Uranium is the heaviest natural element, it is radioactive and it is relatively simple to break it to genereate energy. Nowadays we are not extracting as much uranium as we did when it was used on large scale for military purposes during the Cold Era, the world largest producer is currently Kazakshtan.
- oceans, using "sponges" it is possible to extract uranium form water, this causes the dissolution of uranium in Earth's mantle, making it potentially unlimited (tens of thousands of years of autonomy)
- dismantling old nuclear weapons
- extraction and refining
- enrichment: In nature, the fissile percentage is approximately 0.7%. A reactor requires between 3 to 5%, while for military purposes, more than 90% is needed
- conversion to Uranium Hexafluoride (gas)
- centrifugation process (the fixile isotope is lighter and it accumulates)
- conversion in uranium dioxide (tablets)
Uranium Consumption: 70,000 tons/year vs. tens of billions of tons/year of fossil fuels. As of today (only from priced mines, many are not exploited due to the low cost of the material), we have reserves until 2100. We don't know if we will have lithium/natural gas for the next 100 years. To make deep-sea mining cost-effective, the price of uranium should be around $500 USD/kg. The price of nuclear energy is inelastic; the cost of uranium influences less than 2% of the price. Currently, it is cheaper to store nuclear waste than to reuse it.
- Naturally 3-5 times more abundant than Uranium, and we don't know when it will run out because it's currently less important.
- Generates very few waste products.
- Unsuitable for military use (emits gamma radiation damaging to electronic equipment).
- Abundant in India, making the country one of the largest researchers.
How a Nuclear Power Plant Works
Uranium pellets are broken, generating heat. Heat is used to heat a thermal fluid (water), which turns turbines connected to a generator. Control rods inside the reactor control the energy production to maintain a constant level (meltdown vs. shutdown).
Note: The water taken from the environment is for the condenser and does not come into contact with radioactive material.
If seawater is used, it is discharged offshore (for cooling). If water is taken from a river, it is discharged into cooling towers.
Not all generated heat can be converted into energy (due to the second law of thermodynamics). This introduces the concept of efficiency.
Efficiency, Capacity Factor, Energy Density, and Environmental Factor
Efficiency represents the percentage of thermal energy converted into electrical energy.
Efficiency of major energy sources:
- Nuclear power plants: 30%
- Photovoltaic plants: 33%
- Coal-fired power plants: 40-60%
- Wind turbines: max 60%
- Combined cycle gas power plants: 70%
- Hydropower plants: 70-80% (easier to harness kinetic energy)
Efficiency is not the only factor; hence we consider the capacity factor, the percentage of time energy is generated according to supply. Here are values for different plants:
- Nuclear power plants: 93-99% (heavy water)
- Combined cycle gas power plants: 50-60%
- Coal-fired power plants: 50-60%
- Hydropower plants: 40-50% (varies with seasons/river flow)
- Wind turbines: 30-40% (Ireland/Scotland/Denmark)
- Photovoltaic plants: 15-20% (Arizona/Nevada/Sicily)
This is influenced by the fact that nuclear power plant fuel lasts 18 months to 2 years, gas plants pump fuel directly, while coal plants need constant loads. Another crucial factor is energy density, measuring how much energy can be generated with 1 kg of material, measured in MJ/kg.
- Biomass: 17
- Coal: 33
- Diesel: 44
- Natural gas: 47
- Hydrogen: 120 (needs to be produced, consuming energy, so it's not a source but a carrier)
- Enriched Uranium: 2M
- Uranium reusing bars until fissile is present: 76M
In the world, there are thousands of oil tankers transporting fossil fuels. One loaded with uranium would cover the world's needs for a year. 1 kg of Uranium provides the same energy as 2500T of coal.
Another essential element is the environmental factor, i.e., how many grams of CO2 are emitted per kWh from when a plant is built to when it is dismantled:
- Nuclear power plants: 12
- Photovoltaic plants: 45 (no emissions during production but in production and dismantling)
- Wind turbines: emit few emissions unless energy is stored in batteries (large emissions for production).
Radioactive waste is divided into 3 categories.
- LLW (Low-Level Waste): low activity (filters, water, personnel suits) (decays in max. 2 years)
- ILW (Intermediate-Level Waste): intermediate activity, does not require cooling (fuel cladding, resins used for processing) (decays in decades)
- HLW (High-Level Waste): high activity (radioactive waste produced by civilian, military, and medical nuclear industries) (decays in hundreds of thousands of years)
Only HLW is problematic to store due to the time it takes to decay into stable isotopes. If the bars were reused, the yield could be increased by up to 50%, but currently, it's not economically feasible. Fast Breeder Reactors (FBR) (economically inconvenient and using non-water cooling) increase the amount of Plutonium-239 generated with each reprocessing. This way, the consumption of fuel (using all the fissile material present in the bars) can be reduced by a factor of 30. Also, in this way, the bars consist only of fission products, which need to be stored for only 200 years.
The storage of nuclear waste is a purely political problem; there are geologically suitable places to store radioactive waste for the necessary time. Finally, after the decommissioning of a nuclear power plant, it returns to a state equivalent to the one before, as evidenced by the former Yankee Rowe Nuclear Power Station, now in this state:
Yankee Rowe Nuclear Power Station
Environmental Impact of Nuclear Power
- Chernobyl Incident: 54 deaths, 18 in the following years due to complications caused by radiation. It's challenging to estimate if cancer deaths are due to nuclear poisoning.
- Fukushima Incident: 0 deaths due to radiation, many due to tsunami/earthquake. A 2018 court ruling recognizes one victim, but experts claim the contracted cancer is not attributable to radiation. The hasty (unnecessary) evacuation of Fukushima Prefecture caused hundreds of stress-related deaths.
- Chernobyl: 6-8 mSv/year, with values up to 193 mSv/year because radioactive waste from liquidators was buried in the Pripyat cemetery.
- Fukushima today: 1.3-5 mSv/year, with peaks of 26 mSv/year.
- St. Peter's Square, Vatican City: 7 mSv/year, due to porphyry paving (radioactive radon).
- Orvieto and Viterbo province: ~5 mSv/year due to tuff (radon).
- Guarapari Beach, Brazil: rich in Monazite containing Thorium, 44 mSv/year with peaks of 175 mSv
The radiation in Chernobyl today is not as dangerous as it is usually reported; the current fear is largely unjustified.
Le radiazioni a Chernobyl oggi non sono cosi' pericolose, la paura di adesso e' in larga parte ingiustificata.
The mortality value for nuclear power (0.07 per TW/h) takes into account deaths resulting from the purely political decision to evacuate Fukushima Prefecture.
https://www.electricitymap.org/map,reports the environmental impact of energy production (for countries that provide data :)). Note that France and Sweden, with substantial nuclear energy use, emit much less CO2 than other states relying on renewable energies.