The word “nuclear power plant” conjures up images of huge facilities with gigawatt outputs and electricity production measured in terawatt hours per year. Enormous amounts of electricity that are only needed in developed, densely populated areas.
However, nuclear power also comes in smaller portions. At the lowest end of the scale are radioisotope generators (RTGs). These generate electricity and heat through the natural decay of heavy atoms – not through artificially induced fission. They are usually based on the non-fissile plutonium isotope 238 and are used in space applications such as the Voyager space probes. But they are also used in lighthouses. They only produce a few watts of power, but do so for decades, while the original material is transformed into lead at an infinitely slow rate down the decay chain. Micro-reactors are giants compared to RTGs, but still dwarfs compared to the classic “nuclear power plant”. The International Atomic Energy Agency classifies micro-reactors in the 1 to 10 megawatt hour (MW, one million to ten million watts) power class. This results in an electricity production of 24 to 240 megawatt hours (MWh) per day. Only above this is the class of “Small Modular Reactors”, which are classified from 10 MW upwards to 300 MW. https://www.youtube.com/watch?t=2481&fbclid=IwAR0XMk46jICYNSsvYqo9OmhNj6jiN0KAwLIHAmpCe8qRWrgF345TGFewLx4&v=aaR-CiapR1o&feature=youtu.be The US Department of Defense (DoD) had micro-reactors in mind when it initiated “Project Pele” in March 2020. As part of a two-year competition, contracts worth a total of 37 million US dollars (31 million euros) were awarded to BWXT, Westinghouse GS and X-energy for design work on transportable nuclear reactors. The reactors are to be able to deliver an output of 1 to 5 MW over a period of at least three years. Transportation should be possible by container freight by road, rail or air. A maximum of three days is estimated for commissioning at the site and a maximum of seven days for dismantling. As part of “Project Pele”, a winner is to be chosen in March 2022 and construction of the prototype is to begin in summer 2022. Tests under full load are scheduled to take place in Idaho at the end of 2023/beginning of 2024. The DoD consumes 30 terawatt hours (TWh) of electricity per year and 38 million liters of fuel per day and wants to use micro-reactors to become more off-grid and reduce the risk to supply convoys. The analysis of the Iraqi Freedom and Enduring Freedom missions in Iraq and Afghanistan revealed that around 18,700 of the total of around 36,000 wounded and killed in these missions can be attributed to attacks on supply convoys. Energy accounts for a significant proportion of this logistical requirement.
But even outside of combat operations, energy supply can be complicated and expensive. The price of fuel in Alaska, for example, is around 2.5 times the US average. Supplying strategically important, permanent bases such as Diego Garcia or Guam is similarly expensive. Added to this is the need for a secure supply of energy-intensive facilities. A large radar system to defend against intercontinental missiles was planned for Hawaii. In addition to an expensive grid connection across a nature reserve, a diesel generator including a tank farm for almost 570,000 liters of fuel was to be installed to ensure reliable independent operation. Specific local conditions or applications and their high energy costs therefore form the basis for quickly making a rather expensive small nuclear reactor economically attractive. The US military had its first experience with micro-reactors from the 1950s to the 1970s. A total of eight small plants were tested and/or operated as part of the “Army Nuclear Power Program” – some of them mobile. Overall, however, the technology was still too immature and complex, and the cost of keeping them in operation and operating them safely was too high. Reactors of this size, which are currently in operation and have been for decades, can be found on nuclear-powered submarines and aircraft carriers. These reactors can easily run for 30 years at a time on a single fuel load. However, they also have significant limitations. They also require highly trained personnel. Very restrictive access to the plant is necessary, but is easy to implement on a warship. The system floats with its ship in an ocean full of coolant, so to speak. And last but not least, its fuel enrichment is almost as high as in a nuclear bomb and therefore far above anything that would be permissible in a civilian environment. The new micro-reactors, on the other hand, are to be built on the basis of technologies that are being developed in the US national and international research network for the 4th generation of civilian nuclear power plants.
The US military is focusing on extremely hard and temperature-stable “TRISO propellant” – tiny uranium oxide spheres with a diameter of less than half a millimeter, multi-coated with carbon, carbon and silicon carbide and embedded in graphite. They cannot melt and do not require water or pumps for cooling. Instead, salt or helium gas, heat pipes and natural circulation are used. In its physical window, a system the size of a shipping container should run reliably and without interruption for years without the need for operating personnel and ensure a constant supply of electricity and heat at the site. In 2023, a full-load test with the winner of “Project Pele” is to be carried out in the containment of the former EBRII test reactor at the Idaho National Laboratory. An outdoor test is then planned. Assuming that the tests are successful, the first possible deployment sites could be US Army facilities in the heart of Alaska, such as Fort Wainwright or Fort Greely. The power supply in Alaska is not provided by an all-encompassing grid as we know it, but is based on small local grids ranging from 100 kilowatts to 385 MW. The military facilities there, such as the 49th Missile Defense Battalion, require a secure energy supply and already offer an environment with appropriately controlled access points. These would therefore be ideal conditions for the first operational experience with modern micro-reactors.
