By BoLOBOOLNE payday loans

The ironic challenge of nuclear power safety

In studying the history of Chernobyl, Three Mile Island and the ongoing events at Fukushima, a subtle but important connection appears.  The problems at Fukushima today share a fundamental similarity with the cause of Chernobyl’s disaster. Moreover, within that similarity lies a path to making nuclear power safer.

Obviously there are huge differences.  Chernobyl was a massive disaster that killed thousands of people, the only accident to ever reach level 7 on the International Nuclear Event Scale (INES).  When I started writing this article, Fukushima was classified as level 4, although that was before the containment building at reactor 3 exploded, and trouble really started in reactor 2.  I had written that it was likely to be re-classified as level 5, and now lots of people are saying they think it might end up as level 6.  I had written that I think it’s extremely unlikely to reach level 7 where thousands of people die from radiation poisoning, but the way things are going, I’m not so confident of that any more.  :(

For a decent explanation of the defense-in-depth strategies of the Fukushima reactors, read this overly-optimistic article.  This article has been widely distributed and republished because its “you’re all over-reacting” message is a nice one to hear and it comes from a seemingly credible source, a scientist at MIT.  But the article has an interesting past, originally including a major technical confusion, mixing up moderators which speed up nuclear reactions with control rods which slow them down.  This mistake was fixed fairly quickly, and then article moved to a new location hosted by MIT, along the way shedding its re-assurances that nobody would get any more radiation than from “a long distance flight”.  Clearly things are worse than that.  Nonetheless, Fukushima was built with many layers of protection, making a Chernobyl-scale disaster much less likely.  But things just keep getting worse there.

Fukushima faces the same problem Chernobyl was trying to fix

As we’ve all probably heard, the Chernobyl reactor exploded while performing an experiment.  The causes of the disaster are many, but most fundamentally the reactor design was unstable.  Relying on cooling water as a nuclear damping material gave the RBMK-style reactors a positive void coefficient meaning that as the water boiled from liquid to gaseous state, the nuclear reaction accelerated.  This is fundamentally unstable since it can create a positive feedback cycle, as it did during their fateful experiment.  The reactor heats up, which boils water, and since steam is less dense than liquid water there is now less nuclear damping material to slow the reaction, so it goes faster.  (Modern reactors don’t do this.)  In fact just 36 seconds after operators started the experiment, somebody hit the “Oh Shit” button (which unfortunately due to even worse design actually exacerbated the problem), and seconds later the reactor core tragically exploded.  Chernobyl’s core didn’t have time to melt — it just exploded.  Then large amounts of radioactive graphite burned in a hot fire which carried toxic ash high into the atmosphere.  Thousands got sick and died.

Despite what the Soviets wanted everybody to think afterwards (and even convinced the IAEA for 7 years), the motivation for the experiment at Chernobyl was wise and well-intentioned.  The operators were not insane, stupid, nor psychotic.  They knew that their reactor relied on the external power grid to run its cooling systems.  Of course they had backup diesel generators on site in case the power grid failed, but they also knew these generators could take up to a full minute to kick in.  That seemed like too long of a gap, so they were trying something creative — using the momentum in the plant’s own steam turbine to power the cooling pumps as the turbine was coasting down, unpowered.  They were thinking to themselves “hey, we’ve got this great power source, why don’t we use it to run the cooling pumps instead of relying on the external grid.”  Great idea.  They’d tried the experiment a couple times before.  It hadn’t worked.  This time it really didn’t work.  But because the reactor was so unstable when the experiment started that a slight decrease in cooling caused it to explode, not because the idea was flawed.

The heart of Fukushima’s problems are the same — the electrical grid around them was taken out by the earthquake.  They shut down their own reactions almost instantly after the quake, and thus were no longer producing their own electricity.  So to power the cooling pumps they needed to switch to backup power.  Unfortunately the backup generators failed, most agree due to the tsunami.

So Fukushima has this ironic problem.  They have an incredibly hot thing.  Even 48 hours after stopping the fission reaction, the core is still producing megawatts of decay heat.  Enough heat to boil 20 tons of water each hour.  They need electricity to run the pumps to cool down this incredibly hot thing.  But they don’t have any electricity.  There’s an electrical power plant (a device to turn heat into electricity) with tons of heat coming off of it, but they don’t have any power to run the cooling pumps, so it overheats.  Ironic, no? This irony was at the core of the experiment that Chernobyl was attempting — use the energy of the offline plant to run the cooling systems.

