Mercedes Mullins
Nuclear submarines are powered by nuclear reactors that use enriched uranium fuel. The amount of nuclear fuel in a submarine is classified information, but it is described as a small volume that can fit under a desk. These submarines have long operational lives, with fuel lasting over 25 years, and do not require refueling. The fuel is highly efficient and enables submarines to operate at high speeds for extended periods, making them valuable military assets. The cost of nuclear-powered submarines is high, and only a few countries operate them. The disposal of nuclear fuel from decommissioned submarines is a complex process, and some countries, like the UK, face challenges in defueling and dismantling their retired nuclear fleets.
| Characteristics | Values |
|---|---|
| Volume of reactor core fuel | Fits under a desk |
| Refueling period | 10 years or 25 years |
| Fuel type | HEU, LEU, Uranium-235, Uranium-238 |
| Number of reactors | 1 or 2 |
| Number of nuclear-powered submarines | 75 |
| Cost of Virginia-class attack submarines | $2.7 billion |
| Cost of Columbia-class ballistic missile submarines | $5.4 billion |
| Countries with nuclear-powered submarines | 6 (US, Russia, France, UK, China, India) |
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What You'll Learn
Nuclear submarines are fuelled with uranium
Nuclear submarines are fuelled by uranium, specifically the isotope uranium-235 (235U). This fissile isotope exists in very small quantities (less than 1%) in natural uranium, which mainly consists of the isotope uranium-238 (238U). To use it as fuel, the proportion of 235U is increased through a process called enrichment. For submarines, the desired proportion of 235U is typically about 50%.
The degree of fuel enrichment is crucial to maintaining a chain reaction that gives a consistent, safe level of energy output. Inside the reactor, uranium-235 is bombarded with neutrons, causing some of the nuclei to undergo nuclear fission and release more neutrons, continuing the process in a "nuclear chain reaction". The energy given off as heat can then be used to drive turbines that generate electricity for the submarine.
Nuclear-powered submarines have the advantage of not requiring refuelling. They are commissioned with enough uranium fuel to last over 30 years. Nuclear power enables these submarines to operate at high speed for longer periods than conventional diesel-electric submarines. Nuclear reactions also do not require oxygen, allowing nuclear submarines to remain submerged at deep depths for months, enhancing their stealth capabilities and enabling longer, more remote deployments.
However, nuclear-powered vessels are extremely costly, with each nuclear submarine costing several billion dollars. Only six countries currently have nuclear-powered submarines: the United States, Russia, France, the United Kingdom, China, and India.
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The amount of fuel is classified information
The amount of nuclear fuel in a submarine is classified information. While it is known that nuclear-powered submarines use uranium fuel, with natural uranium consisting of uranium-238 mixed with small amounts of uranium-235, the specific quantity of fuel loaded in a submarine is not publicly available. This information is considered confidential or secret by the military, and disclosing such details could potentially compromise a submarine's capabilities as a deterrent or hunter-killer.
The volume of the reactor core fuel in a US nuclear submarine has been described by some as "fitting under a desk," indicating that it is not a particularly large volume. However, the amount of fuel is not the only factor that determines a submarine's capabilities. The power output of the reactor and the speed it can achieve are also crucial considerations.
The duration of a submarine's deployment is influenced by various factors, including the amount of food stored on board. In the case of nuclear-powered submarines, fuel is not a limiting factor as they are designed to operate for extended periods without refuelling. The fuel in a nuclear submarine is typically sufficient to last more than 25 to 30 years, and the high efficiency of nuclear power enables these vessels to stay submerged at deep depths for months.
While the exact amount of nuclear fuel in a submarine remains classified, it is important to note that the disposal and storage of spent nuclear fuel from decommissioned submarines pose significant challenges. The process of defuelling and dismantling a nuclear submarine is complex and requires specialised facilities. In some cases, spent nuclear fuel may be stored indefinitely rather than recycled or disposed of in geological disposal facilities.
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Nuclear submarines don't require refuelling
Nuclear submarines are powered by onboard nuclear reactors. The atoms in the nuclear reactor split, releasing energy in the form of heat. This heat is then used to create high-pressure steam, which turns the propulsion turbines that provide the power to turn the propeller. Nuclear submarines have been in use since 1954 when the Navy launched the USS Nautilus, the first submarine to use radioactive material as a power source.
