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Lead-Cooled Fast Reactor (LFR)

The Lead-cooled Fast Reactors (LFRs) feature a fast neutron spectrum, high temperature operation, and cooling by either molten lead or lead-bismuth eutectic (LBE), both of which support low-pressure operation, have very good thermodynamic properties, and are relatively inert with regard to interaction with air or water. They would have multiple applications including production of electricity, hydrogen and process heat. System concepts represented in plans of the Generation IV International Forum (GIF) System Research Plan (SRP) are based on Europe’s ELFR lead-cooled system, Russia’s BREST-OD-300 and the SSTAR system concept designed in the US. Numerous additional LFR concepts are also under various stages of development in different countries including China, Russia, the USA, Sweden, Korea and Japan. 

 LFR

LFRThe LFR has excellent materials management capabilities since it operates in the fast-neutron spectrum and uses a closed fuel cycle for efficient conversion of fertile uranium. It can also be used as a burner to consume actinides from spent LWR fuel and as a burner/breeder with thorium matrices. An important feature of the LFR is the enhanced safety that results from the choice of molten lead as a relatively inert and low-pressure coolant. In terms of sustainability, lead is abundant and hence available, even in case of deployment of a large number of reactors. More importantly, as with other fast systems, fuel sustainability is greatly enhanced by the conversion capabilities of the LFR fuel cycle. Because they incorporate a liquid coolant with a very high margin to boiling and benign interaction with air or water, LFR concepts offer substantial potential in terms of safety, design simplification, proliferation resistance and the resulting economic performance. 

The LFR has development needs in the areas of fuels, materials performance, and corrosion control. During the next 5 years progress is expected on materials, system design, and operating parameters. Significant test and demonstration activities are underway and planned during this time frame.  

Primary Advantages

Lead is peculiar among the coolants available for nuclear reactor systems for a number of reasons. As a dense liquid (when maintained above its normal melting temperature), it has excellent cooling properties while its nuclear properties (i.e., its low tendency to absorb neutrons or to slow them down) enable it to readily sustain the high neutron energies needed in a fast reactor while providing the designer with great flexibility.  These characteristics enable improved resource utilization, longer core life, effective burning of minor actinides, and open fuel pin spacing, important features in achieving sustainability, proliferation resistance, fuel cycle economics and enhanced passive safety by enabling fuel cooling by natural circulation.  

As a result of the very high boiling temperature of lead, namely 1749 °C, the problem of coolant boiling is for all practical purposes eliminated. The high margin to boiling leads to important safety advantages that also result in design simplification and improved economic performance.  

As a coolant operating at atmospheric pressure, the loss of coolant accident (LOCA) can be virtually eliminated by use of an appropriately designed guard vessel. This is not only a safety advantage, but also offers additional potential for plant simplification and improved economic performance since the complex process of simultaneous management of temperature, pressure and coolant level (as is seen in water-cooled reactors) is not necessary.  

One of the most important characteristics of lead as a coolant is its relative chemical inertness. In comparison with other coolants, especially sodium and water, lead presents a benign coolant material that does not support rapid chemical interactions that can lead to energy release in the event of accident conditions. Further, the tendency of lead to retain fission products and other materials that could be released from fuel in the event of an accident is another important advantage. The elimination of the need for an intermediate coolant system to isolate the primary coolant from the water and steam of the energy conversion system represents a significant advantage and potential for plant simplification and improved economic performance.  

Following the Fukushima-Daiichi reactor accidents, it is important to consider future reactor technologies in light of the severe conditions encountered. The LFR can demonstrate superior features to avoid the consequences of such a severe set of accident scenarios. First, one of the primary problems in the Fukushima incident was the common mode failure of diesel generators during an extended blackout condition. An LFR would not need to rely on such backup power and would be resilient in the face of blackout conditions by virtue of passively operated decay heat removal enabled by the natural circulation capabilities and other characteristics of the lead coolant.  

Second, the loss of primary coolant at the Fukushima-Daiichi reactors resulted from pressurization of the water coolant. An LFR with guard vessel would not suffer a loss of primary coolant, even in the event of a failure of the reactor vessel. 

The steam-cladding interactions at the Fukushima-Daiichi reactors resulted in the liberation of hydrogen and associated explosions. With the chemical inertness of lead as a coolant, no hydrogen generation would be enabled.  

Research Challenges 

Of course, as is the case for all the Gen IV advanced reactor technologies, there are research challenges associated with development of the technology. In the case of the LFR, these challenges include those related to the high melting point of lead; its opacity; coolant mass as a result of its high density; and the potential for corrosion when the coolant is in contact with structural steels.  

