Sunday, July 23, 2017

How Much Fuel Was in Fukushima Daiichi Unit 3 Reactor?

I've followed the Fukushima Daiichi disaster so closely for so long that I was surprised to discover this morning that I really don't know exactly how much fuel was in reactor 3.

I have the data on fuel contained in the spent fuel pools, but NOT the data on fuel in the REACTOR CORES.  

Below find the spent fuel pool data:
TEPCO. Integrity Inspection of Dry Storage Casks and Spent Fuels at Fukushima Daiichi Nuclear Power Station (16 November 2010),
[PARAPHRASING] The total spent uranium fuel inventory at Daiichi in March 2010 was reported as 1,760 tons. The 2010 report asserts that approximately 700 spent fuel assemblies are generated every year. The report specifies that Daiichi’s 3,450 assemblies are stored in each of the six reactor’s spent fuel pools. The common spent fuel pool contains 6291 assemblies. The amount of MOX fuel stored at the plant has not been reported.

SO, 700 spent fuel assemblies were generated at Daiichi each year. There were 6 reactors at Daiichi, although not all were operational at time of earthquake. Assuming they were operational, can we infer that each reactor core contained approximately 100 assemblies? 

That estimate is supported by the US Nuclear Regulatory Commission's information on fuel assemblies found here, which suggests a reactor may contain up to 200 assemblies, with each assembly containing 200 or more rods:
US NRC (2017, April 10). Fuel assembly (fuel bundle, fuel element).

A structured group of fuel rods (long, slender, metal tubes containing pellets of fissionable material, which provide fuel for nuclear reactors). Depending on the design, each reactor vessel may have dozens of fuel assemblies (also known as fuel bundles), each of which may contain 200 or more fuel rods.
The website titled Nuclear Power Net, described as non-profit and founded by nuclear engineers, suggests a typical reactor  contains 157 fuel assemblies but those are composed of over 45,000 fuel rods (which is more than 200 in each assembly):
Nuclear Power Net (no date).

An 1100 MWe (3300 MWth) nuclear core may contain 157 fuel assemblies composed of over 45,000 fuel rods and some 15 million fuel pellets. Generally, a common fuel assembly contain energy for approximately 4 years of operation at full power. Once loaded, fuel stays in the core for 4 years depending on the design of the operating cycle. During these 4 years the reactor core have to be refueled. 
During refueling, every 12 to 18 months, some of the fuel – usually one third or one quarter of the core – is removed to spent fuel pool, while the remainder is rearranged to a location in the core better suited to its remaining level of enrichment. The removed fuel (one third or one quarter of the core, i.e. 40 assemblies) has to be replaced by a fresh fuel assemblies.
The variation in data is puzzling but I think we can move forward assuming that there were approximately 100 fuel assemblies in each reactor.

A typical fuel assembly for a Pressured Water Reactor (PWR) "stands between four and five metres high, is about 20 cm across and weighs about half a tonne" according to the World Nuclear Association (

USING THESE DATA POINTS, I can infer that Unit 3's reactor core contained approximately 50-75 tons of fuel. Does that sound roughly correct? A ton is 2,000 pounds so 50 tons of fuel is 100,000 pounds. For metric users, that converts into 45359.237 kilograms.

Why is it so important that I determine how much fuel was in reactor 3?

The reason lies in the media representations of TEPCO's robotic probe, Little Sunfish, which allegedly has (likely) located unit 3's  missing reactor fuel, illustrated in the media as "rocks on the floor":

Kohei Tomida (July 23, 2017). Melted nuke fuel images show struggle facing Fukushima plant. The Asahi Shimbun, 
In particular, what is believed to be nuclear fuel debris is scattered in the form of rocks in the area directly beneath the pressure vessel. 

My point is not to deny that these found rocks might be nuclear fuel debris. Rather, my point is that these shards of melted fuel and debris can hardly be construed as representing the entirety of the fuel.

Put otherwise, there is no compelling evidence that TEPCO has located the majority of fuel that was contained in Unit 3.

I decided to search my notes, books, and the web validated statistics on how much fuel each reactor contained. I was struck by how little information is available about the missing fuel and the sanitized accounts of what happened at unit 3, the one running MOX fuel.

