A suite of computer programs has been developed to analyse the structu
ral dynamic response of the coolant circuit of the PWR Nuclear Steam S
upply System in the event of an extremely hypothetical Loss of Coolant
Accident or LOCA in short. This paper firstly introduces the computat
ional procedures and steps of the programs to analyse the structural e
ffects of this event. These programs calculate the thermo hydraulic re
sponse of the two phase fluid and the propagation of the depressurisin
g wave through the complex geometry of the pipe system and equipment i
nternals. From these time dependent thermal hydraulic quantities, the
forces arising from the depressurising wave are calculated and transla
ted into time history forces and moments. These forces act on the stru
ctures and are input to a structural lumped mass model and analysed by
a dynamic piping analysis code. Resulting from this analysis are the
time dependent impact forces at pipe whip restraints and system intern
als and supports upon which the integrity of the system must be assess
ed. This paper also discusses the modelling of the nonlinear supports
and restraints, and the sensitivity analysis to find a computationally
acceptable and sufficiently precise model for the design qualificatio
n of these structures. The nonlinear modal superposition technique use
d is of recent interest as being the computationally efficient and is
gradually being used in conventional plant piping analysis. However, t
his method for the structural dynamic transient analysis of a large nu
mber of degrees of freedom structural model with nonlinearities is sti
ll computationally intensive.