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Plutonium belongs to the class of elements called transuranic elements whose atomic number is higher than 92, the atomic number of uranium. Essentially all transuranic materials in existence are manmade. The atomic number of plutonium is 94. Plutonium has 15 isotopes with mass numbers ranging from 232 to 246. Isotopes of the same element have the same number of protons in their nuclei but differ by the number of neutrons. Since the chemical characteristics of an element are governed by the number of protons in the nucleus, which equals the number of electrons when the atom is electrically neutral (the usual elemental form at room temperature), all isotopes have nearly the same chemical characteristics. This means that in most cases it is very difficult to separate isotopes from each other by chemical techniques.

The amount of material necessary to achieve a critical mass depends on the geometry and the density of the material, among other factors. The critical mass of a bare sphere of plutonium-239 metal is about 10 kilograms. It can be considerably lowered in various ways. The amount of plutonium used in fission weapons is in the 3 to 5 kilograms range. According to a recent Natural Resources Defense Council report (1), nuclear weapons with a destructive power of 1 kiloton can be built with as little as 1 kilogram of weapon grade plutonium(2). The smallest theoretical critical mass of plutonium-239 is only a few hundred grams.

The even isotopes, plutonium-238, -240, and -242 are not fissile but yet are fissionable–that is, they can only be split by high energy neutrons. Generally, fissionable but non-fissile isotopes cannot sustain chain reactions; plutonium-240 is an exception to that rule. The minimum amount of material necessary to sustain a chain reaction is called the critical mass. A supercritical mass is bigger than a critical mass, and is capable of achieving a growing chain reaction where the amount of energy released increases with time.

Plutonium-239 and plutonium-241 are fissile materials. This means that they can be split by both slow (ideally zero-energy) and fast neutrons into two new nuclei (with the concomitant release of energy) and more neutrons. Each fission of plutonium-239 resulting from a slow neutron absorption results in the production of a little more than two neutrons on the average. If at least one of these neutrons, on average, splits another plutonium nucleus, a sustained chain reaction is achieved.

In contrast to nuclear weapons, nuclear reactors are designed to release energy in a sustained fashion over a long period of time. This means that the chain reaction must be controlled–that is, the number of neutrons produced needs to equal the number of neutrons absorbed. This balance is achieved by ensuring that each fission produces exactly one other fission. All isotopes of plutonium are radioactive, but they have widely varying half-lives. The half-life is the time it takes for half the atoms of an element to decay. For instance, plutonium-239 has a half-life of 24, 110 years while plutonium-241 has a half-life of 14.4 years. The various isotopes also have different principal decay modes. The isotopes present in commercial or military plutonium-239 are plutonium-240, -241, and -242. Table 2 shows a summary of the radiological properties of five plutonium isotopes. The isotopes of plutonium that are relevant to the nuclear and commercial industries decay by the emission of alpha particles, beta particles, or spontaneous fission. Gamma radiation, which is penetrating electromagnetic radiation, is often associated with alpha and beta decays.

Table 3 describes the chemical properties of plutonium in air. These properties are important because they affect the safety of storage and of operation during processing of plutonium. The oxidation of plutonium represents a health hazard since the resulting stable compound, plutonium dioxide is in particulate form that can be easily inhaled. It tends to stay in the lungs for long periods, and is also transported to other parts of the body. Ingestion of plutonium is considerably less dangerous since very little is absorbed while the rest passes through the digestive system.

Plutonium-239 is formed in both civilian and military reactors from uranium-238. The subsequent absorption of a neutron by plutonium-239 results in the formation of plutonium-240. Absorption of another neutron by plutonium-240 yields plutonium-241. The higher isotopes are formed in the same way. Since plutonium-239 is the first in a string of plutonium isotopes created from uranium-238 in a reactor, the longer a sample of uranium-238 is irradiated, the greater the percentage of heavier isotopes. Plutonium must be chemically separated from the fission products and remaining uranium in the irradiated reactor fuel. This chemical separation is called reprocessing. Fuel in power reactors is irradiated for longer periods at higher power levels, called high “burn-up”, because it is fuel irradiation that generates the heat required for power production. If the goal is production of plutonium for military purposes then the “burn-up” is kept low so that the plutonium-239 produced is as pure as possible, that is, the formationo of the higher isotopes, particularly plutonium-240, is kept to a minimum. Plutonium has been classified into grades by the US DOE (Department of Energy) as shown in Table 5.