Basically, at Daiichi Unit 3 TEPCO has misplaced 50 plus tons of reactor fuel that was "enriched" with plutonium and now were are being encouraged to think that shards of melted-fuel debris represent the entirety of the missing reactor core....a core that weighed more than a school bus....

Saturday, July 22, 2017

Where is the fuel from Fukushima Daiichi Unit 3 Spent Fuel Pool and Reactor?

Fukushima Daiichi Unit 3 had an explosion that resembled a nuclear bomb detonation. Fukushima Daiichi unit 3's reactor was running MOX fuel, which is uranium based but "enriched" with plutonium. I was never clear how much MOX was stored in unit 3's pool.

The authorities told us all 4 explosions at Daiichi were hydrogen-caused, resulting from ineffective venting after the quick shutdowns of the reactors (the 4th explosion in unit 4 was blamed on hydrogen from unit 3).


Nuclear Engineer Arnie Gundersen suggested that a prompt criticality occurred in melted fuel located in unit 3's SPENT FUEL POOL:
A. Gundersen (26 April 2011) ‘Gundersen Postulates Unit 3 Explosion May Have Been Prompt Criticality in Fuel Pool,’ Fairewinds,, date accessed 26 April 2011
The images at Cryptome are illuminating and suggest the explosion at unit was pretty catastrophic:

Read what John Monger said in the US Nuclear Regulatory Commission (NRC) discussions March 16, 2011 about the state of unit 3's spent fuel pool as documented in the NRC Transcript March 16, 2011

John Monger page 62: “unit 1 and 2 is boiling down, and unit 3 and 4 is having zirc/water reaction. They believe there is essentially no walls on unit 3. The explosion – I’m sorry – unit 4. The explosion leveled the walls, leveled the structure for the unit 4 spent fuel pool all the way down to the approximate level of the bottom of the fuels. So, there’s no water in there whatsoever.” 
I figure the fuel from unit 3's spent fuel pool is all over the globe now. I hope I'm wrong.

TEPCO doesn't talk much today about the fuel in reactor 3's pool other than to say its being cooled, as part of the 300 tons of water injected at the site daily to prevented melted fuel, located in ruptured containment, from having "zirc reactions."


From the beginning of the disaster, TEPCO claimed to have no direct knowledge of the location/status of unit 3's REACTOR fuel, although in 2014 the company stated it believed it had all melted and dropped beneath the pressure vessel:
TEPCO: Nearly all nuclear fuel melted at Fukushima No. 3 reactor. (August 7, 2014). The Asahi Shimbun,
According to the latest estimate, fuel at the No. 3 reactor began melting at 5:30 a.m. on March 13, and almost all the melted fuel had dropped to a broad area on the bottom of the containment vessel soon after 7 a.m. on March 14.

TEPCO officials said they believe part of the melted fuel still remains inside the pressure vessel, citing the fact that the temperature inside the pressure vessel fell after a later water injection.

The estimated start of the fuel melting is roughly consistent with when neutrons were detected near the front gate of the nuclear plant, according to the officials.

Neutrons were also detected when nuclear fuel started to melt at the No. 2 reactor at midnight on March 14. For this reason, TEPCO estimates that radioactive substances released from the No. 3 reactor emitted neutrons near the front gate.

All of nuclear fuel at the No. 1 reactor is estimated to have melted after the disaster, while around 60 percent is believed to have melted at the No. 2 reactor. TEPCO said it will now consider how to remove the melted nuclear fuel from the No. 3 reactor. 

 Now TEPCO is telling us that nearly ALL the fuel from the REACTOR is accumulated in the bottom of the containment vessel:
Kohei Tomida. July 20, 2017. Fukushima robot reveals collapsed scaffolding in nuclear reactor
Almost all of the nuclear fuel in the No. 3 reactor likely melted and dropped from the pressure vessel and accumulated at the bottom of the containment vessel, according to analysis by Tokyo Electric Power Co., the crippled plant’s operator.
This narrative is being repeated especially strongly in The Asahi Shimbun:
Images of fuel debris 1st step in deactivating Fukushima plant. The Asahi Shimbun, July 22, 2017

Operator Tokyo Electric Power Co. said the manner in which the solidified material was found within the No. 3 reactor suggested the material is fuel debris.

