Regional Basic Professional Training Course in Korea

Regional Basic Professional Training Course (BPTC) on Nuclear Safety
234
U92 ( 0.006%) 235
U92 (0.714%) 238
U92 (99.28%)
Enrichment is an artificial (manufactured) increment of abundance of one isotope. The
fuel fabrication process includes steps to increase the number of 235
U atoms with respect
to the number of 238
U atoms because it is easier to cause the 235
U atoms to fission (split)
than in the much more abundant 238
U. In light water reactors, enrichments of 2 to 5
percent are common.
1.1.2. Radioactive decay
It has been determined that a few naturally-occurring substances consist of atoms, which
are unstable, meaning that they undergo a spontaneous transformation into more stable
products. These types of substances are defined as radioactive and the transformation
process is known as radioactive decay. Henri Bequerel was the first scientistto realize
that some elements were naturally radioactive in 1896. He observed the blackening of
photographic film in the vicinity of a uranium compound. This was later attributed to the
radiation being emitted by the uranium. Unstable radioactive nuclei emit three main
types of radiation: alpha, beta, and gamma radiation.
Alpha radiation, as denoted by the symbol (α), consists of a helium nucleus with two
neutrons and two protons (see Figure 1.1). It is the most energetic (densely ionizing), but
the least penetrating type of radiation. Alpha particles can be stopped by a sheet of paper.
Although they are unable to penetrate the human skin, alpha emitters may be very
harmful if they enter the body through a cut, inhalation, or ingestion of food or water.
Once insides the body, the alpha particle decays or gives up its energy causing highly
localized damage to the surrounding tissue. For example, if an alpha emitter is inhaled,
and the radioactive material becomes trapped in the lungs, the lung tissue could absorb
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