Spent fuel is stored within the reactor building in a swimming pool-like concrete structure near the top of the reactor vessel
This spent fuel must be kept underwater to prevent severe releases of radioactivity, among other reasons. A meltdown or even a fire could occur if there is a loss of coolant from the spent fuel pool. The water in the spent fuel pool and the roof of the reactor building are the main barriers to release of radioactivity from the spent fuel pool.
source
At the Fukushima Daiichi nuclear power plant we are missing all sorts of roofs, walls etc..and the plants may or may not be on fire at this point. hard to tell what is going on now.
One of the reasons given early on for the explosions was hydrogen build up from venting.
Hydrogen is generated in a nuclear reactor if the fuel in the reactor loses its cover of cooling water. The tubes that contain the fuel pellets are made of a zirconium alloy. Zirconium reacts with steam to produce zirconium oxide and hydrogen gas. Moreover, the reaction is exothermic - that is, it releases a great deal of heat, and hence creates a positive feedback that aggravates the problem and raises the temperature. The same phenomenon can occur in a spent fuel pool in case of a loss of cooling water
Source
It's hard to know the exact amount of fuel beings stored but
The Fukushima Daiichi plant has seven pools for spent fuel rods. Six of these are (or were) located at the top of six reactor buildings. One "common pool" is at ground level in a separate building. Each "reactor top" pool holds 3450 fuel rod assemblies. The common pool holds 6291 fuel rod assemblies. [The common pool has windows on one wall which were almost certainly destroyed by the tsunami.] Each assembly holds sixty-three fuel rods. This means the Fukushima Daiichi plant may contain over 600,000 spent fuel rods
Source
And
Japanese commercial nuclear power plants began operation in 1970. Currently there are 53 nuclear power plants in operation. To date close to 20,000 tons of spent nuclear fuel has been generated by Japan's nuclear power program
The quantity of fission products (spent nuclear fuel) produced each year at a full-sized commercial nuclear power plants is massive. A total of approximately 50,000 times the fission products of the Hiroshima bomb are created by Japanese nuclear power plants each year, and this for the most part is cumulative, in other words the material remains radioactive. Most of this waste is being temporarily stored at nuclear power plant sites and must remain segregated from the natural environment
Source
Now this info does not apply to the MOX fuel one of the reactors use...spent Mox fuel may or may not be stored on site, I have been unable to find out about that.
Mox is a fuel that contains plutonium. There are Threads here on ATS that explain that better than I could..
Now that the news from Japan shows that we may have a spent fuel rod fire...How bad will it be?
Well this type of thing has been studied before,,just not in Japan..we have some U.S. studies we can use.
If a fire were to break out at the Millstone Reactor Unit 3 spent fuel pond in Connecticut, it would result in a three-fold increase in background exposures. This level triggers the NRC's evacuation requirement, and could render about 29,000 square miles of land uninhabitable , according to Thompson. Connecticut covers only about 5,000 square miles; an accident at Millstone could severely affect Long Island and even New York City
A 1997 report for the NRC by Brookhaven National Laboratory also found that a severe pool fire could render about 188 square miles uninhabitable, cause as many as 28,000 cancer fatalities, and cost $59 billion in damage. (The Brookhaven study relied on a different standard of uninhabitability than Thompson.) While estimates vary, "the use of a little imagination," says Thompson, "shows that a pool fire would be a regional and national disaster of historic proportions."
Source
Again this study was done in the U.S and not based on current Japan population levels around the power plants..
It also does not factor in MOX fuel
Another article says
The consequences of severe spent fuel pool accidents at closed U.S. reactors were studied by the Brookhaven National Laboratory in a 1997 report prepared for the U.S. Nuclear Regulatory Commission. According to the results, the damages resulting from such accidents for U.S. Boiling Water Reactors could range from $700 million to $546 billion, which would be between roughly $900 million and $700 billion in today's dollars. The lower figures would apply if there were just one old spent fuel set present in the pool to a full pool in which the spent fuel has been re-racked to maximize storage. Other variables would be whether there was any freshly discharged spent fuel in the pool, which would greatly increase the radioactivity releases. The estimated latent cancer deaths over the years and decades following the accident was estimated at between 1,300 and 31,900 within 50 kilometers (30 miles) of the plant and between 1,900 and 138,000 within a radius of 500 kilometers (300 miles) from the plant.
The range of consequences in Japan would be somewhat different from those outlined in the Brookhaven report, since the consequences depend on population density within 50 and 500 kilometers of the plant, the re-racking policy, and several other variables. It should also be noted that Daiichi Unit 1 is about half the power rating of most U.S. reactors, so that the amount of radioactivity in the pool would be about half the typical amount, all other things being equal. But the Brookhaven study can be taken as a general indicator that the scale of the damage could be vast in the most severe case.
