in this article i will try to give you some information about Nuclear reactors, a topic which is often misunderstood from the majority of people. We will start with the basics of Nuclear fission, which is the working principle of these reactors, then we will continue comparing efficiency, safety and CO2 emissions with other technologies.
Index:
- What is nuclear fission?
- Energy comparison with other reactions
- How nuclear plant works?
- Safety
- CO2 emissions
- Conclusions
What is Nuclear fission?
Is now common knowledge that matter is made of atoms, and atoms are made of electrons floating around a nucleus. Nuclei, in turn, are made of protons and neutrons. Oxygen for example is an atom made of 8 electrons whose nucleus contains 8 protons and 8 neutrons.
Fission reaction is a type of nuclear process which consist in the split of the nucleus in 2 or more pieces. This event can be spontaneus (Californium – 252) or induced by an impinging neutron (Uranium-235)
n + ^{235}U \rightarrow FP_1 + FP_2 + neutrons + energy
This kind of reaction releases an huge amount of energy, we can say that daughter nuclei are in a more stable configuration, which requires less energy. The energy released is transferred to the surrounding material and have the effect of increasing its temperature.
Energy comparison
The energy produced in fission events is measured in electronvolt (eV) , if we take as example the fission of Uranium 235, we get a release, more or less, of 211 MeV (mega electronvolt, 211000000 electronvolt).
To understand why this is a huge number let’s compare it with the energy produced in coal or natural gas power plants: in coal combustion Carbon reacts with Oxygen and produce Carbon dioxide:
C + O_2 \rightarrow CO_2 + 3.6 eVand in case of Methane:
CH_4 + 2O_2 \rightarrow CO_2 + H_2O + 9.22 eVIt is clear that chemical combustion is very inefficient with respect the fission of Uranium-235, in fact the fission reaction releases one million times more energy!
Indeed, in order to produce the same amount of energy of 5 grams of Uranium-235, we would need to burn (approximately) 400 kg of Carbon, 200 kg of Methane, 640 kg of woods or 350 kg of oil. it is 5 grams versus hudreds of kilograms!
From these data we see that nuclear energy is very dense compared to other technologies. Also from the point of view of the surface occupied, NPP are smaller than oil/coal plants with same power, and obviusly are smaller than wind farm or photovoltaic fields.
How it works
Nuclear, Carbon and Gas power plants have one thing in common. To produce electricity they exploit some kind of reaction in order to produce energy and heat up a fluid, usually water. Heat boils water and produces vapor that flows in turbine putting it in rotation. The rotative motion is converted in electrical energy through an alternator (like a dynamo). Et voila, electricity is produced.
Conventional Nuclear reactors use Water, and tipically are called Pressurized Water reactors PWR or Boiling Water Reactor BWR. I Won’t lose time talking about the differences among different nuclear reactors, what is important is that some fissile material in the core heat up itself (thanks to fission reactions) and the surrounding water act as coolant. Then the fluid flow in the turbine putting it in rotation to produce electricity. Finally return in the core after being cooled passing through an heat exchanger.
Most used fissile material is Uranium dioxide UO2, and it is assembled in pellets loaded inside stainless steel (or other alloys) cylinders.
safety
Safety is one of the most important topics in Nuclear reactors, Indeed is the technology in energy sector with the highest standards. Today most of the scientific research (in this field) is devoted to the improvement of active and passive safety systems for new generation reactors.
In the chart below we can see the mortality rates for each technology (In terms of deaths by CO2 emissions), we can appreciate how Nuclear plats are by far the safest technology. Even safer than rooftop solar and wind farms.
Here you can find a similar plot from Statista website.
Of course there are different methods to evaluate the mortality, see for example this other chart, however the result is similar, nuclear is safer than you think.
You may say: “well yes, but what about Chernobyl and Fukushima?”. And you are right, Chernobyl was a disaster but data don’t lie. If you want to take a look at this page, i listed some disasters related to coal, hydro and gas technologies just to make a fair comparison with Chernobyl.
CO2 emissions
The increase of CO2 in athmosphere is related to global warming. Coal, Gas, Biomasses directly produce CO2 when burned. other technologies like Solar, Wind, Hydro do not produces CO2 directly. However some CO2 is prodecued during the productive cycle. And Nuclear? There is not a direct production of this gas during the operation of a NPP, however like Solar, Wind and Hydro some pollutants are generated during the fabriation of the plants.
It’s interesting to compare various technologies from this point of view. If we put on a graph the amount of CO2-equivalent produced per kilowatt hour by Coal, Gas, Nuclear ecc… we see that Nuclear is one of the cleanest technologies:
This bring to my mind a funny fact. Very often media talk about global warming and pollutants using images like the one below, representing a Nuclear plant emitting harmful gasses. They obviusly don’t know that it is just emitting water vapor.
Some conclusions…
The final message i want to give you si that Nuclear energy is Green, is safe and it’s cool. By the way, there is a lot more to say about this topic. For example we will talk about how we deal with radioactive waste and how it is possible to recycle it with new generation reactors, we will discuss why nuclear reactors costs so much and why are not affected by price fluctuation of Uranium, we will compare capacity factor of renewables and the possibility to produce hydrogen for clean transportation. Finally we will mention the importance of nuclear reactor for the production of radionuclide for medicine.
Stay tuned!