Comparison of Sodium and Lead-Cooled Fast Reactors Regarding Severe Safety and Economical Issues

A large number of new fast reactors may be needed earlier than foreseen in the Generation IV plans. According to the Special Report on Emission Scenarios commissioned by the Intergovernmental Panel on Climate Control nuclear power will increase by a factor of four by 2050. The drivers for this boost are the increasing energy demand in developing countries, energy security, but also climate concerns. However, if one stays with a once-through cycle the amount of high-level nuclear waste will increase substantially and there will be an upward pressure on the price of uranium in the next few decades. Therefore, it appears wise to accelerate the development of fast reactors and efficient re-processing technologies. In this paper, two fast reactor systems are discussed ¿ the sodium-cooled fast reactor, which has already been built and can be further improved, and the lead-cooled fast reactor that could be developed relatively soon. An accelerated development of the latter is possible due to the sizeable experience on lead-bismuth alloy coolant in Russian Alpha-class submarine reactors and the research efforts on accelerator-driven systems in the EU and other countries. First, comparative calculations on critical masses, fissile enrichments, and burn-up swings of mid-sized SFRs and LFRs (600 MWe) are presented. Monte Carlo transport and burn-up codes were used in the analyses. Moreover, local Doppler, coolant temperature and axial fuel expansion reactivity coefficients were also evaluated with MCNP and subsequently used in the European Accident Code-2 to calculate reactivity transients and unprotected Loss-of-Flow accidents (ULOF). Further, unprotected Loss-of-Flow as well as decay heat removal (total Loss-of-Power, TLOP) were calculated with STAR-CD CFD code for both systems. The tight pin lattice SFRs (P/D=1.2) showed to have a better neutron economy than wide channel LFRs (P/D=1.8), resulting in larger BOL actinide inventories and lower burn-up swings for LFR. The reactivity burn-up swing of LFR self-breeder could be limited to 3$ in 3 years. The calculations revealed that LFRs have an advantage over SFRs in coping with the investigated severe accident initiators (ULOF, TLOP). The reason is better natural circulation behavior of LFR system and much higher boiling temperature of lead. An unprotected Loss-of-Flow accident in LFR leads to only a 250 K coolant outlet temperature increase whereas in SFR coolant would boil. Regarding the economics, the LFR seems to have an advantage since it does not require an intermediate coolant circuit. However, it was also proposed to avoid an intermediate coolant circuit in an SFR by using a supercritical CO2 Brayton cycle.

CARLSSON Johan;  WIDER Hartmut; 

TUCEK Kamil; 

2008-02-08

American Society of Mechanical Engineers (ASME)

JRC33909

http://www.asmeconferences.org/ICONE13/TechnicalProgramOverview.cfm,    https://publications.jrc.ec.europa.eu/repository/handle/JRC33909,