Background on Japan’s stricken nuclear reactor — Fukushima Daiichi No 1

According to recent media reports an explosion has blown the roof off an unstable reactor north of Tokyo. The reactor is Fukushima Daiichi nuclear power station’s unit no 1. World Nuclear News reports:

Television cameras trained on the plant captured a dramatic explosion surrounding unit 1 at around 6pm. Amid a visible pressure release and a cloud of dust it was not possible to know the extent of the damage. The external building structure does not act as the containment, which is an airtight engineered boundary within. The status of the containment is not yet known.

Here’s some background on Fukushima Daiichi and the events leading up to the incident.

Number of reactors: The Fukushima Daiichi nuclear power station has six reactors. According to the Tokyo Electric Power Company (Tepco), when the quake hit three of the reactors were shut down for periodic inspection (units 4, 5 and 6). The other three (1, 2 and 3) were shut down in response to the quake.

Type of reactor: The reactors at Fukushima Daiichi are boiling water reactors (see diagram below).

According to the US Energy Information Administration:

In a typical commercial boiling water reactor the reactor core creates heat, a steam-water mixture is produced when very pure water (reactor coolant) moves upward through the core absorbing heat, the steam-water mixture leaves the top of the core and enters the two stages of moisture separation where water droplets are removed before the steam is allowed to enter the steam line, the steam line directs the steam to the main turbine causing it to turn the turbine generator, which produces electricity. The unused steam is exhausted to the condenser where it is condensed into water. The resulting water is pumped out of the condenser with a series of pumps, reheated, and pumped back to the reactor vessel. The reactor’s core contains fuel assemblies which are cooled by water, which is force-circulated by electrically powered pumps. Emergency cooling water is supplied by other pumps which can be powered by onsite diesel generators. Other safety systems, such as the containment cooling system, also need electric power.

What caused the problem?: After a reactor is shut down it needs to be cooled. According to Ron Chesser, director for the Center of Environmental Radiation Studies at Texas Tech University:

Reactors are not like your car that you can turn off and walk away. They’re going to continue generating a great amount of heat until the core is disassembled. Without cooling water, then you stand a real chance of a meltdown of core that could result in a large release of radiation, potentially.

Water for cooling is relies on electric pumps. These are normally powered by the electricity grid but in an emergency most reactors rely on diesel generators. When the reactors at Fukushima Daiichi automatically shut down, power from the grid was lost and the back-up diesel generators supplied powered the pumps. However after an hour the diesel generators suddenly stopped. This triggered an emergency.

According to a report in World Nuclear News a lack of cooling caused pressure within the containment of Fukushima Daiichi 1 to rise:

The company has decided to manage this "for those units that cannot confirm certain levels of water injection" by means of a controlled release of air and water vapour to the atmosphere. Because this water has been through the reactor core, this would inevitably mean a certain release of radiation. The IAEA said this would be filtered to retain radiation within the containment.

Some news agencies are reporting that the explosion was caused by the release of hydrogen gas. According to the BBC:

The BBC’s environment correspondent Roger Harrabin says he understands the blast at the nuclear plant may have been caused by a hydrogen explosion – also one of the possibilities laid out by Walt Patterson of Chatham House. "If nuclear fuel rods overheat and then come into contact with water, this produces a large amount of highly-flammable hydrogen gas which can then ignite," our correspondent says.

According to a recent report by AFP (posted on the BBC’s site) "Government spokesman says the nuclear reactor container at the Fukushima-Daiichi plant has not been damaged, and the level of radiation has dropped following the explosion earlier on Saturday".

Scientific American has posted an interview with Scott Burnell, public affairs officer at the U.S. Nuclear Regulatory Commission (NRC) where Burnell explains how nuclear reactors are cooled during an emergency.

Previous safety problems: In 2002 Tepco was involved in a major scandal when it [was accused of falsifying] data to cover up the discovery of cracks in pipes at Fukushima Daiichi and another nuclear plant, Kashiwazaki Kariwa. According to a report by Steve Connor in the Independent:

Officials from Tepco found that more than half of the 61 pipes it had inspected in its Fukushima plant’s number three reactor showed signs of damage. Corrosion was so severe in six of the stainless steel pipes that they measured less than half their original thickness.

Akira Kawate, vice-governor of the Fukushima prefecture, said Tepco and the national government had covered up details of the inspections since at least 2000.

According to Ikuko Kao at Reuters, the scandal delayed Tepco’s plans to build two more reactors at Fukushima Daiichi.

