-3, give a situation of pressure increaseinside the containment in this morning . However, TEPCO decided not to releaseit since the pressure becomes stable later.

・Ministry of Defense performed activity of measuring surface temperature ateach of unit 1,2,3 and 4 from the sky using Helicopter to evaluate the effect ofthe operation of filling the pool with water from the ground today and yesterday.Ministry of Defense expressed the opinion that surface temperature of each unitseems to be 100 degree Celsius or below.

Some other interesting reads from the last day or two:

1. Dan Yurman from Idaho Samizdat reviews the last weeks’ events, and asks some pointed questions about NRC Head Jaczko’s sources of information:

What remains to be known is how much distrust and incomplete information played a role in what has turned out to look like a decision that didn’t have to be made in time for a congressional hearing. Yes, that’s hindsight, but these questions deserve answers and soon.

2. Rod Adams from Atomic Insights has a lot more details on the possibility (or lack thereof) of a zirconium fire in the spent fuel ponds. His bottom line:

Despite all previous word, a fire in any used fuel pool is a fantasy that will only occur in a simplified model. It is not a concern in the real world of water, metal and ceramics. (Note: I struggled with whether or not I should waffle and couch that statement with “in my opinion”, but decided against it. Please feel free to conduct experiments that would prove me wrong.)

3. Charles Barton from Nuclear Green looks at some lessons from Daiichi:

If the Dai-ichi crisis fails to teach us the importance of moving forward on the implementation of a more advanced and safer nuclear technology, it would be a tragedy.

In the coming weeks, I will also be dissecting this new lesson of history on BraveNewClimate. But I want to wait a little longer yet — at least until all those units are in cold shutdown and the spent fuel pools are lukewarm once again!

The the Japan Atomic Industrial Forum has provided their 19th reactor-by-reactor status update (10:00 March 21):


Finally, here is the latest FEPC status report:


  • Radiation Levels
    • At 07:00PM (JST) on March 20, radiation level outside main office building (approximately 1,640 feet from Unit 2 reactor building) of Fukushima Daiichi Nuclear Power Station: 2,623 micro Sv/hour.
    • Measurement results of ambient dose rate around Fukushima Nuclear Power Station announced at 4:00PM and 7:00PM on March 20 are shown in the attached two PDF files respectively.
    • 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
    • At 3:00PM on March 20, pressure inside the reactor core: 0.187MPa.
    • At 3:00PM on March 20, water level inside the reactor core: 1.7 meters below the top of the fuel rods.
    • At 3:00PM on March 20, pressure inside the primary containment vessel: 0.17MPaabs.
    • As of 6:00PM on March 20, the injection of seawater continues into the reactor core.
    • As of 7:00PM on March 20, activities for recovering the external power supply are underway.
  • Fukushima Daiichi Unit 2 reactor
    • At 3:00PM on March 20, pressure inside the reactor core: -0.016MPa.
    • At 3:00PM on March 20, water level inside the reactor core: 1.4 meters below the top of the fuel rods.
    • At 3:00PM on March 20, pressure inside the primary containment vessel: 0.125MPaabs.
    • At 3:05PM on March 20, injection of seawater into the spent fuel storage pool has begun, until 5:20PM (total about 40 tons)
    • As of 3:46PM on March 20, the distribution board began to receive the external power.
    • As of 6:00PM on March 20, the injection of seawater continues into the reactor core.
  • Fukushima Daiichi Unit 3 reactor
    • At 4:00PM on March 20, pressure inside the reactor core: 0.119MPa.
    • At 4:00PM on March 20, water level inside the reactor core: 1.65 meters below the top of the fuel rods.
    • At 4:00PM on March 20, pressure inside the primary containment vessel: 0.290MPaabs.
    • As of 6:00PM on March 20, the injection of seawater continues into the reactor core.
    • As of 7:00PM on March 20, about 2,605 tons of water in total has been shot to the spent fuel storage pool.
    • As of 7:00PM on March 20, activities for recovering the external power supply are underway.
  • Fukushima Daiichi Unit 4 reactor
    • At 8:20AM on March 20, 10 Self Defense Force vehicles began to shoot water aimed at the spent fuel pool, until 9:29AM.
    • As of 7:00PM on March 20, about 83 tons of water in total has been shot to the spent fuel storage pool.
    • As of 7:00PM on March 20, activities for recovering the external power supply are underway.
  • Fukushima Daiichi Unit 5 reactor
    • At 2:30PM on March 20: cold shutdown
    • At 4:00PM on March 20, the temperature of the spent fuel pool was measured at   95.2 degrees Fahrenheit.
  • Fukushima Daiichi Unit 6 reactor
    • At 10:14PM on March 19, ump for Residual Heat Removal (RHR) started up and cooling of spent fuel storage pool has started.
    • At 4:00PM on March 20, the temperature of the spent fuel pool was measured at   82.4 degrees Fahrenheit.
  • Fukushima Daiichi Common Spent Fuel Pool
    • At 09:00AM on March 19, the temperature of the spent fuel pool was measured at 134.6 degrees Fahrenheit.

