The pressing need for low carbon energy means engineers and politicians are replacing fossil fuel power plants with renewables, carbon capture and storage and nuclear.
Large nuclear power plants offer carbon-free gigawatt scale baseload electricity. But, although technically well-proven, their massive budgets, long construction timescales and complex designs, make them difficult and often uneconomic to build.
Small modular reactors (SMRs) for civil power generation offer an alternative route to predictable, low carbon energy supply. Reactors of under 300MWe potentially offer several benefits, not in the least shorter construction timescales, scalability and a much more palatable economic case.
Engineers around the world are therefore advancing SMR designs. However, despite the potential advantages, not a single SMR has yet made the leap from drawing board to reality.
US company Nuscale Power is set to change that. The Oregon-based firm plans to switch on its first 160MWe reactor in 2023 in Idaho. The reactor would become the world's first operational SMR, heralding what many believe will be a new class of civil nuclear reactor.
Backed first by the US Government and now by global engineering giant Fluor, Nuscale's reactor has been in development for 15 years, and is widely seen as the most advanced.
So, with expectations high and international attention increasing, PE caught up with executive vice president of program development at Nuscale Power, Tom Mundy, the engineer responsible for managing the project to build the world's first SMR at a recent conference in London.
What's the progress on the project?
Over the last several years we've worked our way through conceptual, preliminary and then detailed design and validation. The design itself is now essentially complete - the official freeze is Q1 next year. We will then submit our application to the Nuclear Regulatory Commission (NRC) in 2016. That process for our design certification will last 40 months – ending in mid 2020.
We are the furthest forward in program development. Certainly in the US, we are the only one that intends in the near term to submit an application to the NRC, which is a critical milestone. That's several hundred million dollars worth of work already.
Then its on to the commercialisation work. How we will test, manufacture and inspect the equipment. And then its design finalisation, when we produce the documentation that is necessary to start fabrication and manufacturing.
It all lines up to the plant in Idaho's first module producing power in 2023.
What can you tell me about the design?
The reactor itself is 160MW thermal and is connected to a power conversion unit that will put out 50MWe. So in terms of just looking at the reactor, it's fairly small. The reactor can be mass produced in a factory, so we fit the definition of an 'SMR'.
But what's unique about us is that each facility will house up to 12 modules, so the entire output can be up to 600MWe gross. The output can also be used for other things: steam assist, desalination, chemical production, refinery operations, district heating.
We've specifically built into these modules the ability to load follow substantially. We want the technology to integrate well into grids with large amounts of intermittent generation. It can support big swings in local grid capacity, from, for example, a large local wind farm. You wouldn't normally find that in large gigawatt plants. They just run flat out.
What shaped the design of the Nuscale reactor?
A lot of vendors have taken their big designs, shrunk them down and made them integral by putting the pressurisers and steam generators inside. The systems that support the operation, like emergency core cooling, are essentially smaller versions of what you would find in a big plant.
That approach can work against economies of scale. But our chief technology officer started with a clean sheet of paper. His thinking was that the only way to make the reactor economic was to limit the size so it's easily transportable – by rail, truck or barge.
So the containment was sized first. The containment is also the heat transfer surface, it accommodates the release of heat from the reactor, so the containment determined the size of the core. That sized everything thereafter. It's how we arrived at 176MW thermal.
The whole thing has to be made in factory, so you capitalise on the ability to mass produced them. He also aimed to produce the strongest safety case and eliminate things to drive the cost down. The approach is simple, safe, scalable and flexible.
The components are all standard, the fuel is the same standard PWR fuel, it's just half height. The control rod drives are standard mag jack mechanisms are all used in PWRs. The valves are similar. It's just innovative use of tried and tested PWR technology.
How does it work?
We don't have forced reactor coolant circulation, we use natural circulation – hot water rises, cold water falls. And it is an integral light water pressurised reactor, so the steam generator, pressuriser and the heat removal and core cooling system is internal to the reactor vessel.