The MOX controversy : A recent controversy involving the Fukushima Daiichi nuclear plant has been the use of mixed-oxide (MOX) fuel. MOX is a mixture of plutonium and uranium. In 2009 Greenpeace protested against shipments of MOX from France to Japan. According to Reuters and Japan Today, the no. 3 at Fukushima Daiichi was to be loaded with MOX in 2010.

The US Nuclear Regulatory Commission has a FAQ page about MOX.

Updates:

Fukushima Daiichi No 1 is a Mark 1 General Electric Boiling Water Reactor. The cut-away diagram immediately below shows the layout of this kind of reactor (from US NRC Reactor Concepts Manual). The diagram below that provides labels for the key features of the containment. The bottom diagram comes from Magdi Ragheb‘s ‘Containment Structures‘. See his paper for an explanation of the diagram (Via The Capacity Factor).

The New York Times has an interactive feature with photographs and a cut-away model of the reactor.

Cooling system fails at No 3 reactor: Reuters reports:

The emergency cooling system is no longer functioning at the No.3 reactor at Tokyo Electric Power Co’s Fukushima Daiichi nuclear power facility, requiring the facility to urgently secure a means to supply water to the reactor, an official of the Japan Nuclear and Industrial Safety Agency told a news conference.

Comparisons to Three Mile Island: A number of reports raise the possibility of a meltdown. In 1979 a meltdown occurred at Three Mile Island Unit 2 nuclear power plant near Middletown, Pa. According to US Nuclear Regulatory Commission "it led to no deaths or injuries to plant workers or members of the nearby community". NBC’s Today show interviewed Richard Lester , head of the department of nuclear science and engineering at MIT about the possibility of a meltdown at Fukushima Daiichi:

Can you give us a sense of what a meltdown would entail? what would happen in that process?

One possibility is that the fuel or some part of the fuel in the core would melt and would gather at the bottom of the reactor vessel and would stay there. that is essentially what happened at the three-mile iceland nuclear power plant in 1979 . there was no significant release of radioactivity outside of the vessel. if a partial meltdown happens in the core, that’s what we would hope to see. of course, let me emphasize that at this point, it’s not at all clear that any melting of the fuel has taken place.

Thoughtful discussion nearly impossible, writes Christine Russell: Writing in the Atlantic, Russell notes that that in the Three Mile Island incident there was "tremendous uncertainty, confusion, and contradictory information about what was actually happening and what might happen." She notes that there are few reporters working today who specialise in covering nuclear energy and technology. She writes:

The current Japanese nuclear energy emergency will undoubtedly have a profound global impact on public views of the safety hazards–and siting–of old and new nuclear power plants. And the speed of communication today–unheard of in the pre-cell phone, pre-Internet Three Mile Island era–means that news and speculation about what is happening, or might happen, in Japan is traveling so far and fast that thoughtful discussion is nearly impossible.

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28 Responses to Background on Japan’s stricken nuclear reactor — Fukushima Daiichi No 1

  1. Gerald Ascencio says:

    Thank you for the very well prepared and informative article.
    I am forwarding it to my grand daughter who is in college presently, accepted for a chemistry and nuclear engineering major.

    Gerald Ascencio

  2. Hugh says:

    Once again the media (unlike World Nuclear News) is doing a poor job of reporting on a serious technical issue. The biggest danger at Three Mile Island in Pennsylvania USA was the scary reporting. People died of either just fright or doing silly things because they were scared.

    The media does not understand that specific words mean specific things when discussing serious technical issues. If the words are not clear because of language translation then the media need to get better translators and better technical experts involved who know how to explain these things to the public.

    e.g. Chernobyl was a very different nuclear plant on at least 3 levels.
    1) Chernobyl had no containment building that could withstand high pressure and contain virtually all radioactivity as it did at Three Mile Island.
    2) Chernobyl’s core contained graphite that could burn and distribute the radioactive elements.
    3) Chernobyl was designed to create plutonium for nuclear weapons so it’s safety and control were compromised. No other type of power reactor is built this way.

  3. wizofaus says:

    People died due to the Three Mile Island incident?

    I’m actually quite seriously concerned the Fukushima incident has the capacity to seriously threaten support for one of the few proven technologies that has a significant capacity to assist in humankind’s efforts to reduce CO2 emissions. Sadly, if it does, the threat to human life could end up being far worse than the consequences of another Chernobyl (and it’s worth reminding readers that even allowing for Chernobyl, nuclear power has been responsible for far less deaths and seriously health risks per kW of electricity produced than any other form of power generation).

