Seismic analysis, including the consideration of soil-structure interaction (SSI), is an important and required
step in the design and licensing of nuclear power plant structures, systems, and components (SSCs) that are
important to safety. Historically, the SSI analysis of nuclear structures has been performed using equivalent
linear methods. However, there has been considerable industry exploration of alternative seismic design
and analysis approaches, such as nonlinear seismic analysis, to reduce the construction cost of new reactors.

Many next generation reactors are characteristically very different from previous designs, including features
such as liquid metal or molten salt coolant, stacked graphite block reflectors, solid pebble fuels, and
seismically isolated SSCs. Nonlinear seismic analysis may offer a more realistic approach to capture the
physics of next generation designs with inherently nonlinear design features and/or performance criteria.
As defined herein, nonlinear seismic analysis refers to an integrated seismic analysis of the site and structure
in the time domain where nonlinear behavior in one or more parts of the system is explicitly modeled.
Nonlinear seismic analysis tools offer the ability to capture the dynamic coupling between
components/subsystems, including SSI effects, while considering nonlinear response in one or more parts
of the soil-structure system. However, commercial grade dedication (CGD) of the nonlinear seismic
analysis software represents a costly hurdle to implementation within the regulatory framework.

To reduce duplicate effort and the overall burden on reactor developers, an industry initiative was
undertaken to develop software dedication guidance for nonlinear seismic analysis tools. The guidance is
intended to assist a commercial software user seeking to perform nonlinear seismic analysis of a nuclear
facility whose quality assurance requirements necessitate CGD. The developed CGD guidance focuses on
the nonlinear features and underlying physical behaviors expected to be important to many reactor designs
in order to achieve tools relevant to many reactor developers. The guidance includes a test matrix, which
defines physical responses and software features that are mapped to corresponding test cases. The test
matrix and test cases help benchmark the specific software features within an end-user’s CGD process.
These tools can also be leveraged to alleviate the regulatory scrutiny associated with a first-of-a-kind
technical approach as they support technical benchmarking of the nonlinear seismic analysis methodology.

This paper discusses the dedication process and how the developed guidance [Doulgerakis et al.
(2021)] can support advanced reactor design and licensing. The paper identifies the location of the publicly
accessible guidance document and accompanying tools. The guidance and test cases are designed to be
technology neutral to support designers of all advanced reactors and other nuclear facilities.