Q: As far as I am aware you need high pressure and high temperatures to initiate the fusion reaction. You can absolutely guarantee there cannot be an uncontrolled reaction?
Q: What safeguards are there in the design and system to ensure there can never be an uncontrolled nuclear fusion reaction?
A: For magnetic confinement fusion, you do need high temperature, but the density of the fuel gas is very low (one ten millionth of atmospheric density), so overall these are not high-pressure devices at all.
Magnetic confinement fusion can’t lead to an uncontrolled (or chain) reaction: fusion doesn’t occur naturally at all on a planet, but only in the cores of stars, where the compression is so huge that fusion automatically occurs.
Whilst fusion reactions don’t occur naturally on Earth, they can be persuaded to occur under the special conditions of a tokamak; if the tokamak is unable to reach these conditions, the reaction stops. A tokamak only holds enough fuel for 10s or so of operation, so again if it needs to be shut down, then this is essentially instant.
We can’t produce that compression on the earth with a tokamak, but we can use a tokamak to cause fusion to occur under specialised conditions where the targets are hot but very, very dilute – the density of material inside the fusion chamber is only 1 ten millionth of the density of air at sea level. If the temperature drops, or if the density increases, the reaction can’t proceed. The magnetic fields keep the hot fuel (at 10 million degrees C) away from the vessel walls where it might damage them. In fact, there is only a few grams of fuel in the reactor at any instant – only enough for 10s or so of operation.
Contrast this with conventional nuclear fission, where there can be weeks or months of fuel inside the vessel; given that the fission reaction is naturally occurring, and can proceed automatically unless prevented, you can see that fusion reactors are fail-safe.
Q: “a well-known industry for protecting coastal sites’….Fukishima?
A: Fission power stations like Fukushima Daiichi can always have the risk of a run-away reaction, since the fission process occurs naturally on the earth. However, fusion reactions only occur automatically if you have the ultra-high pressures at the cores of stars; tokamaks can sustain a fusion reaction only if the gas density is ultra low (less than one ten-millionth of air at sea level) and the temperature is ultra high (ten times hotter than the sun’s core): the strong magnetic fields of a tokamak ensure that the plasma is kept away from the tokamak walls. If any of the fusion conditions in a tokamak fails, the reaction stops: it can’t occur naturally on earth. Moreover, a tokamak in any event can only hold enough fuel for around 10s of operation, whereas a fission power station can hold weeks or months of fuel. Hopefully you can see now why a Fukushima-type runaway disaster couldn’t possibly occur in a magnetically confined fusion reaction (ie a tokamak).
Q: I understand the process, but fusion is used in nuclear bombs and is uncontrolled once initiated
A: Good to raise this – the magnetic confinement fusion (MCF) process in the STEP reactor can’t initiate a chain reaction, and has no weapons application. Fusion bombs are essentially compressional: conventional explosives symmetrically placed about a cold fuel pellet produce a compression not unlike that in stellar cores, and that compression triggers a fusion reaction, causing an explosion of the compressed material and subsequent reactions that release energy through the design of the bomb components.
MCF uses ultra-low-density material and high temperatures to harness fusion – conditions that can’t lead to an uncontrolled reaction. Please be assured that there is no connection between STEP and a fusion bomb, and no possibility of an uncontrolled chain reaction.
Q: This project must therefore include a pressurised system that converts heat energy from the reaction to electrical energy probably through water and turbines etc – is this the case for this design?
A: Yes, there will be a conventional steam turbine driven by the heat from the fusion reactor.
Q: Is there any radiation by-products and consequently any risk to the environment or workers? Also seems to require a lot of energy to operate. Is there a size below which it uses more power than it generates?
Q: Please give us an idea of the radiative materials produced in the process and end of life?
A: There are no radioactive waste by-products from the fusion reaction itself – it converts hydrogen to helium, and helium is the waste. The process will mean that the vacuum vessel itself will become irradiated (from the neutrons), and as it reaches the end of its useful life, the vessel will be removed and stored on site as intermediate level waste – similar to a medical isotope facility.
A replacement vacuum vessel can be installed, and the site returned to full operation. After a period not too much longer than its operational lifetime – certainly very short compared to any fission process – the stored vessel can be recycled into steel for other products – including a fusion vessel. The input power required is to service the cryogenics (for the super-conducting magnets) and other ancillary services, plus to initiate the burning plasma; after that it will produce net power for the grid. STEP is designed to be the correct scale for net energy delivery.
Only the vessel at the end of its life constitutes intermediate level waste; there are no radioactive by products produced by the fusion process.
Q: Will this proposed fusion reactor produce any radioactive materials that will have to be disposed of either during life or at end of the project’s life?
A: The fusion reaction produces helium as the waste product, and neutrons as the main energy source. These neutrons are captured in the lithium blanket, heating it up and allowing this heat to be transferred to a steam turbine for electricity generation (there are also additional possible applications of this heat).
