Report: Nuclear Plants Should Focus On Risks Posed By External Events

mdsolar (1045926) writes "Engineers at American nuclear plants have been much better at calculating the risk of an internal problem that would lead to an accident than they have at figuring the probability and consequences of accidents caused by events outside a plant, a report released Thursday by the National Academy of Science said. Accidents that American reactors are designed to withstand, like a major pipe break, are "stylized" and do not reflect the bigger source of risk, which is external, according to the study. That conclusion is one of the major lessons from the Fukushima Daiichi nuclear accident in Japan in 2011, which began after an earthquake at sea caused a tsunami.

Comments

already done

[Mr D from 63]

External events are considered in US plant design already, this author seems to be a bit ignorant on how the safety case for plants is built. Who cares if we refine the probability of an event is if the plant is already designed to withstand it? More total stupidity disguised as a serious study. Even highly unlikely events are designed against in our plants.

Now, Post-Fukushima, plants are adding response capabilities for apocalyptic type scenarios even though three is nobody that can provide an example of how such an event may happen for the particular site short of some major war type event. Fukushima was simple...don't put reactors that were not design to operate underwater where they can find themselves underwater. Given the situation, the outcome was quite easily predictable.

Re:already done

[mdsolar]

Matthew Wald does his homework and reports pretty accurately. Perhaps you should give some examples where he has misread the report.

Re:already done

[tp1024]

It gets better, all the way back in 1975, the Wash-1400 report listed tsunamis as one of the potential ways to knock out the safety systems of a nuclear power plant, leading to the exact same outcome we have seen. All the way to the point of having to evacuate a few thousand square kilometers, given the BWR Mark I containment. (Actually, it was just one thousand, but the rest was off-shore.)

The main problem was that just about ALL the tsunami protection in Japan (both for cities and nuclear power plants) was based on the 1960 tsunami, that came all the way across the Pacific from Chile. The result was quite a disaster, but the worst part was the completely unprotected population and certainly not the nuclear power plants. Contamination is quite reversible, 18500 dead people not so much.

Re:already done

[HangingChad]

Given the situation, the outcome was quite easily predictable.

If it was that easy FP&L would be making plans to close Turkey Point instead of expand it. That whole site is going to be underwater and, before that happens, there's going to be a storm surge high enough to swamp it. That's a guarantee which seems to fly in the face of your supposition.

I worked in the nuclear industry for nearly a decade. What I saw with my own eyes could best be described as straining out a gnat and swallowing a camel.

Re:already done

[Mr D from 63]

It will, in fact the reactors near Fukushima experienced major quakes beyond their design basis, remained intact and actually saw little or no structural damage. Only those plants that got flooded by the tsunami had problems, because they were not designed to be underwater.

If a major natural disaster hits, a nuclear plant is probably one of the safest places to be.

Re:already done

[multi io]

Now, Post-Fukushima, plants are adding response capabilities for apocalyptic type scenarios even though three is nobody that can provide an example of how such an event may happen for the particular site short of some major war type event. Fukushima was simple...don't put reactors that were not design to operate underwater where they can find themselves underwater. Given the situation, the outcome was quite easily predictable.

Can you cite any pre-Fukushima regulation that mandates this? Because if you can't, then that's a case of "hindsight is 20/20". I'm pretty sure the type of thing that happened at Fukushima has always been thought to be a "there is nobody that can provide an example of how such an event may happen for the particular site" type of scenario -- until it did happen.

Re:already done

[tp1024]

If your definition of "reasonable" is "one millionth" you'd be right, but also perfectly unreasonable. There is such a thing as natural radioactivity, it is everywhere. And if you demand that "artificial" radiation must be less than 1/10.000th of natural radioactivity in the worst contaminated areas to be "reasonable", then you suffer from a gross form hubris. Your claims about Iodine-129 neglect to mention that is has 1/1.000.000.000th of the activity of I-131. Even by your stupid definition, it's not a problem. This is further compounded by the fact that Iodine is highly mobile, most of all, it is water soluble. This means that it will be dispersed in the environment at a much greater rate than it will be concentrated in humans. In fact, it is not even detectable around Fukushima Daiichi.

