Nuclear scientists and engineers have not been idle over the last decade in designing new small nuclear reactors that can’t melt down, and that will be essential to address our environmental and industrial needs in the coming decades.
Ever since the world’s top climate scientists, including Dr. James Hansen, Dr. Tom Wigley, Dr. Ken Caldeira and Dr. Kerry Emanuel, urged world leaders and environmental campaigners to support the expansion of nuclear energy as essential for addressing global warming, many new smaller and modular reactors have appeared on the scene in different stages of development.
One of the latest to emerge is the SLIMM – the Scalable LIquid Metal–cooled small Modular reactor. This is a fast reactor that uses liquid sodium (Na) to cool and exchange heat, and that generates 10 to 100 MW for many years, even decades, without refueling, depending on what power level is desired. It’s very smaller version, the VSLIMM, generates 1 to 10 MW.
Its designers, Drs. Mohamed S. El-Genk, Luis Palomino and Timothy Schriener from the University of New Mexico’s Institute for Space and Nuclear Power Studies in Albuquerque, describe it thus:
"Fully passive operation with no single point failure, cooled by natural circulation of sodium during operation and after shutdown, high negative temperature reactivity feedback and redundant control and safety shutdown, walk-away safe, long life without refueling, factory fabricated, assembled and sealed, shipped to the construction site by rail, truck, or barge, installed below ground to avoid direct impact by missiles or aircraft, and mounted on seismic oscillation bearings to resist earthquakes.”
The reactor has redundant and passive decay heat removal by heat pipes and natural circulation of ambient air.
In other words, it can’t melt down, is cheap to construct and only needs ordinary outside air to cool off if it does shut down quickly for any reason. With Na’s very low vapor pressure, the reactor operates below atmospheric pressure so there is no pressure vessel to worry about.
The reactor core height is not much larger than the height of a human, but it has a long chimney that can be varied in height (2-8 m, depending on the reactor thermal power). The figure shows a longitudinal cross-sectional view of the SLIMM reactor with an 8-meter-tall chimney, the reactor core, and the Na/Na helically coiled tubes heat exchanger (HEX), the primary and guard vessels separated by a small argon gap, the in-vessel control drives, and the core support structure.
The reactor primary and guard vessels are made of two identical sections. The lower section houses the reactor core and the control drives, and the upper section houses the chimney and the Na/Na HEX. Thus, the height of the chimney and that of the upper sections of the primary and guard vessels increase with increasing reactor thermal power, but using the same reactor core and control drives.
This reactor is compatible with different energy conversion technologies such as supercritical water and CO2 Brayton cycles, in super-heated steam Rankine cycles, and closed and open air Brayton cycles, so it can be used in most any electricity-generating configuration.
The smaller VSLIMM plant can use open air-turbo-Brayton energy conversion, which eliminates the need for active cooling, uniquely qualifying this reactor for use in arid regions.
This reactor is also designed to produce process heat for a multitude of industrial uses such as desalination,fracking for fissile foil, hydrogen fuel production, aluminum smelter, etc. and has a high thermal efficiency for electricity generation. It is compatible with renewable energy sources on a common grid, and can load-follow.
The SLIMM and VSLIMM have very small physical footprints and can be deployed on a portable platform or installed at a permanent site. This is ideal for isolated and small communities in dire need of energy, to help eradicate global poverty, for island nations, advanced military bases and remote sites, even on other planets. It is also ideal on floating platforms to aid in recovery after natural disasters like hurricanes.
It only takes one to two years to construct and install, and when a module is used up, it can easily be transported back to the factory. There is no reason to store either new or spent fuel on-site for any length of time.
In fact, the real time sink with any of these new reactors is the NRC licensing period, which can take many years, especially for new and different designs. So it’s critical that Congress pass bills that lower this hurdle.
S. 903, Nuclear Energy Leadership Act, passed out of the Senate Energy and Natural Resources Committee in July, and aims to restore U.S. leadership in the civil nuclear industry by helping to develop a range of advanced reactor technologies that are clean, safe and reliable - exactly what SLIMM is.
Another bill, the Nuclear Energy Renewal Act, was introduced by a bipartisan group of senators to extend the life of the country’s existing nuclear fleet. S. 512, the Nuclear Energy Innovation and Modernization Act was actually signed by the President in January.
The Nuclear Energy Innovation Capabilities Act (NEICA), passed in September 2018, and aims to eliminate some of the barriers to advanced nuclear and establish some of the infrastructure to get there, again something that helps SLIMM and other new designs.
The SLIMM technology is just one of many that are ready, and needed, to address our environmental and energy needs, here and around the world.
We just need to deploy them.
