What do meltdown or super meltdown mean?

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Nuclear disaster and the possible consequences for health

It is still unclear how big the nuclear disaster is in Japan. Almost every minute, people receive new horror news from the Japanese disaster area. If the cooling of the affected reactors of the nuclear facilities in Fukushima cannot be restored, there is a risk of meltdown. Radioactive contamination would have devastating health consequences for people in Japan. In the media reporting, technical terms come up again and again that are hardly understood by non-experts. For this reason, we have put together a glossary to explain the most important terms.

What does meltdown mean?
If the cooling and all emergency cooling systems of a nuclear reactor fail over a certain period of time, a meltdown can be started. In this context, physicists speak of an irreversible process. The fuel rods that contain radioactive fuel heat up so much that they lose their original shape and melt. In such a very critical process, highly radioactive material can escape from the nuclear reactor into the environment in an uncontrolled manner and endanger the health of humans and animals to a great extent. Because the melting mass can literally eat up through the steel walls of the reactor vessel. There is a great danger, for example, because the radioactive mass can reach groundwater, because the mass burns into the ground. If the containers and the building are damaged, radioactive substances also get into the breathing air and thus contaminate the oxygen. Something similar had happened during the nuclear disaster in Chernobyl. At that time, the building was damaged by an explosion. In Japan, people are now trying to achieve cooling from the outside with the help of sea water. In addition, one tries to lower the pressure in the reactor significantly. In principle, every type of reactor can be affected by such a process.

What is radioactivity?
Radioactivity refers to the property of some substances that spontaneously convert into other atomic nuclei while releasing energy. The terms radioactivity and radiation are often confused in the public debate. Especially in media reports, the term does not refer to the material but the radiation. The radioactive energy is released in alpha, beta or gamma rays. Radioactivity also occurs in low concentrations in the natural environment. Radioactivity also arises during nuclear transformations in nuclear facilities. A radioactive load cannot be detected by the human senses. Radioactive substances can damage the genetic material in humans to a great extent and lead to deformities of newborns. In addition, the development of cancer is greatly promoted.

Radiation sickness
Radiation sickness is a direct result of radioactive radiation. The rays mainly destroy human body cells. The effects of radiation sickness always depend on the duration and the exposure to radiation. The higher and longer the dose affects people, the worse the effects on health. Typical symptoms of acute radiation sickness include burn-like skin conditions, hair loss, severe redness, fever, nausea, internal bleeding and anemia. An obvious characteristic of a serious radiation sickness is the obvious dissolution of the skin all over the patient's body. The higher and longer the radiation exposure, the lower the chances of survival. If the dosage was relatively low, there can be long-term consequences that are not initially visible after contamination. Thyroid cancer and leukemia in particular are typical complications of radioactive contamination.

What is cesium
Low levels of cesium also occur in nature. The radioactive isotope cesium 137 is a product of nuclear fission. If the element reaches the environment through the exhaust air or groundwater, it is absorbed by plants and animals. For this reason, cans can be found in milk, meat, mushrooms and fish. If humans are exposed to a high dose of cesium 137, the muscle tissue and the kidneys can be permanently damaged.

International rating scale "Ines"
Ines (International Nuclear Event Scale) is an internationally valid rating scale that uniformly categorizes accidents or nuclear accidents. The scale ranges from 0 to 7. The lowest level is a safety-related error that initially has no relevance to humans. The highest level is the so-called atomic “super meltdown”, in which severe effects on health for animals and humans in the wider environment can no longer be prevented. The rating scale 7 was last proclaimed in the serious reactor accident in Chernobyl. Seven means: heaviest release, effects on health and environment in a wide environment, late health damage over large areas, possibly in more than one country. A nuclear emergency was declared in Japan, but not the worst case scenario. According to the information currently available, the nuclear accident is numbered four on the Ines scale.

Plutonium fuel
The extremely toxic and highly radioactive heavy metal plutonium is used as a fuel in nuclear power plants. Plutonium also arises in every reactor as a by-product from the splitting of uranium atoms. In this context, environmentalists repeatedly criticize the fact that plutonium is a major shortcoming of atomic energy. Because the half-life of the substance is a whopping 24,000 years. After this time, only half of the radioactivity is reduced. If a person is contaminated with the toxic substance, serious illnesses arise, which can also lead to death. Plutonium is highly toxic and particularly damages the kidneys. It also binds proteins in the blood plasma and is also deposited in the bone tissue and liver. The human lethal dose is very likely to be in the tens of milligrams. A proven dose of 0.32 mg / kg body weight is sufficient for dogs.

What is a super meltdown? One speaks of a super meltdown when the “super greatest presumed accident” of a nuclear reactor takes place. The absolute worst-case scenario occurs when humans can no longer control the nuclear accident. As a result, politicians and the media speak of a super meltdown. The last Super Gau again took place in 1986 in Chernobyl, Ukraine. According to the INES guideline, the accident was classified as seven. In Japan, accidents are currently rated four. This means: "Low radiation exposure of the population approximately at the level of natural radiation exposure." According to the information available, a super meltdown in Japan cannot currently be assumed. (sb)

Also read:
Doctors are calling for the shutdown of all nuclear power plants
Mass protests against nuclear power expected
Radioactive radiation: consequences for health

Image: Gerd Altmann, Pixelio.de

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