How nuclear energy has evolved over the years

In 1938, the German nuclear scientist Otto Hahn made the seminal discovery of nuclear fission that paved the way for getting power from nuclear reactors. He uncovered the process of nuclear fission, wherein nuclei of heavy elements breakup into smaller nuclei, and in the process, release vast amounts of energy. For some years, he studied the manner in which nuclei of uranium transformed when bombarded by uncharged particles called neutrons.

However, in all these neutron-induced nuclear reactions, including those studied by noted Italian physicist Ermi Fermi, the energies released were typical of radioactive transmutation and only neighbouring elements of the periodic table were produced. But Otto found that when uranium was undergoing neutron reactions, something strange was happening. Much lighter elements like barium were being produced and much larger amounts of energy were being released, 50 to 100 times more than the usual radioactivity.

Uranium nuclei are extremely massive, and are made up of numerous protons and neutrons, and eventually, they split into smaller parts by neutron bombardment (lighter nuclei). The only way to explain this was to invoke a process where the uranium nuclei actually broke up into two halves of lighter elements, like barium and krypton. This was called
nuclear fission.

Interestingly, the fission reaction also produced more neutrons, which further split more uranium nuclei so that a chain reaction could start and lead to an explosive energy release. The energy thus released was several million times more than that produced by burning coal or fossil fuels undergoing chemical combustion. However, not all uranium nuclei can split. Only Uranium 235, a very rare isotope that is present at the concentration of 0.7% in natural uranium, undergoes fission.

Varied uses

After the Nazi rise to power, most of the Jewish scientists fled to the US. They were worried that German scientists following Hahn’s discovery could now utilise the uranium fission chain reaction to make powerful nuclear weapons. This ultimately led to Einstein writing his famous letter to the then USA President Franklin D Roosevelt, which kickstarted the Manhattan project to enrich lighter isotope Uranium 233 by converting uranium to a gas and allowing the lighter isotope to diffuse faster. Now, giant gas centrifuges are used to separate isotopes.

The better aspect was the commissioning of large nuclear reactors by several countries to produce gigawatts of nuclear power, using much less fuel than fossil fuels. A hundred tonnes of uranium can power a gigawatt plant. Compared to Uranium 238, the half-life of Uranium 235 is much shorter — it stands at 0.7 billion years. This implies that its concentration would have been above 3% two billion years ago. At that time, no enrichment was necessary. It was discovered that two billion years ago, 17 natural nuclear fission reactors operated at Oklo, Gabon in many rich uranium deposits.

Suppose humans had emerged on earth a billion years earlier. They could have used these nuclear ovens by flooding the natural uranium ores by flowing water. Nuclear power could have preceded fossil power, no coal or oil required. Indeed, the ratio of samarium isotopes, analysed at Oklo proves nuclear fission was naturally taking place. On the contrary, if human
life had emerged two billion years from now, all the Uranium 235 would have
decayed.

Five billion years hence, practically no uranium would exist. Thus it is a coincidence that the lifetime of uranium isotopes and the evolution of humans are comparable. Humans emerged at the just right time to harness nuclear power cheaply. When the universe was 10 billion years old, that is when the earth was formed, there was hundred times more Uranium 235 than now. The sun is a third generation star, so stars twice as old could potentially have had planets where creatures evolved to make use of much higher Uranium 235. Nuclear fission power would have been freely available. Hence, there wouldn’t have been any need for diffusion plants or centrifuges.

At present, there are more than 300 fission reactors worldwide operating with uranium and plutonium as fuels. There are several new design concepts for future fission reactors. In fact, there is an effort to have miniature reactors for specific power requirements. NASA recently announced that it had conducted successful tests of a small, portable nuclear reactor that can generate a reliable power supply ranging from one kilowatt to 10 kilowatts. Nuclear fission power, despite its shortcomings, is here to stay.