You also neglect to say that the total radiotoxicity of all longlived fission isotopes is less than the radiotoxicity of the natural uranium before it went through the reactor. It is LESS than what was naturally there anyway. I know you don't care about such facts, lots of other people do.

Your body is full of potassium-40, carbon-14, thorium, uranium and their decay products. If you're so scared of radioactivity that you must demand Cs-137 to decay to one-millionth of the current concentrations before you feel safe, then go commit suicide. There is no place in the solar system that will satisfy your demands. You, sir, are a lunatic.

Re:already done

[Mr D from 63]

Plants do address what they call "beyond design basis" events with various coping scenarios over and above the prescribed design basis accidents and events. Post Fuku response is really an extension of that severe accident management element. But that is not in response to a specified event, rather the approach is to simply imagine the plant is left crippled badly in various ways and put mitigations in place to cope. Now, they simply imagine a more crippled starting point. That's all well and good and conservative, but it doesn't address an event, which was the failing at Fukushima.

Re:already done

[Mr D from 63]

Shouldn't we be designing reactors to handle any quake that is reasonably likely to occur? Japan is highly prone to earthquakes - I'd expect any reactor design to account for a very strong one.

They do, but you have to prescribe a specific requirement in the license and that is on the regulator. The actual designs handle quite a bit more than the licensed design specification, because a reactor designer will typically consider the worst site where a reactor is expected to be built, and the site specific design can be augmented if necessary. US plants have conservative earthquake requirements to start with as prescribed by the NRC, and they do consider the location. Designing a facility to withstand an earthquake is really not that big of a technical challenge.

Withstanding a tsunami is a whole different ball game... there is no margin for something like that, you either place the plant where it won't get hit, or you design it to operate underwater with destroyed surroundings... that latter is not practical.

Re:already done

[tp1024]

Go read WASH-1400, that one said 36 years before Fukushima Daiichi what would happen when a tsunami hits a nuclear power plant. The predicted result is easily comparable to what we have seen, because Japan (just like the USA) didn't bother to implement major upgrades that were demanded by law in France, Germany and Sweden. Among those are hydrogen recombiners that the Japanese demanded by law in 2012 and were bought in France where they have been implemented for decades. You may remember the hydrogen explosions? Those were predicted. The same countries also installed filtered containment vents. Which would, by themselves, have prevented uncontrolled venting into the reactor buildings, they would have filtered out 99.99% of the Cs and they also have hydrogen recombines by default. In Germany those were required in 1988, Japan followed in 2013. Japan managed to require all reactors to have at least 2 emergency generators for each reactor in 2002 (before that 3 emergency generators were sufficient for 2 reactors). By comparison, at the same time, Germany required at least 2 WORKING emergency generators for each reactor, even if one generator is out for maintenance and another breaks down due to some technical fault. In other words, they required at least 4 generators and even more, if some of them were put in a place were they might fail due to some other causes (like flooding or a plane crash).

There is no tsunami risk in Europe. But nuclear power plants must be protected against 10.000 year floods. Fukushima Daiichi (along with all the coastal cities) was protected against a rather small tsunami that hit Japan in 1960 and nobody bothered that there were larger tsunamis in 1933 and 1896 (and many more before that).

It's not about hindsight. It's a matter of a complete lack of disaster planning in Japan, which is why you had almost 20.000 dead and 400.000 lost homes (that latter figure is without the additional evacuations due to the reactor accident).

Re:already done

[Hussman32]

The reactors are fine during an earthquake because they are effectively bolted to bedrock, and the move with the earth. There was a serious earthquake a few years ago at the Kashiwaszaki-Kariwa site, and the primary systems didn't move at all. There was a lot of damage to the switchyard and non-safety systems, and there was some water sloshed out of the spent fuel pool, but the reactor started up fine after all systems were requalified.

