Feasibility study for a Small Modular Reactor (SMR)

Assystem conducted a stress assessment of the SMR’s close-coupled vessel nozzle arrangement by FEA. An optimisation approach was taken using Opti-struct software within Hyperworks.

The optimisation study investigated the following parameters:

• Variation in the distance that the Steam Generator (SG) is positioned from the RPV
• Increase in wall thickness of the pipework and nozzle reinforced zones
• Consideration of allowable stress in line with ASME III primary and secondary stress limits
• Normal operation and representative design basis event seismic loading
• SG orientation

A more detailed study was conducted on a representative section of primary loop pipework to ascertain the feasibility of a close-coupled SMR arrangement. This took into account NOC loading and a more appropriate estimate of external force from seismic excitation; an extension to the detailed study to determine the maximum allowable movement of the SG for the pipework and nozzles to remain within ASME III allowable stress limits.

Production of a written report related to the work carried out as well as recommendations for the design. The report’s recommendations helped to determine that the close-coupled design was feasible as long as certain criteria such as allowances for expansion were met. The stress assessment enabled to emphasize the benefits offered by the design changes:

• The optimisation approach allowed a better understanding of the sensitivity and trends of the key design features
• Assystem ensured the client passed the technical review gate in line with ASME III limits. The report was well-received and the design is currently in progress.