Monday, March 14, 2011

Meltdown at Fukushima (2 articles)

(The jet stream flows from Japan to the northwestern US. In WWII, Japan experimented with hydrogen balloon weapons by releasing them into the jet stream, some of them made it to the US though none to populated areas. But it showed that the jet stream is pretty much a direct shot from Japan to the US.




Cut to today, the fallout from the explosion from the meltdown at Fukushima unit 1 contains cesium-137, which is extremely toxic. Also, these reactors use plutonium as well as uranium, and plutonium produces more toxic fallout than uranium. It's basically a dirtier reactor.

Have you connected the dots yet? The jet stream WILL bring that fallout to the United States 3 days after it enters the atmosphere. It exploded Saturday, and another one exploded today. Nuclear explosions produce fallout. The jet stream brings that fallout here. That means the west coast will be exposed starting today or tomorrow, but big time exposure will occur in the following days, enough to make people sick by next week. Those of us inland can expect exposure to occur by the end of the week at the latest.

From Wikipedia: "Potassium iodide (KI), administered orally previous to or immediately after exposure, may be used to protect the thyroid from ingested radioactive iodine in the event of an accident at a nuclear power plant..." The thyroid is the body's most susceptible organ to radiation poisoning. Protect it. Start taking potassium iodate today if you live on the west coast, or this week if you live inland. Protect yourselves!--jef)


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All Bets Are Off
By ROBERT ALVAREZ

Japan's government and nuclear industry, with assistance from the U.S. military, is in a desperate race to stave off multiple nuclear reactor meltdowns — as well as potential fires in pools of spent fuel.

As of Sunday afternoon, more than 170,000 people have been evacuated near the reactor sites as radioactive releases have increased. The number of military emergency responders has jumped from 51,000 to 100,000. Officials now report a partial meltdown at Fukushima's Unit 1. Japanese media outlets are reporting that there may be a second one underway at Unit 3. People living nearby have been exposed to unknown levels of radiation, with some requiring medical attention.

Meanwhile, Unit 2 of the Tokai nuclear complex, which is near Kyodo and just 75 miles north of Tokyo, is reported to have a coolant pump failure. And Japan's nuclear safety agency has declared a state of emergency at the Onagawa nuclear power plant in northeastern Japan because of high radiation levels. Authorities are saying its three reactors are "under control."

The damage from the massive earthquake and the tsunamis that followed have profoundly damaged the reactor sites' infrastructure, leaving them without power and their electrical and piping systems destroyed. A hydrogen explosion yesterday at Unit 1 severely damaged the reactor building, blowing apart its roof.

The results of desperate efforts to divert seawater into the Unit 1 reactor are uncertain. A Japanese official reported that gauges don't appear to show the water level rising in the reactor vessel.

There remain a number of major uncertainties about the situation's stability and many questions about what might happen next. Along with the struggle to cool the reactors is the potential danger from an inability to cool Fukushima's spent nuclear fuel pools. They contain very large concentrations of radioactivity, can catch fire, and are in much more vulnerable buildings. The ponds, typically rectangular basins about 40 feet deep, are made of reinforced concrete walls four to five feet thick lined with stainless steel.

The boiling-water reactors at Fukushima — 40 years old and designed by General Electric — have spent fuel pools several stories above ground adjacent to the top of the reactor. The hydrogen explosion may have blown off the roof covering the pool, as it's not under containment. The pool requires water circulation to remove decay heat. If this doesn't happen, the water will evaporate and possibly boil off. If a pool wall or support is compromised, then drainage is a concern. Once the water drops to around 5-6 feet above the assemblies, dose rates could be life-threatening near the reactor building. If significant drainage occurs, after several hours the zirconium cladding around the irradiated uranium could ignite.

Then all bets are off.

On average, spent fuel ponds hold five-to-ten 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 radioactive 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.

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. Earthquakes and acts of malice are considered to be the primary events that can cause a major loss of pool water.

