When the slug of sodium reaches the vessel plug, an impact results and the head will be damaged in two ways: the vessel plug may deform and lift against its restraints, and lateral forces after the initial impact may cause radial deformation of the vessel just below the head.

It is important to be able to compute whether any ingress of sodium is possible into the containment area above the vessel. Therefore the plug jump and radial deformation of the vessel head need to be computed from the sodium hammer impact. Codes do exist that perform this computation: The following equations illustrate a method of deriving the plug jump from a static load analysis

Momentum is conserved:

M3vs = MT i/p (5.25)

In these equations, M and v are mass and velocity, respectively, and the subscripts s and p refer to the sodium slug and the plug, respectively.

MT = Ms + Mp (including shields, etc.) (5.26)

Assuming that the plug restraint system, say bolts, is designed to hold the plug on while absorbing the energy of the sodium slug in the stretch of the bolts themselves, we can calculate this stretch knowing the number and size of the bolts. Bolts absorb energy,

Eb = average stress x elongation x volume (5.27)

and to absorb the total sodium slug energy

Eb = MTv* (5.28)

From this set of equations, knowing the initial sodium slug energy, the elongation of the bolts can be derived and thus the possibility of allowing a path for the ejection of sodium may be evaluated. Note that this calcula­tion is very pessimistic since some of the energy of Eq. (5.24) would actually be expended in the radial deformation of the vessel referred to above.