Re:already done

[BitZtream]

Ironically, the longer the half life, the less dangerous the material is. The truly dangerous ones have relatively short half lives which will easily have them dissipate well within a human lifetime.

Re:already done

[Mr D from 63]

^you can make stuff up all you want, but there are no such thing as safety related electrical pillars. Offsite power supply is not credited in a safety analysis of the plant, and failure of those systems is just fine, as the safety related systems could more than handle the earthquake. The plant was doomed when it was inundated by water and the safety related systems became inoperable.

You should learn more about how a plant safety design basis is developed, and in particular the difference between safety related and non-safety related systems and components.

Re:already done

[Mr D from 63]

Outside power is not required to shut the plant down. There nearby plants, the ones right next door, the ones not hit by the tsunami, also lost power but shut down just fine. The Fukushima Daiichi plants were in the process of shutting down after the quake and before the tsunami, even though offsite power was lost. The emergency diesel generators had started and the units were just fine to shut down. Had the tsunami not hit, regardless of the quake, you would never have heard of Fukushima Daiichi, just like you probably can't name any of the units that survived the severe earthquake without googling.

Re:already done

[Mr D from 63]

You claimed the plant was not at all affected by the earthquake, which is wrong.

I never said the plant was not at all affected, that is another fabrication by you. The safety systems, those designed to operate after such an event, were quite capable of safety shutting down the plant after the quake. They were not capable after the tsunami hit.

Re:already done

[brambus]

Gah, the stupid, it burns!

Natural radioactivity is mainly something that hits you from the 'outside'... it hits your skin

Except for the ~5kBq of K-40 in your nerves. And the C-14 in all of your tissues. Also, cosmic radiation doesn't stop on your skin - it's comprised of extremely high energy particles at 1 GeV or more. Those sort of energies make the radiation from nuclear reactors seem like child's play. That is not to say that you'd rather be inside of a nuclear reactor - most definitely not, the flux there is many orders of magnitude larger - but it does show that cosmic rays don't just "hit your skin", but instead fire right through you and irradiate your internals quite easily.

First of all a healthy person has no Uranium or Thorium in his body.

I'd be careful with throwing around superlatives like "none", but it's probably fair to say that the abundance of actinides in most humans would be classed as "trace" at best.

you are again mixing up external radiation by natural sources with radioactive elements incorporated into the body

Except that both K-40 and C-14 are both natural and inside your body. In fact, we use C-14 abundance in tissues to date when organisms died. Whether something is or isn't natural has no bearing on where it is harmful.

The fallout is measurable every where in north Japan.

This statement, while true, is misleading, or at the very least oversimplified. We have extremely sensitive measurement equipment, but the mere detection of the presence of a radionuclide does not in itself imply any danger from it. What needs to be assessed is the particular type of radionuclide, its abundance and sample distribution, in order to be able to at least roughly assess the potential biological impacts. In pretty much any scoop e.g. topsoil you'd be able to find all manner of toxic stuff, from mercury through arsenic, lead and even to uranium - this is simply a consequence of the magnitude of Avogadro's number.

I'll leave you with just one tiny factiod: long-haul flights are associated with elevated exposure to cosmic rays, easily 20-30x sea-level background and comparable to some of the hotter parts of the Fukushima exclusion zone. This has been repeatedly assessed and demonstrated. As such, one would expect to find radiation-related cancer clusters among airline crew, who spend a sizable amount of their lives in this elevated radiation environment. And yet, no reliable evidence for this has been found so far.

Re:already done

[Solandri]

External events are considered in US plant design already, this author seems to be a bit ignorant on how the safety case for plants is built. Who cares if we refine the probability of an event is if the plant is already designed to withstand it?

Technically, the Fukushima plant was also already designed to withstand this type of event. It had sufficient backup power systems necessary to continue operating the cooling pumps in the event of a catastrophic disaster of this type.

