On Friday, the first small modular reactor received design certification from the US Nuclear Regulatory Commission, which means it meets safety requirements and could be chosen by future projects seeking clearance and approval.
The design comes from NuScale, a company born out of research at Oregon State University that received substantial funding from the Department of Energy. It is a steel cylinder 76 feet high and 15 feet wide (23 meters by 5 meters) capable of producing 50 megawatts of electricity. (The company also has a 60-megawatt iteration.) They envision a plant employing up to 12 of these reactors in a large pool like those used in current nuclear power plants.
The basic design is conventional, using uranium fuel rods to heat water in an internal pressurized loop. This water transmits its high temperature to an external steam loop through a heat exchange coil. Inside the plant, the resulting steam flowed to a production turbine, cooled, and returned to the reactors.
The design also uses a passive cooling system, so that no pumps or moving parts are needed to keep the reactor running safely. The pressurized internal loop is arranged in such a way that it allows hot water to rise through the heat exchange coils and back down to the fuel rods after cooling.
In the event of a problem, the reactor is also designed to manage its heat automatically. Control rods – which can wrap fuel rods, block neutrons, and stop the fission chain reaction – are actively held in place above fuel rods by an engine. In the event of a power failure or circuit breaker, it will fall on the fuel rods due to gravity. The valves inside also allow the pressurized water loop to escape into the vacuum of the double wall thermos type design of the reactor, removing heat through the steel exterior, which is submerged in the cooling pool. An advantage of the small modular design is that each unit contains a smaller amount of radioactive fuel, and therefore has a smaller amount of heat to remove in a situation like this.
NuScale submitted its design at the end of 2016, and approving a new type of reactor was no small feat. The company claims to have submitted more than two million pages of requested information throughout the process. But in the end, the agency approved: “NRC concludes that the passive features of the design will ensure that the nuclear power plant will shut down safely and remain safe under emergency conditions, if necessary.
A few more modular light water reactors are about to start the certification process. Also, a handful of companies are planning to submit very different designs, such as molten salt reactors. But these are even further away.
NuScale, for its part, affirms its intention to deploy its first reactors “by the mid-2020s”.