Our official sources are:

  • Office of The Prime Minister of Japan
  • Nuclear and Industrial Safety Agency (NISA)
  • Tokyo Electric Power Company (TEPCO) Press Releases
  • Ministry of Education, Culture, Sports, Science and Technology (MEXT)

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.

213 replies on “Fukushima Nuclear Accident – Monday 21 March update”

@bks: Bill Borchardt, Operation Executive Director of the US NRC is currently updating the US Senate. He stated that they believe the situation at units 1, 2 and 3 has been stabilized. He also said that they do not know the source of the grey smoke from Unit 3; however, there has been no increase in temperature or radiation readings. I’m no expert, but I take that to mean the smoke may be from something mechanical rather than nuclear?



First time to post. Fantastic job of providing very level-headed commentary and common sense.

First off, I’m in Huntsville, Alabama, USA. Live 20 miles downwind from Browns Ferry Nuclear Plant. So, I have more than a passing concern about nuclear safety.

The question has been raised about the safety of nuclear plants and what we need to do in the wake of the Sendai Disaster. The Enviro-nazis will scream “Shut them all down”. The shills for the nuclear industry will say “Nothing bad happened.”

What does common sense say?

Japan suffered two, TWO, once-in-a-hundred-year natural disasters within 45 minutes of each other. Both of these disasters exceeded the worst case scenario designs of the nuclear power plants in question. Although the damage to the area is devastating, the nuclear plants survived with enough system integrity to allow the workers to shut down the reactors and engage (with extreme difficulty, admittedly) the emergency systems to insure that a deadly/very harmful release of radiation to the general public did not occur.
We should first praise the designers of these facilities for their excellent job.

But, there are still major problems to be addressed. As you have well documented, the backup emergency systems were not “hardened” in order to survive the disaster. This is a fantastic opportunity for “lessons learned”. THAT should be the focus of the investigation of the disaster, and how to apply those lessons in the future.

We have been driving automobiles for a hundred years now. Who would like to see all of the vehicles still providing the safety systems available in 1971? No front air-bags, no side air bags, no designed-in crumple zones, no anti-lock brakes, no widespread availability of shoulder harnesses, no radial tires, no traction control, no padded dashboards, no collapsible steering columns, no halogen headlights, very primitive tempered glass, no collapsible bumpers… the list goes on and on. But we still manufacture automobiles in ever increasing numbers. And drive them in ever increasing numbers.

Let us take this opportunity to re-examine the designs of our nuclear power plants. And instead of trying to kill or limit their use, use this opportunity to make them safer, learn the lesson of Sendai and expand the use of nuclear power.


In discussing design changes one topic I hear discussed a bit, but not that much is the location of the storage ponds outside the secondary containment. This apparently is not the case in later designs, and would seem to be a flaw in the light of the current situation. Don’t know how difficult it would be to provide some protection for the storage ponds, but I imagine this may become a requirement.


Interesting how that later correction – “water only to be used in the concrete pump” changes the context :-)

The CNN article also says this:

“That meant that power could now be funneled to all six of the plant’s reactors for its cooling systems. But electricity was still not moving to units No. 1 through No. 4, because the quake and tsunami had damaged numerous pumps and other gear…

A Tokyo Electric official said that spare parts were being brought in, so that everything could work again.”

Which answers the question as to “how long it’s taking” to get power restored. That implies quite a bit of needed reconstruction, as was also speculated here in the commentary.


@David Lewis
“Computer simulation done in US national labs means nothing to Rod. A computer simulation done by a US national lab is the best assessment we’ve got and they say what can happen if a pool doesn’t have water in it and even if it is only partially full, is a propagating zirconium fire.”

Didn’t this simulation that you speak of, “Spent Fuel Heatup Following Loss of Water During Storage,” conducted at SNL and previously posted by others, show the only credible scenario to be blockage of convective cooling via low water level?

Meaning that hot fuel in the assembly could cool its self without bursting into flames given air could flow over the assembly unimpeded.

Here is the link again if someone wants to read the whole report.


@bks: I did not hear him state the worst was over, but I did not hear his entire testimony. From what I did see, he did not seem overly concerned.

Also, I should point out that I misread the screen on C-SPAN this morning. He was addressing the NRC, not the US Senate. C-SPAN has not yet posted the video on their website, but they do state it will be available shortly. If you wish to see it, you may want to monitor


Has anyone seen this photo of reactor 3?

I don’t know how the cooling pond is still intact? It looks like the top half of the pool must be heavily damaged and the reminder full of debris.


The idea of using a conctrete pump originates from this post. DrD if i recall correctly. The one who passed it on to Tepco, … some nutcase. Who would ever do that?

The best invention i ever made was the part time idiot in my own head. The greatest discovery i ever made was to find out everybody has one. The difference is, i know. Its been paying off ever since.

If that concrete pump’s deployment makes one bit difference, i’ve done more for this situation than most of you. By being nuts!

Moderate that.


