Nuclear Experts Explain Worst-Case Scenario at Fukushima Power Plant | Hacker News Reader

Nuclear Experts Explain Worst-Case Scenario at Fukushima Power Plant

scientificamerican.com

94 pointsgommm77 comments

"we're in a land where probability says we shouldn't be."

You, sir, need better advisors.

Go easy... "it was the earthquake and tsunami." they didn't go together in any of the scenarios they ran.

Are you shitting me? This is Japan. Earthquakes happen very often and it's well known even by common people that they are closely followed by tsunamis. The fact that they didn't go together in any of the scenarios is mindblowing.

Fairly sure Ratfish was being sarcastic.

Your comment broke my sarcasm detector.

According to Wikipedia: http://en.wikipedia.org/wiki/Tsunami#Generation_mechanisms

"The principal generation mechanism (or cause) of a tsunami is the displacement of a substantial volume of water or perturbation of the sea. This displacement of water is usually attributed to either earthquakes, landslides, volcanic eruptions, or more rarely by meteorites and nuclear tests."

Like the previous gentleman stated. Better advisers?

EDIT: spelling

Yes, this part of the article was incredibly hilarious.

To be fair, the plant has operated through thirteen [1] previous earthquakes in Japan since its first reactor reached criticality in 1970 [2].

[1] http://en.wikipedia.org/wiki/List_of_earthquakes_in_Japan

[2] http://en.wikipedia.org/wiki/Fukushima_I_Nuclear_Power_Plant...

The earthquake and tsunami weren't the coupled failures they were talking about. It was the loss of external power and backup generators. This is what they didn't expect, because it is hard to predict the probability of an event big enough to trigger these two things failing at the same time.

Yes, it's indeed hard to predict an earthquake to take out the external power and the subsequent tsunami to take out the backup generators on a coastline facility.

(Note: This was sarcasm)

How big of a tsunami was required? How big of a earthquake would be required to generate such a wave? How much water would be needed to reach the facility? How much to damage it? What about damaging backups?

Sarcasm aside, it is easy to predict that the facility would be at risk for an earthquake/tsunami combo. The hard part is to predict how much of one to prepapre for. Remember, even in this neck of the woods, the was a quake of historic proportions.

Isn't that partly why they have a secondary backup?

It's interesting. I've been reading the science subreddit and a lot of people are holding this up and some kind of engineering triumph, but to me it's an absolute engineering failure. Even if nothing bad happens from this point forward, two reactors were almost certainly destroyed and they'll have to sit dormant for a long while before they can be properly cleaned up. And as far as I can tell, there's still a very real risk of meltdown/containment vessel breach.

From my perspective, the root cause of what happened is that no one anticipated an event that would simultaneously cause failures in multiple systems (power loss, and destroy probably multiple redundant generators). It's easy to say after the fact that of course someone should have thought about that, in your words they should have had "better advisors", but I'm not sure how useful it is. All nuclear accidents that I'm familiar with were unanticipated. Can anyone really argue that they all just had bad advisors or engineers?

To me, this is the real argument against nuclear power and I say this as someone who still thinks that overall it's a good idea. How can we say something is truly safe when the accidents that did happen were not anticipated?

I think it's too soon to say that this failure mode was never considered or even conceived of in the contingency planning for the power plant. If you have a source that says otherwise, please provide a link.

Keep in mind that this is currently estimated to be the biggest earthquake in the recorded history of Japan. It's completely unreasonable to expect stuff to totally not break when the big one hits. If some reactors are damaged beyond repair, that's understandable, as long as the radiation is contained well enough to keep the public safe. After all, good safety plans will always be willing to sacrifice expensive infrastructure in order to save lives.

Using "biggest in recorded history" as an approximation for "biggest possible" seems weak to me. Proper engineering will look at the numbers and account for events outside of the historically observed range, but within the probability distribution. The "biggest event we see in 1,000,000 simulations of the lifetime of the plant" is likely much larger than the "biggest we've seen in history."

Which isn't to say that it was bad engineering. Just that this being the biggest quake in history is not an excuse.

Sure you can't expect everything not to break when the mother of all earthquakes hits, though surely you'd expect a nuclear reactor to be failsafe in a self-sufficient manner.