Some of these neutrons will react with the lithium to produce more tritium, which can be used as fuel for the reactor (in fact, the expectation is that STEP will produce its own fuel in exactly this way). Those neutrons will irradiate the steel vacuum vessel itself, and so eventually – when it has reached the end of its operational span – the vessel will need to be stored as ‘intermediate level waste’: this can be done safely on-site, and does not need the extensive storage facilities and protection that nuclear waste from fission reactors demands.
After a period not too much longer than its operational lifetime, and very short compared to any fission process, the vessel can be recycled into a new reaction chamber (or other application).
There are no radioactive by-products at any stage, and the vessel is no riskier than any large-scale manufacturing plant at end-of-life – in fact, this is similar to radioisotope production for medical therapies (eg cancer treatment or CT scans).
Q: What about a conventional explosive problem from the nearby explosive factory?
A: A good point: the STEP team have already been in touch with HSE regarding the COMAH zones associated with other industry on the site and what might be possible. Should STEP come to Ardeer, it will only go ahead if HSE deem it safe.
The Health and Safety Executive will have both their own regulatory powers and full input into any planning decision regarding the siting of STEP at Ardeer, so please rest assured that the explosive risk from the other factory will be fully taken into account.
Q: What size of safety zone does a fusion plant need? There are plenty of residents near to the peninsula who will concerned about the impact a fusion plant would have to their ability to continue to live where they currently do.
A: It’s unlikely that the STEP site will need to be licensed in the same way as a nuclear fission plant. The government’s recent consultation on fusion regulation recommended that the Health and Safety Executive and Scottish Environmental Protection Authority will be the regulating bodies. It is currently not anticipated that there will be a need for a safety zone outside the NPL land holding on the Ardeer peninsula.
Q: Fusion relies on fission for tritium to get started so can’t be completely separate.
A: Actually, fusion generates its own tritium, so this is not entirely correct; there is no co-requirement for fission to make fusion a success.
Q: There is only a very small amount of Tritium available worldwide. Where will the additional tritium needed for this plant be sourced from?
Q: Where are the other sources of Tritium from if they aren’t from fission?
A: Note that fusion will generate its own tritium supply via neutrons interacting with the Lithium blanket – STEP should generate more than enough to satisfy its own needs; similarly, ITER.
Fusion reactors breed their own tritium using the reaction between lithium in the reactor heat-exchange blanket, and the neutrons produced by the fusion reaction itself. It’s anticipated that a fusion reactor will generate more tritium in this way than it consumes.
Q: Are there alternatives to Tritium if it is in short supply?
A: UKAEA don’t anticipate that tritium supplies will be problematic- see responses above.
Q: We might disagree about whether Fusion is a renewable energy source
A: I hope not: given the tritium generation via the lithium blanket around STEP, I hope you will agree that there is no carbon in the fuel cycle, and that there is no waste product except for the reaction vessel itself (apart from the Helium gas, of course)
Q: Where will we source the tritium to initially fuel this plant?
A: This is to be resolved, but there are a number of possible sources – including ITER, since fusion can generate its own tritium.
Q: Bit alarming that you do not know where the fuel is coming from?
A: Please don’t be alarmed: there will be a requirement for an initial charge of tritium – hopefully sourced from ITER, but the tritium sources will be assessed closer to the time when needed; after that, STEP will generate its own tritium. Deuterium is widely available from water – 1 part in 6000 or so of seawater contains deuterium, and lithium is widely available in both seawater and as a terrestrial mineral (about 20mg for each kg of rock).
Q: Doesn’t Lithium usually come from Chile? How will you find a sustainable source, could it be local? And if it is going to come from Chile, what will power it getting here?
A: Lithium may well come from Chile, too – it’s the world’s 25th most abundant element. There is about 20mg for every kg of rock anywhere, on average, so there are no geographic/political restrictions on sourcing lithium; it’s also available from seawater (about 2 parts per million, estimated at 230 billion tonnes)
Q: Would it not be better situated in a remote area that is already a nuclear site such as Dounray etc?
A: A fusion power station is intrinsically safe – in fact, fusion sites are likely to be controlled by the HSE, rather than a nuclear regulatory board (the exact regulatory framework is being decided at the moment); fusion sites do not need a nuclear licence.
In keeping with any safe large-scale industrial enterprise, it’s best to be located where there is space and a workforce – and a location where the workforce want to live and raise their families. Given that STEP is a power station, it is also best located where the consumption of that power can be close, to minimise transmission losses. There is no need for a fusion power station to be built on a former nuclear fission site.
Q: The EU ITER project is much further ahead and on a much bigger scale. Would it not be a good idea for the UK to collaborate with the rest of the EU to get to practical, energy-producing Nuclear Fusion?
A: Indeed: the UK is directly involved with ITER, and playing a full role as one of the 35 participating nations. The UK is the host to JET – the world’s largest and most successful fusion experiment, and the design predecessor to ITER. STEP will learn valuable information from the early operation stages of ITER (due to begin operation in 2025/6). It’s important to note that STEP is a different design, though: STEP is a spherical tokamak, so more of a compact ‘cored-apple’ shape than the very large doughnut of JET and ITER. The superconducting magnet coils required for STEP are smaller, making it quicker and cheaper to build without compromising on its power capacity. ITER is designed as an experimental test-bed, and is not intended to be a power station; STEP has power generation in its fundamental design remit.
