Unit #1 has had a loss-of-coolant accident (LOCA) that has presumably resulted in partial core damage. Tokyo Electric Power (TEPCO) has had to do repeated emergency ventings of steam, and Cs-137 and I-131 have been detected in the environment, both around the plant and further downwind, indicating that the cladding around the fuel rods has been degraded enough to have the steam reacting directly with fission products. There has been a hydrogen explosion in the building that surrounds the actual containment, but the containment--and more importantly the reactor pressure vessel--remain intact. TEPCO, however, has been unable to establish normal recirculation of coolant to the reactor and has resorted to pumping seawater directly into the reactor in an effort to cool it, making the reactor itself a write-off. However, because there is no circulation, TEPCO is periodically having to release radioactive steam to get the pressure low enough to pump in more water.
Unit #3 has almost exactly the same story as unit #1: Same LOCA, same partial core damage, same hydrogen explosion in the outer building, same seawater feed-and-bleed, although everything happened about a day later than in unit #1.
Unit #2 has also had the same LOCA, but it appears that the condensing torus below the reactor has partially failed, going from 3 atmospheres of hydrostatic pressure to only about 1. During the actual failure, very high levels of radiation (tens of milliSieverts an hour) were detected outside the buildings, but this has since declined. This seems (to me) to be consistent with unfiltered reactor stream going straight into the environment without being first filtered through the torus. I'm a bit hazy on exactly when the torus is used for stream venting, but I'd kind guess that the idea here is to quench as much of the steam as possible before it goes into the environment. If there's less water in the torus, we can expect the vented stream to be more radioactive in the future, but not as radioactive as when the radioactive stuff already in the torus spilled out, presumably mostly in liquid water.
Unit #4, which was shut down for maintenance, has had a fire in or near the cooling ponds for spent fuel. If the spent fuel became uncovered and caught fire, then radioactive particulates will have been wafted into the air during the fire, producing a fairly high-dose radiation cloud. The fire is now out. I'm assuming that it's not a huge deal to keep the cooling ponds at all 5 reactors covered up, but the fact that the fire occurred either means that this is harder than I'd expect or somebody is suffering from task overload. It'd be hard to blame them if it's the latter.
Up until today, the highest reading I'd heard for environmental radiation was about one milliSievert (mSv) per hour, but during the torus incident, levels as high as 8 mSv/hr were observed, falling back to about a third of that (let's called it 3 mSv/hr). For comparison, levels of 250-1000 mSv per day are considered enough to produce mild radiation sickness, so it's entirely possible that workers have spent enough time on-site to be moderately poisoned.
Radiation has been detected offshore by both the Seventh Fleet and on land in Tokyo proper, where levels are reported (on the cable news networks) as being approximately 10 times normal background, which would be something like 14 microSieverts (uSv) / day. For comparison, a chest X-ray imparts about 40 uSv. This is obviously not healthy but it's far from disastrous.
Readers of this blog (all 2 of you) will know that I'm about as pro-nuke as you can be. In terms of comparative risk, nuclear power is by far the safest form of energy ever invented. As a global warming non-denier/non-alarmist, I think that, if you're really serious about reducing CO2 emissions, nuclear power is the only option that will scale up in any reasonable time frame. And as a follower of geopolitics, I'm convinced that, in a world where world energy demands are going to skyrocket from increasing affluence in south and east Asia, adoption of nuclear power could be one of the only hopes for maintaining the fragile Pax Americana.
But that may all be out the window now.
I am still confident that the crisis in Fukushima will ultimately be brought to a less-than-catastrophic conclusion. It's gonna be worse than 3 Mile Island, but way, way, way, way better than Chernobyl. In many ways, it will be the best existence proof we have that, even when pretty much everything that can go wrong does go wrong in the middle of a 1000-year black swan event, the impact to the environment is quite minor.
But the amount of hysteria that has been whipped up by the media on this story simply is not going to subside without a long-term impact on public opinion. These people have been absolutely despicable in their eagerness to translate a pretty serious situation into a catastrophe in the interests of selling a few more eyeballs to their advertisers. I have a hard time faulting these guys for wanting to make money--that's what they're in business for, after all--but one would hope that a little bit of action in the public interest would be appropriate. Apparently not. I'd like to say that I'll consume less mainstream news, but mainstream news is still the predominant source for information, all bloggy pretense aside. These people suck, but they suck in a mission-critical kinda way.
So what now?
First, let's be clear that something went seriously wrong with the engineering. One unit having a LOCA during a giant tsunami is one thing; 3 having almost identical failures is evidence of a systemic design flaw. I've seen very little coverage of this point yet, and it is going to be the single most important lesson learned out of this whole mess.
