Session: 05-04: Nuclear Engineering and Safety Analysis

Paper Number: 136867

136867 - Analysis of the Dynamic Behaviour of a Nuclear Containment Structure Under Missile Impact 

Abstract: 

The physical protection of the nuclear structure, system, and components (SSCs) relevant to ensure the safety of the plant is one of the main design criteria to fulfil and requires the investigation of all the possible (operation and accident) scenarios, the determination of consequences they will cause, and the evaluation of the structural integrity.

The resistance of the NPP structures to missile impact requires considerable attention because of several physical problems, like the well-known penetration problem where a structure is designed to resist wall perforation by a high velocity projectile.

This study deals with the current general procedures and criteria used for a suitable design of SSCs against the effects of impact of missiles. Particularly, it covers the evaluation of global and local effects due to missiles impacting on the reinforced concrete structural elements, like the containment system, and the overall structural response to missile impact loads.

It is known that the impact of a non-deformable/rigid missile may have determine penetration, cracking, spalling, scabbing or perforation of the concrete target. To assess whether such type of thread may determine the failure of the safeguard system the effects associated to both the impact force, which is dependent on the striking missile stiffness, impact angle to maximize impact effects velocity, mass, shape, etc., and the resistance force must be determined. Furthermore, the striking missile is assumed impacting the reinforced concrete structure (RCS) along the normal direction, with reference to the considered structure cross-section: in all the points of the impact surface the forces acting at both bodies are assumed the same. The impact velocities which are considered in this paper fall in a range between the minimum impact velocity that initiates one of the local impact effects (they are identified mainly in penetration, scabbing, spalling and penetration) and the maximum impact velocity that satisfies the assumption of a rigid projectile, which is roughly between 10 and 10³ m/s.

To the aim, a numerical approach based on the use of the finite element (FE) code was adopted.

As the analysis of reinforced concrete is made complex by the several arising dominant energy absorbing and failure modes mechanisms, a methodology which was validated with reference to experimental data available in the open literature from large-scale impact tests was employed.

Therefore, a 3D FE model of the RCS was implemented with structural 3-D Solid element to represent the dynamic interaction occurring at the impact surface. The strain-rate effects are considered through the dynamic increase factor (DIF) to account for strain-rate hardening effects on both deformation and failure; for the steel behaviour the Cowper–Symonds’ model was assumed.

Results showed that at the instant of the impact, the intense shock wave that characterise the instant of the projectile-target impact is responsible of the cracking, and penetration of the RCS wall. For a striking velocity of about 150m/s the wall penetration extends over about 80 mm.

Presenting Author: Rosa Lo Frano DICI - University of Pisa

Presenting Author Biography: Rosa Lo Frano is appointed full professor at the University of Pisa.
She is reposnsible of several UE projects

Authors:

Rosa Lo Frano DICI - University of Pisa
Salvatore Angelo Cancemi University of Pisa
Michela Angelucci DICI- University of Pisa
Giovanni Pugliese University of Pisa