Latest JAIF reactor status report has been out for a while. The only significant difference I can see between the last 2 reports is that they have changed the Pressure of the Reactor Pressure Vessel item from stable to unknown for unit 3. Maybe instrunentation problem? Radiation levels basically the same at West gate and North of service building. Ok west gate is old reading, so no information on change there.

I do find the map of Japan interesting at the bottom of the report. The coloured area off the west coast seems to indicate the area affected by the tsunami. There are 14 reactors in this area. Three were operating at Fukushima Dai-ichi and 4 at Fukushima Dai-ni. Three of the reactors at Dai-ni have been given an INES rating of level 3. Still don’t understand that rating when that is the same rating they are giving Fukushima Dai-ichi unit 4 where the building was blown apart and there is a serious problem with the SFP. Anyway, the same report lists all units operating at Onagawa Nuclear Power Station at the time of the quake and the 1 unit at Tokai Dai-ni (unit 2, so the othe probably decommission, but I don’t know this for sure). The tusnami hit all these NPS, but only Fukushima Dai-ichi had real problems. Onagawa NPS is particularly interesting as it is much closer to the quake/tsunami source. Why did it have no problems. Design, tsunami height, luck? It will be interesting to see what a full analysis will bring out.


It has been dicussed on this site that the trucks could not get close enough. What was not clear is that this is not a radiation problem. Radiation comes in two varieties: on its own or travelling on a particle. As far as the particles are concerned it really doesnt matter where you stand. They travel up, down, around corners, you name it. Radiation on its own doesnt. It travels in a sraight line, like light. You can hide for it.

The trucks had to keep distance on account of ballistics. If you pump that much water at that much pressure at close range, you create a fountain that wavers of before it hits anything.

The idea of the concrete pump was absolutely brilliant. Knowing that both fire fighters and nuclear specialists are human and humans are generally specialists, i realised they might not be able to think that far out of the box. So i contacted Tepco. So what if they think i’m a fool? If there is a remote chance they dont, this will help. Real on the spot help.

I used to work for a volunteer fire chief. Nasty pyromaniac little bugger, but his knew his stuff and he loved talking about it. I also did my odd bit of concrete pouring. I know what those pumps can or can not do.

I though finding that kind of stuff was what you were all talking about. That and putting ppl at ease.



While it is true that gamma radiation travels in a straight line, a gamma ray can interact with an atom and reflect off of it, changing its travel path at a reduced energy. Thus, gammas can scatter and travel around corners, or over shield walls.


Try think of Gamma as light. Imagine you are hiding behind a shield that holds Gamma, and then look at how much comes around the corner compared to how much doesnt. Do you see what it depends on?

It is my lucky guess it works that way.Gamma coming around corners or not, i’d duck.



I am very familiar with the way gammas scatter, as I have performed many calculations to determine their effect compared to the direct radiation level contribution. If you have no shielding, their contribution is very small. However, if the direct route is very shielded, then the contribution of the scattered radiation can be the main source of radiation at some locations. When you are trying to develop the shielding for a very intense source, effectively shielding the scattered radiation can be a challenge.


Correct me if i’m wrong, but doesnt it still get significantly higher in front of the shield than behind it? Or is there actually some kind of Gamma Turbulence effect, like over a stalling wing. I’ve got a hard time visualising a Gamma radiation as almost particle.


William Fairholm, quite right to ask questions about JAIF report on Unit 3. If someone in my group turned in reports like that I would give them one warning and on the second offense they’d be on the street looking for a new job.



Don’t know if it has been reported here, but the smoke from the reactors has stopped.

and they have released a survey of the plant for various radioactive materials and only iodine 131 was above limits for workers without protective masks.

Doesn’t say where these measurements were made and whether these were maximum or average readings. I assume they were made were the workers are most in danger from these radioactive materials.

The smoke from reactor 3 appears to be coming from the SFP.

Smoke has also been seen coming from a crack in the roof of unit 2. The secondary containment of that reactor was not completely destroyed and so this is not directly from the reactor primary containment as that would be very radioactive and there has not been an associated spike in radioactivity that I have seen reported. In other words, source of the smoke unknown.


Thanks for the home work. This is whole lot harder to visualise for me. If i understand it correctly, behind the wall is far from safe, but ducking would still be a smart move right? Or am i missing it? Gamma does not reflect on particles the way light does on dust or smoke.


The physics of the scattering is different for gamma rays and light, but they are both photons. Those designated gamma rays just have a lot more energy than light photons, and thinking of them scattering as light off of smoke or dust is probably not a bad analogy. Certainly, if there is shielding between you and a radiation source, you are better off behind it than not. Its just that it may not protect you from all the radiation.


??? Its the obstacle that causes the reflective pattern that leads to local consentrations behind the obstacle, higher than there would be if there wasn’t any obstacle???
Am i getting this right?


No; if you look at the example in the link above, you see that there is a wall between the source and the point of interest. The “skyshine” (scattered) radiation is interacting with the atoms in the atmosphere and scattering over the wall. For instance, a gamma ray could travel up above the wall, then reflect off an atom in the atmosphere, and back down to earth. Kinda like a bank shot in pool, where you want to hit one ball that is behind several others that you don’t want to hit.



