In this increasingly industrious day and age, we feel the need for renewable and non conventional sources of Energy. Among them, Nuclear power is special in a sense that it appears dangerous and outlandish to general public in that regard.

What is Nuclear Power?

The term refers to production of energy from Fissionable material. Let’s say you make a small dog house using wooden planks, nails and fasteners etc. What would be the mass of the dog house? It would simply be the sum of all their masses.

Let’s think of Nucleus in a similar way. Let’s say we make it using a Z number of protons and N number of neutrons. If we assume proton to be more or less equal in mass to neutron, the mass of nucleus is N+Z times mass of proton.

In reality, Nucleus doesn’t exactly weigh that much. Sometimes, it weighs more than that, sometimes less. How do we think of this? We understand that this lost mass, in the latter case, is the energy that was released when the nucleus was formed. More is the last mass, stronger is the nucleus being held, more difficult is it to split them apart. This concept is called as Binding Energy in technical circles.

Make no mistake, we can split those apart too. But, you would be putting more energy into it than you would be getting out of it. So, Naturally only some nuclei seem feasible for such a process to be power generating.

Some of those materials are Uranium 235, Uranium 233, Plutonium 239. These are typically large and massive nuclei. When they are split apart, they release energy in form of Gamma rays and Kinetic energy of products.

How does this work?

Let’s start with a typical fissile material; Uranium (235,92). When we bombard this nucleus with a neutron, it changes to Uranium (236,92). This is a temporary state, since this form (technicaly, isotope) is not quite stable. In fact, this form spontaneously breaks down into Krypton 92 and Barium 141, large number of free neutrons plus some problematic radioactive dust.

The truly best thing about this process is it can proceed into a chain reaction state. The free neutrons emitted from one fission proceeds to bombard into other Uranium 235 nuclei if available. Let’s start with 3 of the free neutrons. Those 3 nuclei fission, emit 9 neutron and those 9 hit 9 nuclei and the chain goes on. This is the idea of a nuclear chain reaction.

This reaction is truly a monster in terms of energy. Each fission step releases around 0.1% of Uranium mass. That’s 200 Million Electron Volt. In terms of Kelvins, that is easily a Trillion Kelvin. A Trillion Kelvin!! For a Single step!!

If we try to take out this output directly, it would be a disaster. For each step which lasts for about 0.1 micro second, we would need tonnes and tonnes of coolant to transport the heat emitted and to make it rotate the turbine to produce electricity. It is impossible without something to control the reaction.

Whatever I have described so far, is not a reactor but a bomb. For it to be a reactor, we need to be able to control it.

How do we control it?

All this doesn’t happen, if it doesn’t have neutrons to go through with. We have something called as moderators which control the neutron energies.

For a neutron to be able to elicit a fission in Uranium 235 nuclei, it should have a mean energy of 1~2 MeV. This is slow. Slow moving neutrons or thermal neutrons bombard more effectively with Uranium 235. This fact was discovered by Enrico Fermi. When the Manhattan boys club were building a nuclear bomb, Enrico Fermi placed a candle at the last minute in the path of neutron beam to improve the process. Nowadays, we use graphite or heavy water to slow them down.

In case, things go out of hand, and they tend to, we need more control. We use boron or cadmium rods to completely absorb the neutrons. Say the place is being hit with an earthquake, we flick the switch and rods come down; Neutrons are absorbed completely and the process is stopped.

This setup is a primitive elucidation of what is called as a Thermal Nuclear Reactor.

We also have something called a Fast Neutron Reactor.

Uranium 235 is not abundant isotope of Uranium. It is Uranium 238. Uranium 235 is 0.72% of all Uranium isotopes. Uranium 238 is 99%

We need to use Ore Enrichment techniques to obtain Uranium 235.

To solve this issue, we also have a Fast Neutron Reactor. Uranium 238 doesn’t do chain reaction much. Because the neutron energies needed for fission is around 6 MeV. Chain reaction doesn’t occur much because the emitted neutron energies are typically lower than that. So, we use higher neutron energies so that the emitted could sustain a reaction. This method doesn’t need moderators because, we are already controlling neutron energies.

For better fuel economy, we have something called as a Breeder reactor but presently, it is out of our scope for this dicussion.

Safety

We all remember Chernobyl. We all remember Japan Tsunami and Nuclear reactor Fukushima.

However, this was not a situation of reactor going out of control spontaneously. These incidents happened due to sudden disruption of steam pathway lead to superheated steam melting down the reactor core.

Meltdown of core caused dozens of airborne radioactive particles being released.

In modern day, electronic control system and rigorous safety protocols, we have changed the landscape of risk to next to nothing.

Nuclear waste

This is the biggest of problems thus far. This is the reason environmentalists are opposed to nuclear energy.

The product of fission consists of energetic atoms and transuranics.

Energetic atoms are those medium mass atom which typically decay through beta process and don’t cause much problem.

Transuranics are elements like non fissionable materials like actinium, thorium etc which are highly radioactive and have a long half life.

Our present method disposal consists of constructing a long lead box and filling them up with this spent fuel and dumping them somewhere. Usually in developing poor countries. Sounds terrible right?

All in all, I am a big advocate for nuclear fuel. Because conventional petroleum products do cause more damage to our environment. All our garments, plastic bags do end up in the ocean strangling the neck of some porpoise.

Further reading : https://www.youtube.com/watch?v=HKTSaezB4p8