Radiation leak reported at Japanese nuclear plant, 10km evacuation radius | Hacker News Reader

Radiation leak reported at Japanese nuclear plant, 10km evacuation radius

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48 pointsanigbrowl51 comments

There's really not much information in this article, and consequently it reads a tad sensationalist to me. Let me try to break this situation down as I understand it.

IAANRO (I Am A Nuclear Reactor Operator. I work part-time at my college's research reactor[1])

Nuclear power reactors are of two main varieties: Pressurized Water Reactors, and Boiling Water Reactors[2]. The plant in question is a Boiling Water Reactor (BWR). BWRs work by using the core's thermal energy to boil the cooling water into steam, and then channelling the steam in order to turn a steam turbine. After it exits the turbine, the steam is cooled in a condenser, where it turns back to water, and then is sent back into the core. The condenser requires cool water to be actively pumped through it, to keep the pipes upon which the steam condenses from becoming too hot. The water/steam that runs through the core and the turbine is referred to as the "primary cooling system", and the water running through the condenser is the "secondary cooling system." The primary is assumed to be contaminated (that is, it is measurably radioactive), whereas the secondary system is not, since it is isolated from the primary.

As far as I can tell, the chain of events for this particular plant went something like this:

Shortly after the quake, the reactor successfully shut down in anticipation of the tsunami. This means that no more fission is occurring in the core. Since a core meltdown is a result of uncontrolled fission, this means that the reactor is now incapable of melting down. This will not be another Chernobyl. However, just because U-235 is no longer fissioning, doesn't mean that the core isn't producing heat. The fission fragments (those isotopes produced as a result of the U-235 fissioning) will continue to decay through alpha, beta, or gamma emission, until stable elements at the bottom of the decay chain are reached. The decay of these fission fragments and their decay products will cause the core to continue to produce heat for some time after shutdown.

Presumably due to the fact that every reactor near the east coast of Japan was being shutdown, offsite power for the secondary cooling system was unavailable, so the power plant had to rely on onsite backup power, but the onsite power only lasted for 8 hours. After that, the secondary cooling system failed, which is what triggered the declaration of the Nuclear Emergency, and evacuation of those living within 3Km of the plant.

Since the core is continuing to produce heat, and consequently steam, the steam pressure inside the primary system is rising above normal levels. They are hesitant to bleed off steam into the containment dome, since the dome was probably damaged in the quake, but obviously bleeding off some steam is better than having the primary system rupture. Thankfully, most of the really nasty decay products have a relatively short half-life. In particular, Nitrogen-16, which gives off pretty high energy betas when it decays, has a half-life of 7.2 seconds.

Therefore, releasing the steam is undesirable, but not catastrophic, and probably not even particularly hazardous. The radioactive materials in the cloud will be longer-lived decay products of hydrogen and oxygen in, and as far as I'm aware none of those are particularly active. The cloud will be dilute itself after release, which will lower the intensity of the radiation field significantly. Therefore, the total radioactivity release will be many orders of magnitude lower than that of Chernobyl or Three Mile Island. The media is playing this up to be bigger than it is, because nuclear power still carries a stigma.

[1]: Reed Research Reactor: http://reactor.reed.edu/

[2]: Wikipedia Article on Boiling Water Reactors: http://en.wikipedia.org/wiki/Boiling_water_reactor

Update: A meltdown at this point is possible, since the decay heat is pretty significant. However, as long as the core remains submerged, it shouldn't be an issue. In the worst case, you could more or less stick a hose into the primary system (one of the chief reasons that the Three Mile Island meltdown occurred is that the operators were unaware of the falling water levels in the core).

The main concern at this point is definitely the steam pressure.

I would like to point out the well-known at this time. This has turned out not to be a scare-mongering media-frenzy at all:

http://www.businessinsider.com/fukushima-nuclear-plant-2011-...

FTA: (Naoto Sekimura, a professor at Tokyo University, told NHK, Japan’s public broadcaster, that “only a small portion of the fuel has been melted. But the plant is shut down already, and being cooled down. Most of the fuel is contained in the plant case, so I would like to ask people to be calm.”)