  4. chumpai says:

    Thank you for this post.

    From what I’ve read even if the rods melt down the reactor will not be breached/destroyed. However, my understanding is that radioactive gases are liberated when the rods melt and these seem to be causing a pressure build-up at these plants – if there is any iodine-131 released then that would be the major ‘fallout’ that may affect people’s thyroids though apparently the Japanese authorities are distributing iodine pills to prevent this.

  5. derrida derider says:

    Its a bit bizarre, isn’t it? Of all the massive problems that can lead to further loss of life in the wake of the tsunami, the nuclear problems must be somewhere around tenth. There are thousands still trapped in wreckage, sanitation systems are knocked out all across northern Japan, at this time of year even warm clothing and housing will be an issue, etc.

    But what is it that gets the headlines? A problem that seems at present to be very manageable (in terms of loss of life, not economic damage), and even if the worst eventuates will kill a tiny, tiny fraction of those killed by the tsunami.

  6. Incurious and Unread (aka Dave) says:

    DD,

    Not too bizarre really.

    Radioactive material Chernobyl very quickly spread around the world and affected many countries. That is of concern to everyone. Apart from sympathy and voyeurism, the suffering of the Japanese is not.

    Put it another way, if we knew (for the sake of argument) that the nuclear problems couldn’t possibly affect us, but were concerned that the Tsunami (or, say, future aftershock Tsunamis) could, we would probably be talking about Tsunamis and ignoring Nuclear.

    The risks of widespread nuclear contamination may be extremely low, but given that the vast majority of people (including myself) have no way of estimating these, that is largely irrelevant.

    Indeed, the fact that it is so hard to understand the risks is a good reason in itself for taking an interest in the media coverage

  7. ennui says:

    aka Dave
    I agree with DD

    You say –

    the fact that it is so hard to understand the risks is a good reason in itself for taking an interest in the media coverage

    That simply begs the question – it is the media coverage balance not peoples curiousty which is the issue.

  8. Incurious and Unread (aka Dave) says:

    ennui,

    Maybe. But I always assume that the media know their readers pretty well.

  9. ennui says:

    aka dave

    But I always assume that the media know their readers pretty well.

    If you are right – which you may well be – then God help us!!

  10. Tel says:

    A good roundup article. May I add a few points:

    The #1 reactor was 40 years old and basically at end of life. However, there’s a huge economic temptation to run reactors past end of life because decommissioning a reactor is expensive and low-return, while running it “just a bit longer” is high profit (everything is already paid for). This is a genuine perverse incentive because the economic value of risk to the public is difficult to measure (until things go wrong).

    Government regulators tend to buckle easily on reactor lifetime, so maybe an economic scheme should be implemented where some percentage of the running profits are put aside continually and released at decommissioning time (incentivate the bean-counters).

    … radioactive gases are liberated when the rods melt and these seem to be causing a pressure build-up at these plants – if there is any iodine-131 released then that would be the major ‘fallout’ that may affect people’s thyroids…

    So I’m told, if you vent the turbine steam it releases tritium oxide which is chemically identical to water and basically impossible to block it out of uptake into humans and the environment.

    The danger of tritium poisoning is arguable but it can’t be good for you.

    Of all the massive problems that can lead to further loss of life in the wake of the tsunami, the nuclear problems must be somewhere around tenth.

    Nothing beats “Nuclear Emergency” as a headline, nothing even comes close.

    Frankly, I regard the ridiculous over sensitivity of the public to nuclear risk as a good thing. When the public starts getting complacent, the risk will just grow to fill the difference. Look how complacent we are to risks in the banking industry, and look at where we ended up on that one, “oh yeah, another financial meltdown, whatever.”

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  12. derrida derider says:

    Na, Tel – tritium is a beta-emitter (ie its radiation can be shielded by a piece of paper) wih a very short *biological* half-life (ie if you swallow it, you soon piss or sweat it out). You have to swallow a lot of tritium to be at risk – see here. Iodine and strontium are the main public health risks from widespread fallout – but strontium has a short half-life (ie local evacuation works), and the body concentrates iodine in the thyroid. Non-radioactive iodine is thus a good prophylactic for I-131 exposure, and even at worst thyroid cancer is about the most treatable cancer around. That’s why Chernobyl caused hundreds, not thousands, of premature deaths despite exposure of the whole of Kiev to relatively massive doses due to Soviet incompetence.

    I’ll make a specific prediction now. Not one single member of the public will get more than the WHO safe limit of annual exposure from these events (a level which is in any case considerably lower than coal miners face from the traces of radon in coal).