Safer designs are possible

In principal it seems you should be able to design a reactor that uses this vast quantity of heat (which is power — heat equals power) to run the systems needed to cool the thing off.  Fundamentally this is just an engineering problem.  Shouldn’t we be able to design something that can keep itself cool using its own energy even when disconnected from the grid?  Happily the answer is yes.  But sadly the answer was not yes in the 1970′s when these plants were built.  Not quite at least.

In fact, these old GE Mark I reactors do have emergency core cooling systems designed to help with this, but were never meant to be a complete solution, and clearly didn’t work.  New experimental designs achieve cooling completely passively without any need for active pumping.  But AFAIK these designs have never made it to commercial scale.

A major lesson of Fukushima is clear: extremely unlikely disaster events are highly correlated with each other.  So safety systems should not have external dependencies.   I believe nuclear power has an important place in our path away from fossil fuels towards renewables, but to get there, we need safer designs.

  1. also called Leo says:

    This is an excellent entry, Leo, bringing up an aspect of the events at Fukushima that no-one else seems to have spotted.

    I would just like to correct you on the current death toll of the Chernobyl disaster being in the “thousands”. As of 2006 the World Health Organisation stated:

    “A total of up to 4000 people could eventually die of radiation exposure from the Chernobyl nuclear power plant (NPP) accident nearly 20 years ago, an international team of more than 100 scientists has concluded.

    As of mid-2005, however, fewer than 50 deaths had been directly attributed to radiation from the disaster, almost all being highly exposed rescue workers, many who died within months of the accident but others who died as late as 2004.”

    By my reckoning, we would have to see at least 70 cancer related deaths per year caused by Chernobyl radiation to reach the figure of 4000 deaths before the affected population dies of old age (it’s the most closely medically studied population in history, so this should be easy to measure). At this rate, we could not talk about “thousands” of deaths until at least 2030. Right now in 2011, it’s not even in the hundreds.

  2. Prasad says:

    We should search other resources to produce power

  3. Gareth says:

    All that is needed is a Stirling engine, a simple single-cylinder engine that will produce power from any heat source.

  4. Kamal Jain says:

    There is a fundamental conflict between energy and safety. Energy spontaneously tend to become heat. So a running reactor, by increasing entropy principle, will tend to produce heat in all kinds of situations.

    On the other hand fast cooling, or tranfer of heat, is not so spontaneous. Conversion of heat energy, kinetic energy, or even chemical energy in to electric energy is not spontaneous either. Pumping of water is not spontaneous. All these would require some intervention mechanism. Just like external sources of power could fail, these intervention mechanisms could fail too.

    Fundamentally this risk is going to be there. It is there even in producing energy on dams, because a powerful earthquake can damage a dam’s wall and then water will spontaneously want to fall and flood towns and cities around it.

    So the practical things to balance out is the level of risk. On an average 1 accident in 10-15 years is not an acceptable statistics. The statistics must be reduced and the amount of human loss per accident must be reduced too. These statistics can be reduced but in the end it comes down to dollars and cents (or yens and yuans), i.e., the price of energy goes up. For an example one could make systems that it is spontaneous for coolent to reach there in case of failure (gravity is spontaneous), but in case of false alarms, it would mean damaging some part of the reactors, and hence increasing cost of energy produced by it.

    If people want more safety they should be willing to pay a higher price for energy. As it is proven in the last 15 years, people are willing to pay a higher price for energy and it does not hurt the economy that much either (the price of gasoline at the pump has increased 4 folds and people are paying it). What people are not willing to do is if there is cheap energy available by dirty, unsafer sources then they are not willing to pay a higher price for energy from clean or safer sources. So people jointly should vote to have increased taxes on dirty source of energy (e.g., coal burning) and a tax on unsafer sources. Many reactor will go undergo security checks after this incident. Many would be found in unsatisfactory safety situation. But it will be hard to close them down as people love cheap energy, so most likely no reactor, even unsafer ones, will be closed. It would look wierd, but in that situation, a right thing will be to put a heavy safety tax on those reactors. This will encourage a bit more safety precautions being taken by those who are running these. The society is willing to take only certain amount of safety risk, and so if the risk is more, one should discourage it.

  5. KeithCu says:

    The generators worked fine until they ran out of gas. They ran out of gas because the tsunami devastated everything including the roads required to deliver more.

  6. Lamont says:

    I’d like to see proof that the diesel generators were ever likely to work, and that means that I’d like to see not just test results of the generators themselves under load, but like to know that the backup cooling system had actually been tested to run the cooling in the reactor under load.

