I keep reading about this amazing claim such as quoted here:
And as it was described in the article, there the passive "walk away" safety system using the freeze plug. This was routinely used in the Oak Ridge MSR experiment, where they would literally shut off the power to the reactor on Friday, letting the fuel pour in to the drain tank, built for maximizing passive cooling, where it would cool and solidify during the weekend. On Monday they would just turn on heaters around the tank, and then pump it back in to the reactor and continue.
Did that really happen?