Great ) Its not the easiest thing to understand. When you get down to that level, there are times when particles act like waves, and waves act like particles.


Thats the beauty of it, isn’t it? Everything changes at that level You’d still expect to see a something, but what you find is almost like a… like a doing. The only way i can grasp it is as space being busy.


Please put your comments in the correct thread. We have let some on radioactivity stay on the Fukushima update thread as they may be of interest to those reading that thread. However you are straying into mere comment and should post these on the Fukushima Open Thread. Further out of place posts will be deleted and you will be asked to re-submit on the correct thread.


I have found a possible explaination about how the SFP loss some of their water. The seals at the gate between the SFP and the reactor are filled with air which is maintain under pressure by electrical pumps. These pumps would have stopped when the station loss powere. All the SFP would have been effected and then the rest could have been lost by evaporation. There may have been other leaks specific to each SFP, but this is a problem all of them would have faced.

Go down to: “Possible Source of Leaks at Spent Fuel Pools at Fukushima”


The same site has a possible explaination how an uncontolled hydrogen release could have occured from the primary containment to the reactor building. A test was done on a prototype containment design where they tried to increase pressure to 71 psi, but could not get beyond 70 since the containment started to leak. They tightened the bolts to reduce the leak, but pressure test on reactors were never done above the design limit of 62 psi. Wheter this is the way hydrogen got into reactor building will have to be carefully analysed.

Go down to: “How Hydrogen May Have Gotten from Primary Containment into the Reactor Building”


A lot of nth hand (and frequently mis-translated) information seems to be arriving here very distorted and taking a long time to be decoded.

The example of the concrete pumping machine springs to mind. Since I have been reading this blog daily I had already seen linked pictures of such a machine and read the discussion about its advantages in the delivery of water to elevated SFPs.

It was obvious to me that the CNN report posted by Professor Brook had somehow got hold of the wrong end of the stick and that the purpose of the machine was pinpoint delivery of water at height.

There were 4 hours of confusion before bchtd1parrot sorted it.

General ad hom: certain people here seem like strong noise generators.


nkinnear at 4:19 AM on 3/22: “Certainly, if there is shielding between you and a radiation source, you are better off behind it than not. Its just that it may not protect you from all the radiation.”

It is still similar to light, right? Imagine a dark room, a light ON, you behind the shield trying to protect you from the light. Light still reaches you, you suddenly can see your skin etc. Even the back side of the shield is suddenly visible…


This is different information then available elsewhere:

“Monday, March, 21, 12:30 p.m. ET, Tokyo

Nuclear Industry and Safety Agency (NISA) press conference: 1,137 tons of sea water was poured into the storage pool of unit 3, and about 90 tons of tank water (not sea water) was poured into the storage pool of unit 4. ”

All other reports I’ve seen have said they have been spraying seawater into units 3 and 4 SFPs and they have injected seawater into unit 2 SFP. A discrepancy and would make recovery of SFP 4 to normal operation easier, I guess, but there is a lot of damage in these buildings.


[comment deleted as off-topic. Please re-submit on the correct thread – Fukushima Open Thread. Thank you.


I noticed a mention of the 60 Minutes interview with Julia Nesheiwat. She is a former military intelligence officer currently employed by the State Department. It is possible that she or someone like her with appropriate clearances is the liaison between our High Res. IR Satellites and other classified data and TEPCO or Japanese Government.


IIRC, isn’t the crane for the rods only about half way up the “box” portion of the building? That would imply that a majority of the reactor vessel is underground? And therefore the Hank Roberts/David photo looks worse that it reall is, in that the pool is below the “halfway” point of the structure height, yes?


My point being that the majority of the building that we can see is actually open space allowing for the crane to move around to remove rods, the “lid” of the RV, etc…


For the past week, spent fuel ponds and the consequences of loss of water from them have been hot topics of speculation. In particular, there have been two questions lurking:
1. How is hydrogen gas generated by spent fuel rods in SFP’s that have some or all of their water lost?
2. If a SPF pond looses all its water, can the spent fuel rods catch fire and release some of the radioactive elements inside them? There is a video of a hollow zirconium rod being heated red hot by a blow torch, but it does not appear to catch fire.

I am a chemical engineer but without any nuclear reactor experience. I have read a fair amount of information and technical reports on spent fuel rods that I will try to summarize here. I welcome any corrections or improvements.

First a description of fuel rods and assemblies in old GE BWR/3 plants: A fuel rod is 0.563” OD by 144” long. The rods consist of stacks of cylindrical ceramic pellets of UO2 0.5” dia by 0.5” long. These UO2 pellets are encapsulated by a Zircaloy metal cladding 0.032” thick. The ceramic pellets are sealed inside the Zircaloy.

There are 49 fuel rods in a fuel assembly package 7×7. The rods have a center to center spacing of 0.738” or a gap of 0.175”. There is about 40 kg of zirconium total in the fuel rod assembly. In a SFP, the fuel assemblies are put in vertically with their tops about 13 ft from the bottom and covered by a further 16 to 26 ft of water.