  13. Scott says:

    I am not an engineer and have no background in any type of powerplant design but lookng at the design, I have this question come to mind. It sounds, from the experts on the news,like a hydrogen build up is a common predicted occurence at some types of reactor “events”. After seeing photos of the reactor that “blew up” it appears that the top portion, the thin “sheet metal” looking top section is what is missing and bottom 2/3 of the structure at least appears ok. Could it be that this is a designed failure mode of this type of reactor to prevent an hydogen gas explosion form being contained and possibly doing even more damage due to it being contained rather than lessing the damage by releasing the explosion?

  14. According to the ABC the hydrogen thingie was a NUCLEAR EXPLOSION. Get yer facts straight, Don. When will Club Troppo stop being a conga line of uranium apologists?!?

  15. Robert Pickell says:

    Good article. I was a Reactor Operator in the US Navy so I do know a thing or two about Nuclear physics and Nuclear reactors.

    That being said, It is EXTREMELY hard for anyone not versed in Nuclear Physics and Reactor design and their operation to truly understand what these technical reports coming out of Japan really mean or are telling us. It is even harder for the person who does not truly understand to pass the information along in the public media channels.

    The human factors of fear / Over simplification / jumping to conclusions / and believing who ‘sounds’ the best to you; really cloud the facts and issue at hand.

    Most people want ‘simple’ answers and we will deceive ourselves often to believe a ‘simple answer’, even when it is totally wrong.

    Without getting into details I will share MY ‘impression’ from what I can find and believe to be factual information.

    1. The owners / operators at the Nuclear site have their hands full as they are in a situation they NEVER foresaw / planned / or practiced for. As such they are trying to do what they believe best (safest) given the situation and resources at hand.

    2. Since this is a situation that has NOT been planned for there is NO way the people at the planet and those making the decisions can be 100% sure of the out come of their choices and actions. (NO guarantee)

    3. From the information at hand and MY understanding of reactors and nuclear physics, I do NOT see that they have made any bad choices so far. Yet it is clear not all has gone as they had hoped it would either. You NEVER plan on an explosion in the reactor building.

    4. Only time will tell if they made the best choices or not. We have to trust them as they are ones there now. I just hope they are up to it. So far they appear to be.

  16. SJ says:

    After seeing photos of the reactor that “blew up” it appears that the top portion, the thin “sheet metal” looking top section is what is missing and bottom 2/3 of the structure at least appears ok. Could it be that this is a designed failure mode of this type of reactor to prevent an hydogen gas explosion form being contained and possibly doing even more damage due to it being contained rather than lessing the damage by releasing the explosion?

    Scott, you’re correct that it’s just the sheet metal bit that got blown to bits. This isn’t what you could call a designed failure mode, the sheet metal bit is irrelevant to the containment structure. It’s just there to keep out wind and rain, it’s not designed to keep anything in.

    At Cherbobyl, the hydrogen explosion took place inside the containment structure itself, and blew the containment structure to bits.

    It’s not clear yet what happened in Japan. Either hydrogen escaped from the containment structure (which isn’t good, because radioactive stuff would have escaped with it) and then exploded inside the weather shield, or else the hydrogen exploded inside the containment structure and enough hot combustion product excaped to blow apart the weather shield (also not good).

  17. derrida derider says:

    Well one of the many things that were wrong at Chernobyl is that, unlike Western reactors, it wasn’t built with a reactor vessel designed to contain a meltdown. Amazing really.

    These explosions are indeed “not good”, but so long as the fuel stays in the reactor vessel the only people likely to come to harm are the workers on site. Think of it as comparable to the oil refinery that blew up after the tsunami.

    Robert Pickell, I’d be astounded if the reactor operators didn’t do a LOT of contingency planning and training – especially in Japan. A big earthquake followed by a tsunami (a Japanese word after all) was actually overdue in Japan, as people there were well aware.

  18. SJ says:

    Well one of the many things that were wrong at Chernobyl is that, unlike Western reactors, it wasn’t built with a reactor vessel designed to contain a meltdown. Amazing really.

    Those of us that know our history are aware of Windscale. That’s a case where there was practically no attempt to contain anything at all.

    The other problem with hydrogen explosions is the production of hydrogen in the first place. It only occurs at temperatures that are above the melting points of both iron and silica, which are the things the reactor vessel and the containment structure are made of.

  19. derrida derider says:

    SJ, Windscale was a very long time ago and very much in the pioneering days of these things. Not even the Rusoians built reactors like that one.