Source
So how bad could it really get??
"That would be like Chernobyl on steroids," said Arnie Gundersen, a nuclear engineer at Fairewinds Associates and a member of the public oversight panel for the Vermont Yankee nuclear plant, which is identical to the Fukushima Daiichi unit 1
Washington Post
Well we could just put a fire out right?
If that fuel were exposed to air and steam, the zirconium cladding would react exothermically, catching fire at about 1,000 degrees Celsius. A fuel pond building would probably not survive, and the fire would likely spread to nearby pools. The Nuclear Regulatory Commission (NRC) concedes that such a fire cannot be extinguished; it could rage for days
Source
Well it won't be as bad as Chernobyl right?
On average, spent fuel ponds hold five to 10 times more long-lived radioactivity than a reactor core. Particularly worrisome is the large amount of cesium 137 in fuel ponds, which contain anywhere from 20 to 50 million curies of this dangerous isotope. With a half-life of 30 years, cesium 137 gives off highly penetrating radiation and is absorbed in the food chain as if it were potassium. According to the NRC, as much as 100 percent of a pool's cesium 137 would be released into the environment in a fire.
In comparison, the 1986 Chernobyl accident released about 40 percent of the reactor core's 6 million curies. A 1997 report for the Nuclear Regulatory Commission (NRC) by Brookhaven National Laboratory also found that a severe pool fire could render about 188 square miles uninhabitable, cause as many as 28,000 cancer fatalities, and cost $59 billion in damage. A single spent fuel pond holds more cesium-137 than was deposited by all atmospheric nuclear weapons tests in the Northern Hemisphere combined.
Source
yeah but Chernobyl had a melt down and explosion and graphite, that helped spread the radiation..
so we need some sort of big plume in Japan to spread the fallout
ABC news reported thick black smoke from the Chiba refinery fire was billowing 3000 ft in the air
ABC News
Last reports were there were 80+ fires burning in the area
so much smoke in fact that it can be seen from space
The photo from NASA's Aqua satellite was taken at 2:46 p.m. Local Japan Time and shows a dark plume of smoke emanating from the Sendai region. The black smoke can be seen blowing far out to sea.
NASA
also have a volcano on the south of the island belching ash as high as 6000 feet in the air
LA TIMES
Okay maybe we should evacuate people then
One of the above reports said up to 29,000 miles could be uninhabitable..but let's just evacuate 500 miles for sake of the post..
but wait a minute..we have important things in that area that have to be tended to and monitered right?
Isn't nuke plant #2 nearby right? and a plant at Onagwa that is already showing trouble..we can's just up and leave. what else is there ?
Anyone remember the Tokai plant? It is a small reconversion plant with a little fame already
The Tokaimura nuclear accident (æ±æµ·æ‘JCO臨界事故, TÅkai-mura JCO-rinkai-jiko?, "TÅkai Village JCO Criticality Accident") was at the time Japan's worst civilian nuclear radiation accident. It took place on 30 September 1999 at a uranium reprocessing facility located in the village of TÅkai, Naka District, Ibaraki. The accident occurred in a very small fuel preparation plant operated by JCO (formerly Japan Nuclear Fuel Conversion Co.), a subsidiary of Sumitomo Metal Mining Co
Wiki
Remember all that MOX fuel we talked about before,,that may or may not be in storage at the plant?
Well north of the Fukushima Daiichi nuclear power plant Is the Rokkasho Reprocessing Plant
Thats where they are making Mox fuel and storing extra spent fuel rods
The Rokkasho Reprocessing Plant (å…ヶ所æ‘æ ¸ç‡ƒæ–™å†å‡¦ç†æ–½è¨, Rokkasho KakunenryÅ Saishori Shisetsu?) is a nuclear reprocessing plant with an annual capacity of 800 tons of uranium or 8 tons of plutonium
Wiki
Rokkasho-mura has the world largest cooling pool (Fig. 4). Spent nuclear fuel transported to the reprocessing plant is stored here and it is ultimately expected to hold 3000 tons of spent fuel
source
That world record spent fuel pool has already had trouble in the past
Other safety problems have plagued Rokkasho. Last year, the cooling system of its spent nuclear fuel storage pool temporarily failed. The ventilation system in the fuel storage building had problems. Last month, the fuel pool, which at that point contained more than 1,000 nuclear fuel assemblies, leaked coolant from a loose valve; it took workers more than 15 hours to identify and fix the problem
Source
So who will be minding the store if everyone evacuates
Remember we have more than one plant in trouble..the news is showing fires, we have 600k spent fuel rods setting there, we have containment vessels leaking and on and on.....
so I leave you with this
Jet Stream
, go & make some money