Like surely they could generate the energy they need to keep the core cool from the heat it is still producing. It sounds like they are trying to do just this (not sure what the battery issue is), though if it were actually designed for this, there'd be much less of an issue.

The earthquake was big, but in building a reactor on the PACIFIC RIM you set up your worst case scenario to cover a 1000-year event centered underneath the structure, and with handsome margins.

This was a contingency that was planned for, but for some reason the systems are failing. The measures being taken now are clearly ad hoc, rather than part of an orderly contingency plan.

Then when the ten-thousand year earthquake happens, you say thousand-year wasn't enough, it was bad engineering etc. Hindsight.

The scenario is slightly more complicated: power loss, loss of backup power sources and not being able to solve either of those two issues before the secondary backup power source, the batteries, ran out.

We're dealing with what is almost the worst case scenario the reactors are prepared for. That the reactors should be considered lost in such a situation is by design. How is it an engineering failure if everything operates as it was designed to?

  And as far as I can tell, there's still a very real risk
  of meltdown/containment vessel breach

There is, but that is the worst scenario that the reactor is prepared for: that the fuel rods melt through the bottom of the containment vessel. There is secondary containment with a huge heat sink down there. Damage will still be contained. But as they are now pumping seawater into the reactor, we won't get to test that bit of engineering.

I'm not supporting a technology which has these kinds of worst case scenarios happening.

I'm having trouble understanding what you mean by that.

Do you mean that you are opposed to the use of technology if it's safety systems are ever fully put to the test, or are you saying that having the reactor core melt and puddle at the bottom of the room where it will eventually cool off and harden is just too catastrophically dangerous?

Either way, it's absurd. Shit happens. In this case, a big earthquake and tsunami. The fact that a safety system has to be used does not reflect poorly on the safety system. The earthquake has already killed far more people and caused more damage than even Chernobyl, and the tsunami has certainly caused more dangerous chemical contamination than whatever radiation may be released from Fukushima.

"There is secondary containment with a huge heat sink down there"

Can I ask an uncomfortable question? If that secondary containment is enough to hold the molten core, why didn't they build the first containment that way?

Oh.. right..

Think about the secondary containment as the graveyard. The primary containment allows production of energy and the system to actually run, while the secondary doesn't. It's hole in the ground to catch the collapsed thing.

If the black box material is enough to survive a plane crash, why didn't they they build the whole plane with blackbox material?

For the same reason your server has a UPS although it also has regular power.

After an earth quake people can move back into the area.

Living in an area where a nuclear accident happened may not possible for many years.

If there is radioactivity released, then we are talking about large scale consequences. Tokio is just 240km away from Fukushima and there are living 30 Million people. Imagine if they have to leave the city behind.

Chernobyl had a certain type of scenario with radioactive particles released of a huge area in Europe. This has still effects. For the economy of the Ukraine in means that the have a region which can 't be developed, they have to pay for the maintenance of the broken reactor for decades and for example agriculture in that area is not really possible. Nobody outside the Ukraine will buy vegetable from them.

Check out the coal power plants. They had problems during the earth quake, but they fail and that's mostly it.

The nuclear reactors are full losses costing billions and need and extremely dangerous type of further maintenance.

I don't know many people who would want to work on Fukushima later. Who should clean up the site??? Which humans do we want to give these tasks???

In Chernobyl there was a lot of radiation released. Workers had a years of typical dose in a few minutes. I don't believe for a second that workers in Fukushima will not exposed to radiation. Even the US Navy pulls a ship away from the site, because it measured radiation in 160km distance.

The worst case scenario of driving a car is meeting a drunken or sleepy driver and dying in the resulting crash. This happens thousands of times every year and seems to be an acceptable risk. I don't understand why a technology with large economic damage as the worst case scenario would be less acceptable.

There are scenarios, where a nuclear accident has a damage that makes living in that area impossible for a long time. Then you don't even have a choice whether you want to drive or not. The people of Prypjat had to leave and the region there is uninhabitable for the next 300 years. There are very few car crashes in that area.

Why do so many people only care about the worst case scenario? You should always consider the expected outcomes when arguing for or against a technology.

Sure, in the worst case a nuclear reactor can kill thousands and make large areas no longer habitable, but this event has only a tiny probability. On the other hand conventional fossil fuel plants don't have such a dramatic worst case but they produce a constant stream of greenhouse gases and other toxic fumes. How many people died because of smog? How much land will become unusable due to global warming?