Zircaloy is almost pure zirconium – ~95% zirconium Zr, 1.5% tin Sn, 0.12% iron Fe, 0.10% chromium Cr, and 0.05% nickel Ni. The Zircaloy thus has the properties of zirconium MWt 40: 6.5 g/cm3, 1855C MP and 4409C BP. When zirconium is oxidized by either O2 or H2O, ZrO2 is formed. ZrO2 is solid, ceramic like material with a 2715C MP. ZrO2 solids crack upon cooling from high temperatures.

The zirconium oxidation equations are:

Zr(s) + 2 H2O(g) => ZrO2(s) + 2 H2(g) exothermic heat liberated 5.8 E5 kJ/kg Zr reacted and 0.044 kg of H2 is formed per kg of zirconium reacted

Zr(s) + O2(g) => ZrO2(s) exothermic heat liberated 1.2 E4 kJ/kg Zr reacted

These reactions are rapid at temperatures above 1000C . It is important to realize that these reactions take place at the zirconium metal surface (not in the vapor phase as hydrocarbon or carbonaceous ordinary fires do) & there is no flame. The rate of reaction is controlled by the amount of O2 or H2O that can reach the metal surface. After Zr oxidation, a thin film of ZrO2 is formed on the zirconium surface which acts as a barrier to O2 or H2O from reaching unreacted zirconium.

With this information, we can try to answer the two questions.
Q1 how is H2 generated in SFP’s that have lost water? The answer is that for H2 generation, the spent fuel ponds must have boiled away (or leaked/lost) the water covering some of the fuel assemblies but all the water must not be evaporated! Only Zr reaction with steam H2O(g) can make H2. Zr reaction with O2 cannot make H2. If the fuel assemblies are ½ uncovered, the top half can be hot enough to react with steam by not cooled by water. The bottom half is still submerged in boiling water, which as it evaporates forms the steam to react with the portion of the fuel assemblies above the water line.

Q2 Can the spent fuel rods catch fire, if dry, with no water & hot and exposed to air. The answer is no, not in the ordinary sense that we think about fires, with flames and combustion of hydrocarbon like material in the vapor phase being fed by convective air. Oxidation takes place at the zirconium metal surface by O2 diffusion which is slowed down by a film of ZrO2.

However, over time, the oxidation of Zr (first by H2O) and O2 forms ZrO2. This film can be flaked away, or sloughed off exposing more fresh Zr. Remember that the Zr metal layer is only 0.032” thick. As the U2O and radioactive elements inside the Zircaloy cladding is heated to high temperatures by the exothermic oxidation reactions and by radioactive decay, the radioactive gases pressures inside the cladding will balloon out the cladding and can rupture it. The soft ZrO2 film can be pushed and flake away exposing the radioactive UO2 pellets.


It is my understanding that BWR fuel rods are designed as pressure vessels in that they are filled with 3 bar of He gas. This improves heat transfer between the ceramic fuel and the Zircalloy cladding. Exposure to fission products and flux significantly changes the mechanical properties of the fuel and the zircalloy. Exposure to higher than design temperatures in the reactor or spent fuel pools takes the rods well beyond of design parameters.

The question of condition of the fuel rods in the spent fuel pools will only be answered by direct examination some days from now.


Hi guys, I have a quick question: Here is an official overview of radiation in Tokyo: Is this only excess radiation or does this include the normal day-to-day background radiation? I would assume so as there are values before March 11th, however these values appear massively small, e.g. 0.88 microsievert for an entire day — isn’t that really low?



From this {Monday] morning’s NYT:

“Hundreds of employees from the Tokyo Electric Power Company, which owns the disabled Fukushima Daiichi Nuclear Power Station, worked through the weekend to connect a mile-long high-voltage transmission line to Reactor No. 2 in hopes of restarting a cooling system that would help bring down the temperature in the reactor and spent fuel pool.

After connecting the transmission line on Sunday, engineers found on Monday that they still did not have enough power to fully run the systems that control the temperature and pressure in the building that houses the reactor, officials from the Japanese nuclear safety agency said.”

Someone on another blog requests clarification. Anybody?


The world average background is about 0.27 microsieverts/hr. Japan has abnormally low natural background. 3-6 times less than world average from what I’ve seen. So 0.88 may be 10 times what was there before, but still only three times higher than world average, and some places in the world have 400 times or more higher than the world average, naturally. 0.88 microsieverts/hr. is of no concern. They are actually measuring in micrograys, so actually sieverts would be slightly higher. If you want to find out more about natural background, go to wikipedia or some other source.


@Leo Hansen

That is very good information, certainly improves my understanding of the Zr ‘fire’ issue.

What does the introduction of seawater, with all of its ionic content, or boric acid do to the equation? Would it affect the passivation process, speed up or slow down the reaction, and what could be the source of the grey smoke?
Your expertise is much appreciated.


Not sure about the background calcs there William. My understanding is that typical natural background is around 2-3mSv per year which would equate to 5-9 μSv/day and 0.2 – 0.35 μSv/hr . So yes, 0.88 μSv per day would be very low.


