SEISMIC STABILITY ANALYSIS OF A CASK TRANSPORTER ON SLOPED SURFACES

摘要

Many commercial nuclear plants are currently in the process of storing excess spent fuel in various dry cask storage facilities on-site. This on-site storage requires loading of the spent fuel from the fuel pool onto a cask and then transporting the cask using a heavy duty transporter to the location of the on-site Independent Spent Fuel Storage Facility (ISFSI). Whilst on the transporter, the cask and the transporter must remain physically stable under postulated seismic loads. Physical stability is defined by evaluating the amount of potential sliding on the road surface as well potential for rocking and in the worst case tip-over of the transporter carrying the cask. Because of the low ratio of the CG height to width of the transporter, typically rocking and tip-over is not a concern, even under the most extreme of the seismic environments. However, sliding of the transporter on the road will occur once the ratio of lateral to normal load exceeds the dynamic friction coefficient that is representative of the interface characteristics between the transporter tracks and the road. For sites located in high seismic environment such as the Diablo Canyon Power Plant (DCPP), this is almost certain, given the high value of the design seismic input. Therefore as a prudent part of the design process, the sliding of the transporter carrying the cask is calculated under the design seismic scenario. This process requires performing non-linear sliding analysis, where appropriate consideration has to be given at any instant of time during the seismic excitation to the friction resistance being overcome, thus resulting in some level of sliding. Once this sliding displacement is calculated, appropriate measures can be provided in order to make sure that the transporter has enough clearance as it travels the intended path, and that it will not bump into any restraints which may result in unwanted impact loads. This process is reasonably straight forward as long as the road surface is a flat one. However, the road from the Fuel Building to the ISFSI at DCPP is sloped at certain locations along the travel path. Thus, the determination of sliding levels under a seismic scenario on a sloped road becomes more complicated, as gravity now plays an additional role in that there will be a component of the gravity that would tend to assist sliding down-slope and would prevent sliding up-slope of the road. In addition, the normal component of the applied load (gravity plus seismic) resisting frictional forces, is also slightly less because of the slope between the road and the horizontal plane. These added complications must be properly accounted for in performing such a stability analysis on a sloped road. This paper summarizes the methodology and the results for performing such analysis for the DCPP Dry Cask transporter on a sloped road. The road has slopes both longitudinally and transversely which had to be accounted for in performing these seismic stability analyses.