Therefore, there has already been a partial meltdown. Your folks' anti-FUD was appreciated, but ultimately this is quite a bad accident after all, and at especially the Business Insider site article, not overblown or using incorrect verbage.

I'll also add the IAEA alert:

http://www.iaea.org/press/?p=1133

Let's not get carried away here.

Edit: here's the current status of each reactor:

http://www.tepco.co.jp/en/press/corp-com/release/11031207-e.... http://www.tepco.co.jp/en/press/corp-com/release/11031212-e.... http://www.tepco.co.jp/en/press/corp-com/release/11031213-e.... http://www.tepco.co.jp/en/press/corp-com/release/11031214-e....

I.e., all shut down. Need cooling, pressure being vented in the Daiichi reactor (hence 10km radius evac).

Unanswered questions in my mind:

i) There does not appear to be any reason to believe that venting the steam would solve the cooling issues, and therefore avert damage to the reactor core. Can you more firmly link coolant solutions to a successful cooling of the reactor?

ii) Can you more firmly address your assertion that a meltdown requires uncontrolled fission? Doesn't a meltdown simply require enough heat to damage the core and/or fissile material? Meanwhile, the term itself is informal and has no set, specific consensus. Perhaps you can begin by defining what you, specifically, mean by "meltdown"?

Thank you.

i) You're correct in that venting the steam won't solve the cooling issues. Venting the steam is being considered in order to reduce the steam pressure in the primary system. If the pressure gets too high, then the primary system could rupture, resulting in an uncontrolled release of radiation.

ii) I falsely conflated uncontrolled fission with meltdown in my explanation. Meltdown is when the core reaches a temperature at which the control rod cladding (which is probably stainless steel, though I can't confirm that) melts. Uncontrolled fission will result in a spectacular meltdown, as happened at Chernobyl. So, being shutdown is not a guarantee against melting down. However, as long as the core stays submerged, then it should stay cool enough to avoid melting down. I haven't read any reports that the operators are concerned about water level in the core, so a meltdown is unlikely. Worst case, you could open up a valve on the primary and stick a hose in it.

The Chernobyl accident was a power excursion during low power operation (high void coefficient region) that lead to a steam explosion. The core was not melted but was literally blown sky high because there was no containment building.

+1. This post was much more valuable than the article.

Nuclear authorities now saying there is a high possibility of meltdown.

http://twitter.com/Reuters/statuses/46439520094273536

> IAANRO (I Am A Nuclear Reactor Operator

WDYJUAULAAATIEIATDTPOTAESYKIWNBUA? - Why did you just use an unnecessarily long abbreviatory acronym and then immediately expand it and thus defeat the purpose of the abbreviation, especially since you know it will never be used again?

To juxtapose with the IANAL that is imprinted in all our minds (just behind our reading eyeballs) to show that he does have authority on this subject.

It was a trap set to catch people with no sense of humour.

It's a long-running Internet meme. I believe it began with IANAL (I am not a Lawyer).

Please be aware that there is a lot of scare-mongering and "worst-case" scenarios being reported in the press. (Enviros don't want to waste a crisis for their anti-science agenda).

It would not be unusual for there to be radiation released during an emergency reactor shutdown (scram) with equipment damage due to the earthquake. It does not necessarily imply core damage or melt down. The primary coolant system of a BWR is radioactive due to neutron activation but that type of radioactivity is short lived, emergency release during over pressure may have been necessary to maintain the integrity of the cooling system. If the reactors are shutdown the situation is fairly stable and the operators have numerous options (and time) to deal with the equipment failure and insure the core is adequately cooled of residual heat. I am waiting for more info as not enough details are getting out at this point...

N.B. I used to design BWR feedwater control systems. AMA

It's a testament to the quality of the reactor's design that it can survive a richter 9 earthquake.

In similar circumstances there would be immeasurable environmental damage caused by a burning coal mine or sunken offshore oil platform.

