![]() īeside its highly corrosive character, its main disadvantage is the formation by neutron activation of 209 Lead-bismuth eutectic allows operation at lower temperatures while preventing the freezing of the metal coolant in a lower temperature range ( eutectic point: 123.5 ☌ / 255.3 ☏). There are two proposals for a sodium cooled Gen IV LMFR, one based on oxide fuel, the other on the metal-fueled integral fast reactor. Neutron activation of sodium also causes these liquids to become intensely radioactive during operation, though the half-life is short and therefore their radioactivity does not pose an additional disposal concern. Sodium is also the coolant used in the Russian BN reactor series and the Chinese CFR series in commercial operation today. This was the case at the Monju Nuclear Power Plant in a 1995 accident and fire. Sodium and NaK do, however, ignite spontaneously on contact with air and react violently with water, producing hydrogen gas. NaK was used as the coolant in the first breeder reactor prototype, the Experimental Breeder Reactor-1, in 1951. Sodium and NaK (a eutectic sodium-potassium alloy) do not corrode steel to any significant degree and are compatible with many nuclear fuels, allowing for a wide choice of structural materials. ![]() However, because of disadvantages including high toxicity, high vapor pressure even at room temperature, low boiling point producing noxious fumes when heated, relatively low thermal conductivity, and a high neutron cross-section, it has fallen out of favor. Some designs immerse the entire core and heat exchangers into a pool of coolant, virtually eliminating the risk that inner-loop cooling will be lost.Ĭlementine was the first liquid metal cooled nuclear reactor and used mercury coolant, thought to be the obvious choice since it is liquid at room temperature. Low vapor pressure enables operation at near- ambient pressure, further dramatically reducing the probability of an accident. Liquid metals generally have high boiling points, reducing the probability that the coolant can boil, which could lead to a loss-of-coolant accident. Suitable liquid metal coolants must have a low neutron capture cross section, must not cause excessive corrosion of the structural materials, and must have melting and boiling points that are suitable for the reactor's operating temperature. with a breeding blanket), such reactors are called liquid metal fast breeder reactors (LMFBRs). When configured as a breeder reactor (e.g. ![]() To date, most fast neutron reactors have been liquid metal cooled fast reactors (LMFRs). Liquid metal coolant has been applied to both thermal- and fast-neutron reactors. Disadvantages include difficulties associated with inspection and repair of a reactor immersed in opaque molten metal, and depending on the choice of metal, fire hazard risk (for alkali metals), corrosion and/or production of radioactive activation products may be an issue. Liquid metals, being electrically highly conductive, can be moved by electromagnetic pumps. This makes them attractive for improving power output, cost effectiveness, and fuel efficiency in nuclear power plants. Additionally, the high temperature of the liquid metal can be used to drive power conversion cycles with high thermodynamic efficiency. Most water-based reactor designs are highly pressurized to raise the boiling point (thereby improving cooling capabilities), which presents safety and maintenance issues that liquid metal designs lack. This makes them attractive in situations where size and weight are at a premium, like on ships and submarines. They have also been used to power nuclear submarines.ĭue to their high thermal conductivity, metal coolants remove heat effectively, enabling high power density. Liquid metal cooled reactors were first adapted for breeder reactor power generation. Nuclear reactor where the coolant is liquid metalĪ liquid metal cooled nuclear reactor, or LMR is a type of nuclear reactor where the primary coolant is a liquid metal.
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