Dr. Tsubokura's Radiation Lecture Vol.78

Author: Masaharu Tsubokura

Editors: Akihiko Ozaki M.D., Yuki Senoo

155. The nuclear fusion reaction produces solar heat

All materials that exist in the world are composed of small, invisible particles called protons, neutrons, and electrons. The numbers behind radioactive substances, as shown in cesium 134 and 137, each indicate the sum of the protons and neutrons. The nature of the substance varies depending on the balance of these numbers of particles.

When a neutron collides with radioactive uranium 235, it causes the 235 particles of neutrons and protons to split and release energy. A fission of uranium also results in the production of a new neutron, which will then collide with another radioactive uranium and produce a new fusion reaction and more energy. Radioactive uranium produces this chain reaction when predetermined conditions are met, and the nuclear power plants and nuclear bombs operate based on this principle of nuclear fission.

On the other hand, when light nuclei with small numbers of protons and neutrons, such as hydrogen, collide with one another at ultra-high temperatures exceeding 100 million degrees, these nuclei will adhere together and convert into another substance. Furthermore, an enormous amount of energy will be released during this reaction. This reaction is the opposite of fission and is called "nuclear fusion."

Nuclear fusion does not occur unless nuclei are under extremely high temperatures or pressure. On the other hand, the sun is able to release a large amount of heat as these predetermined conditions are met.

156. The fuel rods in nuclear reactors contain concentrated uranium.

Radioactive uranium produces a chain reaction when a neutron collides with it. Nuclear power plants generate electricity by turning turbines using water vapor, which is obtained from heating the water using the energy released from the nuclear fission reaction of uranium 235.

Nuclear power plants use concentrated radioactive uranium of approximately 3〜5% as fuel. This fuel is packed into a fuel rod, which is a long, cylindrical rod of about 1 cm in diameter and about 4 m in length. The rod is called a "fuel assembly" when several sets of 10 fuel rods are bundled together. This fuel assembly produces energy that is used to heat the water surrounding the fuel assembly so as to obtain water vapor.

Fuel rods containing uranium 235 are designed to withstand temperature changes and various amounts of pressure from their surroundings. The outer frames of the cylindrical fuel rods are made of a metal called zirconium, which caused the hydrogen explosion that occurred at Fukushima Daiichi Nuclear Power Plant on March 11, 2011.

This marks the fourth year since the first article from Dr. Tsubokura's radiation lecture was launched in 2015. I would like to express my gratitude to everyone who has supported the series so far. Thanks for your kind support.


The Japanese version of the manuscript was originally published in Fukushima Minyu, a local newspaper in Fukushima prefecture, Japan, on 31th December 2017 and 7th January 2018 was reproduced for MRIC Global under the author's permission.

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