Small modular reactors: a Nu design

10 May 2017 (Last Updated May 10th, 2017 05:12)

NuScale has become the first American company to have a small modular reactor design accepted by the Nuclear Regulatory Committee, the body in charge of nuclear innovation in the US. Could this be the first of many?

Small modular reactors: a Nu design

Small modular reactors (SMRs) have been talked about for decades. Past attempts, however, have proved unsuccessful as costs spiralled out of control. But that could be changing, after NuScale, a company which grew out of SMR research at Oregon University and was officially incorporated in 2007, achieved approval from the Nuclear Regulatory Committee (NRC) to review its application to create SMRs. 

“Small modular reactors are defined as nuclear reactors, generally 300MWe equivalent or less, designed with modular technology using module factory fabrication, pursuing economies of series production and short construction times,” according to the World Nuclear Association.

NuScale has been working on the project since 2000 at Oregon University, US, and has already invested $30m on testing and development. A 12,000-page application detailing every technical aspect of the SMRs was submitted.

“We reached this tremendous milestone through the efforts of more than 800 people over eight years,” said NuScale COO and CNO Dale Atkinson. “We have documented, in extensive detail, the design conceived by Dr Jose Reyes more than a decade ago. We are confident that we have submitted a comprehensive and quality application, and look forward to working with the NRC during its review.”

But many people have tried and failed to make SMRs commercial in the past, so why is NuScale’s different?

The Nu SMR

NuScale SMRs are still light-water reactors, but they are only 65ft-tall by 9ft-wide, a fraction of the size of conventional reactors. Once in its casing, a module containing a reactor and steam generator is still only 76ft by 15ft. These modules are designed to work together in groups of up to 12 to make up the NuScale Power Module.

NuScale’s SMRs are designed to be simple, with the reactor using convection instead of pumps. The water heats as it passes over the core, and the temperature forces it to rise within the interior vessel of the reactor. It then cools as it is drawn down through steam generators and returns to the core where the process is repeated.

This method can produce 160MWt of thermal capacity and 50MWe (gross) of electrical capacity as the steam turns turbines attached by a single shaft to an electrical generator. They use standard LWR fuel in a 17 by 17 configuration, a well-understood and easily available fuel. The SMRs have a 24 month refuelling cycle, with fuel enriched less than 4.95%. But unlike their bigger cousins, NuScale’s SMRs do not require the full nuclear plant to be shut down in order to refuel.

The benefits of small modular reactors

Size is the obvious benefit. It is possible to house SMRs on much smaller and less specialised sites with just one small control room needed to monitor a power module of 12. This means that SMRs have the potential to be used for commercial sites. They have been suggested for use on mining sites in remote areas of Canada and other countries, for operations that cannot be connected to a grid and therefore rely on generators, to provide an economic and reliable alternative.

"The SMRs can be entirely constructed in a fabrication shop using predominantly off-the-shelf parts, which ensures quick construction at a low cost (<$5,100/KW)."

The simplicity of design also boasts numerous benefits. The SMRs can be entirely constructed in a fabrication shop using predominantly off-the-shelf parts, which ensures quick construction at a low cost (<$5,100/KW). The modules can be packaged in their entirety and distributed on trucks and barges as they weigh around a mere 700t.

Nuclear power’s reputation has been hard hit by the Fukushima disaster, with its popularity plummeting and its safety questioned. NuScale SMRs can’t meltdown due to their surface-area-to-volume ratio. This means that heat can easily be siphoned off should a problem with a reactor arise. Following a complete blackout, the reactor can cool naturally, as the core is situated in an underground super seismic-resistant heat sink. This makes it much safer than conventional reactors.

Why haven’t SMRs been used before?

The original concept for SMRs dates back to the 1940s when the US Army, Navy and Airforce all initiated R&D projects. While the navy’s project proved useful in helping to power submarines, it has never been done on a commercial scale. As commercial nuclear power has grown since the 1950s so has the size of reactors. In order to take advantage of economies of scale, reactors have become bigger and bigger, and SMRs have predominantly fallen by the wayside until recent years.

"In order to take advantage of economies of scale, reactors have become bigger and bigger, and SMRs have predominantly fallen by the wayside until recent years."

That is not to say they haven’t been attempted at all, but projects have universally been delayed, become expensive and had too short a shelf-life. Construction began on an SMR in the Elk River in 1959, but ran for more than three and a half years behind schedule due to engineering problems. This meant that the cost of the project more than doubled, costing $16m. The SMR worked successfully but in 1968 a crack appeared in the cooling pipe, which would have cost more than a million dollars to fix. Faced with this bill, the project was deemed uneconomical and shut down at a further cost of more than $16.15m.

Such early setbacks have greatly damaged SMRs’ popularity and no other SMRs were commissioned in the US until now. NuScale will have to prove that, unlike predecessors, its project can remain economical, as promised. As others have posed before it, the economics of the project relies on the economies of mass production. By keeping the design simple, and using standard parts, it hopes the factory-like production will enable the smaller size to be profitable.

What’s next for modular nuclear?

NuScale’s project has been moving forward at an impressive pace, but a lot remains to be done before an SMR is up and running. Now that the NRC has accepted the application it will be summited for a 40-month review before the agency can conclude that the design is acceptable for US use. Following this, NuScale will be issued with a design certificate that is valid for 15 years.

During the certified years, NuScale must fully construct the SMR and prove its success in order to become fully licensed. This will be the first SMR that the NRC has ever licensed and it is therefore expected to be a lengthy process. The reactor is going to be constructed at Idaho National Laboratory for the Utah Associated Municipal Power Systems (UAMPS), US, where it will be operated by Energy Northwest.

“We are delighted that our friends at NuScale have completed this step, which is key to our project licensing and our target commercial operation date of 2026 for the UAMPS Carbon Free Power Project,” said UAMPS CEO Doug Hunter.

"Currently, an estimated 55GW and 75GW will come from SMRs around the world by 2035."

NuScale predicts that its first reactor will be completed in the early 2020s, after which it intends to get production into full flow quickly. Currently, an estimated 55GW and 75GW will come from SMRs around the world by 2035. NuScale is expected to play a big role in this, but as that would require over 1,000 SMRs, factory production will need to increase quickly.

“There is still much to do and we firmly believe that not only will NuScale be the first SMR certified by the US NRC, but that the size and simplicity of the NuScale design will change the way we think and talk about nuclear going forward,” said Atkinson.

NuScale’s project could be the first of many, with SMRs providing a host of benefits, particularly for remote communities. But economic difficulties must be overcome if they are to become a competitive form of energy.