Lead-cooled system design and challenges in the frame of Generation IV International Forum
Introduction
The development of the combined technologies of fast reactors and their associated closed fuel cycles has the potential to increase by a factor of about up to 100 the energy output from a given amount of uranium (through full use of U238), while enabling enhanced approaches to the management of high level radioactive waste through the transmutation of minor actinides. The resulting fast reactor systems are therefore potentially able to provide energy for the next thousand years with the currently known uranium resources.
R&D on the most promising concepts is currently being coordinated at the international level through initiatives such as the “Generation IV International Forum” GIF [1]. The European Community (EC), through the Sustainable Nuclear Energy Technology Platform (SNETP), has defined its own strategy and priorities for fast neutron reactors that are the most likely to meet Europe’s energy needs in the long term in terms of security of supply, safety, sustainability and economic competitiveness [2].
The application of lead technology to nuclear energy had its start in the Soviet Union in the 1950s where nuclear systems cooled by Lead–Bismuth Eutectic (LBE) were developed and deployed for submarine propulsion. More recently, attention to heavy liquid metal coolants for reactors has arisen in several countries around the globe as their advantageous characteristics have gradually become recognized. Moreover the features and the associated technologies of heavy liquid metal coolants inspired several projects in the emerging field of Accelerator Driven System (ADS), and in particular lead and LBE have been considered as both coolants and neutron spallation targets for several such projects under development throughout the world.
In 2004, the Lead Fast Reactor (LFR) Provisional System Steering Committee (PSSC) was organized to develop the LFR System Research Plan (SRP). The committee selected two pool-type reactor concepts as candidates for international cooperation and joint development in the GIF framework: these are the Small Secure Transportable Autonomous Reactor (SSTAR) [3]; and the European Lead-cooled System (ELSY) [4].
In evaluating and planning research for these LFR concepts, the LFR–PSSC has followed the general aims of the Generation IV Roadmap; thus, efforts have focused on design optimization with respect to sustainability, economics, safety and reliability, and proliferation resistance and physical protection.
The needed research activities are identified and described in the SRP. It is expected that in the future, the required efforts could be organized into four major areas of collaboration and formalized as projects. The four areas are: system integration and assessment; lead technology and materials; system and component design; and fuel development.
In 2006 the EC partially funded, within the Euratom Framework Programme 6 (FP6), the ELSY project, conducted by a large consortium of European organizations to demonstrate the feasibility of designing a competitive and safe lead fast critical reactor using simple engineered features, while fully complying with Generation IV goals.
The ELSY project was completed in February 2010, but follow-on LFR development will continue within the Lead-cooled European Advanced DEmonstration Reactor (LEADER) project. The LEADER project will be built on the ELSY results with the objective to finalize the design of a large size LFR and to develop the conceptual design of a down-scaled demonstrator.
ELSY in fact is part of an extensive R&D program related to heavy-metal cooled systems involving FP5, FP6 and FP7. These efforts were initiated in FR5 with the development of the Accelerator Driven System. In the 6th FP these efforts were extended with the development of the critical system ELSY, the subcritical system IP-EUROTRANS and the development of basic technology by establishing the Virtual European Lead Laboratory (VELLA). The efforts now continue in the 7th FP with the further development of critical systems (LEADER), a subcritical system (CDT) and basic lead technology (GETMAT, HeLiMnet).
Section snippets
The heavy liquid metal coolants
Lead–Bismuth Eutectic-cooled reactors were developed and built in the Soviet Union as naval submarine propulsion reactors and supporting land prototypes. However, those reactors were strictly for military purposes. There has never been a LFR demonstration or prototype for commercial purposes.
Heavy Liquid Metal Coolants (HLMC) have several properties which, if properly exploited by the designer, together with specific design features, can potentially reduce the plant cost and improve safety (see
SSTAR LFR design
A critical issue for all designers has been the design of structures able to accommodate the mechanical loads, especially in seismic conditions, resulting from the use of a coolant with very high density (Table 1, column h). SSTAR can overcome this issue thanks to the small size; in fact 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 (Fig. 1).
It should be noted that the genesis for the SSTAR
ELSY design
The ELSY project is aimed at demonstrating the possibility of designing a competitive and safe fast critical reactor using simple engineered features, whilst fully complying with the Generation IV goals of sustainability, economics, safety, proliferation resistance and physical protection [7], [8], [9].
ELSY is an ambitious project; several challenging design provisions had in fact to be developed to face expected issues and new ones, discovered in the course of the project activity, related to
Conclusion
This paper provides a description of the current status of development of the major LFR reactor concepts in the frame of Generation IV International Forum, including their design characteristics and approaches to overcoming the challenges associated with heavy liquid metal coolants. We believe that the SSTAR and ELSY concepts incorporate a variety of innovative approaches to address these challenges in delivering viable LFR designs. The results to date indicate that the LFR is a very promising
Acknowledgments
The work on LFR in GIF is supported by the European Commission through the Euratom Framework Programmes, by the U.S. Department of Energy Generation IV Nuclear Energy System Initiative and by the Tokyo Institute of Technology. The ELSY, CDT and IP-EUROTRANS consortia in Europe are coordinated by Ansaldo Nucleare, SCK-CEN and KIT respectively.
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