This updates the monumental catastrophe that is unwinding in Japan as cooling problems and meltdowns are underway at six nuclear reactors damaged by Friday’s earthquake and tsunami.
What is taking place now is very similar in ways to the Macondo blowout in the Gulf.
Teams are working at the limits of technology against a relentless clock under the most difficult imaginable circumstances.
- In the Gulf the blowout took place a mile under the ocean. In Japan, the breakdows are within a zone of earthquake devastation. Both environments are farthest from ideal for engineering solutions to enormous technical challenges.
- Both events have world- altering environmental consequences. The blowout contaminated the Gulf. The meltdowns threaten the northern Pacific Ocean basin including the Western US.
- Both events are gigantic in scale One meltdown is bad enough, six are hard to fathom.
- Both events are open- ended. Oil still leaks from the bottom of the Gulf and will for a long time. Radiation will leak from the multiple plants for years: parts of Japan will be ‘off limits’, perhaps for centuries.
- Both events pose larger issues as to energy sustainability. Macondo upended the cost to benefit assumptions of deepwater oil drilling. The meltdowns in Japan will do the same for nuclear power. Both nuclear and deepwater are now much more costly, perhaps unaffordably so.
All six damaged Japanese reactors share an identical problem. Their cores generate large amounts of heat by way of residual reactivity. This heat cannot be shed due to breakdowns of the reactors’ cooling circuits. Managing the reactors is easy within certain parameters. Fixing the reactors’ cooling is a task beyond the time frame reactor management allows.
- The cores produce heat even when control rods are inserted and most reactivity stops.
- Part of this is latent heat of the cores and related equipment such as pressure vessels, steam lines, turbines and pumps.
- Part of it is decay heat which is a nuclear reaction that takes place after a shutdown occurs.
- The only place for the excess heat to flow is outside the pressure vessel and containment which means the risk of radiation outside the plants.
Any reactor is a paradox. To be safe and to function as a reactor, the core must be contained within a closed system or loop. At the same time, the reactor must be thermodynamically grounded outside the loop. Without a heat sink the reactor cannot do any work. Heat must flow from inside the core to outside the plant while the carrier of the heat is contained within the loop. Managing this contradiction under ‘reasonable’ circumstances is the reason well- designed and constructed nuclear stations are among the most complex and expensive industrial facilities on Earth.
The material that transfers the reactor’s power lives inside a complex bottle. Heat flows by way of pumps from the core through pipes to a heat exchanger or sink. It is the flow that does the work not the heat itself. This is the reason most reactors are located near large bodies of water. The water provides the ‘sink’ for the reactor core. The difference between the heat of the core and the relative coolness of the sink is the installation’s thermal efficiency.
The reactor working fluid is ordinary fresh water in commercial power reactors. This water not only transfers heat but acts as a moderator to the nuclear reaction, slowing neutrons so that these might be captured by Uranium atoms allowing them to split. This water is lightly radioactive along with the equipment in the system that manages it. The loop is isolated from the rest of the world by a containment structure that is designed to hold the water or radioactivity in case of ruptures.
In a nuclear installation the interfaces between the closed reactor loop and the outside world are vitally important. Besides the containment building and pressure vessels the other critical bits of infrastructure are the heat exchanger(s), pumps, relief and isolation valves, insulation, pipes and flanges, monitoring devices, along with needed spares. All of these have to work properly or none of it does.
Water is a good reactor working fluid. It is readily available along with equipment to manage it. There is a multi- century basis of experience with managing high- pressure steam boilers and turbines in ships, industrial plants and large building complexes. Outside of reactor management itself, a ‘super’ in any large New York City apartment house can manage the steam side in a Japanese nuclear power station.
- The steam- side is where the problem is, not the nuclear side. The problem isn’t as much operator error or faulty equipment but the built- in limitation of reactors themselves and their need for heat transfer after shut down.
- The heat transfer mechanisms don’t work because of a lack of electricity to run pumps.
- The heat transfer mechanisms don’t work because critical items at all six plants are malfunctioning due to the earthquake: a broken pipe here, a malfunctioning valve there, a damaged heat exchanger in line with other bits of gear that also may be damaged or destroyed. One damaged item in a chain will render the entire chain out of service.
The managers of the plants were unprepared for a disaster of this magnitude. There were no protocols to deal with the complete structural failure of heat transfer.