Nuclear submarines have several advantages over their diesel-powered counterparts. One of the most significant advantages is that nuclear submarines do not require refuelling. While the amount of nuclear fuel in a submarine is classified information, it is known that this type of fuel lasts much longer than any other type of provision needed. Nuclear power allows submarines to operate for about twenty years without needing to refuel, with some sources claiming that they can run for up to thirty years or more.
The long duration of nuclear fuel means that food supplies become the limiting factor for a nuclear submarine's time at sea. This is because the power output of the reactor far surpasses the boat's speed limit, and the speed of a submarine is typically limited by the materials on the exterior of the hull, which can be damaged if the vessel moves too fast through the water.
While nuclear submarines do not require refuelling of their nuclear reactors, they typically have backup diesel generators that may need to be refuelled. These diesel generators are used for battery charges, ventilation, power generation, and testing. They are also necessary to restart the reactor if it shuts down. However, it is important to note that the use of diesel generators on nuclear submarines is rare and typically only occurs during specific circumstances, such as when the reactor scrams.
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The fuel is enriched to contain uranium-235
The fuel used in nuclear submarines is enriched to contain uranium-235. Uranium is a naturally occurring element that consists of two isotopes: U-235 and U-238. While U-235 is fissile, meaning it can be easily split with neutrons, U-238 is not. In nature, more than 99% of the extracted uranium ore is U-238, while only about 0.7% is U-235.
To be used as nuclear fuel, uranium must undergo a process of enrichment to increase the concentration of U-235. This is typically done through commercial enrichment processes such as gaseous diffusion or gas centrifugation, which use uranium hexafluoride to produce enriched uranium oxide. The enriched product has a higher concentration of U-235, while the 'tails' have a lower concentration and are known as depleted uranium (DU).
The level of enrichment required depends on the type of reactor. Most commercial nuclear power reactors require low-enriched uranium (LEU), with a concentration of U-235 ranging from 3% to 5%. However, some reactor designs, such as the Canadian-designed Candu, can operate using natural uranium as fuel without the need for enrichment.
On the other hand, highly enriched uranium (HEU), with a concentration of U-235 above 20%, is used in nuclear weapons and certain specialized reactor designs. In the context of naval reactors, HEU often contains at least 50% U-235 but typically does not exceed 90%. These specialized reactor systems rely on HEU to meet their unique operational requirements, including high neutron flux and precise control over reactor dynamics.
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Nuclear fuel is costly to produce
The amount of nuclear fuel in a submarine is confidential and classified information. However, it is known that nuclear fuel is costly to produce.
Nuclear power plants are significantly more expensive to build than coal-fueled or gas-fueled plants. Nuclear power plants have high capital expenditure for building plants, and construction costs have varied significantly across the world and over time. For example, construction costs have rapidly increased in the United States during the 1970s, but have been stable or declining in countries like Japan and Korea. The construction time of nuclear power plants also has a significant impact on the overall cost, as the longer the construction time, the more requirements, technical changes, and legal actions are needed, increasing the cost.
The cost of nuclear fuel itself is also impacted by the cost of waste disposal. The disposal of waste from reprocessed spent nuclear fuel is expensive and the costs are often assumed by governments. The waste disposal process includes used fuel storage or disposal in a waste repository, which can contribute up to 10% of the overall costs per kWh.
Additionally, the proven dangers of nuclear power have led to calls for stronger regulations and improved safety features for nuclear reactors, which will likely result in higher costs for nuclear power. The interest rate for the capital required for construction also impacts the total cost of building a nuclear plant.
Despite the high costs of nuclear fuel production, it is important to note that the economics of nuclear power is influenced by various factors, including government policies, subsidies, and the market into which the power is sold. Nuclear power can be cost-competitive with other forms of electricity generation, especially when taking into account the negative externalities associated with fossil fuels, such as pollution.
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Frequently asked questions
Nuclear-powered submarines are fuelled with enriched uranium. The amount of fuel is confidential and classified information. However, it is known that the fuel is designed to last 25 to 30 years without needing to be refuelled.
Submarines use enriched uranium-235 as their nuclear fuel. This is created by increasing the proportion of the fissile isotope uranium-235 relative to uranium-238, in a process known as enrichment.
Nuclear submarines are designed to last 25 to 30 years without needing to be refuelled.
Once a nuclear-powered submarine is decommissioned, it is placed into long-term storage and monitored. Engineers then begin the complex process of defuelling and dismantling the vessel.
