What's at the forefront of reactor research? A must-read digest/discussion.

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14. A sodium fire closed a Japanese plant (Monju) for fifteen years

"On December 8, 1995, the reactor suffered a serious accident. Intense vibration caused a thermowell inside a pipe carrying sodium coolant to break, possibly at a defective weld point, allowing several hundred kilograms of sodium to leak out onto the floor below the pipe. Upon coming into contact with the air, the liquid sodium reacted with oxygen and moisture in the air, filling the room with caustic fumes and producing temperatures of several hundred degrees Celsius. The heat was so intense that it warped several steel structures in the room.[3] An alarm sounded around 7:30 p.m., switching the system over to manual operations, but a full operational shutdown was not ordered until around 9:00 p.m., after the fumes were spotted. When investigators located the source of the spill they found as much as three tons of solidified sodium."

http://en.wikipedia.org/wiki/Monju_Nuclear_Power_Plant

Out of the 10 fast reactors that actually entered commercial service 1 has had a significant fire - not a great safety record. Without its coolant you're left relying on thermal expansion of fuel pins to separate the fuel. What happens if a pin is cracked, or defective?

"This fuel is based on experience gained through > 25 yr operation of the Experimental Breeder Reactor II (EBR-II) with a uranium alloy metallic fuel. The ultimate criteria for fuel pin design is the overall integrity at the target burnup. The probability of core meltdown is remote; however, a theoretical possibility of core meltdown remains."

http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=6178770

I agree it would be much better than what we have, but MSRs appear to have all the advantages of IFRs with none of the negatives.