Without heat transfer mechanisms, plant managers confront a difficult choice: to ‘bottle up’ the reactors inside the containment structures and hope heat dissipates and reactions slow by themselves. Taking this choice contains radioactivity inside the reactor vessel. The alternative is to allow water and heat to flow through the core into the containment. This cools the core but allows the possibility for radioactive material to escape to the outside.
So far, managers have chosen or are constrained by protocols to bottle up their reactors. This has led to pressure problems and overheating leading to the one explosion so far.
During normal operation the water is heated by the reactor past the boiling point. This is called supercriticality and is central to the general operation of high- pressure boilers. The heated water remains under pressure in a liquid state. When the superheated water is injected into a turbine it expands instantly or ‘flashes’ into steam.
Tn the stricken reactors the temperature also increases past the boiling point. As the pressure rises a decision must be made. Relieving pressure becomes problematic. Heated, pressurized water instantly flashes to steam when pressure drops. This is another similarity to the Macondo blowout where natural gas in solution expanded in the well as pressure dropped within the drill pipe causing a ‘Kick’. The kick blew out the remaining drilling mud in the pipe and riser and led to the Deepwater Horizon explosion.
A steam explosion along with the violent combustion of hydrogen is what likely took place within the containment structure @ Daiichi unit #1 yesterday. What was seen on TV was a version of the blowout with steam substituted for natural gas.
If the pressure is allowed to build the design limit of the reactor vessel will be reached. It must either be vented or the reactor vessel will fail resulting in an even greater explosion and an accompanying large release of radioactivity.
Steam/hydrogen explosions are also likely to take place in the other five reactors as managers have not figured out where to put the heat generated within the nuclear fuel assemblies. Pressure is building within reactor vessels along with hydrogen gas which ultimately must be vented. When this happens, there are explosions which become the heat transfer mechanisms. The containment structures — along with the air — become the heat sink.
- As with BP’s Macondo crews, spare parts needed to put the heat transfer infrastructure back in order are not at hand. The equipment is gigantic in scale and parts needed must be built from scratch. This is normally a time- consuming (as in multi- month or year) process
- Workers to do the work are dead, missing or not available due to the disaster.
- Work rules and safety protocols do not allow ‘jury rigged’ heat transfer mechanisms because of the risk of contamination.
- Stop- gap and jury rigs may not work at all. The ‘junk shots’ and ‘Top Kill’ failed in the Gulf. It is too soon to tell whether the sea- water flood of Daiichi unit #1 succeeded in cooling the reactor core. When fuel assemblies are damaged by runaway reactions the outcome is unpredictable since the arrangement of the fuel ‘blob’ @ the bottom of the core is unknown.
Keep in mind that the Japanese reactors are designed with structures to capture and hold fuel that escapes from the pressure vessel. Capturing runaway fuel is very much different from keeping fuel from causing a massive steam explosion or a fuel fire with a significant radiation release.
The schematic illustrates the operators’ dilemma.
- (A) is the piping by which sea water and other cooling water was forced into the cores of Daiichi units 1 and 3
- (B) is the catchment for any fuel that might escape from the pressure vessel.
- (C) is the heat transfer loop that is non- functional at all the reactors. Without it the reactors overheat.
What can be done?
The core can be flooded at a low rate. This water can then dump into the containment. The risk here is that the containment has fissures or holes that would allow this water — which would be radioactive — to escape into the outside. Opening the core and the pressure vessel would reduce the possibility of a steam explosion. The flow of water would remove heat from the core. The floor of the containment would be the heat sink.
Another approach is to start the main pumps and run the primary circuits as if the power stations are operational. Sea water could be pumped into the containments onto the primary piping and the turbines to cool them and remove heat from the core. Water would be allowed to drain out of the containment. Since this water would not reach the core it would not carry any radiation.
Cooling the primary circuit with seawater could not be done if the circuits are broken outside the pressure vessel.
Another alternative is for the operators to pump a seawater/boron cocktail into the cores. This has been done with two cores so far. The boron stifles reactivity. The water provides cooling but cannot carry heat away from the core.
It is hard to say whether the cocktail has effected the heat generating capacity of the cores. These may be too damaged to be effected by boron. If the heat cannot be tempered, managers will face additional pressure dilemmas with rising risks of more explosions.
Another alternative is to pump a concrete and boron slurry into the cores. The concrete would increase the cores’ mass and make them the heat sink. The boron would cut reactivity.
In every alternative, the reactors will be too damaged to put back into service.
The Big Picture
It is instructive to make the comparison between the Japan quake and its consequences and the similar earthquake and tsunami which took place off the Sumatran coast in 2004.