Evening David,

All I can say is wait for the final word (real life, unfortunate data) on the zirc water reactions in the spent fuel pools… I have struggled with that event explaination for unit 4 since the start.

Most things I have seen require the fuel to still be critical after or just prior to a complete loss of coolant to generate the intitial temperatures to acheive the self sustaining generation of hydrogen from the cladding.

Units 1 & 2 fit this description. I withhold judgement on unit 4 until all the facts are released….

I still believe all the hydrogen explosions came from primary containment vents via the secondary contaiment paths, or possibly secondary plant hydrogen sources (generator venting operations).


@Matt L

I don’t know the effect seawater and its ions etc would do. Ditto on the grey smoke.

However, liq seawater hitting hot fuel rods which have a ZrO2 film would quickly and violently vaporize. This may blow off any ZrO2 film and expose fresh Zr to further oxidation. Seawater salts would be deposited on rod surfaces and may help protect them, but that’s speculation.


” the IAEA radiation monitoring team took measurements at distances from 56 to 200 km from the Fukushima nuclear power plant. At two locations in Fukushima Prefecture gamma dose rate and beta-gamma contamination measurements have been repeated. These measurements showed high beta-gamma contamination levels. Measurements by the IAEA and the Japanese authorities were taken at the same time and locations. The Japanese and independent IAEA measurements gave comparable results.”
I’m curious of the take on this IAEA quote from today’s report. its the first time they’ve used the terms high beta gamma contamination levels.


Remember we are talking self sustaining zirc water reaction producing hydrogen…. Not cladding failure and fission product gass or worse fuel pellet release… Cladding failure occurs at much lower temperatures as we have seen occur with this event based on the radiation release rates.

I have no doubt there was zirc water reaction that occurred in the operating cores following the station blackout (loss of power) and their associated explosions in the reactor buildings due to vent operations and system leakage.

But I am still not 100 % convinced about unit 4 due to the spent fuel pool, even with a full core off load recently done. All data I have seen was it was offloaded more than a week prior and cooled adequately prior to the event.

I have not seen a positive confirmation that fuel pool level was lost enough to create the exposed clad steam environment required either for unit 4.

This data will ultimately come out and all should learn from it… either way….


M. Elliot,

I think the IAEA considers 160 μSv/hr as a very high level, as do I. Not immediately dangerous, but if you remained in that area, you would be getting several times natural background each day. If you are inside you would reduce exposure by up to ten times depending on the structure. This is a spot measurement. If there were anyone living near there, they would remove them.


Sorry William, you are quite right that our per-hour figures agree. The Tokyo figure as the original post gave 0.88 μSv per day is very low.


I mean more than the yearly dose from natural background, each day.

160*24= 3860 μSv

Assume 2400 μSv as the natural background yearly dose. So a little less than double that. Not something they are going to subject people to, unless there is no choice.



I discounted that being a per day reading, and interpreted that as the reading for that day on a per hour basis. Now I see why he was saying 0.88 is very low. Impossibly low, which is why I reinterpreted it. Which is still low as an hourly rate.


Without further data, and unless some other source can be suggested, structural guys at my employer think the grey/dark smoke is almost certainly high temperature concrete failure.

An infra-red or false colour map of the buildings would be known and should be published.


I’m curious of the take on this IAEA quote from today’s report. its the first time they’ve used the terms high beta gamma contamination levels

They’re referring to the 0.855 MBq/m^2 ground activity measurement from surface contamination taken along road 50 some 28 km from Fukushima on Sunday 1525 JST.

This value (about 24 Ci/km^2) is higher than the Cs-137 contamination observed in some of the restricted areas around Chernobyl years after the accident and it accordinly exceeds values that would require evacuation.

However, those thresholds are extremely conservative, you would only expect some 3 mSv as an extra yearly dose when living in that area.

The activity will also come down by at least two orders of magnitude in a couple weeks when the most active radionuclides (I-131, I-132 and Te-132) decay.


Hydrogen and oxygen are continuously generated in spent fuel pools by radiolysis (the dissociation of water by radiation from the fuel rods). To prevent these gases from collecting in the reactor building, this area is normally ventilated. Of course, when there is no electricity to power the ventilation …

The French agency “Institut de Radioprotection et de Surete Nucleaire” concluded that the explosion in reactor 4 was due to hydrogen created by radiolysis. Many analysts appear to be assuming that the explosion means that the fuel rods in the pool were uncovered (the UCS/All Things Nuclear guys, perhaps even the NRC). They are apparently incorrect, as water was sighted in the reactor 4 pool from the helicopters involved in the initial water drop effort. See these links:


Has anyone noticed that official reactor parameter status updates started to include the temperature at unit 2’s spent fuel pool!

Check the last couple of updates here and within the first few pages of each pdf report you will see the table that includes this info:

Temp was 49C at 08:30 Monday and 50C at 14:25 Monday. Given that they seem to have mentioned pumping 40t of water into this particular fuel pool in recent days, I wonder what the temp was before they did this.


