[en] The differences between nuclear and conventional seismic standards are considered and their potential significance discussed. The approach to the design of nuclear facilities is appropriately both more rigorous and conservative than that required by conventional seismic standards and codes. For nuclear seismic design the requirements can be presented as assessment principles, e.g., NII SAPs or a safety guide e.g. IAEA; Seismic Design and Qualification for Nuclear Power Plants. The adoption of novel methods or designs are required to be supported by appropriate research and development with the ability to cite a precedent within the industry being a powerful endorsement. The method adopted must reliably predict the seismic response of the item to be qualified, including the seismic response of attached or supported Structures, Systems and Components. (SSC's) The traditional method adopted for seismic qualification by analysis has been based on linear elastic analyses. This is justified on the basis that the response is reliably predicted and realistic, provided that the elements remain elastic. In contrast the benefit of ductile behaviour of conventional structures within the design envelope has long been recognised and used as the basis to justify significant reductions in the seismic demand. Provided the acceptance criteria are met, the SAPs do not preclude and the IAEA safety guide specifically permits non linear behaviour within the design envelope for category 1 items. Both the current nuclear practice and the current conventional seismic standards can be classified as 'force based'. The displacement based approach, also referred to as performance based engineering (PBE), has been developed as a powerful tool in the evaluation and seismic retrofit of existing structures. This approach could be equally valid to the design of new structures and can be used to represent elastic or non linear behaviour although the full benefit will only be realised in the latter case. PBE shares many common features with the nuclear ideals, namely: - Defining the performance objectives specific for a particular structure; - Ready evaluation of multiple limit states; - Seeking to predict real behaviour as closely as feasible by considering the combination of soil and foundation effects, cracking and stiffness and strength degradation etc. and permitting the tracking of the development of mechanisms; - Enhancing the understanding of the seismic response by the identification of redistribution between load paths and the identification of the potential and probable controlling mechanisms; - Enabling the provision of a consistent level of protection against reaching a specified limit state. An initial evaluation of the relevance of displacement based methods to nuclear power plant structures has been undertaken by the U.S. Nuclear Regulatory Commission. They concluded that the approach has no advantages over force based methods for the design where the response is required to remain within the linear elastic range. They also identified advantages over the use of non linear time history analyses in the evaluation of seismic margin and the production of fragility curves. The displacement based methods require explicit consideration of many previously implicit or hidden assumptions. Recommendations: The reluctance of the nuclear industry to adopt the displacement based analysis and design methods is identified as a significant discrepancy between current nuclear practice and the conventional design methods that are available. The ideal and recommended course of action is to encourage use of PBE and displacement based analysis and design where appropriate and support nuclear industry focussed research on methodologies. The development of guidelines on the appropriate use of PBE and displacement methods would encourage the adoption of the approach. Before guidelines could be developed and agreed, studies and research to assess the various displacement based analysis methods available and to demonstrate that the methodologies would be sufficiently robust to yield reliable outputs, particularly for SSC's would be required