It's the expected harm we should be worried about, not the worst case scenarios.

This scenario you mention about global warming is still an assumption that relies at least somewhat on probabilities. Many scientists believe global warming from CO2 emissions is highly likely, while others don't (they tend to be labeled as skeptics). Though there are too many variables that we as humans don't fully understand. So even if it is true and it makes some land unusable, it may well make other areas such as existing desert usable.

So I don't really know that this makes a tiny probability of a nuclear accident all that acceptable. That said, I'm not against nuclear energy, but the probability of accidents needs to be next to nothing. Build enough reactors near fault lines and the probability of one of them receiving an 8.9 earthquake would surely approach certainty.

This does not help the people of the Ukraine. It happened there and it affected millions of people.

The nuclear industry has a couple of worst case scenarios which are extremely frightening. From the sabotage of a nuclear facility to large scale accidents like in Japan. I know not many industries which have that.

I remember years ago, the air here in Germany was very dirty. Then there were tighter regulations and improved technology. Now the air is much better, still not good enough in some areas - but the difference is huge.

When you have an exposure of radiation here, then you can't clean it up. The particles are everywhere. Tighter regulations will not bring improvements. The damage is done. Possibly for decades.

People here accept neither coal plants nor nuclear technology. They demand that most of the investment in future energy technology goes into renewables. This will not bring improvement in a day, but after a few decades a multitude of actions will make dirty and/or energy production phased out.

This scenario is planned here for Germany in 2050. Fourty years from now. Under the impression of the Japanese problems with their nuclear power plants, people are willing to accelerate that.

This means that for years there will be investments in new technologies, there will be implementations of those that not everybody will like, but Germany is a country with engineering tradition and this is a challenge people like.

Good engineering prepares for worst-case scenarios. Fact of life and the only reason why good engineering is trustworthy.

I think that the greatest problem with nuclear is that we are still using reactors that were commisioned over 40 years ago!

Why the hell have they not been replaced with newer, safer, more effient reactor designs?

I'll tell you why, environmentalists. We need energy, we NEED electricity. Because of this need, and the fact that we can't build any new reactors thanks to the green lobby we are stuck with old reactors(which become riskier with age).

We cant turn them off because we need them and are not allowed to replace them.

The green movement, because of it's anti-nuclear stance is putting increasing number of lives at risk. If they were worried about safety they would make sure old plants are shut down and replaced with new ones. But they don't want this, they will only accept wind or solar.

The reason these plants haven't been replaced with newer ones is NOT environmental lobbying - it's because no-one has figured out how to do it economically. Decommissioning a highly radioactive power station is extremely expensive. When these things were built their proponents optimistically expected the decommissioning problem to be have been solved by now - but it hasn't.

I fully expect US nuclear power stations to end their useful lives by being sold to shell companies that promptly go bankrupt, leaving the problem (and cost) of rendering them safe to the usual suckers - the taxpayers. For generations. And generations. And generations. Our descendants are going to curse us for this for ever.

What is it that is difficult about decommissioning the plants? The leftover fuel/waste? Or is it that the equipment itself has been contaminated. If it's just the fuel/waste, then why can't it be used in one of those whizz-bang reactors that people keep talking about whenever a discussion about nuclear shows up here (or reddit, slashdot, etc)?

difference between waste products that have short lifespans and ones that have long lifespans..

In a power plant near its operational life span end you only have those waste products with long lifespans of radioactivity which no one has figured out how to do a reasonable cost decommission of as remember the plan infrastructure of the reactor vessel, etc also contains those long lifespan radioactive elements form being bombarded for 40+ years.

I was under the impression that quite a bit of the waste can be dealt with through reprocessing (which also makes money, as you get useful stuff out of it), except of course reprocessing of waste is illegal in the US...

The leftover fuel/waste is the bulk of the problem. Although the majority of the "waste" is actually usable nuclear fuel, it is illegal in the US to recycle it.

So instead, it needs to be safely buried in a place like Yucca Mountain under extremely stringent criteria (must survive 10k years with no maintenance, etc).

In France (and other places), the leftover fuel/waste is actually a valuable resource. They recycle it and get new nuclear fuel. Some of the waste products are used as radiation sources in medicine.

