From Neil Craik
The recent question by Andrew Daley about Sodium Fast Reactors reminds me that when I first got into nuclear power at the Hunterston A MAGNOX reactor in Scotland. I attended a conference in Glasgow in 1960. There were papers given about the Dounrey Fast reactor being built in the north of Scotland in which the authors claimed that the technology was much superior than the Hunterston A Magnox gas cooled reactors. However one attendee from Dounrey told me privately that the DFR would never be practical because the sodium solidifies if the heat transport system becomes cool on a reactor shutdown. The HTS had therefore to be kept hot making maintenance difficult. This 14 MW DFR was taken to power in 1962 and was operated with difficulty for only 15 years. I went back to Hunterston and got the 2 x 160MWe reactors to full power in 1964 after when operated for 25 years.
Gas or water may be the only practical coolants.