The high melting temperature of lead (327 °C) requires that the primary coolant system be maintained at temperatures to prevent the solidification of the lead coolant or at least to maintain a recirculation at core level to allow its cooling. Use of a pool type configuration and appropriate primary system design can provide effective and definitive solution to this issue.  

The opacity of lead, in combination with its high melting temperature, presents challenges related to inspection and monitoring of reactor in-core components as well as fuel handling. Also this issue can be faced by appropriate and specific design features, as an example, innovative core configurations with fuel elements extended with a stem above the lead free level, as shown in the recent European projects alleviate this issue.  

The high density and corresponding high mass of lead as a coolant result in the need for careful consideration of structural design to prevent seismic impacts to the reactor system. Innovative primary systems configurations with short reactor vessel coupled with the introduction of seismic isolators can solve this issue.  

Perhaps the most significant challenges result from the tendency of lead at high temperatures to be corrosive when in contact with structural steels.  This tendency, which is accelerated at higher temperatures, will require careful material selection and component and system monitoring during plant operations.  

Pending the development of materials resistant to lead corrosion at higher temperature, surface treatment (e.g., aluminization) is proposed as an effective way to protect materials immersed in lead from corrosion. In presently-proposed design configurations, the relatively low operating temperatures included in the design reduces the potential impact of this issue.  

Each of the above areas of research challenge is a topic of ongoing research.  

Summary and Conclusion  

The LFR is an advanced Gen IV reactor type that offers significant advantages in achieving the goals set by NERAC/GIF ten years ago. Among the 6 reactor types considered to be promising by the NERTAC/GIF, the LFR may well offer the best combination of characteristics and advantages. 

The events at Fukushima-Daiichi have increased international attention to the need for advanced reactors to be resilient in the face of unforeseen and/or severe accident conditions. In this context, the intrinsic characteristics of lead as a coolant as well as the potential to exploit passively operated heat removal from lead-cooled systems leads to particular advantages of the LFR as an advanced reactor technology to meet present and future needs.

Further reading

  • Weeks J.R., "Lead, bismuth, tin and their alloys as nuclear coolants". Nucl Eng Des. 1971; 15:363–72.
  • Smirnov V.S., Lead-cooled fast reactor BREST—project status and prospects [presentation]. In: International Workshop on Innovative Nuclear Reactors Cooled by Heavy Liquid Metals: Status and Perspectives; 2012 Apr 17-20; Pisa, Italy.
  • Dragunov Y.G., Lemekhov V.V., Moiseev A.V., Tocheny L.V., Umansky A.A., “Lead-Cooled Fast-Neutron Reactor (BREST)(Approaches to the closed NFC)” Proceedings of Global 2015 September 20-24, 2015 - Paris (France) Paper 5435.
  • Alemberti A., Frogheri M., Mansani L., The lead fast reactor: demonstrator (ALFRED) and ELFR design [presentation]. In: International Conference on Fast Reactors and Related Fuel Cycles: Safe Technologies and Sustainable Scenarios (FR13); 2013 Mar 4-7; Paris, France.
  • Alemberti A., Frignani M., Villabruna G., Agostini P., Grasso G.,Turcu I., Constantin M., “ALFRED and the Lead Technology Research Infrastructure”, European research reactor Conference, RRFM2015, Bucharest, April 19-23, 2015.
  • Takahashi M., National status on LFR development in Japan [presentation]. In: 11th LFR Prov. SSC Meeting; 2012 Apr 16; Pisa, Italy.
  • Smith C.F., Halsey W.G., Brown N.W., Sienicki J.J., Moisseytsev A., Wade D.C., SSTAR: the US lead-cooled fast reactor (LFR). J Nucl Mater. 2008; 376(3):255–9.
  • Choi S., Hwang I.S., Cho J.H., Shim C.B., URANUS: Korean lead-bismuth cooled small modular fast reactor activities. In: Proceedings of ASME 2011 Small Modular Reactors Symposium; 2011 Sep 28–30; Washington, DC, USA. ASME Digital Collection; 2011. p. 107-112.
  • Smith C.F., Halsey W.G., Brown N.W., Sienicki J.J., Moisseytsev A., Wade D.C., SSTAR: the US lead-cooled fast reactor (LFR). J Nucl Mater. 2008; 376(3):255–9.
  • Wu Y.C., Bai Y.Q., Song Y.,  Huang Q.Y., Zhao Z.M., Hu L.Q., Development strategy and conceptual design of China lead-based research reactor. Ann Nucl Energy. 2016; 87 (Part 2):511-6.

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