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An integrated head assembly (IHA) is equipped with the missile shield to absorb the missile energy from postulated control element drive mechanism (CEDM) missile during the dynamic event of accidental conditions. Once a CEDM nozzle breaks, reactor coolant jet discharges from the broken nozzle, then .it impinges at the bottom of the CEDM, and gives a thrust force to the CEDM missile until it impacts on the missile shield. After the missile impacting on missile shield, it is necessary to evaluate the structural responses on the local area of the missile shield, as well as behaviors of overall IHA structure. The jet has been previously assumed to be ô single-phase flow. However in order to reduce excessive conservatism for the jet characteristic, the jet is assumed to be a two-phase critical flow, and accordingly Fauske slip equilibrium model is applied to estimate the jet velocity. In this paper jet impingement models are proposed to estimate the missile velocity depending on jet expansions and size of objects. With the calculated missile velocities using the jet impingement models, the nonlinear CEDM missile impact analysis is performed to investigate structural responses of the missile shield of advanced power reactor 1400. Finally, the results show that the structural integrity of the missile shield and the IHA can be maintained due to CEDM missile impact. [ABSTRACT FROM AUTHOR]