NON-LINEAR SEISMIC ANALYSIS OF STEAM GENERATOR MOUNTED ON TRANSPORTER

摘要

Many commercial nuclear plants are currently undertaking major capital improvement projects such as Steam Generator Replacement (SGR), Reactor Head Replacement (RHR), Pressurizer Replacement (PR), or Turbine Rotor Replacement (TRR). Replacement of such heavy equipment typically requires transportation on heavy-duty industrial grade transporters, specially designed for the cargo and the limited purpose. Whilst en-route, the transporter and cargo may traverse areas of the plant that are shared by more than one unit, and because there usually is a desire to keep the unaffected unit(s) operational, the moving loads and seismic loads associated with the transporter and the heavy cargo become an added parameter that must be accommodated when evaluating the load path. In addition to evaluating the structural capability of the supporting structure along the load path subject to the moving load and associated seismic loads, the potential for sliding and rocking (thus stability of the cargo), must also be evaluated to ensure that proper clearances are maintained, and potential seismic II/I interaction issues are avoided. In support of a recent project for the Diablo Canyon Power Plant undertaking steam generator replacement; this issue had to be considered, since the load path traversed areas of the plant that were shared by both units. Even though the nature of the loading was transient, and the probability of a seismic event during transient movement of a steam generator is very low, due to the high magnitude of the footprint load, the plant conservatively decided to evaluate implications of possible seismic loads associated with movement of the steam generators. The steam generator sits on a specially designed saddle on top of the transporter, and is tied to the transporter using wire rope slings to prevent separation. The combined system exhibits geometric non-linearity associated with the transporter and the cargo, potentially sliding and rocking relative to the supporting structure. In addition, there is also geometric non-linearity associated with how the steam generator is being supported by the transporter that must be properly accounted for during a postulated seismic event. This geometric non-linearity is associated with the tension only nature of the wire rope slings attaching the steam generator to the transporter saddles. The overall system is then analyzed in order to ensure seismic stability of the transporter and the cargo, as well as extraction of proper seismic reaction forces for both evaluations of the structural elements along the load path, and the internal design of saddles and attachments to the transporter. This paper discusses the methodology and the results of performing such non-linear seismic analysis for a case of a steam generator resting horizontally on a transporter, en-route to and from the containment structure during a steam generator replacement project. The paper focuses on modeling techniques to properly allow for geometric non-linearity that exist between the steam generator and the transporter, as well as the transporter and the supporting media.