Both were powerful undersea quakes of 9.0 on the Richter scale. The Sumatra tsunami killed 200,000, largely because there was no warning system in places where the tsunami ultimately struck. In Japan, the tsunami warnings gave residents enough time to scramble for high ground. This warning system is an outgrowth of a high technology ‘good society’.
At the same time, the effects of the tsunami in the Eastern Indian ocean were limited. The countries’ coastlines surrounding the ocean were industrially undeveloped. There was little in the way of ‘infrastructure’ to break down. There were no nuclear power plants on the coast of Malaysia or Sri Lanka to melt down and contaminate the environment for decades. There were no refineries or industrial centers to add toxic goo to the seawater to soak farmland and poison children for generations.
It is Japan’s embrace of industrialization as a cultural imperative that represents the ‘bad society’. What has been happening over the past ten years is that instrument panel indicators on the on our space ship are flashing red. We have warning lights from the Gulf of Mexico, from Northern Africa, from the PIIGS, from within Washington’s corridors of power, from Wall Street’s banking houses, from homeless shelters … from mountaintops removed, from dying bats and vanishing honeybees, to rivers reduced to trickles and lakes turned to mud. More warnings are giant wildfires, insect infestations, melting glaciers and nuclear cores.
Nature is reacting indirectly to human overreach. There are limits to cultural complexity and limits to the ability of our space ship to absorb more outrages such as this nuclear disaster.
It is too early to tell what the ‘bill’ for Japan’s devastation will be. Obviously, there will be fewer lives lost there than in the East Indian basin. The social and economic costs will be very much higher for the Japanese. They may lose to a great extent their means of generating electricity which will effect their industries and the country’s ability to earn. There are 54 nuclear generating stations in Japan: six are in desperate trouble. This equals six chances of a catastrophic meltdown disaster with very large releases of radiation. It may be beyond the ability of Japan Inc. to pay this bill.
Right now I would say the ‘double dip’ has arrived.
Concerns about Japan’s earthquake-induced nuclear-power shutdowns spread to another reactor at the Tokai No. 2 Power station, but authorities said a pump is keeping the reactor cool, according to reports early Monday.
One of the two pumps used to cool the water of a suppression pool for the nuclear reactor at the Tokai plant stopped, but a second system is working, according to the English-language version of Kyodo News, which cited the nuclear safety section of the prefectural government.
Japan Atomic Power said the reactor core at Tokai No. 2 Power station has been cooled, “without any problem,” Kyodo News reported.
When authorities say, “No problem” I tend to think, “Mo problem”. I suspect reactors are having hiccups all over Japan. The pumps and pump controls as well as power supplies are the most vulnerable. These are complex, have moving parts, are temperature sensitive and carry large loads. I would not be surprised to hear of more reactor shutdowns over the next few days.
According to a statement posted on the IAEA Web site on Sunday:
Japanese authorities have also informed the IAEA that the first (i.e., lowest) state of emergency at the Onagawa nuclear power plant has been reported by Tohoku Electric Power Company. The authorities have informed the IAEA that the three reactor units at the Onagawa nuclear power plant are under control.
As defined in Article 10 of Japan’s Act on Special Measures Concerning Nuclear Emergency Preparedness, the alert was declared as a consequence of radioactivity readings exceeding allowed levels in the area surrounding the plant. Japanese authorities are investigating the source of radiation.
The count is problems with ten or eleven reactors @ four different sites. Look for that number to increase dramatically.
Keep in mind that a singe reactor problem tends to lead to others in long chains. Reactors are not out of trouble even @ cold shutdown.
Second explosion reported at Kurushima Daiichi complex.
A new explosion rocked the stricken Fukushima Daiichi nuclear power complex, wire services reported, sending a plume of smoke into the air. Japan’s nuclear safety agency said it could not confirm whether the hydrogen explosion at the plant’s No. 3 reactor had led to an uncontrolled leak of radioactivity.
The government reported Monday that radiation levels again rose above legal limits outside the crippled nuclear complex at quake-battered Fukushima, about 150 miles north of Tokyo, where authorities have been pumping seawater into overheated reactors to try to cool them down. Several other nuclear installations were under close watch for potential problems.
This is a very energetic explosion, moreso than the first. I am concerned that the pressure vessel itself has blown up as the direction of the blast is upward with large bits of debris.
If it is Daiichi unit #3 it is ominous as the core of this reactor had been flooded with seawater and boron in an attempt to cool it. One thing to keep in mind is that information has been spotty and contradictory.
Here are other sites with information and discussion of the nuclear disaster: