The Nuclear Regulatory Commission (NRC) staff recently agreed with NuScale Power’s proposal for the NuScale small modular reactor to eliminate the use of Class 1E electrical systems as part of its reactor design certification process. Class 1E is a safety classification used at all currently-operating commercial nuclear power reactors for electrical equipment and systems that are essential to emergency reactor shutdown, containment isolation, reactor core cooling, and containment and reactor heat removal. The NRC staff’s first-of-a-kind approval recognizes the inherent passive safety features and designs of an advanced reactor, which should result in attendant benefits in the ease of procurement, construction, and operation of the relevant systems. Although the NRC staff’s approval is currently limited to the NuScale design, this approval is significant as it supports the important evolution of the NRC regulatory framework to account for the design, operation, and safety enhancements of both small modular reactor and advanced reactor designs.
NuScale submitted a topical report (TR-0815-16497), “Safety Classification of Passive Nuclear Power Plant Electrical Systems,” to the NRC in October 2015 related to the safety classification of the NuScale electrical systems, and a revision to the topical report in February 2017. The topical report requested the NRC’s review and approval of certain NuScale reactor plant design and operational attributes that justify a determination that none of the electrical systems requires a Class 1E classification. After a detailed multi-year safety review, the NRC staff issued a safety evaluation report (SER) accepting NuScale’s proposal.
In the SER, the staff explained that “[i]f a reactor was designed so that no electrical equipment was ‘essential’ such that it met the definition of Class 1E (i.e., the reactor plant design did not include safety-related equipment dependent on electric power), then the design would not require Class 1E ac or dc power systems.” The SER analyzed a wide array of technical issues including reliability of safe shutdown, core cooling, reactor coolant pressure boundary integrity, containment integrity, and control room habitability—among many others. The Advisory Committee on Reactor Safeguards, NRC’s independent technical advisory panel, also reviewed the topical report and concluded that it is acceptable for the NuScale plant electrical systems design subject to certain limitations and conditions.
NuScale now must demonstrate that the final design information in its design certification application meets the conditions of applicability and that the other limitations and conditions are satisfied. But this is nevertheless a substantial step forward in establishing an improved regulatory framework that recognizes and credits inherent safety features of advanced reactor designs.