There is still no answer for the drawbacks of using sodium. Simply focusing on the advantages might be good salesmanship, but it is more piss-poor science from an industry that makes it's money distorting, misrepresenting and outright lying about the work of actual scientists.
Also note the timeframe for potential deployment of a PROTOTYPE of this most advanced of the GenIV reactors is sometime within the next 35 years. It's obvious to anyone outside the nuclear industry bubble that this line of research is a waste of resources if addressing climate is the goal you are pursuing.
"While it seems possible..."
On the basis of its examination, IRSN considers the SFR system to be the only one of the various nuclear systems considered by GIF to have reached a degree of maturity compatible with the construction of a Generation IV reactor prototype during the first half of the 21st century; such a realization, however, requires the completion of studies and technological developments mostly already identified.
The main advantage of SFR technology in terms of safety is the use of low-pressure liquid coolant. The normal operating temperature of this coolant is significantly lower than its boiling point (margin of about 300°C), allowing a grace period of several hours during loss-of-cooling events. The advantage gained from the high boiling point of sodium, however, must be weighed against the fact that the structural integrity of the reactor cannot be guaranteed near this temperature.
The use of sodium also comes with a number of drawbacks due to its high reactivity with water and air. While it seems possible for SFR technology to guarantee a safety level at least equivalent to that targeted generation III pressurised-water reactors, IRSN is unable to determine whether it could significantly exceed this level....
...The feasibility of the system, however, has yet to be determined; it will chiefly depend on the development of fuels and materials capable of withstanding high temperatures, the currently considered operating temperature of around 1000°C being close to the transformation temperature of materials commonly used in the nuclear industry.
...No operating experience feedback from the other four systems studied can be put to direct use. The technological difficulties involved rule out any industrial deployment of these systems within the time frame considered.
...At the present stage of development, IRSN does not notice evidence that leads to conclude that the systems under review are likely to offer a significantly improved level of safety compared with Generation III reactors, except perhaps for the VHTR, whose feasibility is however not acquired.
http://www.irsn.fr/EN/newsroom/News/Pages/20150427_Generation-IV-nuclear-energy-systems-safety-potential-overview.aspx
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