Abstract
Applicants and licensees of nuclear power plants have struggled to address United States Nuclear Regulatory Commission (NRC) expectations to assess if high energy line break (HELB) jet impingement on safety-related structures and components can lead to dynamic amplification. In this paper, evaluation of the potential for such amplification and the occurrence of resonance conclusively demonstrates that the phenomenon does not occur. Specifically, NRC Standard Review Plan Section 3.6.2 Revision 3 identifies a potential for jet load amplification associated with formation of unsteadiness in free jets that induces time varying oscillatory loads on obstacles in the flow path. In a HELB, several physical parameters of steam and two-phase jets issuing from a ruptured pipe – such as non-equilibrium condensation of steam in the jet, unsteady separation between the jet exit and impingement target, non-orthogonal alignment of jet axis to impingement surface, uneven or soft impingement surfaces, or mismatch of jet excitation frequency and impingement target natural frequency – prevent occurrence of the phase lock conditions needed to initiate and maintain a resonance. Justification is provided that the physics, thermodynamics, and geometry of a HELB jet in a light water reactor preclude occurrence of dynamic amplification and resonance of impinged downstream structures and components. Available data from single and two-phase impinging jet experiments and analyses confirm this conclusion.