I can think of only two failure modes that might be responsible for this. The first, and less likely, is that the heat exchangers for all units were fouled by the tsunami. These are boiling water reactors. In a BWR, the coolant water actually boils, creating (slightly radioactive) steam, which is expanded through turbines to generate electricity. The steam is then condensed (cooled) in a heat exchanger, so that the reactor pump can pump relatively cool liquid water back into the reactor. (You want to use the same water over and over if you can, because it's mildly radioactive with N-17 and tritium.) This basic recirculation loop forms the cooling cycle for the reactor.
The heat exchanger needs cool water, presumably from the ocean, to cool the purified steam/water in the reactor itself. If, perhaps, the heat exchanger is damaged because it's getting nothing but tsunami muck, then it can't re-condense the stream to liquid water. No liquid water means that the recirculated pump won't work. Voila! LOCA.
But I'd think that providing fail-safe mechanisms to get cool water would be easy to provide. Perhaps the earthquake and tsunami wiped out redundant piping for the heat exchangers? Or maybe the inlets got buried in debris? I'm guessing--no clue.
The second, more likely--and more alarming--possibility is hinted at in an article from the New York Times, on Sunday:
Christopher D. Wilson, a reactor operator and later a manager at Exelon’s Oyster Creek plant, near Toms River, N.J., said, “normally you would just re-establish electricity supply, from the on-site diesel generator or a portable one.” Portable generators have been brought into Fukushima, he said.This would be a pretty serious design flaw. And it's also a plausible one: If I were designing a redundant system, I'd consider what I had in front of me: A seawall designed to accommodate a 7 meter tsunami, a diesel backup system, and a battery backup. And I'd assume that those systems would allow me enough time to fly in a portable generator if everything went pear-shaped. But I could see myself overlooking the fact that the electrical connections I start out with are the only ones I'll ever get to use, because the switching area is flooded out.
Fukushima was designed by General Electric, as Oyster Creek was around the same time, and the two plants are similar. The problem, he said, was that the hookup is done through electric switching equipment that is in a basement room flooded by the tsunami, he said. “Even though you have generators on site, you have to get the water out of the basement,” he said.
So, at the very least, there's going to be a significant "lessons learned" phase to any rehabilitation of the nuclear industry. It will be incredibly painful, because the industry has marketed itself as having thought of everything. That won't fly, now. Instead, they're going to have to re-brand themselves a bit more humbly. That's a bit of a tight-rope act. Nuclear power needs to be perceived as being absolutely bullet-proof.
The other piece of fallout, if you'll pardon the expression, from the unit #4 fire is that the waste problem is going to go from being something that reasonable people could pooh-pooh to an absolute showstopper. I predict that we'll have legislation outlawing the use of temporary cooling ponds for anything other than waste that's simply too hot to move, and I'm also willing to bet that ponds will be mandated to be retrofitted with hermetic, fire-proof containments. That's a big expense, and it's also yet another licensing hoop to jump through. At the end of the day, I think the argument that a centralized storage facility isn't really necessary just went out the window. At the same time, I'll bet that this accident significantly weakens the case for closed-cycle reprocessing, which of course is really the proper solution to the waste disposal problem.
Ultimately, the one thing that may save the nuke industry is the fact that containment held: "Look everything went wrong, and we destroyed the plant, but the amount of radiation released was minimal." Making that case will require a lot of careful marketing and much more education on when radiation is and isn't dangerous. The public is scared to death of this stuff, and the media is more than happy to prey on their fears in the interest of ratings. This is going to be a tough slog.
UPDATE 1:19 PM CDT: The radiation dose level for a while was higher than I understood (search for the "15 March, 2011, 11:25 UTC" update):
At 00:00 UTC on 15 March a dose rate of 11.9 millisieverts (mSv) per hour was observed. Six hours later, at 06:00 UTC on 15 March a dose rate of 0.6 millisieverts (mSv) per hour was observed.
These observations indicate that the level of radioactivity has been decreasing at the site.
As reported earlier, a 400 millisieverts (mSv) per hour radiation dose observed at Fukushima Daiichi occurred between Units 3 and 4. This is a high dose-level value, but it is a local value at a single location and at a certain point in time. The IAEA continues to confirm the evolution and value of this dose rate. It should be noted that because of this detected value, non-indispensible staff was evacuated from the plant, in line with the Emergency Response Plan, and that the population around the plant is already evacuated.
Update 3/20/11: Here's a handy-dandy radiation dosage chart.