There's also the breeder reactor:

http://en.wikipedia.org/wiki/Breeder_reactor

The other ones that people mention are Thorium reactors, though I gather those are still theoretical...

U.S. reactor sales must be approved by the NRC, which reviews the buyer's financial position. Ad, operators must pre-fund decommissioning costs over the life of the reactor. (Obviously there are issues with estimating the cost, but it's not like they can just ignore the issue.)

So, no.

Since the development of commercial nuclear power the costs of building new reactors has risen dramatically primarily as a result of regulation introduced as a result of anti-nuclear lobbying.

https://secure.wikimedia.org/wikipedia/en/wiki/Anti-nuclear#...

Entire stations don't need to be decommisioned, but new reactors built on existing sites.

Existing U.S. plants will continue operating for another 60 years as their licences to do so are being extended by another 20 years(with a review each additional 20 years, with the same happening in other countries).

I thought it was the industry who wanted to get the profits from existing reactors instead of investing hundreds of millions to shut down a site and billions to build new ones.

The environmentalists just think that the new ones don't solve the underlying problems of security, waste disposal, etc.

I'm pro-nuclear because I care about the environment. Greens are no more monolithic than proponents of nuclear power. Maybe if you stereotyped a little less, you'd find you have more allies than you think.

Old nuclear power plants are profitable as hell for operators. That's why they want to keep running them.

Sadly, Fukushima was scheduled for retirement by the end of this month.

Citation? I haven't seen this before.

http://www.swissinfo.ch/eng/news/international/Special_Repor...

"The 40-year-old nuclear reactor facing a possible meltdown in Fukushima was originally scheduled to go out of commission in February but had its operating licence extended another 10 years."

Wow. Positive spin: So the facility was recently inspected and was in safe shape to continue operating for a long time, so the safety measures are probably working as designed right now.

Negative spin: Just as the anti nuke groups are claiming, Tepco and the govt have colluded to hide gross mishandling of normal safety procedures, leaving us in a situation with unknown dangers.

I'm hoping the reality is in the middle.

In other words, it's a magnificent example of Black Swan. Nassim Taleb will be happy.

Building a nuclear power plant on the coastline of a subduction zone in a country with a long history of earthquakes and tsunamis does seem like a questionable idea.

Yeah I don't understand why these plants weren't built on the West coast, and why they weren't built on higher ground to mitigate against tsunamis.

You can't build reactors on high ground because they need a very high coolant flow. The (elderly) Fukushima BWRs pumped 480Mw into the grid while they were running -- but that's at the far end of a lossy thermodynamic chain (steam is used to spin turbines which drive dynamos); the thermal power output is probably something like three times that. So you need a heat sink into which you can continuously dump about 1.5Gw of heat. Water fits the bill, but you need a lot of it -- either a big river, or an ocean.

Which is why civil nuclear reactors are almost always built close to the coastline.

Is it feasible/economical to have a secondary power plant to convert all that heat into electricity?

Not unless you repeal the second law of thermodynamics -- the 1.5Gw of heat was already used to generate 0.5Gw of electricity. In general, no thermal power plant can convert much more than about 40% of the input heat into useful work.

In the case of a meltdown, what exactly is the damage?

Everything?

If a meltdown does occur, damage will depend on whether or not the reactor's containment structure holds. In the case that it does hold, the plant itself is FUBAR'd but, otherwise, there isn't significant cause for concern. This would be analogous to the Three Mile Island accident -- in which a partial meltdown occurred but was successfully contained.

If the containment structure is breached, the resulting fallout will be comparable to that of the Chernobyl disaster which, like most Soviet reactors, had no containment structure whatsoever. Wikipedia has a good article on the effects of the Chernobyl disaster: http://en.wikipedia.org/wiki/Chernobyl_disaster_effects

Chernobyl was worse than just a meltdown. The graphite moderator caught fire and helped carry fallout into the atmosphere. This would not likely happen at Fukushima, as it is water-moderated, nor would the uranium fuel be able to catch fire as happened at Windscale, because modern reactors use uranium oxide instead of metallic uranium. In the event that containment is lost, there will still be contamination, but it probably couldn't be spread anywhere near as widely as the fallout from Chernobyl.