When I was in the nuclear business we used to say the best place to be during the proverbial big-one was onsite.

The operator is saying they've "lost control of the ability to control pressure in some of the reactors". The cooling systems of three reactors at another plant are "malfunctioning".

How do we read that?

I would read that in knowledge that a Japanese company producing cell phone camera gaskets where any two in a batch of 1,000 were defective would report "the manufacturing process is out of control" and the $10 an hour operator would have scrammed production until the engineers investigated and fixed the machinery.

If you knew nothing of Japanese engineering culture, would today's unceasing, relentless drumbeat of lack-of-catastrophe worry you?

When a government minister reports that the cooling system is offline and the pressure is 2.1x design norms, I don't think that's a cultural thing comparable to a 2-in-1000 bad gasket production shutdown. But maybe it is.

These guys seem pretty matter-of-fact: http://www.tepco.co.jp/en/press/corp-com/release/index-e.htm...

For example: "Reactor Core Isolation Cooling System was used to inject water into the reactor to cool it. Today at 4:50AM, water injection by Make-up Water Condensate System begun. Subsequently, at 5:32AM, the temperature of the suppression chamber exceeded 100 degrees. As the reactor pressure suppression function was lost, at 5:32AM, it was determined that a specific incident stipulated in article 15, clause 1 has occurred."

This sounds like a mechanical regulatory reporting issue.

Other text like:

"We have decided to implement measures to reduce the pressure of the reactor containment vessel for those units that cannot confirm certain level of water injection by the Reactor Core Isolation Cooling System, in order to fully secure safety."

I'm just wondering how to interpret this. For example, when they say "reactor containment vessel" do they mean the "reactor vessel" or the "containment building" in en.wikipedia.org terminology?

Why couldn't they "confirm certain level of water injection" in some units? Is it that the plant design didn't include the necessary sensors, or that they were damaged?

Its hard to read at this point... I am assuming the reactor is shutdown (rods all in) and they are dealing with residual heat (still hot enough to melt the core). The cooling systems (primary and backup and emergency core cooling) may be damaged and they are working around these problems... I would be very surprised if the failures were such that it prevented any method to cool the core. They almost certainly were able to establish some kind of core cooling but it may be temporary and require more actions to fully stabilize.

Also, don't forget these quotes are translations from Japanese and may be mis-translations or inadvertent exaggerations (very common when I worked with Japanese engineers).

I would say it's technically correct. They have lost primary and backup power to the pumps. This means they really don't have the ability to do much about the pressure right now. The reactor is basically running uncontrolled. They've been scrammed but it takes a long time to stop the reaction. They still have emergency options available like venting the primary coolant loop if the pressure gets too close the limits of the reactor. There is still plenty of time before the reactors go critical.

My details may be off (its been over 10 years) but the post scram core needs to be cooled with forced coolant for something like 30-40 hours. After that it can be cooled by boil off (assuming no core damage) but the down side is radiation release mostly due to neutron activated nitrogen dissolved in the coolant water (which dissipates in 36 hours or so).

Yeah, I meant the control rods are all in. This is a potentially dangerous suitation but there is time to still get the reators under control. I doubt the worse case would be a meltdown because you could open the primary loop and stick a hose I it.

Edit: this is a good explaination http://en.wikipedia.org/wiki/Boiling_Water_Reactor_Safety_Sy...

"(Enviros don't want to waste a crisis for their anti-science agenda)"

Let's reevaluate this in a few days. It's not looking good at this point. My experience is the opposite of yours, and it's to be highly skeptical of official statements right after a disaster.

For which reactors? Are they still operational? Is your name available somewhere that we could verify?

You're asking us to accept your authoritative statements based on credentials, but you haven't really left open the option of verifying either with research.

As a junior engineer I worked on Kashiwazaki-Kariwa Nuclear Power Station: Units 6 and 7 or K6/K7. I assisted in control system designs for the reactor internal pumps (RIPs) including supporting seismic qualification of the RIP motor controllers. Later I was the lead system engineer for the Feedwater Control System for Lungmen Units 1 and 2 going up in Taiwan. No way to prove it so I could just be a dog posting on the internet.