All of that is surrounded by a high pressure steel container. That containment is placed within the ultimate heat sink. Unlike other designs where in the event you need water, you have to get it from some external reactor, in our case it's right there already, which really strengthens our design. The heat transfer goes from the reactor wall straight into the water. It's the only SMR that has the containment as part of the module.
The primary coolant flows up through the tubes and down through a centre column through natural circulation. It removes its heat to helical coiled steam generators. Our really slow flow is compensated for by the large surface area of the heat exchangers. We get 100 degrees of super heat, which tends to increase the overall thermal efficiency. The tubes are about half inch in diameter, made from Alloy 69, nothing out of the norm.
What's most innovative about the design?
In a large PWR steam generator the primary coolant system flows through the interior of the tubes on the high pressure side. So the tubes are always in tension. But in our case the primary system flow is on the outside of the tubes, so the tubes are always in compression. It's completely the opposite, and improves the integrity aspect of the tubing. They are prevented from through leaking outward, because the higher pressure is on the outside. It's an excellent design.
Also, in a large PWR there is high flow over the tubes, which can cause flow induced vibration. Because we have natural circulation that is much lower. These are clear design advantages, that give greater assurance to integrity over time.
So, what's the expected lifetime of the reactor last and how is it maintained?
It will last 60 years. It's shipped in three pieces. It's lowered into its stand and you bolt it up through normal flanging. You have the upper containment, the lower containment and the lower reactor vessel. By separating those three things you gain access to the reactor core and you can do your refuelling.
When you take the upper containment off and put it in a dry dock. You pump down the dock and you can do all you steam generator inspection and valve work in a low rad, dry environment. You wouldn't have that when you do eddy current testing on a large PWR. You're in the manway in high rad fields. We eliminate that completely.
How much time will the Nuscale reactor spend offline compared to large commercial reactor?
The nominal refuelling period is ten days. That's not driven by the fuel shuffle. The longer duration activity is doing the inspection work on the steam generator stuff. Since we have such a small core, with only 37 fuel modules, a three cycle core, we can do all the fuel moves in eight hours. It's not our critical path. But it's worth remembering, in a 12 module facility, if you take one offline you still have 92% of the facility still running.
Does 12 reactors grouped together mean you need extra safety and redundancy systems, of similar levels to current generation large reactors?
We have less systems than what you would find on other plants. You just don't need them. Our decay heat removal are two heat exchangers mounted on the outside of the containment. They are in contact with the cool water. The emergency core cooling system is just four valves, two at the top and two nearer the bottom. There's no pump or piping and under failsafe conditions they fail open. The simplicity is amazing.
How do the costs compare to existing large nuclear power plants?
As soon as you put first module in you're making money. In a big plant you've just got one turbine and reactor and you have to wait. You're cashflow is completely different. Plus owners don't have to buy and install all 12 modules. We have clients that have said they need six to start, and will install modules as their load growth increases. There is flexibility over the capex.
Plus, a 12 module facility's construction is just 36 months. The interest on a 10 year construction program is tremendous. Ours is just 36 months, the capex is less, you're deferring costs. The economic profile is just much better.
Have you got an actual cost yet?
We are probably the only vendor that is putting cost information out for our technology. The numbers for large advanced nuclear, is around $100-110 dollars per MW. Ours is around $100 as well. But they have cost capital, a dead equity position and a long project lifetime, so that number can change.
So, our price is $2.8 billion for 600MW - $5,078 per kwhr. Right in the ball park to be competitive with a number of technologies.
What are the potential showstoppers for the 2023 commissioning timescale?
We've worked very hard on a pre-interaction plan to make sure that the NRC has anything that might be different or that they might not have experience of with our design, so they can review the application in the 40 month period they have said they can do it in.
Yes, the NRC experience recently has been of GW size plants. But there has been small reactors in the course of the industry they have reviewed.
Does civil nuclear no longer have to be massive?
We provide an alternative and complementary solution to large base load generation. I believe as a utility person that there are places and applications where a large unit will be best. But we provide a solution for locations that aren't suitable for large units. Here's another option for safe, clean, affordable reliable, energy generation.