Frequently asked questions

There is a whole range of radioactive species produced by the nuclear industry. Solutions are available for the least radioactive short-lived waste. It is sufficient to bury it after conditioning at a shallow depth and to wait. Spent fuel from reactors containing fission products is highly radioactive. In France, these materials, processed at the La Hague plant near Cherbourg, are immobilized in a glassy matrix and then placed in containers. They are currently stored in ventilated shafts at La Hague. As their radioactivity is slowly decreasing, it is planned to store them at great depth, protected from water, in a layer of clay in the Paris Basin.

See also :  Waste management, HA waste duration

Radioactive atoms are spread in very small proportions throughout our environment. Living beings are no exception. For example, a human being weighing 80 kg emits 8000 radioactive disintegrations per second. This may seem like a lot, but it is very little compared to the billions of billions of billions of atoms belonging to the same human being.

See also : Human radioactivity

The most common measurement is that of the radiation exposure dose over a certain period of time, using dosimeters worn by the exposed persons. This is done for personnel who may be exposed to radiation, for example in a nuclear power plant or research facility. Small radiation counters, such as Geiger counters, are also used to monitor the evolution of radioactive activity from one place to another.

See also : Dosimetry, Geiger Counters

Natural radioactivity is due to the presence of radioactive atoms in our environment. Some, like uranium, were already present at the time of the formation of the Earth and have given rise to radioactive descendants, including radon, a gas that is the main component of natural radioactivity. Others, such as carbon-14 or potassium-40, come from cosmic rays that constantly bombard the atmosphere.

Human activities are also the source of radiation exposure. The main contribution to this artificial radioactivity is from medical sources (imaging, scanners, therapies), well before the nuclear fallout.

See also: Natural and artificial radioactivity

It all depends on the severity of the accident.  In case of radioactivity release in the environment, it is necessary to confine the population, which was the case in Fukushima and allowed to avoid deaths. This was not the case at Chernobyl. One of the dangerous releases in the first days and weeks, is that of a radioactive variety of iodine that fixes itself on the thyroid. One protects oneself from it by ingesting iodine tablets. In the longer term, we protect ourselves from other radioelements by controlling the radioactivity of food.

See also:  Exposition modes (accident)

Radioactivity from the soil comes from traces of uranium and thorium present in rocks such as granite, which are abundant in Brittany or in the Massif-Central in France. These two radioactive species, which have the age of the earth formation, are transformed into lead after a series of transformations. The emitted rays do not leave the rock and do not present any danger, except for radon emanations. This gaseous descendant of uranium is the main source of exposure to natural radioactivity. Another source is exposure to cosmic rays, which increases with altitude during air travel.

See also :  Natural radioactivity, Cosmic rays exposure

Radiation and radioactivity are used in medicine. Gamma rays, now delivered by small accelerators, are used for examinations as common as scans and radiotherapy. Radioactivity itself is used for nuclear imaging and in certain treatments such as brachytherapy. In scintigraphic imaging, a radioelement such as technetium is fixed on the organs or tissues to be examined to provide a diagnosis.

See also :  Nuclear scintigraphies

Radioactivity occurs when the nucleus of an atom is unstable. To regain stability, the nucleus transforms itself by emitting radiation in the form of an alpha ray, a beta electron or a gamma ray.  Apart from this event, the radioactive atom behaves normally. The instability is very variable, depending on whether the species is slightly or very radioactive. Gamma emission is usually immediate, beta emission can occur quickly or take a few years, alpha emission requires times that can reach billions of years. Radioactivity decreases with time.  A radioactive species is characterized by its half-life, the time after which half of the decays will have occurred.

See also :  Activity and half-life

Radioactivity is mostly dangerous in case of internal exposure, following the ingestion of radioactive elements. The emitted rays, especially alpha and beta rays, pass through living cells over a generally short path, mainly damaging their DNA. Cells have repair mechanisms that are sufficient in case of low exposures. This is no longer the case for high exposures, which cause so-called deterministic effects that can lead to death.

See also: Effects of radiation

Some big atomic nuclei are very fragile, like uranium-235 and plutonium-239. The capture of a neutron by these so-called fissile nuclei causes them to explode into two fragments accompanied by several secondary neutrons. This explosion releases a very high energy, much higher than that of conventional energy sources.

See also:  Fission energy