Good enough for me. Now there's a record of it, and I thank you for your honesty.

> Is your name available somewhere that we could verify?

Does it matter? Sheesh, it's a comment on a forum. He's probably legit. If he's not, who cares? Are you a government leader needing to make a decision that will effect millions and it's all hinging on the veracity of some forum comment here on HN?! :-)

This is why we should be investing in thorium reactors:

http://en.wikipedia.org/wiki/Thorium#Thorium_as_a_nuclear_fu...

They apparently self-regulate in the event of a power loss, plus they can be used to "burn up" spent fuel from traditional reactors.

That doesn't really apply here. Any decent nuclear reactor will shut itself down when things get hairy. The reactors in question all shut down, very nice and orderly. The remaining issue here is dealing with the decay heat from the fission products in the fuel. That is what's overtaxing the cooling system right now.

In the meanwhile, I'm glad we have invested in conventional safety systems for legacy reactors.

'150 micro sievert per hour in control room' - not so bad as I feared, as long as it's not rising.

http://www.yomiuri.co.jp/national/news/20110312-OYT1T00153.h... via google translate.

Correction: 3km evacuation radius (TEPCO bulletin [1]), 10km radius residents urged to remain indoors (NHK).

Evacuation has been instructed by the national government to the local residents within 3 km radius of Fukushima Daiichi Nuclear Power Station

Measurement of radioactive material (Iodine, etc.) by monitoring car indicates increasing value compared to normal level. One of the monitoring posts is also indicating higher than normal level. We will continue monitoring discharge of radioactive material from exhaust stack and discharge canal, etc.

We have decided to implement measures to reduce the pressure of the reactor containment vessel for those units that cannot confirm certain level of water injection by the Reactor Core Isolation Cooling System, in order to fully secure safety.

http://www.tepco.co.jp/en/press/corp-com/release/11031210-e....

Updated: NHK now says evacuation zone expanded to 10km after all. http://www3.nhk.or.jp/daily/english/12_25.html

Your guess is as good as mine.

Asahi Shimbun has the most detailed English-language report so far: http://www.asahi.com/english/TKY201103110812.html

Situation is somewhat ambiguous, understandable given the confusion and circumstances. Commentator in Japan expressed '90% confidence', however.

http://yokosonews.com/live English audio live, mainly translation of...

http://www.ustream.tv/channel/tbstv live japanese tv

Ustream pages have annoying 30 second advert on load.

http://www3.nhk.or.jp/nhkworld/index.html English, but slow to update

http://www.tepco.co.jp/en/press/corp-com/release/index-e.htm... Power company hourly bulletins

http://www.bbc.co.uk/news/world-asia-pacific-12720219 some live material, updates a bit erratic at the moment.

> Situation is somewhat ambiguous, understandable given the confusion and circumstances.

In fact, I am amazed how well-understood the situation is considering the circumstances. We're less than 24 hours after one of the five strongest earthquakes on human record, half a world, a language, and a culture away - that we know as much as we do about the situation is a marvel in itself.

Yokoso news is Ueno Katz, open source curator and web programmer, BTW.

http://en.katzueno.com/about/

>Three of the Fukushima Daiichi reactor's six units shut down because of the earthquake, while operations at the other two were out due to "regular inspection," the Tokyo Electric Power Co. said in a news release Saturday.

I always wondered what happened to the sixth replicant.

Both reactors at the plant have been damaged, and officials say they have "lost control" of the pressure, according to Reuters.[1]

[1] http://www.businessinsider.com/fukushima-nuclear-plant-2011-...

EDIT: this is the latest update from business insider

Updated, but no new information - just a compliance statement.

http://www.tepco.co.jp/en/press/corp-com/release/11031213-e....

http://www.tepco.co.jp/en/press/corp-com/release/11031212-e....

http://www.nsc.go.jp/NSCenglish/documents/laws/8.pdf

Well, it's certainly reassuring to see that people here don't fall for these scare tactics easily. Can't say the same for most other web communities.

