There is a rather remarkable article at the IEEE site. That’s the Institute of Electrical and Electronics Engineers. As nuclear power plants have a lot of electrical equipment in them, and it was a failure of electrical power that lead to the cascade failure, these folks have a strong interest in just what really happened. Their description is, IMHO, likely to be the most correct we’re likely to get for quite a while.
I strongly suggesting reading the whole thing and not just the snippets I’m going to put here as a ‘tease’. It reads better as written and it has some good and technically oriented pictures in it.
The “bottom line” is that there were several simple things that could be done differently that would prevent such an accident from happening again; yet since they were not done, the cascade failure has resulted in several cities being abandoned for the foreseeable future and nuclear power being ‘on the rocks’ in the industrialized west.
Some selected quotes:
24 Hours at Fukushima
A blow-by-blow account of the worst nuclear accident since Chernobyl
By Eliza Strickland / November 2011
On the other hand, close study of the disaster’s first 24 hours, before the cascade of failures carried reactor 1 beyond any hope of salvation, reveals clear inflection points where minor differences would have prevented events from spiraling out of control. Some of these are astonishingly simple: If the emergency generators had been installed on upper floors rather than in basements, for example, the disaster would have stopped before it began. And if workers had been able to vent gases in reactor 1 sooner, the rest of the plant’s destruction might well have been averted.
There is a picture of a room full of very large electrical equipment (that looks like giant motors and perhaps pumps) that are all under water. It is a gallery of pictures of equipment where clicking on the image let’s you page through the kind of photos that technical folks take, documenting the equipment and its condition. One shows a large control panel with a bunch of batteries in a row, connected by ‘jumper cables’, clearly scrounged from vehicles. Looks like 10 or 11 batteries, so at 12 VDC each, that would be 132 max and at 10 VDC (about where they are tapped out) 120 VDC. I wonder if the equipment was designed to run on DC, or if they were able to tap in just after a full wave bridge rectifier that made 120 VDC in normal use, followed by a DC Chopper and high frequency (so smaller sized inductors) DC power supply? Just wondering how ‘creative’ these guys had to become…
The world’s three major nuclear accidents had very different causes, but they have one important thing in common: In each case, the company or government agency in charge withheld critical information from the public. And in the absence of information, the panicked public began to associate all nuclear power with horror and radiation nightmares. The owner of the Fukushima plant, the Tokyo Electric Power Co. (TEPCO), has only made the situation worse by presenting the Japanese and global public with obfuscations instead of a clear-eyed accounting.
In the basements of turbine and reactor buildings, 6 of the 12 diesel generators shuddered to a halt as the floodwaters inundated them. Five other generators cut out when their power distribution panels were drenched. Only one generator, on the first floor of a building near unit 6, kept going; unlike the others, all of its equipment was above the water line. Reactor 6 and its sister unit, reactor 5, would weather the crisis without serious damage, thanks in part to that generator.
The isolation condenser, which relied on convection and gravity to perform its cooling function, should have helped keep the water level high in unit 1’s core through the crisis. But operators had turned off the system just before the tsunami by closing its valves—and there was no electric power to reopen them and let steam and water flow. Workers struggled to manually open the valves on the IC system, but experts believe the IC provided no help after the tsunami struck.
In the plant’s parking lots, workers raised car hoods, grabbed the batteries, and lugged them back to the control rooms. They found cables in storage rooms and studied diagrams. If they could connect the batteries to the instrument panels, they could at least determine the water levels in the pressure vessels.
TEPCO did have a backup for the emergency generators: power supply trucks outfitted with high-voltage dynamos. That afternoon, emergency managers at TEPCO’s Tokyo headquarters sent 11 power supply trucks racing toward Fukushima Dai-ichi, 250 km away. They promptly got stuck in traffic.
At around 9 p.m., operators finally plugged the car batteries they’d collected into the instrument panels and got a vital piece of information—the water level in reactor 1. The information seemed reassuring. The gauge registered a water level of 550 millimeters above the top of the fuel assembly, which, while far below normal safety standards, was enough to assure the operators that no fuel had melted yet.
But TEPCO’s later analysis found that the gauges were wrong. Months later, calculations would show that the superheated water inside the reactor 1 pressure vessel had dropped all the way below the bottom of the uranium fuel rods shortly before operators checked the gauge, leaving the reactor core completely uncovered.
It was after midnight when the first power supply trucks began to arrive at the site, creeping along cracked roads. The trucks parked outside the unit 2 turbine building, adjacent to the troubled unit 1, where workers had found one undamaged power control panel. In the darkness, they began snaking a 200-meter-long power cable through the mud-caked building in order to connect it to the power control panel. Usually trucks are used to lay such a cable, which weighed more than a ton, but that night 40 workers did the job by hand. It took them 5 hours.
That left one fire engine to cool the overheating reactor 1. This truck was the best hope for getting water into the pressure vessel quickly, but it took hours to maneuver it through the plant’s wreckage.
At 3:36 p.m., a spark flashed in the darkness of the reactor building, and hydrogen gas ignited. With a roar, the top of the reactor building exploded.
The roof shattered and the walls splintered; fragments of the building flew through the air. Chunks of rubble cut into the cable leading from the power truck, and the flow of current stopped; now the pumps could not be turned on, and freshwater could not cascade into the core. Other pieces of debris sliced into the fire engine hoses leading from the seawater pit. Smoke billowed upward, radiation levels soared, and the workers fled Fukushima’s first radioactive ruin. It wouldn’t be the last: The battle to contain the catastrophe during the first 24 hours was lost, and the explosions would keep coming.
If the explosion had not happened, it is likely the rest of the disaster would have been averted. They were making progress on cooling and stabilizing. How could the explosion have been avoided? A simple catalytic recombiner in the higher areas of the roof structure. (Or, one might suggest, a window biased open that is held closed by electromagnets…) Just having the electrical equipment control panels located on upper floors instead of in the basement. Generators located higher up slope, or in higher stories. Several specific ‘lessons learned’ are listed. Generators in places away from where water accumulates. Having systems intended to run without power manageable without power and with the ability to turn it on without power. Have standby power trucks close, not 250 km away (but not IN the likely disaster area…) Have independent and very secure batteries to power the instruments installed. Put in those H2 recombiners. Put filters on vents that do not need power to work (so if you need an emergency venting, you don’t need power to do it safely).
In other words, design more of the plant to be passively safe and not need electricity while making the electricity more disaster tolerant. And plan how to get rid of H2 from a core accident and / or spent fuel rod coolant failure. WITHOUT electric power…
It also looks like preventing accidental gas coupling between buildings is also important:
TEPCO reports say the problems in reactor 4 were probably due to hydrogen gas that leaked in from reactor 3; despite early reports to the contrary, the spent fuel rods stored in pools in reactors 4, 5, and 6 were covered with water throughout the accident and never posed a threat.
I’d also suggest that parking a half dozen nuclear reactors on the same chunk of sea shore in a Great Quake and tsunami region is not so bright on the face of it. Spread them out a bit more and put them up slope some more. Longer pipes to the ocean are not THAT expensive, considering the alternative of ‘fratricide’… I’d also suggest that maybe having some kevlar fire hoses and kevlar shielded power cables on those emergency trucks might be a good idea too.
The article also lists a main index article with more about Fukushima:
That link has about 9 other links on the top page. Several look interesting. From “Germany’s Nuclear Free Future” to “Aftermath of a Disaster Zone” to “China Remains Committed to Nuclear Power”. It is clear from the quality of the first article that those others are going to be information dense and prone to direct and honest evaluation of the facts.