"It clearly appears to be something that solidified after melting out of the pressure vessel," said one official. "We believe the material emerged after nuclear fuel mixed with structural matter within the pressure vessel."

Past analysis of the No. 3 reactor led to the assumption that almost all the nuclear fuel had dropped through the pressure vessel after burning a hole in the bottom and dripping down. The latest robot survey confirms that is what likely happened.
Do people remember the explosion of unit 3? It was huge. The building was wrecked. I find it hard to believe that all the fuel from reactor unit 3 resides cooling, in a singular space.

It was UNIT 3 that appeared to have fires in the fall of 2011. Unfortunately almost all the videos posted at Youtube have been taken down and I only have a few screenshots from that time, saved in this pdf, which I strongly recommend viewing:
Unit 3 has always been the source of the most visible atmospheric emissions at Fukushima visible on the webcams.

I always presumed it was because of the MOX. The low-end estimate of 32 mox assemblies is contained in the reactor core is from France’s Areva, which provided the fuel for unit 3. As the French Fukushima 3/11 Watchdog group points out, the low-end estimate of 32 mox assemblies translates into 5.5 tons of fuel containing more than 300 kg of plutonium: “300 kg is therefore equivalent to 300 billion lethal doses.”

I don't know where the fuel from unit 3's reactor is, but I will say, as a Webcam Watcher, there is a METAPHORIC DRAGON either in or below unit 3 that seems particularly active after the last earthquake a few days ago:

Friday, July 21, 2017

Fukushima Unit 3 in the News and Glowing on WebCam

Fukushima Unit 3 has been in the news because Toshiba, working with the International Research Institute for Nuclear Decommissioning, "a government-funded consortium," created an amazingly innovative robot, labeled Little Sunfish, that has been sent into this reactor, which had been running MOX fuel at the time of the disaster and had, by far, the largest explosion.

Here are some interesting screenshots from unit 3:

Spent fuel pool unit 3: and

Little Sunfish is now investigating the reactor conditions:
Mari Yamaguchi (July 19, 2017). Swimming Robot Captures Underwater Images of Damaged Fukushima Nuclear Reactor. Time,
... The robot used Wednesday was designed to tolerate radiation of up to 200 sieverts — a level that can kill humans instantly.  Kimoto said the robot showed that the Unit 3 reactor chamber was "clearly more severely damaged" than Unit 2, which was explored by the scorpion probe.
I recommend visiting the Time link because it provides a history of robotic efforts to investigate the ruined reactors at Daiichi. Sunfish is a major achievement because it can withstand up to 200 sieverts of radiation. Congratulations to Toshiba and their collaborators.

TEPCO needs to know the reactor conditions in order to move forward with "decommissioning." The best way to decommission these reactors is to have them filled with water. However, the bad news is that it appears most, if not all 3 of the reactors, cannot hold water (which is why TEPCO must add up to 300 tons of water a day to the reactors and also to the damaged spent fuel pools).

TEPCO is planning an alternative approach to decommissioning but this alternative approach is "dirtier" in the sense that its going to spread more radioactive particles into the environment. You can read what has been reported about the proposed plan here:
Fuel debris extraction plan for crippled Fukushima reactors to be revealed soon: sources. (July 5, 2017) The Japan Times
The Nuclear Damage Compensation and Decommissioning Facilitation Corp., tasked with providing technical support for decommissioning the complex, may propose a method to remove nuclear debris without completely filling the reactor containment vessels with water, the sources said Tuesday. 
The plan means the debris inside reactors 1, 2 and 3 at the crippled Fukushima No. 1 complex is likely to be shaved off gradually with a drill or laser equipment as a shower of water is poured remotely, the sources said.
It is indeed unfortunate that the reactors cannot contain water because the proposed process of shaving off graduation with a drill or laser equipment under a shower of water sounds very, very messy. Will the process be encased in plastic or something to contain the resulting radioactively contaminated spray?

The Chairman of Japan's nuclear regulator recently decried TEPCO's lack of urgency and described a sense of danger.

I echo that sense of urgency. Yesterday's earthquake left Daiichi looking worse than it has been and recently its not been looking great.

Unit 3 appeared to be glowing this morning: