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Type of nuclear reactor cooled by molten lead

The lead cooled fast reactor is a nuclear reactor design that use molten lead or lead bismuth eutectic coolant. These materials can be used as the primary coolant because they have low neutron absorption and relatively low melting points. Neutrons are slowed less by interaction with these heavy nuclei (thus not being neutron moderators) so these reactors operate with fast neutrons. The concept is generally similar to sodium cooled fast reactors, and most liquid metal fast reactors have used sodium instead of lead. Few lead cooled reactors have been constructed, except for some Soviet nuclear submarine reactors in the 1970s. However, a number of proposed and one in construction new nuclear reactor designs are lead cooled. Fuel designs being explored for this reactor scheme include fertile uranium as a metal, metal oxide or metal nitride. The lead cooled reactor design has been proposed as a generation IV reactor. Plans for future implementation of this type of reactor include modular arrangements rated at 300 to 400 MWe, and a large monolithic plant rated at 1,200 MWe.

Lead cooled fast reactors operate with fast neutrons and molten lead or lead bismuth eutectic coolant. Molten lead or lead bismuth eutectic can be used as the primary coolant because especially lead, and to a lesser degree bismuth have low neutron absorption and relatively low melting points. Neutrons are slowed less by interaction with these heavy nuclei (thus not being neutron moderators) and therefore, help make this type of reactor a fast neutron reactor. In simple terms, if a neutron hits a particle with a similar mass (such as hydrogen in a Pressurized Water Reactor PWR), it tends to lose kinetic energy. In contrast, if it hits a much heavier atom such as lead, the neutron will "bounce off" without losing this energy. The coolant does, however, serve as a neutron reflector, returning some escaping neutrons to the core. Smaller capacity lead cooled fast reactors (such as SSTAR) can be cooled by natural convection, while larger designs (such as ELSY) use forced circulation in normal power operation, but will employ natural circulation emergency cooling. No operator interference is required, nor pumping of any kind to cool the residual heat of the reactor after shutdown. The reactor outlet coolant temperature is typically in the range of 500 to 600 °C, possibly ranging over 800 °C with advanced materials for later designs. Temperatures higher than 800 °C are theoretically high enough to support thermochemical production of hydrogen through the sulfur iodine cycle, although this has not been demonstrated. The concept is generally very similar to sodium cooled fast reactor, and most liquid metal fast reactors have used sodium instead of lead. Few lead cooled reactors have been constructed, except for some Soviet nuclear submarine reactors in the 1970s, but a number of proposed and one in construction new nuclear reactor designs are lead cooled.

Fuel designs being explored for this reactor scheme include fertile uranium as a metal, metal oxide or metal nitride. Lead undergoes almost no activation by neutrons. Thus, virtually no radioactive elements are created by absorption of neutrons by the lead. This is in contrast to the lead bismuth eutectic which was used in other fast designs, including in Russian submarines. The bismuth 209 in this mixture (which has a lower melting point, 123.5 °C, than that of pure lead) is activated to some degree to 210Po, polonium 210, which is a very radiotoxic alpha emitter. Although lead virtually absorbs no neutrons, because of its high density (10.66 g/cm3, when liquid at melting point), lead is very effective at absorbing gamma rays and other ionizing radiation. This ensures that radiation fields outside the reactor are extremely low. In contrast to molten sodium metal, another relatively popular coolant that is used in fast reactors, lead does not have issues with flammability (although the combustion of sodium in air is a mild reaction, not to be confused with the violent reaction between sodium and water), and will solidify from a leak. The very wide temperature range at which lead remains liquid (more than 1400 K or 1126 °C) implies that any thermal excursions are absorbed without any pressure increase. In practice, the operational temperature will be kept at around – , mainly because of other material properties and physico chemical limitations, a. o. their sensitivity to corrosion by a liquid metal (liquid metal embrittlement) and amalgam driven metal dissolution (continuous Cr and Ni extraction from stainless steel). As with all fast reactor designs, because of the high temperature and the high thermal inertia, passive cooling is possible in emergency situations. Thus, no electrical pumping assistance should be required, natural convection being sufficient to remove residual heat after shutdown. To achieve this, reactor designs include dedicated passive heat removal systems, that requires no electrical power and no operator action. All fast reactor designs operate at substantial higher temperatures in the core than water cooled (and moderated) reactors. This allows a significantly higher thermodynamic efficiency in the steam generators. Thus, a larger portion of the nuclear fission energy can be converted into electricity. More than 40% efficiency is achievable in real life, compared to around 30% in water cooled reactors. Similarly, as with all fast spectrum reactors, the coolant is not pressurized. This means that no pressure vessel is required, and the piping and ducts can be constructed with non pressure resistant steel and alloys. Any leak in the primary coolant circuit will not be ejected at very high pressures. Lead has a high thermal conductivity (35 W/m・K) compared to that of water (0.58 W/m・K), which means that heat transport from the fuel elements to the coolant is effective. Instead of regular refueling, the whole core can be replaced after many years of operation. Such a reactor is suitable for countries that do not plan to build their own nuclear infrastructure. Lead's nuclear properties allow it to prevent a positive void coefficient, which is difficult to prevent in large sodium fast reactor cores. Lead does not react significantly with water or air, unlike sodium which burns readily in air and can explode in contact with water. This allows easier, cheaper and safer containment and heat exchanger/steam generator design.