Oh and sorry that I didnt post this in the open discussion, but as it was status info for March 21st , I thought it was kind of on-topic, but maybe I made a mistake?


The wroding I assume came from TNYT that I quoted earlier today does not appear in the print edition I just finished reading.

Incidently, TNYT did commendably in that print article.


BTW, regarding sites 31, 32, and 33 with the anomalous high readings outside the 30km zone

(see here:

If my google map fu is correct, it looks like this place is a little valley, fairly high up the mountain range. (,140.754261&num=1&t=h&sll=37.760723,140.473356&sspn=0.282548,0.512238&ie=UTF8&ll=37.564718,140.789623&spn=0.072117,0.169086&z=13&iwloc=A
Nearest named feature is “Tsushima ES”)

Must not be getting the winds other places are getting, allowing things to accumulate.

Any news on whether this area has been evacuated? If so, mext really should show that on their maps.


Every time an original failure of this system, or a barrier to recovery in the failed system is mentioned, it just seems obvious to me that the major problem in Gen I, II, III, and likely IV is that the system analysis and its effective recovery depends on consideration of only single point failures. This is a complete disaster. This is a highly volative system, with huge consequences of failure (noting that design standards simply define prob of a radiiation leak ) and a more appropriate design methodology would involve standardised and unit specific what-if scenario’s, markov chain modelling , propoper employment of conditional probabilities in the system/ sub-system availabilities, and consideration of correlated internal and external events in the design, testing, compliance and certification. These reactors are not home heating systems and should instead face the kind of analysis reserved for rockets !


I don’t know the effect seawater and its ions etc would do. Ditto on the grey smoke.

However, liq seawater hitting hot fuel rods which have a ZrO2 film would quickly and violently vaporize. This may blow off any ZrO2 film and expose fresh Zr to further oxidation. Seawater salts would be deposited on rod surfaces and may help protect them, but that’s speculation.

Nitride formation in air and oxidation of U02 to U308 could become issues under dry conditions. The reaction in dry air is faster: it apparently has close to linear rather than quadratic kinetics, due to the formation of non-protective oxide (nitride) scales.

And this is all my speculation – but for that scenario to occur there would likely have to be a near total loss of water in the spent fuel pool, and this doesn’t seem to have been the case, given the still apparently limited releases of fission products and the non-observation of activated zirconium in the limited CTBCO and KEK data that I’ve seen (someone put up links on this blog, a while back).


(1) Prototypical experiments relating to air oxidation of Zircaloy-4 at high temperatures

Martin Steinbrück

Journal of Nuclear Materials
Volume 392, Issue 3, 1 August 2009, Pages 531-544

(2) Separate-effect tests on zirconium cladding degradation in air ingress situations

C. Durieza, Corresponding Author Contact Information, E-mail The Corresponding Author, M. Steinbrückb, D. Ohaic, T. Melegc, J. Birchleyd and T. Hasted

Nuclear Engineering and Design
Volume 239, Issue 2, February 2009, Pages 244-253


@ fusefiz: thank you for providing a plausible explanation for the hydrogen explosion in the spent fuel ponds! This fits perfectly with my model which says the fuel rods would not reach over 600 degrees C in any case when there’s a hole at the top to the outside air. Radiolysis occurs at room temperatures even, so that’s a highly plausible explanation.

Thanks again for suggesting this!


I’m confused about a possible contradiction with what we are presently told about unit 2 spend fuel pool. As I mentioned in a comment above, temperature readings from this pool have started to appear in official data as of Monday afternoon. But there are articles in the press today which mention an official called Hidehiko Nishiyama saying that unit 2 spent fuel pool may be around boiling point. I guess he is saying this because of steam in the area, but this raises questions about the data that has started appearing about this pools temperature.

An example of the boiling point story is:

One thing the official data does show is that the temp is slowly climbing, now up to 53C at 11.20am JST Tuesday.

News agencies such as Kyodo occasionally mention that seawater was pumped into number 2 spent fuel pool on Sunday.

I also note that IAEA are trying to get more info about the common fuel pool as reports yesterday indicated that some kind f water spraying operation was said to have taken place there. I seem to recall seeing info a fe days ago that suggested temps in this pool were 60something degrees.


BBC 11:45 GMT Tuesday:
No radiation release associated with the plumes of smoke. Levels remained constant.
Power cables now attached to all 6 reactors. Checking for integrity prior to switch on may take until Wednesday or later.


Steve Elbows,

Yes, I had noted and mentioned that here earlier. The boiling reference may have been for unit 3 SFP. That one has had the most problems given the amount ot water they have sprayed into it. Still don’t know if it is actually boiling. That would be serious. Note that they say injected seawater into unit 2 SFP. That means they have a more normal way of getting water into there. Concerning the common SFP. I would not be concerned. That is far enough from the reactors, that they shouldn’t have much problem dealing with it. I was concerned about it last week, when information was lacking and they only had 50 people at the reactor complex trying do deal with all the problems. That was stupid in my opinion.