It is important to remember that this classification of plutonium according to grades is somewhat arbitrary. For example, although “fuel grade” and “reactor grade” are less suitable as weapons material than “weapon grade” plutonium, they can also be made into a nuclear weapon, although the yields are less predictable because of unwanted neutrons from spontaneous fission. The ability of countries to build nuclear arsenals from reactor grade plutonium is not just a theoretical construct. It is a proven fact. During a June 27, 1994 press conference, Secretary of Energy Hazel O’Leary revealed that in 1962 the United States conducted a successful test with “reactor grade” plutonium. All grades of plutonium can be used as weapons of radiological warfare which involve weapons that disperse radioactivity without a nuclear explosion.

Benedict, Manson, Thomas Pigford, and Hans Wolfgang Levi, Nuclear Chemical Engineering, 2d ed. (New York: McGraw Hill Book Company, 1981). Wick, OJ, Editor, Plutonium Handbook: A Guide to the Technology, vol I and II, (La Grange Park, Illinois: American Nuclear Society, 1980). Cochran, Thomas B., William M. Arkin, and Milton M. Honig, Nuclear Weapons Databook, Vol I, Natural Resources Defense Council. (Cambridge, Massachusetts: Ballinger Publishing Company, 1984) Plutonium(IV) oxide is the chemical compound with the formula PuO2. This high melting point solid is a principal compound of plutonium. It can vary in color from yellow to olive green, depending on the particle size, temperature and method of production.[1]

However, the fast neutron reactors also have potential drawbacks, including a potentially riskier cooling system.

Under this new approach, the reactor can still be sealed and run without being reopened for 40 to 60 years, Reynolds says.

He says that “inhaling 910 becquerels or more of plutonium-238 is believed to slightly raise the possibility of cancer.” He adds that this will equal a cumulative radiation exposure of 100 millisieverts in 50 years… just from the plutonium-238. “Even if one were to have inhaled plutonium soon after the explosions took place, it’s hard to think that the amount was enough to have any effects health-wise.” Even the Nuclear Safety Commission of Japan disagrees, saying “We do not take the position that plutonium is safe in amounts up to 910 becquerels.” Read More: Unknowns about radioactive materials warrant vigilance amid delayed gov’t action

The angler/journalist Abe did die of acute lymphocytic leukemia on September 16 at the age of 24 after having been hospitalized on August 26. His friends and people at the magazine didn't think it was because of the nuke accident, but they do not rule that out. It is unknown at this point, they say. (If you read Japanese, you can read about it on this site.)

the sheer amount of radioactive rubble is proving difficult to process. The municipal government of Kashiwa, in Chiba Prefecture to the west and south of Tokyo, recently shut down one of its main incinerators, because it can’t store any more than the 200 metric tons of radioactive ash it already has that is too contaminated to bury in a landfill.

According to the California-based Fukushima Fallout Awareness Network (FFAN), burning Fukushima’s radioactive rubble is the worst possible way to deal with the problem. That’s because incinerating it releases much more radioactivity into the air, not only magnifying the contamination all over Japan but also sending it up into the jet stream. Once in the jet stream, the radioactive particles travel across the Northern Hemisphere, coming back down to earth with rain, snow, or other precipitation.

