Flexible conversion fast reactors

Special Section, Nuclear Engineering and Design, Volume 239, Issue 12, Pages 2581-3178 (December 2009)

Guest Editors:
Neil Todreas and  Pavel Hejzlar, Massachusetts Institute of Technology
Yassin Hassan, Texas A&M University

The Generation IV program has internationally revitalized the prospects for fast reactors worldwide.

These reactors would operate at a unity conversion ratio (CR = 1) on a sustainable transuranic (TRU) fuel cycle regime providing needed electricity generation.

Reactors operating in such a closed cycle in time would also manage the legacy LWR spent fuel actinides, since these actinides would be needed to provide the large start up fuel inventory for these unity conversion ratio reactors.

However the alternative path of a smaller fleet of dedicated fertile-free fast burner (near CR = 0) reactors to manage both legacy LWR spent fuel and that from the continued operation of LWRs is another option, particularly being studied in the US where transition to the closed cycle may be a more protracted process.

Hence the concept arises of a fast reactor plant which can be fuelled sequentially of cores with increasing conversion ratios CR   0.3 to CR   1, i.e., a flexible conversion ratio fast reactor.

Such a reactor could effectively respond to the dynamically changing needs and priorities of the nuclear industry as well as those of society, by managing transuranic materials such that resources are effectively used and the waste burden minimized while maintaining high safety, proliferation resistance, and attractive economics.

The eight papers of this special issue address this design objective for each of the viable fast reactor coolant alternatives – sodium, lead, liquid salt, and gas.

Supercritical carbon dioxide was chosen here, although, of course, helium is a leading contender. Flexible conversion ratio core designs which are compatible with an optimized plant design are investigated and presented for each coolant type with particular focus on lead and liquid salt. The liquid salt design which has been performed here is among the first concepts of this coolant type to be developed.

Further, the relative characteristics of plants employing these four coolants are cross compared to identify the most favorable performance features. The comparison illustrates how difficult it is for alternative fast reactor coolant concepts to overcome the sodium property advantages inherent in the sodium cooled approach.

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