Are the containment domes intact in Japan? Edit: found this on IAEA site: "Containment remains intact at Fukushima Daiichi Units 1, 2 and 3". It doesn't even mention the 4th, but does say the explosion occurred outside unit 1s primary containment dome. What does that mean? It's outer shield is wrecked?

There's no containment dome.

http://i.imgur.com/CckjP.jpg (X)

The reactor is the red cylinder in the middle, the containment is the pear-shaped cavity it sits in, closed on top with the yellow hood and connected to that torus in the lowest-level which in case of an accident is supposed to condense the steam back into water, thereby removing heat from the containment.

The part that's exploded is the flimsy metal "hut" on top of the concrete building.

(X) from another HN comment I can no longer find, sorry, no attribution for who posted it initially

Original was

NRC: "Reactor Concepts Manual | Boiling Water Reactor (BWR) Systems"

http://www.nrc.gov/reading-rm/basic-ref/teachers/03.pdf

Here's one with labels:

http://i.imgur.com/Oj4kg.png

Magdi Ragheb, "Containment Structures"

https://netfiles.uiuc.edu/mragheb/www/NPRE%20457%20CSE%20462...

It doesn't even mention the 4th,

There are six, and units 4,5,6 were already in a cold state before the tsunami (for maintenance); they're not involved.

You could be thinking of Fukushima Daini, which has four reactors.

That comparison is not correct.

The chernobyl plant exploded because of a instantaneous power excursion to many times the rated maximum, and it contained a huge amount of Graphite (=Coal!) which caused a fire that dispersed a lot of fine-grained core material.

The activity in the reactor core(s) in Japan right now should have decayed to a heat-output that is a few % of their rated power and, to make up some vivid comparison with the reality as we know it: The reactor core should look like what you get if a blacksmith puts glowing-hot iron (which in the reactor-case magically heats itself up constantly) in water, the resulting steam bubbles are what creates the increase in containment pressure.

Even if there would be another hydrogen induced explosion there's no chance that even a tiny fraction of the amount of radioactive material set free in Chernobyl would be released to the environment.

The plant itself would not be FUBAR'd. As it stands, that reactor will never be brought back online, but the other units at the plant can still generate power. (This is assuming that containment at reactor 1 succeeds and that it would be safe for humans to be working at the plant.)

This is what happened at Three Mile Island. Reactor 2 was taken offline and retired, but reactor 1 has continued operation. [1]

[1] http://en.wikipedia.org/wiki/Three_Mile_Island_accident#Curr...

Why aren't all reactors mandated to keep a huge tank of emergency water at some height, so that you only need to open some bulkhead and gravity will ensure that the reactor gets cooled during the 7 or so days it takes to cool down. No batteries, no diesel, no offsite power needed.

This is actually the case for the design of some of the newer ALWR style reactors.

There are 3 or more holes at different heights, designed so that the most water flows in the early hours of cooling when the most cooling is needed, then tapering off to 2 then 1 holes with the water flow lessening over time.

As someone who lives in Shanghai, 1850km away, I wonder if I should go a bit further away as a precaution? During the Chernobyl accident the nuclear clouds reached up to 2500 kms away from Chernobyl...

You should probably move away to avoid the air pollution in Shanghai.

Depends on the prevailing winds, which I think generally go from west to east in the northern hemisphere, but no idea how things actually work in that area.

Dominant winds go to the Pacific, even if there is meltdown and containment breach, California is more at risk than China is.

As someone who lives in California, 8800km away, I wonder if I should go a bit further away as a precaution...? ;-)

You should probably move away to avoid the air pollution in California.

Things are moving fast. TEPCO(Tokyo Electric Power Company) reported that they have restored AC power to all units.

http://www.tepco.co.jp/en/press/corp-com/release/11031302-e....

You were linking to Fukushima Daini and not Daiichi http://www.tepco.co.jp/en/press/corp-com/release/11031305-e.... It doesn't mention that the AC power is restored

No, that is not the plant where the main problems are.

They are talking about the Daiichi reactors here:

http://www.tepco.co.jp/en/press/corp-com/release/11031305-e....

Lesson: Don't build systems whose steady state is a catastrophe.

Serious suggestion for our Japanese friends http://nukalert.com

added: looks like they have a page for Japan http://nukalert.jp

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