Radiation used to be a word that evoked serious concern in a lot of people. However, the nuclear industry and its supporters have done a masterful job in allaying public fears about it. They do this in significant part by relying on outdated and highly questionable data collected on Japanese atom bomb survivors, while at the same time ignoring and dismissing inconvenient but much more relevant evidence that shows the actual harmful effects of radiation exposure from nuclear accidents. Author Gayle Greene explains this well in a recent article here. In their attempt to win the public over to their viewpoint, nuclear proponents even trot out the dubious theory of radiation hormesis, which says that low doses of radiation are actually good for you, because they stimulate an immune response. Well, so does something that causes an allergic reaction. But I digress…

“Plutonium is biologically and chemically attracted to bone as is the naturally occurring radioactive chemical radium. However, plutonium clumps on the surface of bone, delivering a concentrated dose of alpha radiation to surrounding cells, whereas radium diffuses homogeneously in bone and thus has a lesser localized cell damage effect. This makes plutonium, because of the concentration, much more biologically toxic than a comparable amount of radium.”

different radioisotopes give off different kinds of radiation—alpha, beta, gamma, X ray, or neutron emissions—all of which behave differently. Alpha emitters, such as plutonium and radon, are intensely ionizing but don’t penetrate very far and generally can’t get through the dead layers of cells covering skin. But when they are inhaled from the air or ingested from radiation-contaminated food or water, they emit high-energy particles that can do serious damage to the cells of sensitive internal soft tissues and organs. The lighter, faster-moving beta particles can penetrate far more deeply than alpha particles, though sheets of metal and heavy clothing can block them. Beta particles are also very dangerous when inhaled or ingested. Strontium-90 and tritium, a radioactive form of hydrogen, are both beta emitters. Gamma radiation is a form of electromagnetic energy like X rays, and it passes through clothing and skin straight into the body. A one-inch shield of either lead or iron, or eight inches of concrete are needed to stop gamma rays, examples of which include cobalt-60 and cesium-137—one of the radionuclides of most concern in the Fukushima fallout

The behavior of radioisotopes out in the environment also varies depending on what they encounter. They can combine with one another or with stable chemicals to form molecules that may or may not dissolve in water. They can combine with solids, liquids, or gases at ordinary temperature and pressure. They may be able to enter into biochemical reactions, or they may be biologically inert.

In her book No Immediate Danger: Prognosis for a Radioactive Earth, Bertell notes that if they enter the body either through air, food, water, or an open wound, “They may remain near the place of entry into the body or travel in the bloodstream or lymph fluid. They can be incorporated into the tissue or bone. They may remain in the body for minutes or hours or a lifetime.”

radioactive elements, also known as radioisotopes or radionuclides, are unstable atoms. They seek stability by giving off particles and energy—ionizing radiation—until the radioisotope becomes stable. This process occurs within the nucleus of the radioisotope, and the shedding of these particles and energy is commonly referred to as ‘‘nuclear disintegration.’’ Nuclear radiation expert Rosalie Bertell describes the release of energy in each disintegration as ‘‘an explosion on the microscopic level.” This process is known as the “decay chain,” and during their decay, most radioactive elements morph into yet other radioactive elements on their journey to becoming lighter, stable atoms at the end of the chain. Some of the morphed-into elements are much more dangerous than the original radioisotope, and the decay chain can take a very long time. This is the reason that radioactive contamination can last so long

the EPA was so confident that Fukushima fallout would not be a problem for U.S. citizens that it stopped its specific monitoring of fallout from Fukushima less than two months after the meltdowns began. But neglecting to monitor the fallout will not make it go away. In fact, another enormous problem with radioactive contamination is that it bioaccumulates in the environment, which means it concentrates as it moves up the food chain.

Matsumoto said he confirmed that the data was uploaded at the NISA's home page, and he will find out why it is not on TEPCO's home page. This TEPCO's attitude toward disclosure of March information is very problematic... If the result of dust sampling analysis was disclosed at that time, it might have proven the core meltdown. Did they hide?

