Radioactivity is part of our live and it has existed all along and everywhere. Naturally occurring  radionuclides are present in the earth’s crust,  our homes, schools, and offices and in the food we eat and drink. And also, our own bodies, muscles, bones and tissues, contain naturally occurring radionuclides. Energy is essential for sustainable economic growth and improved human welfare. Nuclear energy is a form of energy released from the nuclei of atoms, consisting of protons and neutrons, which form the nuclei of atoms. Nuclear energy is a significant part of the world energy. It provides access to clean, reliable and cost-effective energy, mitigating the negative impacts of climate change. Nowadays, over 400 such reactors in 32 countries provide about 10-15 per cent of the world’s electricity. This study focuses on the place of nuclear energy in our lives and addresses the following: radiation and radiation sources, radiation protection, nuclear energy, nuclear reactors.