IAEA TECDOC On SSI

General Comments

  1. In the Objectives section of Chapter 1, the following is stated, “This TECDOC provides a detailed treatise on SSI phenomena and analysis methods specifically for nuclear safety related facilities. It is motivated by the perceived need for guidance on the selection and use of theavailable soil-structure interaction methodologies for the design of nuclear safety-related structures. The purpose of the task is to review and critically assess the state-of-the-practice regarding soil-structure interaction methods. The emphasis is on the engineering practice, not on methods that are still at the research and development phase. The final goal is to provide practical guidance to the engineering teams performing this kind of analyses in present and in near future.

The document seems to contain more state-of-the art and beyond, with not sufficient emphasis on state-of-the-practice. Methods that are still mostly research tools are presented as recommended alternatives for site response/SSI evaluations without sufficient guidance on appropriate use of these tools. For example, in Chapter 6, Section “3D vs 3x1D vs 1D Material Behavior and Wave Propagation Models,” the following statement is made, “If soils will be excited to feature a full nonlinear/inelastic response, full 3D analysis and full 3D material models need to be used.” I agree that in some circumstances it is important to utilize alternative tools to assess nonlinear, 2D and 3D effects in our evaluations instead of just relying on 1D equivalent linear analyses to define strain compatible properties for linear SSI analyses. However, application of tools as described seem to be far from the state of the practice in the nuclear SSI field. I am not sure this document should be stating that these models need to be used. It may be better to state that when sufficient justification is not made for the use of standard of practice methods, more advanced analyses may be needed to justify that the design process is sufficiently conservative. If a design team were to just implement a non-linear 3D analysis methodology, I don’t think there is adequate guidance in this document to guide these analysts to produce valid results or sufficient information that would allow a regulator to assess the validity of such analyses.

  1. In practice, there is typically some handoff of strain compatible properties from the seismologists/geotechnical engineers to the structural engineer to use in the SSI analysis. Practical guidance issues that the document could address include: 1) Given that the design basis ground motion is likely somewhere between two annual exceedance frequencies, what input motion levels should the seismologists be using for their site response analyses? What information does the seismologist/geotechnical engineer need to know in order to provide appropriate strain compatible properties? 2) If the seismologist/geotechnical engineer uses method 3 as described in Chapter 6 of the document to develop a site specific design basis ground motion, is there any practical guidance that should be provided on the hand off on strain compatible properties?
  1. This review does not address grammatical editing of the document. I recommend technical editing of the report at later stages of completion.
  1. The format for citing references is not consistent through the document and citations in the text do not always align with information in the references section.