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World Is Ignoring Most Important Lesson From Fukushima
mdsolar writes "Kenichi Ohmae, an MIT-trained nuclear engineer also widely regarded as Japan's top management guru, is dean of Business Breakthrough University. In the CSM he writes: 'Fukushima's most important lesson is this: Probability theory (that disaster is unlikely) failed us. If you have made assumptions, you are not prepared. Nuclear power plants should have multiple, reliable ways to cool reactors. Any nuclear plant that doesn't heed this lesson is inviting disaster.'"
Or use a different type of reactor that doesn't rely on electricity for cooling. See any of Kirk Sorensen's liquid-fluoride thorium reactor talks on YouTube. His talk at Ted is a good 10,000 overview and only 10 minutes long: http://www.youtube.com/watch?v=N2vzotsvvkw
That has nothing to do with probability theory. It turns out that you can predict how much wealth people have from one to the next very neatly. Failure comes in when you assume that the distribution is Gaussian. It's not; it's log-normal. The billionaire is no more an outlier in that distribution than a pauper.
For those who don't follow reactor tech and don't know whats being talked about, liquid sodium reactors use literally a vat of salts and radioactive material in a magma-like sludge. There is a plug at the bottom of the vat with a melting point that is well above operating spec, but well within reach if the reactor lost cooling. If all other failsafes are disabled, the plug melts and all the molten sludge runs into 2-3 smaller tanks. The reaction then stops being self sustaining, and you just have to recover the containment units and repair the reactor. Its literally idiot proof barring a fault line opening a chasm beneath the plant or a direct asteroid impact.
There are also gravity-fed means of cooling conventional reactors, but I wouldn't call any of them fool proof. Liquid sodium seems like the best bet to me from a safety standpoint, at least as far as using up existing nuclear material. Thorium reactors show promise as well, but since we have a ton of reusable nuclear material liquid sodium would be my choice from a practicality standpoint.
He is referring to a passive cooling systems (aka. convection cooling, gravity cooling or natural cooling). Such systems are great and essential safety feature in modern reactors, and Fukushima Daiichi actually had a passive emergency cooling system. However, with current technology such systems can only contain the decay heat for up to 72 hours. It is only a temporary system, giving technicians time to restore external power to cooling pumps. This can be problematic in a catastrophic situation (such as natural disaster).
I am an MIT trained nuclear engineer than specializes in Probabilistic Risk Assessment. The first thing we should note is the PRA has had many benefits for the nuclear industry. Once you calculate the risk, and understand the contributors, you understand how to make things safer.
http://mydocs.epri.com/docs/CorporateDocuments/SectorPages/Portfolio/Nuclear/Safety_and_Operational_Benefits_1016308.pdf
The thesis of this article has a few problems, though the conclusion isn't horribly off base. The first problem is that he believe probability theory was applied to ignore the risk of the tsunami. The opposite is true. In fact, probabilistic hazard assessment of the tsunami showed the site to be horribly under prepared in 2006 (10% chance of exceeding the design basis in 50 years or about 1 in 500 per year [which is high for nuclear reactors]). There were even more studies in later years before the tsunami hit. This was just plain bad management and shows what may happen when you ignore updated risk information.
http://enformable.com/2011/10/new-exposed-scandal-shows-tepco-calculations-in-2006-showed-probability-of-worst-case-tsunami-dramatically-increased-10-over-50-years-utility-took-no-countermeasures/
The main point though, that no matter how unlikely a single event is (in this case a tsunami), you ought to have some countermeasures, is not bad. That is why PRA is used in combination with deterministic defense-in-depth measures at well designed, operated, and managed nuclear reactors. Mobile emergency diesels should be available to all reactors and are in the United States. This is a feature that Fukushima did not have. At the end of the day though, ceoyoyo is right. Even with multiple methods of cooling a reactor, you can not eliminate the possibility of core melt and release of radionuclides to the public. You can only ensure the release is acceptably infrequent. This brings us full circle to the fact that using probability theory to focus on the high risk stuff is good and that Fukushima failed to do this.
That being said, even in the case of passively cooled reactors such as fast reactors, massive earthquakes (1 in 1,000,000 per year or less), could destroy the water tank or piping required for passive cooling to take place. I would argue that while one should not ignore earthquakes and other rare external events below a certain probability. The burden would be onerous to use events below 1 in 100,000 per year as a design basis. This is in line with previous regulatory safety goal and can be seen in use in debate over the transition break size rule. A plug for my journal article is below. If you are wondering which author I am, the hint is that I am not the NRC commissioner.
http://www.sciencedirect.com/science/article/pii/S0029549311008284
From what I understand pebble-bed reactors don't even count on gravity-fed cooling. The reaction simply stops if it gets too hot, effectively setting a maximum temp that won't burn through concrete.
Of course, pebble-bed was more about demonstrating idiot-proof safety than practical power generation, but it would actually work just fine (if not as cheaply as more sophisticated designs).
Socialism: a lie told by totalitarians and believed by fools.
Actually, the plug in the bottom is not made of any other substance. It is simply reactor melt that is cooled by an external system to keep it from flowing.
You are correct however in that if, for any reason, external cooling of this "freeze plug" is stopped, the plug melts and the reactor content drains to split storage tanks stopping the reaction.
The stopping of external cooling may be due to all power generation is lost (no power to cooling), external system is destroied or ruined (natural disaster) or everybody on the plant has already left and the plant is left to fend for itself and fails (zombie invasion).
As you say however, it seems to me too, to be the best solution so far.
A benefit of Fukushima (if we look hard) is that the research on other types of reactors are now starting again, even though they can't produce nuclear weapons.
Molten salt reactors introduce a new problem though: the material is highly corrosive, and there are few materials that have even been tested that could provide a proper lifespan to the reactor. Furthermore, maintenance on the entire primary loop is like maintenance on the containment vessel for water cooled reactors: you just don't do it. This means that while the system is safer from a human fuck-up perspective, it presents brand-new engineering, construction and maintenance challenges.
Those who can, do. Those who can't, sue.
The "only" problem with pebble bed reactors is that if the pebbles are exposed to air, such as if the coolant is lost, they violently burst into flames and spew forth high radioactive and toxic smoke. Not exactly idiot proof if you ask me.
To prevent that from happening even if air leaks in, there's supposed to be a coating on ALL the pebbles that needs to be good and intact. I don't call that significant redundancy, hence I don't consider the design that safe.
The prototype pebble bed reactor in Germany was complete failure. Not only was there some serious leaks and breaches during operation, but it has also become a decommissioning nightmare. That was without anything going "seriously" wrong. They are not the magic nuclear energy elixir you have been lead to believe they are.
The Grey Goo disaster happened 3 billion years ago. This rock is covered in self replicating machines!
Then it did not work very well, considering that one of the two pebble-bed reactor ever built and operated is classified as the highest beta-contaminated site worldwide. In the other one, the pebble design caused a number of issued with feeding, as pebbles would get lodged (maybe only 0.0001% of the time) and required, well, someone to open the tube and shovel'em. Letting out lots of radioactivity in the process.
That, and pebble-bed reactors are the only ones using compressors (as opposed to liquid pumps) in the primary circuit. Compressors are mean beasts and are not unknown to surge and explode, plus the most efficient type (the axial) has its highest efficiency at the closest point to the stall line.
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