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Part 1 of 2 Parts
       Small modular reactors are a being developed by a number of different companies. They are defined as producing three hundred megawatts or less. They will be built in factories in order to improve quality control and moved in modules to the site where they will be operated. Multiple SMRs can be connected together to generate more than three hundred megawatts. There are a lot of design innovations being explored which may prevent melt downs. Some of the designs will not need to be refueled for decades.
   One of the more recent designs being worked on is named the Scalable Liquid Metal-cooled small Modular Reactor or (SLIMM). This is what called a fast reactor that uses liquid sodium as a coolant and a heat exchange medium. It will generate from ten million to a hundred million watts of electricity for decades without the need to be refueled depending on how much power it will be generating. It has a small version that is called the Very Scalable Liquid Metal-cooled small Modular Reactor (VSLIMM).
    This new design was created at the University of New Mexico’s Institute for Space and Nuclear Power Studies in Albuquerque. Mohamed S. El-Genk, Luis Palomino and Timothy Schriener are the scientists who produced the new design. They said, "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 SLIMM incorporates redundant and passive decay heat removal accomplished by heat pipes and ambient air. It cannot melt down; it is inexpensive to build and it only needs ordinary outside air to cool it if it shuts down quickly for any reason. The sodium coolant has very low vapor pressure. This means that the reactor can operate below atmospheric pressure so there is no need to surround it with a high-pressure vessel necessary for common power reactors.
    The SLIMM reactor is about six feet high. It also has a chimney that can be between six feet and twenty-four feet  depending of what level of power is being generated. The reactor has a primary vessel surrounded by a guard vessel. Each has two sections. The lower sections contain the reactor core and the control drivers. The upper section contains the chimney and the helically coiled tubes heat exchanger (HEX). The primary and the guard vessels are separated by a small gap that contain argon gas, in-vessel control drives and support structure for the core.
     The height of the upper sections of the primary and guard vessels and the height of the chimney increase as the reactor thermal power increases but the same core and control drives are used regardless of the power level.
Please read Part 2