Where they screwed up was in the redundancy of the backups. This is unfortunately a fairly common failure mode in engineering designs. Say a single diesel generator has a 10% chance of failing to start up if you try to run it during an emergency. People then naively think that if you just put 6 diesel generators into the design, then that reduces the statistical probability of failure to 1 in a million. The chance of all six generators failing is (10%)^6 = 1 in a million.

That's the correct math for generator failures due to independent internal causes. But everything changes when you talk about external causes. Suddenly you have a cause like, oh, say, a tsunmai, which can affect all the generators simultaneously. The failure mode for each generator is no longer independent, and your redundancy does nothing to decrease the odds of a failure. All they had to avoid this effect was put the generators and diesel fuel tanks in different places. But no, the typical Japanese obsession with order and symmetry* mandated that they put all their generators in a row in the same place. And the tsunami took them out and contaminated their fuel all at once. Indeed the two newer Fukushima reactors where the generators and fuel were stored in a different location got through the earthquake and tsunami just fine.

* I rag on the Japanese, but the same thing happened with the Space Shuttle Challenger. They were having problems with poor O-ring seals in the solid rocket boosters. So to reduce the probability of a failure, they just added more O-rings. That worked to stop the independent failures (burn-through due to improper seating of an O-ring in one spot). But when an external factor popped up which caused all O-rings to fail simultaneously (cold weather), the safety of the redundant O-rings was negated.

Re:already done

[tp1024]

But
a) Nobody died. (Unlike due to the direct effects of the tsunami.)
b) In places like Ishinomaki, Kesenuma, Rikuzentakata or Ofunato the people are essentially in the same situation. People can't just go back, because they now realized that those places are too darn dangerous to live in, because of the tsunami hazard. If history provides any pattern there, the towns will be abandonned for several decades upon which people will start ignoring the danger again, rebuild former settlements and then suffer the next big tsunami. All very much on the same time-scale as for the evacuation zone around Fukushima Daiichi. With the difference that the next tsunami WILL come and WILL NOT be prevented, while nuclear power plants can simply be build properly to modern standards (i.e. designed to contain a meltdown, which General Electric said this containment wasn't designed to do all the way back to 1966, as you can read in the CR-6042 manual).

c) The number of people evacuated because of radiation is a fraction (10-20%) of the total number of people who lost their homes. Most of those will be free to return in the next few years. (There is no statistic that I'm aware of saying how many people's homes were destroyed in the area that was later declared off-limits. Extrapolating from the number of dead people in the area it ought to be about 10% or 50,000, but that could be wrong.)

Re:already done

[brambus]

Comparing the 'natural' intake of C14 and other elements 'in a normal' amount with the levels in Fukushima makes you a moron. Not C14 or other minimal intake.

Contrary to your quite uneducated assertion that background radiation in a "normal" amount is somehow inconsequential compared with the radiation levels at Fukushima, they are rather comparable. We have quantified these things quite accurately. Terrestrial background is anywhere from 0.1 uSv/h (Japan) to 0.3 uSv/h (USA) in most places on the planet, ignoring outliers. By comparison, the Fukushima exclusion zone typically ranges from 0.1 uSv/h to ~15 uSv/h with the median being somewhere close to 3 uSv/h or about 10-30x background. This is comparable to radiation exposure on a long-haul flight, as I've shown you, and that has so far not been shown to result in any increased risk, even in people who work for the airline industry and spend a sizable amount of their lives in this environment.

Cosmic Ray != radioactive iod or caesium

From a radiotoxicity standpoint, they are in fact not really distinct. You may recall that Sievert is a unit of committed dose, so it expresses biological effects, not just raw counts, and is capable of accounting for the differences between internal and external emitters. Now you could argue that whole-body exposure numbers are too simplistic to accurately asses ionizing radiation impact, and I'd agree (for certain radionuclides), but this has been considered and more accurate models are available, they're just not used very often in discussions, because they're too complex to easily wrap your mind around. For a first-degree approximation, though, whole-body exposure numbers seem to be quite a good rule of thumb.