“William Fairholm, on 22 March 2011 at 11:19 PM said:

and they only had 50 people at the reactor complex trying do deal with all the problems. That was stupid in my opinion.”

My own lay opinion on that was that with elevated levels of radiation they were concerned with running through their technicians, who would need to be permanently rotated out of the game, so to speak, as each was dosed up to near the 100mSv limit. I don’t think this issue has been discussed previously so I bring it up for comment by those who understand how this problem is managed.


But there are articles in the press today which mention an official called Hidehiko Nishiyama saying that unit 2 spent fuel pool may be around boiling point.

Nishiyama is the DD of NISA, a key nuclear safety agency official in the crisis, he does daily press conferences. I believe the only reasonable explanation for the Independent story is that they got their Tuesdays mixed up. Nishiyama had that concern on Tuesday LAST WEEK, March 15th , not today March 22nd.

Water spraying has not been done to reactor number 2, because there is no access from the outside of the reactor hall (refueling floor). The only blowout panel that has popped out is on the east side above the turbine hall and you cannot get any fire trucks there.

Seawater has been pumped to reactor 2 spent fuel pool through the fire fighting line (called “water injection”, whereas operations from the outside are called “water spray”). It’s possible this pumping is done with the reactor unit’s own Diesel-Driven Fire Pumps or with a fire truck. The actual work done would have involved reorienting the fire extinguishing system valves to feed the SFP. The fire fighting pipe system is a listed backup water source for the SFP (after the SFP make-up water line).


Interesting comment from the recent JAIF report 23 dated March 22 21:00

Click to access ENGNEWS01_1300795995P.pdf

“The operation to inject water to the spent fuel pool of Unit-4 was started with
special vehicle at 17:17. This vehicle has a long arm that enables to pour
water to a target. The spent fuel pools lost cooling function at Unit-3 and
Unit-4. The Self-Defense Force and Tokyo Fire Department have been
conducting operation of spraying water to fill these pools. (18:20, March 22)”

Note “special vehicle” and “pour” verses the term “spray” used previously. That might suggest the implementation of the cement truck idea to pour water.

There is a new report #24 listed on their linky page:

But that report #24 link is incorrect and links to #23.


I don’t know if you guys have seen the thermal images of the plants from yesterday.

Can you guys comment on this analysis from CNN?

KING:… Here to talk over the nuclear crisis Arnie Gundersen. He’s is a nuclear safety advocate who consults with the Vermont state government about the Vermont Yankee nuclear power plant.

Mr. Gundersen, thanks for coming back. I want to draw your attention to these infrared images that we have received. The Japanese government put them out. I want to start with reactor one. These are infrared images obviously taken from above.

You see here the casing in the reactor one building and you see the heat signature here, the yellow and red. In reactor one, the government says the Ministry of Defense says the highest temperature 58 degrees centigrade so about 136.4 Fahrenheit the government say, what does that image tell you?

ARNIE GUNDERSEN, NUCLEAR SAFETY ADVOCATE: I don’t believe the highest temperature is anywhere near that. It’s probably much nearer to thousands of degrees, but — what it does show me is you’ll see sort of like a line, a straight line of hot material.

I don’t know anything inside that nuclear containment that’s a straight line. It’s all curves. So it shows me that the geometry of the hot material is distorted.

KING: What is that — if it’s been distorted, what that mean is happening inside?

GUNDERSEN: It will be — it will be harder to cool it because it looks to me like the energy is not in the spot where it should be. Looks to me like it’s formed a long line and it’s not good, but I’m more concerned about some of the other reactor there.

KING: Well, let’s close this picture down and move it over. I want to bring up reactor two. Now we don’t see as red hot here in reactor two as we did in reactor one.

But the entire, you see heat in the entire building. This is where TEPCO has said there’s a possibility of a breach in the core self. What does this picture tell you?

GUNDERSEN: Well, in the words that go with that the Ministry of Defense says that the containment vessel is at 262 degrees and that’s 50 degrees above the boiling point of water. That’s the containment vessel that’s believed to have a crack in it.

So water cannot exist inside it because it’s at atmospheric pressure as a result of the crack. It tells me the suppression pool is likely dry, and that’s the one I would be most worried about, because it seems to me that what you’re seeing there is super heated air with no water in sight.

KING: So, super heated air, a possible breach. What are the risks of trying to going and contain this to get in close what you need to do?

GUNDERSEN: You know, the vessel at 262 degrees, if you spray water, the water won’t even get to the vessel. It will begin to vaporize even before it gets there according to the Ministry of Defense. That one is the — will be the toughest nut to crack out of the three of them. …


NHK reports that during the periods of grey smoke yesterday/today, site radiation levels spiked to nearly 3000milliSV and personnel were of course withdrawn. When the smoke went away, levels dropped somewhat.

I’ve just heard the BBC reporting Tepco are speculating the smoke might be from “oil” left by damaged equipment and that the very high rad levels are from a wind change.

I think the only real explanation is that the fuel is moving/settling as the structures are collapsing.

IIRC, the World Trade Centre Towers were discovered to have an expansion rate problem in the steel re-enforcement of the concrete.


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