2 years, 8 months ago
There is a dearth of quality, technically correct information and commentary on the Japanese reactor accidents occurring at the Fukushima nuclear power plant. In fact, some of it is downright wrong. There is no hope of comprehensively reproducing a time line or of surveying all of the available news releases or reports. I’ll link some very good sites shortly that will assist you in studying the future commentaries and reports. Just to set the tone, if you are interested in one-and-a-half minute reading and tabloid hysteria, close this web page now. Go to the tabloids – or most MSM sites – or so-called news television (with their “nuclear expert” du jour). I won’t purvey hysteria or ignorant analysis. I’ll begin with things that can’t happen, and phrases and terms to avoid in your reading and viewing. We’ll move to a quick summary of what we know thus far about the accident(s), and close with an assessment of the consequences of this reactor accident for the future of Japan.
Perhaps the worst tabloid journalism thus far has come from Geraldo Rivera on Foxnews on Sunday evening. Thousands of souls had been swept into the sea, and Geraldo was discussing how “radiation was like that voodoo stuff – you can’t see it, and that’s what makes it scary!” The kind of hysteria extends to supposedly smart people like Charles Krauthammer, who said:
It’s a terrible potential. If you get a meltdown, of course, there is a catastrophe for the region. But also every 20 years we say let’s try again with nuclear energy, it’s clean energy — it doesn’t put stuff into the atmosphere. [Now] if you get a “China Syndrome” as in 1979 … it could put the nuclear [industry] out of business for decades.
The Daily Mail reports that “As fuel rods melt, they form an extremely hot molten pool at the bottom of the reactor that can melt through even the toughest of containment barriers.” To dispense with the myths, the China Syndrome was a movie. What happens in the analytical models, and also in actual reactor accidents like Three Mile Island (TMI) Unit 2, is that the corium, that mixture of melted fuel, cladding and other internal reactor components like control rods and guide tubes, forms in some of the channels, further blocking fluid flow. Eventually in an extreme reactor accident, much of the fuel shatters and becomes rubblized in the lower reactor vessel head. This is in fact what happened at TMI in large measure, along with some core melting.
It doesn’t require melted fuel to release fission products. Having written computer codes that model such releases, I can observe that much of the fission products are released in fuel heatup, and most releases occur prior to achieving fuel melt temperature, including most or all of the Noble Gases (Kr, Xe), much of the semi-volatiles (halogens) and some of the alkali metals (e.g., cesium). Don’t forget this point. This is important and I’ll come back to this later.
The corium isn’t modeled to melt through the lower vessel head except in the worst accidents where there is no coolant at all. This isn’t the case for the Fukushima reactors. Even in the event of complete breach of the lower vessel head, the corium doesn’t under any circumstances achieve melt-through of the lower basemat, which in some U.S. reactors is as much as 12 feet of concrete. The corium disperses and cools from the dispersal. There is no such thing as the China syndrome. That’s just a dumb ass movie. And reactors also don’t explode like nuclear weapons. Nuclear radiation isn’t voodoo, and we know how to achieve protection against it.
Now to what we know about the accident. When the tsunami occurred it disabled the offsite power to the plant. Emergency diesel generators automatically started, and they functioned for approximately one hour until they shut down due to tsunami-induced damage to their fuel supply. Power to the control valves in the reactor makeup operated until they lost battery backup. DC power from batteries was consumed after about eight hours of operation. The plant sustained a complete blackout (loss of all power), and it was at this point that fuel damage and Zirconium alloy (Zircalloy) – water interactions occurred, i.e., cladding oxidation. This is an exothermic reaction and produced more heat, adding to the fuel fission product decay (or residual) heat to be removed by the cooling system. It also produces hydrogen.
During some point in the past several days, hydrogen explosions occurred on Unit 1. In an attempt to prevent the hydrogen concentration from being above the explosive limit, releases were made from Unit 3. Ironically, it was likely a valve opening or some other electrical arc that caused the hydrogen explosion that occurred on Unit 3, further damaging not only Unit 3 but apparently also parts of Unit 2. Any hydrogen explosion that looks like this has already degraded a lot of nuclear fuel.
In spite of Russian experts who wax eloquent about how the world learned from the Chernobyl accident and how we’re better able to handle reactor accidents because of the Russian experience, the Japanese reactor accidents aren’t like Chernobyl, and it isn’t because we learned from the Russian design. I studied thousands of documents concerning Chernobyl and performed many calculations. I trained the DOE safety analysis engineers on the nuclear design characteristics of the RBMK-1000 reactor (not as a DOE employee).
