Nuclear (Fission Power)

by Sérgio Granato de Araújo

  

Nuclear reactors harness nuclear fission (splitting apart heavy atoms) to heat water and produce steam to power turbines.  Unlike many renewable energy sources, power from nuclear energy can be generated around the clock and isn’t dependent on the weather conditions, like wind & solar power [NG, 2023].

  

Energy production & ICAP

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Today, nuclear power, the 2nd largest source of low-carbon electricity today (after hydropower), provides about 10% of the world's electricity from around 440 power reactors, located in 50 countries, producing 2,545 TWh (2022), which demanded 62,496 tons of Uranium in 2021 [WN, 2023].  The U.S. has about 93 (104 in 2012) nuclear power plants (NPP), w/ installed capacity (ICAP) of 95.5 GW  (2021), followed by China (56), w/ ICAP of 57 GW (2022), and France (54), w/ ICAP of 61 GW (2022).

  

A total of 103 reactors are currently in operation in 13 EU member states, accounting for about 25% of the electricity generation [ECFR, 2023].  With few fossil fuel resources, the Land of Enlightenment is the most dependent country on nuclear energy, accounting for about 70% of its electricity production.  However, as its NPP are aging, France currently faces maintenance issues with a quarter of its nuclear reactors [CGTN, 2023].

  

Uranium: reserves & production

 

Uranium is naturally found in rock or mineral deposits.  Quite abundant, it is 40 times more common than silver and 500 times more common than gold.  Australia's Uranium reserves are the world's largest, with around 30% of global resources, followed by Kazakhstan (15%), Canada (9%), and Namibia (8%).  In 2022, Kazakhstan, however, produced the largest share of Uranium from mines in 2021 (45%), followed by Australia, Namibia, and Canada [INN, 2023].

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Uranium enrichment

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Enrichment process increases the Uranium-235 concentration from 0.7% to 3%-5%, which is the level used in most reactors.  Before enrichment, Uranium oxide is converted to Uranium hexafluoride (UF6), a gas at relatively low temperatures.  The enrichment process is carried out using a centrifuge that separates heavier atoms (U-238) from lighter ones (U-235) [NCR, 2020].

  

The enriched Uranium is then converted to Uranium Dioxide (UO2) powder, which is then pressed to form small fuel pellets and heated, making a hard ceramic material.  These pellets are subsequently inserted into thin tubes known as fuel rods, which are grouped together to form fuel assemblies, each with around 90 to well over 200 fuel rods [WN, 2023].  Figure 1 shows nuclear fuel in its powder & pellet form.

  

Density, life cycle & capacity factor

  

1 kg of Uranium equals 2.7 million kg of coal.  Some new-generation nuclear power stations are now certified for 80 years of operation, far longer than a gas- & coal-fired power stations (45 & 35 years, resp.) and unconventional renewable installations (solar: 25 years; wind: 20 years).  Also, nuclear has the highest capacity factor of any other energy source, producing reliable, carbon-free power more than 92% of the time in 2021, nearly twice as much as coal (49.3%) or natural gas (54.4%) plant, and almost three times more often than wind (34.6%) and solar PV (24.6%) plants [EG, 2022].

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Development timeline

  

First developed in the 1940s, and during the WWII research initially focused on producing bombs, in the 1950s attention turned to the peaceful use of nuclear fission, for power generation [WN, 2023].  In 1954, the world's first nuclear power station to generate electricity for a power grid, the Obninsk NPP, began operations in Obninsk, Soviet Union.  However, the world's first full scale power station, Calder Hall in the U. K., opened on October, 1956.

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CO2 emissions, waste disposal & recycling​

  

In an emissions sense, nuclear power is considered to be clean.  Nuclear fuels, such as the element Uranium, are not considered renewable as they are a finite material mined from the ground and can only be found in certain locations.  Moreover, there are concerns around what to do with spent fuel from reactors, as there’s still no definitive way to dispose of it indefinitely without risk: high-level waste (HLW) must be stored isolated from the biosphere with sufficient shielding so as to limit radiation exposure.

  

Nuclear waste generally is over 90% Uranium.  Thus, the spent fuel (waste) still contains 90% usable fuel.  It can be chemically processed and placed in other reactors to close the fuel cycle: a closed fuel cycle means much less nuclear waste and much more energy extracted from the raw ore [WIN, 2023].  The U.S. does not currently recycle spent nuclear fuel, but France does [EG, 2023].

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NPP Generations

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NPP designs can be classified into generations.  The first commercial nuclear reactors built in the late 1950s & 1960s are classified as 1G.  2G systems include commercial reactors built from 1970 to 1990. 3G reactors incorporate evolutionary improvements over 2G systems [EE, 2022].  4G NPP describe a set of advanced reactor designs, with techs like i) liquid metal (sodium, lead) cooled fast reactors, ii) advanced high temperature, and iii) gas cooled reactors, reactors that use non-conventional burning (CANDLE & molten salt), and direct conversion.  Sodium cooled fast reactors (SFR) could allow use both fissile material & spent fuel from current reactors to produce electricity [EG, 2023].

  

A boiling water reactor (BWR) is a type of light water nuclear reactor (LWR) used for the generation of electrical power.  LWR, as opposed to heavy water, whose H atoms are all deuterium, uses normal water as both its coolant & neutron moderator.  BWR is the 2nd most common type of electricity-generating nuclear reactor after the pressurized water reactor (PWR), which is also a type of light water nuclear reactor [WN, 2023].  Figure 2 shows Palo Verde, the largest NPP in the U.S. (PWR-type reactor), w/ ICAP of about 4 GW.