Some very low level nuclear waste can go into landfill-type settings. But low level waste consists of low concentrations of long-lived radionuclides and higher concentrations of these short-lived must remain sequestered for a few hundred years in subsurface engineering facilities. Medium-and high-level wastes require placing hundreds of meters below the ground for hundreds of thousands of years in order to ensure public safety. Intermediate waste containing high concentrations of long-lived radionuclides, as high-level waste, including spent fuel reprocessing and fuel waste. Because they are extremely radioactive high level waste that emits heat. There is no repository for high level nuclear waste disposal wherever in the world.

All types of energy production, money is on the front end of the process and of waste management in the back end. Macfarlane argues, however, that a failure to plan for the disposal of waste can cause the most profitable front end of a company to collapse.

Nuclear fuel discharged from a light water reactor after about four to six years in the kernel. This should be cool, because the fuel is radioactively and thermally very hot to discharge, in a pool. Actively cooled with borated water circulated, spent fuel pools are approximately 40 feet (12 meters) deep. Water not only removes heat, but also helps to absorb neutrons and stop a chain reaction. In some countries, including the United States, metal shelves in spent fuel pools hold four times the originally planned amount of fuel. The plans to reprocess fuel have failed for both economic and political reasons. This means that today is more fuel pools from reactor cores, and the fuel endangers big radiation in the event of an accident-loss of coolant, as happened in Fukushima.

Japan’s Fukushima Daiichi plant spent fuel has seven pools, one at each reactor and large shared swimming pool, dry storage of spent fuel on site. Initially, Japan had planned a brief period of storage of spent fuel in the reactor before reprocessing, but Japan’s reprocessing facility has suffered long delays (scheduled to open in 2007, the installation is not yet ready). This caused the spent fuel to build the reactor factory sites.

Countries should include additional spent fuel storage nuclear projects from the beginning, and not the creation of ad hoc solutions, after spent nuclear fuel has already begun to build. Storage location is a technical issue, but also a social and political.

"They identified this before Fukushima and before the earthquake in Virginia, but that takes on heightened significance now," Sheehan said.

The report estimated each of the 16 isotopes released by the "Little Boy" bomb and 31 of those detected at the Fukushima plant. NISA has said the radiation released at Fukushima was about one-sixth of that released during the 1986 Chernobyl disaster. "Little Boy," dropped Aug. 6, 1945, destroyed most of the city and eventually killed as many as 140,000 people. Most of the Hiroshima victims were killed in the initial heat wave, while others died from the neutron rays generated by the midair explosion or the deadly radioactive fallout. No one has died yet from radiation emitted by the Fukushima plant, where explosions caused by unvented hydrogen blew apart the upper halves of the reactor buildings but left the reactor cores in place.

he report estimated that iodine-131, another isotope that accumulates in the thyroid gland, and strontium-90, which has a 28-year half-life and can accumulate in bones, leaked from the plant in amounts roughly equal to 2½ higher than the Hiroshima atomic bomb. A separate government report released Thursday said that 22 percent of cesium-137 and 13 percent of iodine-131 released from the plant landed on the ground, with the remainder landing either in the ocean or outside its simulation area.

The National Institute for Environmental Studies said its simulation of aerial flow, diffusion and deposition of the two isotopes released from the tsunami-hit plant showed their impact reached most of eastern Japan, stretching from Iwate Prefecture in the north and to Tokyo and Shizuoka Prefecture further south. The study also showed that iodine-131 tended to spread radially and cesium-137 tended to create "hot spots.

Ministry of Education, approximately two primary – the first from the soil collected in the town Hukuzima Ookuma 3 km Fukushima, announced that it has detected trace amounts of radioactive curium. Outside the premises at the primary site has been detected for the first time. The ministry “has been released to the outside by accident. But internal exposure to radionuclides that need attention,” he explained. Curium was believed to be from this time with the operation of the reactor plutonium. Detected in soil collected on May 1 and April 29 at the point of the town Ookuma 2. On the other hand, even trace amounts of americium were detected from the soil, the ministry is “a small amount detected in the atmosphere by nuclear tests in the past” has said.

Via tsutsuji at the Physics Forum:

Low concentrations of curium were found in soil samplings in Okuma town 2 or 3 km away from the plant. This is the first time curium is found outside of the plant. It is a by-product of plutonium. The Education and Science ministry says it is a concern for internal exposure.