The RBMK reactor design was loosely neutronically coupled, and had an overall positive power coefficient. That is, it was graphite-moderated, and since the water was a neutron poison rather than the moderator, the reactor was “over-moderated.” This means that upon a loss of coolant, the reactor experienced a power excursion. It had a positive void coefficient, leading to an increase in reactor power by a factor of 100 in less than 1 second. Furthermore, its containment structure was little more than a sheet metal “Butler Building.” The core was in flames and pouring fission products into the atmosphere. More than 30 souls perished attempting to mitigate the accident, and many more contracted cancer from the releases of radioactivity.
Despite what some of the more “conservative,” pro-nuclear “experts” have said on national TV, the Chernobyl accident was a catastrophe. I was in training with an engineer from Kiev not too many years ago, and he informed me that residents of Kiev still have to frisk their food with a GM detector and pancake probe prior to eating to ensure that they aren’t ingesting radioactivity.
So why was the RBMK reactor designed this way? For the production of weapons-grade fissile material. I have pictures of the Russians performing online refueling operations at the Chernobyl site to remove the weapons material. The Russians tried to combine commercial nuclear power with weapons production. The RBMK design is the result. U.S. reactors are designed by federal code with a negative overall power coefficient (GDC 11), which shuts the reactor down in a loss of coolant or fuel heatup.
The Fukushima reactor accidents aren’t Chernobyl because they have a hard containment design and a negative power coefficient like U.S. reactors. Unfortunately, that containment design is being breached periodically to release steam from the sea water that is flooding the core, and with the steam releases come radioactivity releases. As I said before, much of the release of fission products to the containment has likely already occurred (meaning that while it’s important to cool the core, its also the case that sedimentation, washout, plateout and other removal mechanisms are acting on the fission products (including radioactive decay).
We in the U.S. had our core melt event; it was TMI. There were essentially no releases of radioactivity and thus no health affects due to the hard containment design. The Fukushima reactor accidents are worse than TMI given the breach of containment, but with the evacuation that has already occurred, the health affects will be minimized.
The main cost now to TEPCO will be the cleanup and decommissioning of the damaged reactors, which likely have rubblized cores sitting in the reactor vessel. It will take a decade and tens of billions of dollars. Just as with the Takaimura criticality accident, we will probably see senior company officers bowing before the nation and asking forgiveness. This will probably spell the end of many careers, and the beginning of much soul searching over design and licensing basis seismic events, flood events and related design criteria.
There are many reports that have incorrect or incomplete information. The reports on exposure to the 7th fleet is remarkable for its lack of technical detail. We could perform a dose reconstitution with the available data, but we aren’t given any. There are incorrect and inconsistent units of radiation being reported, and there are technical facts gotten wrong. It’s best not to speculate on what we don’t know, and it’s best not to listen to the “experts” on television.
This is a serious reactor accident, one for the books. Nuclear engineers will be studying this accident for decades to come, and it will affect reactor regulation in both Japan and the U.S. But the Japanese worked remarkably efficiently to evacuate residents, and thus radiation exposure will be minimized. This was yeoman’s work given the state of transportation after the tsunami. The Japanese faced the perfect storm of problems, and they performed admirably.
But what this accident should not do is cause us to jettison the promising future of nuclear power because there might be some cesium uptake in Tuna in the Pacific. When nuclear workers receive regular body burden analysis to assess the radioactive content in their body, the technician can tell if they are hunters. “Do you hunt, sir? Yes, I hunt deer. Oh, that explains the Cs-137 spike I see.” The Cs-137 doesn’t come from commercial nuclear reactors. It comes from fallout from nuclear weapons testing during the 1950s and 1960s. We’ve been there and done that. It’s not a problem.
Only tabloid media could take a situation where thousands of souls were swept away in a tsunami and ignore that story for the real drama of a melted core (in which one soul has perished, and that from an industrial accident). We need to maintain our perspective, and the proper perspective isn’t to have nightmares of melt-throughs to China. We should leave that to the purveyors of hysteria.
Some good links (I will add to these later):
ANS Nuclear Cafe (for the best coverage and analysis of the Fukushima reactor accidents)
NUREG-1250, “Report on the Accident at the Chernobyl Nuclear Power Station.”
EPRI, NSAC-127, “Multidimensional Analysis of the Chernobyl Accident” (if you’re really interested in Chernobyl).