In 2003, my colleagues and I published a study that indicated if a spent fuel pool were drained in the United States, a major release of cesium-137 from a pool fire could render an area uninhabitable greater than created by the Chernobyl accident. We recommended that spent fuel older than five years, about 75 percent of what's in U.S. spent fuel pools, be placed in dry hardened casks — something Germany did 25 years ago. The NRC challenged our recommendation, which prompted Congress to request a review of this controversy by the National Academy of Sciences. In 2004, the Academy reported that a "partially or completely drained a spent fuel pool could lead to a propagating zirconium cladding fire and release large quantities of radioactive materials to the environment."

Given what's happening at the Fukushima Daiichi nuclear complex, it's time for a serious review of what our nuclear safety authorities consider to be improbable, especially when it comes to reactors operating in earthquake zones.

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The Post-Tsunami Situation at the Fukushima Nuclear Plants

By ARUN MAKHIJANI
On March 11, 2011, the Fukushima Daiichi and the Fukushima Daini nuclear power plants (or Fukushima for short) experienced a severe earthquake, followed by a tsunami. This analysis relates to the Daiichi plant, which has experienced the more severe problems as of this writing so far as is known (9 p.m. March 13, 2011 Eastern Daylight Time, United States). Power from the grid was lost, and the reactors were successfully shut down as part of the emergency. But power to operate the site was still needed to remove the heat from the reactors. The Dai-chi plant has six operating boiling water reactors. The oldest, Unit 1, which appears to have had a partial meltdown of the fuel, first went critical in 1970 (and was connected to the grid in 1971. Unit 3, which also appears to have had similar problems as Unit 1, whose fuel includes mixed plutonium oxide uranium oxide fuel ("MOX fuel") first went critical in 1976. Both reactors are of the Mark 1 Boiling Water Design. They do not have the sturdy secondary containment buildings of concrete that is several feet thick typical of later reactor designs. (March 14, 6:30 a.m. note: Unit 3 has also experienced an explosion and Unit 2 appears to have lost cooling. The problems described here would likely apply to Unit 3; Unit 2 may be headed to similar problems.)

A special feature of the Mark 1 design is that the used fuel, also called spent fuel, is stored within the reactor building in a swimming pool like concrete structure near the top of the reactor vessel. When the reactor is refueled, the spent fuel is taken from the reactor by a large crane, transferred to the pool, and kept underwater for a few years. 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.

An explosion associated with Unit 1 occurred on March 12, at 3:36 p.m.[2] At first the authorities stated that this was in the turbine building next to the reactor building. However, it is the reactor building roof and part of the walls near the roof that were completely blown off leaving only a steel skeleton at the top of the building. This indicates an explosion inside the reactor building – probably a hydrogen explosion, since hydrogen is much lighter than air, it would accumulate near the top of the building. The explosion therefore seems to have occurred near the level where the spent fuel pool would be located in a Mark 1 reactor.

While Japanese authorities have stated that the reactor vessel is still intact, there has been no word regarding the status of the spent fuel pool structure, except indirectly (see below) Is it still intact? This is a critical question as to the range of potential consequences of the reactor accident.

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. In addition, there can be a fire. The mechanisms and consequences of such an accident are reasonably well known. A National Academy of Sciences study, published in 2006, is worth quoting at length:
The ability to remove decay heat from the spent fuel also would be reduced as the water level drops, especially when it drops below the tops of the fuel assemblies. This would cause temperatures in the fuel assemblies to rise, accelerating the oxidation of the zirconium alloy (zircaloy) cladding that encases the uranium oxide pellets. This oxidation reaction can occur in the presence of both air and steam and is strongly exothermic that is, the reaction releases large quantities of heat, which can further raise cladding temperatures. The steam reaction also generates large quantities of hydrogen….