  20. trev says:

    People are looking at each reactor indavidualy, are they close together and if they are all in one area what happens if one lets go properley and causes a chain reaction with the other reactors is nucler mist still number 10 on your not important list cuase to me theres a bigger problem than just one reactor, everyone is stuck with there head up there buts as anyone is always an expert,10 degrees,done this done that,fact is there is no water ,hot rods = chooks with there heads cut off running around with this theory that theory, ya just need to get water there no water it going to rip japan a new orffice and make alot of people sick around the world. So start praying these b_ckers don’t have a chain reaction as you wont need to cut your hair anymore, It will be on the floor already. Hope I wrong and dumb as dog poo about this for everyones sake

  21. Robert Pickell says:

    Robert Pickell, I’d be astounded if the reactor operators didn’t do a LOT of contingency planning and training – especially in Japan. A big earthquake followed by a tsunami (a Japanese word after all) was actually overdue in Japan, as people there were well aware.

    derrida derider,

    I would NOT be surprised if the personnel in Japan had NOT practiced for the situation they find themselves in now at the plant. I have worked and lived in Japan and it is a very different culture compared to America.

    As of today (15 March 2011) they have an uncontrolled release of core material into the environment. This is not good by any standard. When the dust settles, both radioactive and normal and political, I am willing to bet that it will show that there where improper choices made by those involved, especially at the management levels.

    This situation is not over. Given that we now have core material escaping uncontrolled it will be even LONGER before it is over.

    What is NOT clear to me is:
    1. if the release is from spent fuel rods outside the reactor vessel (best case now, but still bad)
    2. or from a rupture in the containment vessel (#2 reactor)
    3. or worst case both are releasing.

    There have been some bad choices made in this endeavor. That is clear to me now.

  22. Ken Parish says:

    Seems to me that whatever now happens the nuclear power option is almost certainly a dead duck in all western nations with free media. Whatever may be the wholly utilitarian risk/benefit analysis, the images and sense of Armageddon we’re seeing coming out of Japan will be imprinted on people’s minds permanently, meaning that politicians from now on simply won’t be able to propose nuclear power solutions without facing terminal electoral consequences.

    The images coming out of Japan mean that it’s game, set and match to the Greens on the nuke power issue and we need to get on and develop other sustainable, low carbon baseload power options.

  23. Patrick says:

    Well, I guess that means it’s game set and match to the do-nothing-meaningful-about-carbon-emissions-ever movement, too.

    Really, now is the ideal time to commission nukes – I bet we’d get a great price!

  24. wizofaus says:

    Ken, at least in Australia, I don’t think there’s much argument there – not that nuclear was likely to be electorally viable for some years anyway. Which, while a shame, it’s necessarily a show stopper for a country like Australia that *does* have vast alternative resources available (even if the technology to tap them still has a way to go). It’s countries where those alternatives are not realistic that are going to have a tough time coming up with a realistic low-CO2 power generation mix.

  25. wizofaus says:

    Oops, insert “not” before “necessarily”.

  26. Robert Pickell says:

    Well .. if the reports out of Japan are true it seems they have lost control of the power plants SITE .. ALL of it. This means there is NO active control of 6 nuclear power plants now. And 4 of the 6 plants are in trouble already.

    Someone screwed up BIG time here. This does not appear as if it will end well for Japan. I hope to God that I am wrong on this.

  27. Johny V says:

    You would think that in this day and age that Japan would have decided upon building a more advanced Reactor with multiple types of redundant emergency shut down systems!

    This type of reactor had one type of emergency shut down system, that being only water!?? NUTS!

    Even reactors in the 50s had multiple types of emergency shut down systems, in case one type failed, like top & side safety rods, backed up by Boric acid balls/solution… there is only one reason to build a nuclear reactor with a single system shut down system (water), and that is for greed and making more profit.

    Here is the statement that screams lip service corporate greed and complete BS:
    “Reactors are not like your car that you can turn off and walk away. They’re going to continue generating a great amount of heat until the core is disassembled. Without cooling water, then you stand a real chance of a meltdown of core that could result in a large release of radiation, potentially.”

    What a bunch of garbage! Corporate greed BS.

    There are many methods to build a reactor that can be shut down relatively fast but such a reactor with multiple types of redundant safety shut down systems are NOT good for the corporate greed’s profit margin!

    Now the world will suffer due to greed and not doing things the BEST way.

    Here is a video of a very old reactor but one that was built with safety in mind if even two shut down systems failed.

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