The Fires in Spent Fuel Pool Number 4, Fukushima-Diiachi

The Japan Atomic Industry Forum at provides links to its “Reactor Status and Major Events Update – NPPs in Fukushima (Estimated by JAIF) March 2011″. Earliest date provided being Update Number 2, Tuesday March 15 2011 at 10.30 hours.

This status update states that Reactor 4 is “safe”. This report notes the evacuation zone is 20 kms from the NPP.

Status update 3 of 13:00 hours 15 March 2011 states that the evacuation zone is “Evacuation Area 20km from NPS * People who live between 20km to 30km from the Fukushima #1NPS are to stay indoors.”

The update reports also notes that “Remarks: Fire broke (out) on the 4th floor of the Unit-4 Reactor Building around 6AM and the radiation monitor readings increased outside of the building:
30mSv between Unit-2 and Unit-3, 400mSv beside Unit-3, 100mSv beside Unit-4 at 10:22.
It is estimated that the spent fuels stored in the spent fuel pit heated and hydrogen was generated from these fuels, resulting in the explosion. TEPCO later announced the fire had been extinguished.
Other staff and workers than 50 TEPCO employees, who are engaged in water injection operation, have been evacuated.”

It can be seen that the order for people to stay indoors in the defined area occurred after the fire commenced. The view was that that overheating fuel in spent fuel pools generated hydrogen resulting in the explosions. Of interest here is the explosion in reactor 4. Prior to the explosion, Reactor 4 building was intact. After the explosion it was not. The fuel overheated in spent fuel pool 4 and this is sufficient cause to generate hydrogen. This of course means that hydrogen generated within the spent fuel pool occurred regardless of events at reactor 3. The fuel rods in these two fuel pools was overheating and radiation levels outside both reactor buildings was high. JAIF ascribes this to the condition and environment of the spent fuel in both pools. However, it was number 4’s spent fuel pool which experienced fire.

What was burning is not specified. However the fuel is implicated, though no attempt is made to clarify exactly what was burning. The further implication is that fuel rods in the spent fuel pool of Reactor 4 were venting into the air. It is a logical progression from overheat, to explosion, to damaged containment and to the order for people with a defined zone to stay indoors.

The JAIF accident update of 15 March 2011 states that for reactor 4 “SFP level low, Injecting Water SFP Temp. Increasing SFP Temp. Increasing” The text is red flagged by JAIF.

The JAIF accident update of 16 March 2011 08:00 hours states in relation to reactor 4 : “SFP Level Low” red flagged text. The update further states :”Remarks A fire broke on the 4th floor of the Unit-4 Reactor Building around 6AM, Mar. 15, and the radiation monitor readings increased outside of the building: 30mSv between Unit-2 and Unit-3, 400mSv beside Unit-3, 100mSv beside Unit-4 at 10:22, Mar. 15.
It is estimated that spent fuels stored in the spent fuel pit heated and hydrogen was generated from these fuels, resulting in explosion. TEPCO later announced the fire had been extinguished. Another fire was observed at 5:45, Mar. 16, and then disappeared later. Other staff and workers than fifty TEPCO employees who are engaged in water injection operation have been evacuated. ”

IN none of the reports is it concretely stated that fires were composed of burning of fuel rods. However, the clear conclusion gained from reading the reports is that regardless of what was burning, the fuel rods were overheating, measured radiation showed an increase and radically changed procedures for people in a defined area around the NPP ie people had to stay indoors. The conclusion reasonably drawn from this is that there was immediate danger off site to people within a defined area.

The biggest danger to nuclear industry comes when an event has an immediate effect on civilians in surrounding areas. Hence people were instructed to stay indoors. At this time, the possibility of severe consequences were being denied by world nuclear industry. However, the nature of the accident had obviously changed with the overheating of the fuel rods in the spent fuel pools. Further, while the first fire was claimed to be extinguished on the 15th March 2011 by TEPCO, another fire was reported as burning at 05:45 on March 16. It “disappeared later”.

