After the absorption of strain energy by the vessel, the remainder of the available energy is, in part, thermal energy (the core fuel is still considerably hotter than the surrounding sodium) and, in part, kinetic energy (the fuel particles are still moving outwards). The kinetic energy would be directed upward by the unruptured walls, while the thermal energy would be depos­ited in the sodium above the core thus vaporizing some of it. Both the kinetic energy and the sodium vaporization would combine to accelerate the sodium above the core upward toward the vessel plug.

The upward acceleration is therefore achieved by both direct momentum transfer and by further flashing of sodium as fuel particles come into contact with it. The sodium slug or hammer would eventually come to rest in contact with the vessel plug, lifting it against its restraint system. The stretching of this restraint system could allow sodium to egress from the vessel after the accident.