    This is a common problem with colo systems where the backup diesels are tested every 3-6 months and they’re fired up for 5 minutes under no load and then ‘passed’ — but when they’re needed in a critical situation for longer than 5 minutes under full load then they fail catastrophically just when they’re needed most. Is there any evidence that this did *not* happen at Fukushima, and that it was solely the tsunami that was responsible for destroying the backup diesels? If there are test results, I would also like to have those vetted by a firm looking for patterns of falsification of records. Given, the lies and spin by TEPCO so far (and given all the lying that I’ve seen by incompetent executives in corporations), i do consider them guilty until proven innocent.

    And this is what I want to see reactor designs stand up against — they must pass the incompetent, lying corner-cutting executive threat. It must not be possible for a plant to melt down no matter how badly it is managed. Just like plants need to be designed to stand up to a magnitude 9.0 quake or a 10m tsunami, it needs to withstand a magnitude 9.0 management level clusterfuck.

    • leodirac says:

      Even if TEPCO execs turn out to be completely blameless, I think designing to be resistant to mis-management is a great idea.

  7. Thao says:

    Some power plants use turbine-driven pumps (thus using directly the vapor produced) to allow emergency core cooling.

  8. Don says:

    I agree with the irony and felt the same as I was listening to the disaster. I think we’re at a point where a larger group of minds/engineers needs to look at the situation. I just heard USA is planning to build more reactors. There needs to be some public oversight. It’s unacceptable, in light of Japan, that we allow short sighted suits and lobbyists to craft back door deals for the future of the human race.

  9. Ever hear of the precautionary principle?

    Instead of finding out whether or not things work by just doing them and only thinking about maybe stopping after they’ve accidentally killed a few million people, you do it backwards, and you don’t do anything that might accidentally kill a few million people until you are absolutely certain that you’ve found ways to ensure that won’t happen.

    Having industry-paid experts and politicians funded by industry investors say it won’t happen doesn’t stop it from happening. All that does is smooth the way to do things without the proper precautions, laugh and say, “What me worry?” and then end the press conference abruptly when some soon-to-be-fired reporter asks why you didn’t have KI pills stockpiled.

    Nobody has yet imagined the worst case scenario. That would be when a drone in Afghanistan or Pakistan accidentally kills the mother of one of the chief engineers of a nuclear power plant in New York or California. But he wasn’t Muslim, didn’t have an Arabic name, and his mother was only visiting with her garden club to see how the school for girls they’ve been funding there has been coming along. Oh well, accidents happen. You can’t let the possible deaths of a few million people stand in the way of progress. In fact, without killing a few million people here and there, mostly in Africa, to get the uranium for the power plants and the coltan for the electronics to run them, progress wouldn’t even be possible.

  10. Mike Griffin says:

    It is also becoming obvious that there was no procedure in place to deal with an emergency situation at Fukushima or if there was a procedure it was not followed. The problem started with the No1 reactor and it seems that all the effort was focused on solving that problem without even considering what was happening with the other reactors. Hence No3 went haywire followed by No2. Meanwhile the water was evaporating or perhaps leaking away from the pond above reactor 4 holding used fuel rods, resulting in the rods becoming exposed. This is going to be the most serious incident of all as in effect we have here a reactor without any containment. A well planned emergency procedure may well have prevented 3 of these 4 problems.

    Just a few minutes ago I was watching a guy in the US talking about two reactors there built on a fault line and on the ocean. Its quite safe he said, the sea wall is 7 metres high (it looked more like 7 feet to me) and it is built to withstand an earthquake of 7.0. The strongest we expect here is 6.5. Well after what we’ve just seen in Japan I wouldn’t be feeling so comfortable.

  11. Chris says:

    This is the best rundown of the current nuclear issue I’ve read. It seems crazy that the Fukushima Daiichi Station should be externally dependent on a diesel backup system to cool the reactors. A tsunami is a inevitable sequalae of a massive earthquake in Japan (the vast majority of their earthquakes have epicentres in the ocean). It beggars belief that commentators shoul think the current disaster an interplay of ‘unique’ circumstances.

  12. Nathan Cook says:

    Wholeheartedly agree with the conclusion that safety systems should not have any external dependencies.

    There are two further ironies:
    1) Fear of unsafe reactors leads to non-development of safer reactors. The Fukushima reactors are old ( salient quote “maintaining an existing nuclear plant is far less costly and takes less time to acquire permits than does building a new plant”), and instead of mothballing 40 year old reactors and using the fuel in newer, safer designs, the economical solution is to extend the operation of existing, less safe designs.

    2) The continued popular equivalence of Three-Mile Island and Chernobyl. I cannot count the number of times I’ve heard/read the two listed side-by-side in the same sentence. The similarity here is that the reactors got hot. The results are orders of magnitude different. Think that the public can’t be lulled into false equivalencies? Think “Saddam Hussein” and “terrorism” and where that’s gotten us.

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