On 16 March 2011, 7:16 PM, by Eli Kintisch, staff writer for Science Insider at wrote an article entitled “Contention Over Risk of Fire From Spent Fuel Pools”

In this article Kintisch states: ” Among the worst case scenarios at the Fukushima plant is that the spent nuclear fuel, which sits in essentially open cooling pools near the six nuclear reactors, could catch fire for a prolonged period and spew tons of radioactive dust in a radioactive plume. It appears some of the spent fuel has been on fire at reactor #4; fire occurs if the rods get hot enough to burn their cladding. Reports say that high levels of radioactivity have made it difficult to fight the fire, which appears to have continued to burn late Wednesday. Today, U.S. Nuclear Regulatory Commission (NRC) head Gregory Jaczko said that the pool at reactor #4 had run dry; Japanese authorities denied this. …”

If it were the fuel rod cladding which was burning then there may very well be grounds for considering that the overheating event in the fuel pool of reactor 4 had produced rapid oxidation (which may or may not produce what is normally considered to be a flame) in the fuel rod cladding. The salient point being the damage done to the integrity of the fuel rod cladding. For where the cladding fails, there is, in the absence of sufficient water in the spent fuel pool, a direct of radiation into the air, and where outer containment has failed, as occurred in reactor 4 resultant from the explosions there, the venting of fission and fuel products enters the outside air unimpeded.

It is easy to conclude therefore that people in a defined area around the NPP were ordered to stay indoors due to the emissions from the nuclear power plant’s number four spent fuel pool and the fresh spent fuel rods stored there.

Turning to the Australian Broadcasting Commission (ABC) we find this report:

Tuesday March 15, 2011, 18:10 hours. Headline “Explosion at No 4 Fukushima Reactor” MARK COLVIN: The Fukushima nuclear disaster has moved up the ladder from the third-worst civilian nuclear accident in history to the second, now behind only Chernobyl. With explosions at three of the plant’s reactors, and now a fire in spent fuel at reactor number four; it’s now a good deal worse than the 1979 Three Mile Island disaster.

The International Atomic Energy Agency says radiation levels around the plant are now 400 millisieverts an hour. That means that every six minutes eight times as much radiation are spewing out as nuclear workers are normally supposed to absorb in a year.

And the authorities are getting no help from the elements. Instead of blowing east and out to sea, as on most days, the smoke from the burning nuclear fuel is drifting south. About halfway to Tokyo at Utsunomiya, radiation is registering 33 times normal, still not a serious threat to health if things get better soon.

In the capital itself the level is less, 23 times normal. Earlier, the prime minister Naoto Kan briefly addressed the nation on television pleading for calm. …”

The Japanese people were, to my eyes, calm. It was the nuclear industry which was in panic.

On 5 April 2011, the New York Times published a piece which cited a confidential NRC report on the events at Fukushima Diiachi.

U.S. Sees Array of New Threats at Japan’s Nuclear Plant
Published: April 5, 2011 New York Times

“United States government engineers sent to help with the crisis in Japan are warning that the troubled nuclear plant there is facing a wide array of fresh threats that could persist indefinitely, and that in some cases are expected to increase as a result of the very measures being taken to keep the plant stable, according to a confidential assessment prepared by the Nuclear Regulatory Commission. ….The document also suggests that fragments or particles of nuclear fuel from spent fuel pools above the reactors were blown “up to one mile from the units,” and that pieces of highly radioactive material fell between two units and had to be “bulldozed over,” presumably to protect workers at the site. The ejection of nuclear material, which may have occurred during one of the earlier hydrogen explosions, may indicate more extensive damage to the extremely radioactive pools than previously disclosed.”

Unless a reactor containment had massively failed, the only source for the fuel rods found “up to one mile from the (reactor) units, the only possible place those fuel rods could have originated was one of the fuel pools. Seeing as every source confirm that the explosion in reactor 4 came from the fourth floor – the floor the spent fuel pool is located on – it is rational to conclude that Spent Fuel Pool Four was the origin of fuel rods found up to one mile away.

There was one explosion and two fires on the fourth floor of Reactor 4.

My opinion is that the fuel rods in that spent fuel pool were damaged by the events and that the fuel pool was venting radionuclides to the atmosphere.

I also think that the following report is legitimate:

IAEA ENAC Data – March 15th – Reactor 4 Spent Fuel Pool Fire – Pages from ML12037A104 – FOIA PA-2011-0118, FOIA PA-2011-0119 & FOIA PA 2011-0120 – Resp 41 – Partial – Group DDD Part 2 of 3. (138 page(s), 1 24 2012)-6 (source link)


I also have the view from following the media at the time that the information released by nuclear authorities was deliberately false, misleading, confusing and inexpert. And that modern journalists are really at a loss at putting two and two together and reporting clearly and accurately with insight. With some remarkable exceptions.

I think also that the fires in the fuel pools and the fact that both were put out, reveals something about fires in spent fuel pools.

How long did the pool vent for ? How much of the contamination and hazard was created by the spent fuel pools?

Nuclear industry has maintained reactors as built at Fukushima are safe. They obviously are not.