Integrated Blast, Fragmentation and Shock Resistance Model of a Nuclear Power Plant Auxiliary Facility

Introduction: Standards, guidelines, manuals and researches, refer mainly to the required protection of a nuclear power plant (NPP) containment structure (where the reactor`s vessel is located) against different internal and external extreme events. The importance of auxiliary facilities (like the control room) protection against external explosions is not emphasized even though they are critical to the NPP operation and safety. A novel conservative integrated blast, fragmentation and shock resistance model (IBFSRM) of a NPP reinforced concrete (RC) auxiliary facility to an external above ground cylindrical cased charge explosions is being developed. This model updates the former integrated blast resistance model (IBRM) which considered the air blast loading effects of above ground bare hemispherical charges explosions. The IBFSRM defines the damage levels of the auxiliary facility based on: (1) single degree of freedom analysis of the structural dynamic response to both air blast loading and fragmentation impact loading at various ranges, and spalling & breaching at contact and close range explosions based on empirical correlations, (2) internal representative equipment resistance to in-structure motions resulted from direct-induced and air-induced ground shock, and (3) external wall perforation by the fragments.

Methods: The control room of the Westinghouse AP1000 NPP is analyzed against an above ground explosion of one ton of Tri Nitro Toluene (TNT) cylindrical cased charge with a 1.8:1 height to diameter ratio (for which blast incident peak pressure and impulse are known) and various case thicknesses. The IBFSRM takes into account different arrival times of the air blast compression wave and fragments impact loading while at certain range amplification of the loading is expected due to these simultaneous action happens only at certain range.

Results: cased charges explosions might cause breaching, spalling and perforate the AP1000 control room`s external wall at much higher standoff distances than bare charge ones. This is due to the fragments` intensive energy and momentum.

Conclusions: considering analytical and empirical correlations limitations, the IBFSRM can be used for a conservative vulnerability assessment of a NPP auxiliary facility to an external above ground cylindrical cased explosion.

It demonstrates the fragmentation importance to the vulnerability assessment of the NPP RC auxiliary facilities, especially in close range explosions, where fragments might perforate the external walls or cause them breaching or spalling.