ASME Codes and Small Modular Reactors

Authors: Sargent & Lundy, LLC: Dennis Demoss, Stefan Janusz, and Richard Niemer. Focus: Codes and Standards. This paper will review new Small Modular Reactor (SMR) designs and implications on ASME Codes and Standards. SMR technologies which will be discussed include B&W mPower (TVA Clinch River site), Westinghouse SMR (Ameren Callaway site), NuScale/Fluor SMR (Pacific NW lab site), Holtec SMR (Savannah River site), and Non-U.S. Designs such as the Russian SMRs. U.S. SMR reactor designs vary from 45 to approximately 225 MWe. SMRs, as defined by the International Atomic Energy Agency, have an electrical output less than 700 MW [1]; however, U.S. SMRs are typically defined as producing less than 350 MWe. SMR goals include significantly reducing plant capital cost requirements and enabling multi-reactor module construction and addition over time providing greater utility flexibility. A primary SMR advantage includes its installation in smaller grids typical of electrical power systems in developing countries. Unique aspects of the SMR technologies include integral reactor and steam generator vessel, integral pressurizer and internal piping, below-grade containment vessel, helical-coil integral steam generators, integral decay heat removal systems, modular plant construction and arrangement, in-service inspection unique requirements, special materials, and welding. SMR technologies provide unique challenges for conformance with ASME Codes and Standards. Non-U.S. designs, such as the Russian floating ship-type configuration SMR (KLT-40S) and Russian land-based SMR (VBER-300), will be discussed from the perspective of compatibility with ASME Codes. Discussion will be provided regarding non-U.S. SMR operational safety and inspection requirements based on ASME Codes. SMR development may require the expansion and clarification of current ASME Code design rules and requirements. For example, Section XI testing requirements and frequencies may require revision due to longer intervals between refueling. New divisions of ASME Codes may be required to address inspection of SMR inaccessible plant components and materials and plant operational differences from previous LWR designs. Additional reactor internal components and equipment may also require additional ASME Code considerations. Finally, higher design temperatures resulting from passive design shutdown considerations may require development and Code acceptance of new materials.