This is the fifth installment in Asia Times Science Editor Jonathan Tennenbaum’s series “Fusion Diary.” Read a series introduction, part 1, part 2, part 3 and part 4. Part 5 is a continuation of an August 22, 2023, interview with Paul Methven, director of Great Britain’s Spherical Tokamak for Energy Production (STEP) program.
Jonathan Tennenbaum: What are the most important decisions that you’re facing right now?
Paul Methven: I think some of the most critical decisions we will make are around the selection of our partners. Because, by definition, trying to get a fusion energy plant designed is an extreme example of a complex major program. In any such endeavor, you’re going to face a myriad of things you can’t predict, a myriad of problems and twists and turns.
If you are not organized and don’t have the right culture and the right partners in place, you will be far less able to navigate through those challenges as they arise. There’s no point in pretending that things won’t be difficult. You have to know that they will be difficult and then get the capability and the organization and the behaviors in place to deal with that difficulty. So, actually, partner selection and organization of the program is the number one set of decisions that we need to deal with.
There are a myriad of technical decisions that arise. Some of those are around the basic architecture to enable maintenance. A number of them are material selection choices, balancing between something that’s optimal but doesn’t quite exist yet, versus something that’s probably suboptimal, but is here today, and that we know we can build from.
Across the whole program, there is balance of risk between do we go with something that’s more established technology, but maybe lower performance, or do we go with not yet established technology, but which might just give us that performance leap that we need to make the whole integrated design work.
Those decisions are day in, day out and sometimes when you make them, you have to go right back down around your design loop again, because the problem is so integrated.
JT: During the time between now and planned operation a number of technological breakthroughs are sure to happen.
PM: Yes, absolutely. So some of this is about determining which things you’re going to deliberately leave as choices to be made later. And there’s some attendant risk with that, but also you’re banking on an opportunity arising later on, versus some things where you think, I just have to cement this now because the whole problem is too uncertain unless I actually make a decision on something.
And the whole program is a balance of those things. Understanding the nature of each of the decisions you have to make and sequencing them is in itself quite a tricky thing to do. But we are trying our best to work through that.
High-temperature superconductors are a key issue
JT: Speaking of technological breakthroughs that might occur along the way, obviously one area is high-temperature superconductors, which are essential to the STEP reactor. It’s hard for me to believe that there won’t be a great deal of progress in that area in the coming period. Are you anticipating that, in your design work?
PM: We are anticipating some improvement. Well, let me rephrase. We would hope, and I think you’re right, there will be really considerable improvement in HTS magnets across the next 20 or so years. What we’re doing at the moment is anticipating some pretty modest improvements, and using that as the basis for design. Any subsequent improvement becomes upside.
With a number of technologies, not just HTS magnets, we’re being not super-conservative but relatively conservative and making sure that in our calculation we can get a positive estimated net power. If we have subsequent efficiency improvements and cost improvements, for example as the demand for high-temperature superconductor tape and so forth goes up, that would be an upside on the project.
STEP targets
JT: Do you regard STEP to be a prototype, so that you could move to an commercialization with a similar design, for example in terms of the size of the reactor?
PM: I would think that a few things would change. There would probably be an increase in scale. This is just the point we’ve been discussing, that efficiency improvements in each of the underpinning systems might actually limit the necessity to increase scale greatly. At the moment we have an energy balance which shows us in design as positive net energy out. But that could get better for two reasons.
One, if you increase the physical scale of the machine. But more particularly if you drive efficiency improvements in the key systems. You might not actually have to grow your size that much, if you make significant efficiency improvements in the underpinning technology.
JT: How much electric power do you expect to get out of STEP?
PM: At the moment we’re looking for a thermal power something on the order of 1.8 – 2 gigawatts. In terms of electrical power — and this sounds relatively unambitious – the prototype would be anywhere from about 100 MW to about 400 MW. We may well do better than that. Our baseline intent is to get at least 100 MW electric out. But if we have plasma performance improvements and underpinning system efficiency improvements, then you get better and better beyond that. But we’ve got to break the back of it first.
JT: I understand that you have set 2040 as a target date for an actual operating system.
PM: For getting to what we would call first plasma. We wouldn’t be at power generation operations in 2040. You have to have the majority of your systems in place in order to deliver a plasma. But we are working on a staged series of operations which would go from plasma demonstration, then probably a maintenance demonstration prior to significant activation of the machine and then into a DT*campaign where you would demonstrate your power operations and your tritium self-sufficiency.
*Note from JT for the reader: A major challenge for utilizing deuterium-tritium (DT) fuel is the supply of tritium, which is present on the Earth only in minute quantities. In order to ensure self-sufficiency in fuel, a favored solution for future fusion power plants is to “breed” tritium in the reactor itself.
This can be done by introducing the element lithium into the “blanket” of material surrounding the reactor chamber. When a neutron generated by DT fusion is absorbed by a lithium nucleus, this triggers a nuclear reaction whose products are tritium and helium.
Next: From submarines to fusion reactors, part 6.
Jonathan Tennenbaum, PhD (mathematics), is a former editor of FUSION magazine and has written on a wide variety of topics in science and technology, including several books on nuclear energy.