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Nuclear startup NuScale has received a landmark final safety evaluation report (FSER) for its modular reactor design, making it the first American modular design to reach this point. NuScale’s design uses classic nuclear fission water reactor technology in a much smaller form factor, which contrasts with the escalating sizes of most current nuclear plant construction around the world.

“As the first U.S. small modular reactor design to be issued a FSER, NuScale is pioneering the way for additional innovative advanced nuclear technologies under development,” Nuclear Energy Institute (NEI) new reactor director Marc Nichol said in a statement.

Most of the planned “advanced reactor” technology close to reality is like NuScale, in that it’s a new shape or application of an existing technology. There’s an intermediate phase of new technology like molten salt. And finally, the next wave of advanced reactors may involve fusion, embodied by ITER as well as much smaller tokamak and stellarator projects around the world.

NuScale’s design is simple … kind of. “NuScale is a natural circulation light water reactor with the reactor core and helical coil steam generators located in a common reactor vessel in a cylindrical steel containment,” the U.S. Nuclear Regulatory Commission (NRC) explains online:

“The reactor vessel containment module is submerged in water in the reactor building safety related pool, which is also the ultimate heat sink for the reactor. The pool portion of the reactor building is located below grade.”

In the event of any runaway reactor event, NuScale says, the reactor quenches itself in its pool, making it “passively safe.” This content is imported from {embed-name}. You may be able to find the same content in another format, or you may be able to find more information, at their web site.

NuScale submitted its reactor design for this approval in late 2016, and the NRC accepted it for review in 2017. It’s normal for nuclear technology to take a long time to be studied and certified step by step. One way NuScale streamlined the process is by designing a small reactor it says is more self-contained and inherently safe than larger, bespoke-to-site nuclear fission reactor plants.

The startup has tried to head off some of the containment and emergency cooling issues for which larger plants must plan, resulting in a more streamlined certification process.

In a way, NuScale is emblematic of next-generation nuclear thinking. The technology inside is mostly made of established parts that are put together in an innovative way. Think of this like the difference between a home library with shelves built into the walls, versus being able to buy modular bookshelves at a furniture store: there are reasons to do one or the other, and both will hold your books. But the furniture store sends along a user manual, continues to make replacement pieces, and so on. Related Story Tiny Nuclear Power Stations Could Be, Well, Huge

Modularity and smallness are key aspects of NuScale and its peers, but these aren’t new ideas, either. NuScale wants to put its small reactor in applications from singles that power small towns or facilities up to bundles that will work like “traditional” large-scale nuclear plants. And these designs harken back, if indirectly, to the origins of nuclear as a “portable” way to power submarines—and potentially carry humans further into space.

The current design, which still has several steps until it can be constructed in the wild, is for 50 megawatts per module. NuScale seeks to apply for a 60-megawatt version next.