[With a loss of coolant] These oxidation reactions can become locally self-sustaining … at high temperatures (i.e., about a factor of 10 higher than the boiling point of water) if a supply of oxygen and/or steam is available to sustain the reactions…. The result could be a runaway oxidation reaction referred to in this report as a zirconium cladding fire that proceeds as a burn front (e.g., as seen in a forest fire or a fireworks sparkler) along the axis of the fuel rod toward the source of oxidant (i.e., air or steam)….
As fuel rod temperatures increase, the gas pressure inside the fuel rod increases and eventually can cause the cladding to balloon out and rupture. At higher temperatures (around 1800°C [approximately 3300°F]), zirconium cladding reacts with the uranium oxide fuel to form a complex molten phase containing zirconium-uranium oxide. Beginning with the cladding rupture, these events would result in the release of radioactive fission gases and some of the fuel's radioactive material in the form of aerosols into the building that houses the spent fuel pool and possibly into the environment. If the heat from one burning assembly is not dissipated, the fire could spread to other spent fuel assemblies in the pool, producing a propagating zirconium cladding fire.
The high-temperature reaction of zirconium and steam has been described quantitatively since at least the early 1960s….[3]
The extent of the release would depend on the severity of loss of coolant, how much spent fuel there is in the pool, and how recently some of it has been discharged. The mechanisms of the accident would be very different than Chernobyl, [4] where there was also a fire, and the mix of radionuclides would be very different. While the quantity of short-lived radionuclides, notably iodine-131, would be much smaller, the consequences for the long term could be more dire due to long-lived radionuclides such as cesium-137, strontium-90, iodine-129, and plutonium-239. These radionuclides are generally present in much larger quantities in spent fuel pools than in the reactor itself. In light of that, it is remarkable how little has been said by the Japanese authorities about this problem. From the tiny amount of information available, it appears that there is a problem of cooling of the spent fuel. According to a TEPCO press release, issued on March 13, at 9 pm, Japan time:

We are currently coordinating with the relevant authorities and departments as to how to secure the cooling water to cool down the water in the spent nuclear fuel pool. [5]

This indicates that there is a spent fuel cooling problem. But there is no information on how serious it is, and whether the pool has been damaged as is leaking. It is reasonable to surmise that pumping seawater into the reactor building from the outside would be directed more at the spent fuel pool than at the reactor. According to TEPCO, the injection of seawater into the reactor vessel of Unit 1 has been successfully done. This also appears to be the case for Unit 3, as of this writing.[6] Boric acid is being added to the seawater to prevent an accidental criticality, which could happen in the reactor or in the spent fuel pool. Venting of radioactive steam from the reactors will likely have to continue.

It is unclear at this stage whether there has been venting of radionuclides from the spent fuel pool in Unit 1. Venting from the reactor has been acknowledged by the authorities. Rather high levels of radiation, over 1,200 microsieverts per hour[7] – which is more than 10,000 times natural background radiation at sea-level – have been reported outside the plant. At this level the annual allowable dose of the radiation to the public would be exceeded in less than an hour. Such levels indicate a partial meltdown in Unit 1 and possibly in Unit 3. However, while it seems to be widely assumed that the radioactivity has been emanating only from the reactor vessel (s), it is unclear whether some of it is also being released from the Unit 1 spent fuel pool, which may have been damaged by the explosion.

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.[8]

The amount of spent fuel in the Unit 1 spent fuel pool is has not been mentioned by the authorities so far. The range of consequences in Japan would be somewhat different, 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.

One hopes that the spent fuel pool in Unit 1 can be kept full of water and the various reactors can be kept cool enough to prevent much more serious consequences than have already occurred (there has been serious worker exposure and some public radiation exposure already, according to news reports[9]). But the accident makes clear that there is ample information and analysis that very grave consequences are possible from lighter water reactors – which are the designs used in Japan, the United States, and most of the rest of the world. Spent fuel pools special vulnerabilities that are different in different specific designs, but all possess some risk of severe consequences in worst-case accidents or worst-case terrorist attacks (which were studied by the National Academies in their 2006 report).

The United States should move as much spent fuel out of the pools as possible into hardened and secure dry storage. The tragedy in Japan is also a reminder that making plutonium and fission products just to boil water (which is what a nuclear reactor does) is not a prudent approach to electricity generation. While existing reactors will be needed to maintain the stability of electricity supply for some time (as is also evident from the earthquake-tsunami catastrophe in Japan), new reactor projects should be halted and existing reactors should be phased out along with coal and oil. It is possible to do so economically in the next few decades, while maintaining the reliability of the electricity system and greatly improving its security, as I have shown in my book Carbon-Free and Nuclear Free: A Roadmap for U.S. Energy Policy published in 2007, and in subsequent work that can be found on the IEER website, www.ieer.org. Carbon-Free and Nuclear-Free can be downloaded free.

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