"Status of Japanese reactors, spent fuel ponds, and possible outcomes"
Video of ruined nukes
The latest NYT banner headline is “Taming Reactors May Take Weeks.” They also have a good story today on “Danger of Spent Fuel Outweighs Reactor Threat.” CP readers learned that crucial fact back on Monday.
The Oil Drum has a useful piece today, “Fukushima Dai-ichi status and potential outcomes,” that may demystify the situation (if that’s possible).
I’ll excerpt those below, but first, an amazing video of the smoldering wreckage shot by intrepid Japanese in a low-flying helicopter:
The Oil Drum quotes one nuclear expert:
These reactors are now a total loss, but I am still disturbed by their inability to bring in portable diesel generators and restart the back-up cooling. I guess the chaos of the catastrophe is the cause.
I do question the use of seawater cooling. I hope the Japanese have considered the danger they have created by introducing oxygenated seawater into this stainless steel piping and pressure vessel at boiling temperatures. These stainless steels are extremely susceptible to chloride stress corrosion cracking:
Since residual weld stresses and tensile stress in piping, valves, control tubing, etc. are always present, Standard Operating Reactor water quality standards require keeping chlorides at parts per billion levels. Seawater has about 3.5% or 35 grams per liter of salinity!!!
I have no way of knowing how many days they have before a stainless steel component suddenly cracks, but if it were me, I would be advocating an emergency program to get pure deionzied cooling water back into this stainless steel system ASAP. In laboratory tests in boiling chlorides, cracking of stainless in tensile stress can occur within days- they have at most a few months if they keep boiling sea water in this system and yet another disaster occurs. I am sure there are competent scientists in Japan’s nuclear industry and government regulators. I hope they are on top of this threat!
ABC News just reported that the Japanese are going to try to turn back on the existing cooling system, and if that fails, the U.S. is in the process of flying in several mammoth portable cooling systems.
As of yet, there is no serious radiation threat to Americans, but the situation remains dire in Japan, as the NYT reports:
Years of procrastination in deciding on long-term disposal of highly radioactive fuel rods from nuclear reactors are now coming back to haunt Japanese authorities as they try to control fires and explosions at the stricken Fukushima Daiichi Nuclear Power Station.
Some countries have tried to limit the number of spent fuel rods that accumulate at nuclear power plants “” Germany stores them in costly casks, for example, while Chinese nuclear reactors send them to a desert storage compound in western China’s Gansu province. But Japan, like the United States, has kept ever larger numbers of spent fuel rods in temporary storage pools at the power plants, where they can be guarded with the same security provided for the power plant.
Figures provided by Tokyo Electric Power on Thursday show that most of the dangerous uranium at the power plant is actually in the spent fuel rods, not the reactor cores themselves. The electric utility said that a total of 11,195 spent fuel rod assemblies were stored at the site.
That is in addition to 400 fuel assemblies that had been in active service in reactor No. 1 and 548 in each of reactors No. 2 and 3. In other words, the storage pools hold more than seven times as much radioactive material as the reactor cores.
Now those temporary pools are proving the power plant’s Achilles heel, as the water in the pools either boils away or leaks out of their containments, and efforts to add more water have gone awry. While spent fuel rods generate significantly less heat than newer ones, there are strong indications that the fuel rods have begun to melt and release extremely high levels of radiation. Japanese authorities struggled Thursday to add more water to the storage pool at reactor No. 3.
Four helicopters dropped water, only to have it scattered by strong breezes. Water cannons mounted on police trucks “” equipment designed to disperse rioters “” were deployed in an effort to spray water on the pools. It is unclear if they managed to achieve that.
Richard T. Lahey Jr., a retired nuclear engineer who oversaw General Electric’s safety research in the early 1970s for the kind of nuclear reactors used in Fukushima, said that the Japanese authorities may not have entirely understood the importance of keeping cool the spent fuel. The zirconium cladding on the fuel rods can burst into flames if exposed to air for hours when a storage pool loses its water, he warned.
When zirconium ignites, it emits extremely hot flames that warm up everything nearby and are very hard to extinguish, added Mr. Lahey, who helped write a classified report for the United States government several years ago on the vulnerabilities of storage pools at American nuclear reactors.
Very high levels of radiation above the storage pools suggest that the water has drained in the 39-foot-deep pools to the point that the 13-foot-high fuel rod assemblies have been exposed to air for hours and are starting to melt, said Robert Albrecht, a longtime nuclear engineer who worked as a consultant to the Japanese nuclear reactor manufacturing industry in the 1980s. Spent fuel rod assemblies emit less heat than fresh fuel rod assemblies inside reactor cores, but the spent assemblies still emit enough heat and radioactivity that they must be kept covered with 26 feet of water that is circulated to prevent it from growing too warm.
Gregory Jaczko, the chairman of the United States Nuclear Regulatory Commission, made the startling assertion on Wednesday that there was little or no water left in the storage pool located on top of reactor No. 4, and expressed grave concern about the radioactivity that would be released as a result. The spent fuel rod assemblies there include 548 assemblies that were only removed from the reactor in November and December to prepare the reactor for maintenance, and may be emitting more heat than the older assemblies in other storage pools.
Even without recirculating water, it should take many days for the water in a storage pool to evaporate, nuclear engineers said. So the rapid evaporation and even boiling of water in the storage pools now is a mystery, raising the question of whether the pools may also be leaking.
The information coming from the Japanese authorities has been wholly inadequate, in part now it appears because they didn’t fully understand the situation themselves.
What comes next? The Oil Drum’s guess is as good as any:
At this point, it is necessary to lurch towards pure conjecture. Day by day, the status at Fukushima has worsened and until the situation is stabilized, it is impossible to predict the final outcome.
Much will depend on the status and location of the fuel rods and pellets in the reactor cores. If these remain largely intact and in place then they will be easier to cool and to moderate, i.e. to have the neutrons being released absorbed by boron or the control rods already in place.
If one of the cores is disintegrating and gathering as debris on the vessel floor then it becomes much more difficult to circulate cooling water and to absorb neutrons being produced. We have had much debate about whether or not it is possible for the fission chain reaction to re-start in a pile of reactor rubble. The consensus is that this is unlikely though possible. Should this happen then the energy to be contained escalates and the situation becomes more critical. Colleagues Joules Burn and Engineer Poet suggest that restarting the fission chain reaction would be self destroying since the energy produced would blow apart the pile of rubble, shutting down the fission process immediately.
The possibility remains that an explosion (hydrogen gas?) or fire (burning what?) destroys one of the containment vessels, rendering the site uninhabitable, in which case the fate of the other reactors would be left to nature. Fire in particular could spread high levels of radiation over a substantial area. Stuart Staniford at earlywarn.blogspot has produced [a] picture of what a Chernobyl scale disaster could mean for Japan.
I’ll spare you the picture. It ain’t pretty (and in any case would depend entirely upon wind patterns). Let’s all hope it doesn’t come close to that outcome