The lead-cooled fast reactor is a nuclear reactor design that features a fast neutron spectrum and molten lead or lead-bismuth eutecticcoolant.
Molten lead or lead-bismuth eutectic can be used as the primary coolant because lead and 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.
The coolant does, however, serve as a neutron reflector, returning some escaping neutrons to the core.
Fuel designs being explored for this reactor scheme include fertile uranium as a metal, metal oxide or metal nitride.
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 with natural circulation emergency cooling.
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 high enough to support thermochemical production of hydrogen through the sulfur-iodine cycle.
The concept is generally very similar to sodium-cooled fast reactor, and most liquid-metal 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 new nuclear reactor designs are lead-cooled.
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.
Modular nuclear reactors
Options include a range of plant ratings, including a number of 50 to 150 MWe (megawatts electric) units featuring long-life, pre-manufactured cores.
The operating pressure is very low and lead has an extremely high boiling point of 1750 degrees Celsius, which is over 1100 degrees Celsius higher than the peak coolant operating temperature. This makes significant reactor pressurization by overheating virtually impossible.
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.
Lead and lead-bismuth are very dense, increasing the weight of the system therefore requiring more structural support and seismic protection which increases building cost.
While lead is cheap and abundant, bismuth is expensive and quite rare. A lead-bismuth reactor may require hundreds of tonnes of bismuth depending on reactor size.
Solidification of the lead-bismuth solution renders the reactor inoperable. However, lead-bismuth eutectic has a comparatively low melting temperature of 123.5 °C (254.3 °F), making desolidification a relatively easily accomplished task. Lead has a higher melting point of 327.5 °С, but is often used as a pool type reactor where the large bulk of lead does not easily freeze.
Lead-bismuth produces a considerable amount of polonium, a highly radioactive and quite mobile element. This can complicate maintenance and pose a plant contamination problem.[dubious – discuss] Lead produces orders of magnitudes less polonium, and so has an advantage over lead-bismuth in this regard.
Two types of lead-cooled fast reactor were used in SovietAlfa class submarines of the 1970s. The OK-550 and BM-40A designs were both capable of producing 155MWt. They were significantly lighter than typical water-cooled reactors and had an advantage of being capable to quickly switch between maximum power and minimum noise operation modes.
A joint venture called AKME Engineering was announced in 2010 to develop a commercial lead-bismuth reactor. The SVBR-100 ('Svintsovo-Vismutovyi Bystryi Reaktor' - lead-bismuth fast reactor) is based on the Alfa designs and will produce 100MWe electricity from gross thermal power of 280MWt, about twice that of the submarine reactors. They can also be used in groups of up to 16 if more power is required. The coolant increases from 345 °C (653 °F) to 495 °C (923 °F) as it goes through the core. Uranium oxide enriched to 16.5% U-235 could be used as fuel, and refuelling would be required every 7–8 years. A prototype is planned for 2017.
Another two lead cooled reactors are developed by Russians: BREST-300 and BREST-1200 The BREST-300 design was completed in September 2014.
WNA mentions Russia role on boosting other countries interest in this field:
In 1998 Russia declassified a lot of research information derived from its experience with submarine reactors, and US interest in using Pb or Pb-Bi for small reactors has increased subsequently.
Proposals and in-development
The MYRRHA project (for Multi-purpose hYbrid Research Reactor for High-tech Applications) is a first-of-a-kind design of a nuclear reactor coupled to a proton accelerator (so-called Accelerator-driven system (ADS)). This will be a 'Lead-bismuth-cooled fast reactor' with two possible configurations: sub-critical or critical.
The project is managed by SCK•CEN, the Belgian center for nuclear energy. It will be built based on a first successful demonstrator: GUINEVERE. The project entered a new phase of development in 2013 when a contract for the front-end engineering design was awarded to a consortium led by Areva.
MYRRHA enjoys international recognition and was listed in December 2010 by the European Commission as one of 50 projects for maintaining European leadership in high-tech research in the next 20 years.
According to Nuclear Engineering International, 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 dual fluid reactor (DFR) is a German project combining the advantages of the molten salt reactor with the ones of the liquid metal cooled reactor. As a breeder reactor the DFR can burn both natural uranium and thorium, as well as recycle nuclear waste. Due to the high thermal conductivity of the molten metal, the DFR is an inherently safe reactor (the decay heat can be removed passively).
^"Lead-Cooled Fast Reactor Systems and the Fuels and Materials Challenges". ResearchGate. Retrieved 20 March 2018.
^Alessandro, Alembertia; Johan, Carlssonb; Edouard, Malambuc; Alfredo, Ordend; Dankward, Struwee; Pietro, Agostinif; Stefano, Montif: "European lead fast reactor—ELSY", published in "Nuclear Engineering and Design",Volume 241, Issue 9, September 2011, Pages 3470–3480
^ abcde"Initiative for small fast reactors". World Nuclear News. 4 January 2010. Retrieved 5 February 2010.
^"Heavy metal power reactor slated for 2017". World Nuclear News. 23 March 2010. Retrieved 26 September 2012.
^"Design features of BREST reactors and experimental work to advance the concept of BREST reactors" (PDF). US DoE, Small Modular Reactor Program. Retrieved 16 May 2013.
^"Design completed for prototype fast reactor - World Nuclear News". www.world-nuclear-news.org.
^"Nuclear Reactors - Nuclear Power Plant - Nuclear Reactor Technology - World Nuclear Association". www.world-nuclear.org.
^Science Magazine, " Reactor-Accelerator Hybrid Achieves Successful Test Run"
^World Nuclear News, "Myrrha accelerates towards realisation"
^AREVA official website, "AREVA TA WINS CONTRACT FOR THE MYRRHA PROJECT"
^European commission, " Targeting nuclear waste with a proton beam"
^"Hyperion launches U2N3-fuelled, Pb-Bi-cooled fast reactor". Nuclear Engineering International. Global Trade Media. 20 November 2009. Archived from the original on 26 November 2009. Retrieved 3 December 2009.