The Lead-Cooled Fast Reactor (LFR) system features a fast-spectrum lead or lead/bismuth eutectic liquid-metal-cooled reactor and a closed fuel cycle for efficient conversion of fertile uranium and management of actinides.
The LFR system 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 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.
The LFR was primarily envisioned for missions in electricity and hydrogen production, and actinide management. Given its R&D needs in the areas of fuels, materials, and corrosion control, a two step process leading to industrial deployment of the LFR system has been envisioned: by 2025 for reactors operating with relatively low primary coolant temperature and low power density; and by 2035 for more advanced designs. The preliminary evaluation of the LFR concepts considered by the LFR Provisional System Steering Committee (PSSC) covers their performance in the areas of sustainability, economics, safety and reliability and proliferation resistance and physical protection.
The LFR concepts that are currently being designed are two pool-type reactors (Table1):
Table 1. Key Design data of GIF LFR concepts
It should be noted that the objective of designing LFR with the high mean core outlet coolant temperatures required for the generation of hydrogen by thermo-chemical processes, could not been addressed simultaneously with the two-track design approach of the systems indicated above, owing to the required longer term R&D necessary for the development of new high-temperature materials that will be needed to provide corrosion resistance with lead as the coolant; this objective will be addressed at a later stage, depending on the success of the nearer term technology demonstration stage, that has been given priority.
The SSTAR is a small factory-built turnkey plant operating on a closed fuel cycle with very long refuelling interval (15 to 20 years or more) cassette core or replaceable reactor module. The current reference design for the SSTAR in the United States is a 20 MWe natural circulation reactor concept with a small shippable reactor vessel (Figure 1). Specific features of the lead coolant, the nitride fuel containing transuranic elements, the fast spectrum core, and the small size combine to promote a unique approach to achieve proliferation resistance, while also enabling fissile self-sufficiency, autonomous load following, simplicity of operation, reliability, transportability, as well as a high degree of passive safety. Conversion of the core thermal power into electricity at a high plant efficiency of 44 % is accomplished utilizing a supercritical carbon dioxide Brayton cycle power converter.
Figure 1. - Conceptual 20 MWe (45 MWt) SSTAR system
The initial design of ELSY is almost complete. The next step in its development is the R&D testing of several design innovations, in order to start with confidence, the detailed engineering design of a reduced-scale demonstration facility.
The ELSY reactor (Figure 2) is rated at 600 MWe. This mid-size rating is the result of the fact that plants of the order of several hundreds MWe are most economically attractive for addition to the European interconnected grids. In addition, a larger plant would require an increase mass of the lead coolant and would entail increased mechanical loads on the reactor vessel and its supporting structure.
The choice of a mid-size reactor power suggested the use of forced circulation to shorten the reactor vessel thereby avoiding excessive coolant mass and alleviating mechanical loads on the reactor vessel.
Thanks to the favorable neutron characteristics of lead, the fuel rods have been spaced further apart than in the case of previous fast-neutron cores. This and the innovative steam generators with flat spirals tube bundle enable the design of a low pressure loss primary loop. The needed pump head, in spite of the higher density of lead, could, therefore, be kept low (on the order of two bars) with reduced requirement of pumping power.
Because of the predicted low primary system pressure loss and the favorable heat transfer properties of lead, decay heat can be removed by natural circulation in the case of loss of station service power (LOSSP).
In terms of efficiency of electricity energy generation, the designers have achieved almost the same thermal efficiency as the Na-cooled SPX1, in spite of the 62 K lower mean core outlet temperature.
The potential of specifying higher operating temperatures of the primary cycle, owing to the low vapour pressure and very high boiling point of lead, depends on the qualification of suitable structural materials, the development of which may prove a long-term task, and has not been included in the near-term development of the LFR. However, the potential for future high temperature operations remains an attractive feature of the LFR.
Priority has been given to the designer’s goal of demonstration of the technical feasibility of the LFR within a relatively short time frame, with features such as a MOX-fuel core self-sustaining because of a conversion ration of about 1 and being adiabatic to (i.e. burner of) the self-generated MA. Development of the LFR to the more ambitious goals of high temperature operation and burning capability of MA beyond the self-generated MA will be considered, but will be pursued in detail in a future stage, depending on R&D and design achievements, and budget.
Figure 2 - ELSY reference configuration. Status at the end of 2008.
Advantages and challenges
The main advantages of the LFR system are its expected fuel efficiency, its capabilities in terms of nuclear materials management (thereby mitigating proliferation risks) and the reduced production of high-level radioactive waste and actinides.
The main features that the members have identified in order to achieve the Generation IV goals are summarized in Table 2. These features are based either on the inherent features of lead as a coolant or on the specific engineered designs.
Table 2 LFR potential performance against the four Goal Areas and the eight Goals for Generation IV.
Overview of key challenges for the LFR is provided in table 3.
Table 3. Key challenges of the LFR design.
¹ The small system operates at a higher temperature but because of the use of natural circulation cooling the erosive effect of lead is reduced
Most challenges have been positively addressed by the conceptual ELSY design configuration as of the end of 2008, but the challenge remains of the follow-on design of a very high temperature reactor, operating beyond 550°C, the design of which has not yet been addressed, mainly because of outstanding information about corrosion resistant, high-temperature materials.
GIF progress in 2008
The LFR R&D development plan incorporates two tracks of development leading to a single joint demonstration facility by 2020. Separate designs for a small, transportable LFR with a long core life and a moderate-sized power plant will be researched in the demonstration facility. The LFR system research plan, which sets out the research required in the system design, fuel and lead technology and materials, was updated in the course of 2008.
Recent LFR research papers and links
Cinotti L., et al., “The ELSY Project”, Paper 377, Proceeding of the International Conference on the Physics of Reactors (PHYSOR), Interlaken, Switzerland, 14-19 September, 2008.
L. Cinotti et al, The Potential of the LFR and the ELSY Project, 2007 International Congress on Advances in Nuclear Power Plants (ICAPP '07).
Y. H. Yu, H. M. Son, I. S. Lee, K. Y. Suh, Optimized Battery-Type Reactor Primary System Design Utilizing Lead, Paper 6148, 2006 International Congress on Advances in Nuclear Power Plants (ICAPP'06).
I.S. Hwang, A Sustainable Regional Waste Transmutation System: P E A C E R, Plenary Invited Paper, 2006 International Congress on Advances in Nuclear Power Plants (ICAPP'06).
W. J. Kim, T. W. Kim, M. S. Sohn, K. Y. Suh, Supercritical Carbon Dioxide Brayton Power Conversion Cycle Design for Optimized Battery-Type Integral Reactor System, Paper 6142, 2006 International Congress on Advances in Nuclear Power Plants (ICAPP'06).
A. V. Zrodnikov, G. I. Toshinsky, O. G. Komlev, Yu. G. Dragunov, V. S. Stepanov, N. N. Klimov, I. I. Kpytov, and V. N. Krushelnitsky, Use of Multi-Purpose Modular Fast Reactors SvBR-75/100 in Market Conditions, Paper 6023, 2006 International Congress on Advances in Nuclear Power Plants (ICAPP'06).
L. Cinotti, C. Fazio, J. Knebel, S. Monti, H. Ait Abderrahim, C. Smith, K. Suh, LFR (2006)
“LFR ‘Lead-Cooled Fast Reactor’", Proceedings of FISA 2006, EU Research and Training in Reactor Systems, Luxembourg, 13-16 March 2006
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