Re:How would that be even helpful?

[Mr D from 63]

Earthquake probability and characterization is a 'continuously improving' science. Knowledge improvement is factored in by the regulator. Fortunately, plants are designed to withstand very large quakes with a large design margin added on top. In reality they will withstand quakes much larger than their stated design capacity.

Stylized

[mdsolar]

It really harms the credibility of the NRC when their risk calculation come to a accident every ten thousand years while the real world rate is one every 18 years. There are ten or more near misses each year http://www.ucsusa.org/news/pre... so nuclear plants are operating far outside the claimed safety envelope.

Re:Stylized

[khallow]

while the real world rate is one every 18 years

Over 400+ nuclear reactors in the world.

Re:Stylized

[Anonymous Coward]

If the 1 in 10.000 years is per reactor, 18 years between accidents is "reasonable". With 400 reactors worldwide, that would mean approximately 25 years (~10000/400) between accidents.* Accounting for older designs, improving risk estimation, worse safety/quality standards in some parts of the world, etc. 18 years is close and not "far outside the claimed safety envelope".

Also, one "near miss" per year suggests luck, ten or more per year implies that there are enough safeties and checks in the systems to catch trouble before a catastrophe happens.

* I know this is not exact. It should be close enough. Fanatics can do the 1/(1 - ((10k-1)/10k)^400) stuff with a calculator.

Re:Stylized

[Mr D from 63]

Add that 'near miss' is not an official event defined event by the NRC , but rather that of the anti nuke group, so they decide what to call a near miss.

Re:Stylized

[khallow]

18 years*435 current reactors=7830 reactor years. Which is close to the claimed 10,000 reactor years of your original post.

Asleep

[mdsolar]

An NRC inspector had a very hard time waking a guard up at Indian Point a few years back.

Re:How would that be even helpful?

[brambus]

Japan is a bunch of islands for crying out loud.

While true, it is quite an oversimplification. Japan is very mountainous even near the shores, in some places, and it would not have been impossible to place the plant a little further "uphill" to prevent this from happening. There are several reason they placed it right on the shore, one of them being construction purposes. LWRs consist of some very heavy single-piece components and it's much easier to ship them in via boat than it is to transport them over the road. In addition, you have a readily available source of large amounts of cooling water in the world's largest heatsink.

However, had TEPCO not been a bunch of colossal asshats and not skimped on the construction and piping costs, they could have just as easily placed the thing a few miles inland and at higher elevation and none of this would have happened. In fact, if Japan ever decides to build liquid-metal cooled fast breeder reactors, it is absolutely imperative they place it somewhere it can't ever get flooded. If OTOH they decide to go with molten-salt reactors (and they should!), they could place them pretty much where ever they want, because fluoride salts don't react with water, aren't water-soluble, don't operate under high pressure and their large liquid range allows for high temperature of operation, which in turn means that passive air cooling in the event of a plant blackout is far easier to do.

Re:Most accident scenarios ...

[tp1024]

Read the NUREG-1150 or whatever more recent document (this one is from 1990 or so). You'll find that your claim is outdated by about half a century.

eight days. Gunpowder dangerous, candles are not

[raymorris]

Iodine is most dangerous because it releases all of it's radiation quickly. With a half-Life of just eight days, it releases enough energy, quickly enough, to do real harm. After a few weeks, the radiation is pretty much gone. You can visualize that as being like gunpowder, it releases its energy quickly, and that's dangerous.

Other substances release energy very slowly, over the course of hundreds of years. That's like the heat energy released from from iron rusting - it takes a long time to release the energy, so it would take a LONG time to be affected by it. You wouldn't want to keep a piece of plutonium in your pocket for 800 years, because after 200 years or so you might start to notice some affects. Except of course you'll die of other causes in about 50 years, so you'd never notice any affects from plutonium.

Iodine and other isotopes with a short half-life ARE dangerous for a little while, until they "burn up".