Clinton is a General Electric-designed 1067 MWe boiling water reactor (BWR) operated by Exelon in Illinois. It already produces cobalt-60 (Co-60) for medical use by inserting non-radioactive target rods of cobalt-59 into the reactor where they capture free neutrons and are transformed into Co-60. Now GE-Hitachi has said it is working alongside the US National Nuclear Security Administration's (NNSA) Global Threat Reduction Initiative to develop a design to allow the insertion and removal of activated molybdenum. This would be done on a weekly basis.

The letter of intent also specifies the division of responsibilities between GmP and TVA for the preparation and NRC review of a construction licence application. The letter also describes the timing of the projects activities for successful completion of major EPC milestones.   Ali Azad, GmP president and CEO, said, "We have been working with TVA for some time to evaluate the technical and regulatory requirements associated with constructing B&W mPower SMRs at its Clinch River site."   In a statement, B&W said, "GmP remains on track to deploy the first B&W mPower reactor by 2020 at TVA's Clinch River site."   The mPower Integrated System Test (IST) facility in Virginia is expected to soon begin a three-year project to collect data to verify the reactor design and safety performance in support of B&W’s licensing activities with the NRC. TVA plans to submit a construction permit application to the NRC in 2012, while GmP plans to submit a design certification application in 2013.   B&W claims that the "scalable nature of nuclear power plants built around the B&W mPower reactor would provide customers with practical power increments of 125 MWe to meet local energy needs within power grid and plant site constraints."

If China’s dash for thorium power succeeds, it will vastly alter the global energy landscape and may avert a calamitous conflict over resources as Asia’s industrial revolutions clash head-on with the West’s entrenched consumption

China’s Academy of Sciences said it had chosen a “thorium-based molten salt reactor system”. The liquid fuel idea was pioneered by US physicists at Oak Ridge National Lab in the 1960s, but the US has long since dropped the ball. Further evidence of Barack `Obama’s “Sputnik moment”,

“If it begins to overheat, a little plug melts and the salts drain into a pan. There is no need for computers, or the sort of electrical pumps that were crippled by the tsunami. The reactor saves itself,” he said.

“The reactor has an amazing safety feature,” said Kirk Sorensen, a former NASA engineer at Teledyne Brown and a thorium expert

Chinese scientists claim that hazardous waste will be a thousand times less than with uranium. The system is inherently less prone to disaster.

“They operate at atmospheric pressure so you don’t have the sort of hydrogen explosions we’ve seen in Japan. One of these reactors would have come through the tsunami just fine. There would have been no radiation release.”

why aren't the nuke reactors in the world thorium-based, by now? Evans-Pritchard says it's because thorium cannot be made into weapons: US physicists in the late 1940s explored thorium fuel for power. It has a higher neutron yield than uranium, a better fission rating, longer fuel cycles, and does not require the extra cost of isotope separation.The plans were shelved because thorium does not produce plutonium for bombs.

Evans-Pritchard further says western-lifestyle needs nuclear power, and no one has died from nuclear power: I write before knowing the outcome of the Fukushima drama, but as yet none of 15,000 deaths are linked to nuclear failure. Indeed, there has never been a verified death from nuclear power in the West in half a century. Perspective is in order.

The International Atomic Energy Agency said the world currently has 442 nuclear reactors. They generate 372 gigawatts of power, providing 14pc of global electricity. Nuclear output must double over twenty years just to keep pace with the rise of the China and India.

As the Fukushima I Nuke Plant accident has made abundantly clear to many people (clearly Evans-Pritchard is not one of them), it is the human errors that make up the accident - from the design of the reactor and the plant, fitting the pipes that don't fit, hiding the condition of the degrading parts and equipments and structures and the regulatory agency who helps the operator to hide them, to name only a few.

It doesn't quite matter how safe thorium is, when the most dangerous and unpredictable component of all is the humans