The MYRRHA project (for Multi purpose hYbrid Research Reactor for High tech Applications) is aimed to contribute to design a future nuclear reactor coupled to a proton accelerator (so called Accelerator driven system, ADS). This could be a 'lead bismuth cooled, or a lead cooled, fast reactor' with two possible configurations: sub critical or critical. It could be a pool , or a loop type, reactor. The project is managed by SCK CEN, the Belgian research center for nuclear energy. It is based on a first small prototype research demonstrator, the Guinevere system, derived from the zero power reactor Venus existing at SCK CEN since the beginning of the 1960s and modified to host a bath of molten lead bismuth eutectic (LBE) coupled to a small proton accelerator. In December 2010, MYRRHA was listed by the European Commission as one of 50 projects for maintaining European leadership in nuclear research in the next 20 years. In 2013, the project entered a further development phase when a contract for the front end engineering design was awarded to a consortium led by Areva. Aiming at a compact core with high power density (i. e. with a high neutron flux) to be able to operate as a materials testing reactor, the fuel to be used in the ADS MYRRHA must be highly enriched in a fissile isotope. A highly enriched MOx fuel with 30 – 35 wt. % of 239Pulink=Plutonium 239 was first selected to obtain the desired neutronic performances. However, according to Abderrahim et al. (2005) Beside the technical challenges identified, they were also financial and economical risks related to the construction and exploitation costs expected to strongly increase when the project should enter a more detailed design stage. Long construction delays related to design complications, underestimated technical difficulties and insufficient budget are not uncommon for such a project. The limited participation of the Belgian State (40% of all the costs) and the uncertain benefits for the external project owners were also pointed out. the front end engineering design (FEED) activities had to be suspended and have not progressed beyond the preliminary stage. Quite surprisingly, the preliminary results of the FEED activities were published in a journal absolutely not related to the field of ADS or fast neutron reactor: the International Journal of Hydrogen Energy (IJHE) while there was never any question of producing hydrogen with MYRRHA. The choice of this journal to present the preliminary results of the FEED activities is disconcerting. The journal where the FEED activities were announced, Physics Procedia, is also discontinued. Beside continuously increasing costs and financial uncertainties, the project still has to address many technical challenges: severe corrosion issues (liquid metal embrittlement, amalgam driven dissolution in the molten metal of Cr and Ni from the stainless steel used for the fuel claddings and reactor structure materials), operating temperature (metal solidification risks versus increased corrosion rate), nuclear criticality safety issues

The mass inventory of the lead bismuth eutectic (LBE) for the proposed pool type design of MYRRHA considered in the preliminary FEED analyses of 2013 2015 represents 4500 tons metallic Pb Bi. This would correspond to an activity of 5.5 × 10 becquerels,

The dual fluid reactor (DFR) project was initially developed by a German research institute, the Institute for Solid State Nuclear Physics, in Berlin. In February 2021, the project was transferred to a newly founded Canadian company, Dual Fluid Energy Inc., to industrialize the concept. The DFR project attempts to combine the advantages of the molten salt reactor with these of the liquid metal cooled reactor. As a fast breeder reactor, the proposed DFR reactor is designed to burn both natural uranium or thorium, as well as transmutating and fissioning minor actinides. Due to the high thermal conductivity of the molten metal, the residual decay heat of a DFR reactor could be passively removed.

ALFRED (Advanced Lead Fast Reactor European Demonstrator) is a lead cooled fast reactor demonstrator designed by Ansaldo Energia from Italy planned to be built in Mioveni, Romania. ATHENA, a molten lead pool used for research purposes, is going to be built in the same site as well.

The BREST reactor is currently under construction. This reactor will employ pure lead as coolant, a plutonium/uranium nitride fuel, generate 300 MWe (electric) from 750 MWth, and is a pool type reactor. The foundation has been completed in November 2021. The reactor sits as the Siberian Chemical Combine's (SCC's) Seversk site.

The company LeadCold is in collaboration with KTH Royal Institute of Technology and Uniper developing the SEALER (Swedish Advanced Lead Reactor) reactor, a lead cooled reactor using uranium nitride as fuel.

British company Newcleo is developing 30 MWe and 200 MWe lead cooled small modular reactors for naval and land use. The first operational reactor is planned to be deployed in 2030 in France.

The initial design of the Hyperion Power Module was to be of this type, using uranium nitride fuel encased in HT 9 tubes, using a quartz reflector, and lead bismuth eutectic as coolant. The firm went out of business in 2018. The Lawrence Livermore National Laboratory developed SSTAR was a lead cooled design.