New TEPCO bulletin just confirms expansion of evacuation zone to 10km around Daiichii and Daini plants (ie #1 and #2). No other news, which is the closest thing to good news.

http://www.tepco.co.jp/en/press/corp-com/release/11031211-e....

This saddens me deeply. Two reactors damaged, the officials stating they have lost control of the pressure. I hope the Japanese people find a way to secure the site, but I'm afraid the world must be getting ready for another Chernobyl.

Multiple nuclear engineers on Hacker News have written that the situation is, effectively, far less dire than Three Mile Island. All of them have said there are still options and time before core damage is even on the radar. You're scaring a lot of people for no reason.

I trust Bob the self-proclaimed nuclear engineer on HN more than CNN, anyway, even though I have no idea Bob is who he says he is.

My post was before the nuclear engineer appeared on this thread and my sources were the publicly available ones, which portrayed things rather grim.

Maybe i was not very subtle, but you must understand that i too am scared, having experienced the Chernobyl events and the aftermath (European here). But most of the downvoters don't even know what that feels like. Did i over exaggerate my worries? Perhaps. I'm not known to be an overly optimistic person.

Thanks for giving me the chance to reply.

One of the fundamental reasons that Chernobyl occurred lies in how that reactor was designed. Russian nuclear reactors were designed to be over-moderated, while modern power reactors are under-moderated.

The moderator is the substance which slows down the neutrons to a speed where they're likely to fission with the Uranium-235 in the fuel. This is typically water. Water can also absorb neutrons, so it has a poison effect as well. When the moderating effect of the water dominates its poison effects, the reactor is said to be under-moderated. When the moderator is reduced (for example, when it boils away), the reactor becomes less efficient, so it reduces power. This is called a negative temperature coefficient.

The Soviets, however, designed their reactors to be over-moderated, for efficiency. Thus, when the water heated up, and started boiling away, the net result was to increase the efficiency of the reactor (a positive temperature coefficient), since the water was more of a poison than a moderator. Because the reactor is now more efficient, it got even hotter, and boiled more water away. You know the rest.

We've learned a lot about designing safe reactors since Chernobyl, and it's extremely unlikely that an accident on the scale of Chernobyl will happen again (not only because of the moderation issue).

I hope this helps to alleviate your concerns. If you have any further questions, please feel free to ask me.

What was so bad aboout Chernobyl?

Just for comparison:

According to Wikipedia (http://en.wikipedia.org/wiki/Chernobyl_disaster): "It is estimated that there may ultimately be a total of 4,000 deaths attributable to the accident, due to increased cancer risk."

According to http://nextbigfuture.com/2008/03/deaths-per-twh-for-all-ener...: In the USA about 30,000 deaths/year from coal pollution from 2000 TWh.

So in the USA each year 7.5 times more people die due to the use of coal energy, than all of the people who died due to Chernobyl.

Unfortunately there is a irrational fear of nuclear power in most European states (and also the rest of the world). It seems that most people would prefer climate-damaging coal energy with a higher fatality-rate per year, compared to relatively safe nuclear energy with an extremly low fatality rate per year (even if you count in the accidents that happen every now and then).

And let's face it: If Japan would replace nuclear energy with other energy types, then a large percentage of those replacements would be coal (as it impossible to obtain all the required energy from renewable sources with today's technology).

The downvotes are undoubtedly because there is far too much FUD around nuclear reactors, and detractors invariably point to Chernobyl and suggest that it's the inevitable consequence of using nuclear power. In fact, the nuclear reactors in use nowadays are very different from that one in ways that effectively prevent another disaster of that type.

Basically, it's a huge shame that such a useful technology is demonized due to the Soviets' shoddy workmanship, so supporters of nuclear power respond very harshly to things perceived as fearmogering.

Chernobyl was a result of Soviet disregard for safety and human lives, not nuclear power.

Chernobyl was the result of a systemic failure too complex to sum up in one sentence.

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