Following the radial strain of the vessel, the chemical explosive analogy (23) would have us imagine that the pressure of the gases in the center of the core are relieved. Nevertheless, these pressures are still quite large and can accelerate the sodium above the core upward. The energy put into the sodium is equal to the work that is done on the hammer in moving it into contact with the vessel head.

For a 2-in. vessel with a diameter of 18 ft, an energy release of 1000 MW — sec would result in the following figures if Proctor’s SL-1 analysis were followed:

Initial chemical charge equivalent to

1000 MW-sec 524 lb TNT

Charge volume 5.52 ft3

Charge volume “chemical” pressures 56562 psia

Pressure after vessel strain of 8.7% 1203.8 psia

Pressure after sodium hammer upward movement 765.0 psia

Work done on the sodium hammer 0.204-108 ft-lb

Sodium final velocity 68.8 ft/sec

Under this sort of impact the vessel plug would suffer considerable strain. It would have a restraint system to prohibit it from becoming a missile

because, if it were restrained only by its weight (say 100 tons), it could rise

92.5 ft into the air. The rise height simply serves to emphasize the potential problem. Some designs provide for bolted-on heads, rub fit heads with friction restraint, or even beam restraint.

However, this momentum calculation is based upon a chemical explosion study interested in radial deformation. The extension of this analogy to the vertical direction may be illogical, since the mechanism is much slower than the shock damage to the vessel and the postulation of an imaginary gas bubble may be quite wrong. It is therefore necessary to study the heat transfer effects by which real energy can be transferred to the sodium hammer. Proctor’s SL-1 analysis (25) did not consider heat transfer and although the results of a momentum analysis were apparently in agreement with observed values, this may well have been fortuitous. The calculation of the upward motion of the water in the SL-1 accident analysis should be repeated with later heat transfer methods to clarify this point.