Q: Why do we need a prototype fusion plant here when this is what ITER does?
A: ITER is not designed to be a power station: it’s an experimental reactor designed to demonstrate a set of particular outcomes, including break-even power generation, materials testing under fusion conditions, and safe operation. STEP will be designed not as an experimental facility, but a prototype power station, based on learning about its predecessor (MAST-U), and also on experience gained from ITER.
Q: The ITER fusion test plant in France is not due to be fully operational till 2035, even if it works. How can you start detailed design once you have the information from that and then have this reactor running in 2040?
A: Key here is design: ITER’s design was finalised a long time ago, and construction will be complete by 2025. There is then a campaign of experimental operation, gradually increasing power, until full power operations in 2035. Hence there will be the opportunity for a significant amount of learning from ITER before STEP is functional. Note also that MAST-U, the design of which is the basis of STEP (not ITER), is already operating, and will continue to do so.
Q: So, is it for power generation in North Ayrshire or as an experiment?
Q: Is it intended that this proposed experimental nuclear fusion reactor sited at Ardeer will input power to the grid and supply electricity? Or is it purely experimental?
A: STEP will be a prototype power station – in other words, elements of the design may be revised as operations suggest better ways of achieving performance.
It will generate power for the national grid, but not necessarily continuously: being a prototype, the first of its kind in the world, STEP will offer the operators the chance to explore how to optimise such a facility to get the most out of the fusion process: STEP can do more than just heat a steam turbine: the high operating temperatures of STEP can supply high-temperature processes directly (for example glass making or cement manufacture) in a carbon-free way. STEP is intended as a prototype for a fleet of fusion power stations (not just in the UK, but across the planet), and so will evolve as more experience is gained from operating such plant. It is not purely experimental in the way that ITER is.
Q: What’s the proposed economic case and funding model?
A: The over-riding imperative is to broaden the base of low-carbon power generation, excluding nuclear fission. The funding model for STEP specifically is likely to be a combination of public and private investment.
Q: What are the three top programme/project risks associated with this development?
A: As with any large-scale infrastructure project, the risks are to do with timescale slippage, cost overrun and unforeseen difficulties with the site having a knock-on effect on the construction. Achieving fusion is not thought to be a major risk, since this has already been demonstrated several times; refuelling is probably the biggest technical challenge, but experience from MAST-U gives confidence that this challenge will be met.
It’s important to bear in mind that a fusion power station has no toxic spent fuel to have to store/reprocess, nor has it to bear the cost of an extensive and expensive decommissioning process – these are the major costs that enter the up-front budgeted costs of producing fission power, and cause such controversy on the unit cost of power production from eg Hinkley Point C. At this early community consultation stage, the final design process for STEP is not completed, since the local conditions pertaining to the selected site will have implications for the final power station design.
Cost overrun caused by e.g. unforeseen complexity or supply-chain delays are always a significant risk factor in all large-scale infrastructure projects. Please be assured that UKAEA and its engineering consultants are experienced in construction at scale, and will account for such risks when the design is finalised.
Q: Can you confirm this reactor uses the nuclear fusion process and is intended to produce more energy than it uses to sustain the reaction?
A: Yes indeed: it is intended that STEP will break-even and produce net power -100MWe minimum; it is not an experimental facility.
Q: Are there plans for the building if the prototype does not work? Could this just be another abandoned building?
A: The STEP team are absolutely confident that this machine will work – based on many years of investigation of the technology, including JET and MAST-U at Culham Laboratories. This is a new and exciting venture.
Q: Will this proposed system actually contribute to the base electrical load?
A: When STEP is operating as a power station, it will contribute to the base load; note that STEP, being a prototype, will be subject to periods where it is being tested and developed, and so may be offline at these times.
Q: What happens if it goes ahead and in the intervening decades a reason arises for this new technology not to go ahead?
A: This is not entirely a speculative project: there is every reason to be confident that all the technology will work, since STEP will be based on MAST-U, a very successful experiment at Culham Laboratories.
There is no doubt fusion can be achieved – it has been achieved several times already, in JET; the remaining obstacles to fusion are (i) trapping the heat and using it for electrical power generation; (ii) refuelling the tokamak to ensure continued operations.
MAST-U researchers have recently proved that (ii) is now feasible in a Spherical Tokamak (a design pioneered by the UK, which is cheaper and easier to build than the conventional doughnut-shapes of JET and ITER); there is every confidence that the lithium blanket will perform as expected, providing the necessary high-temperature handling that will allow a steam turbine to operate efficiently, and also offer possibilities for other uses – such as cement manufacture or glass making – industries that need high temperatures in manufacturing, but are real challenges to finding alternative, carbon-free energy sources.
Q: Taking into account the cost of building the plant; the relatively short life it will have; and the cost of decommissioning the hugely radioactive buildings and machinery, what will be the actual cost of electricity per unit?
A: Until the design phase is completed (in which the site selected has a fundamental role), then the final cost can’t be determined. The assumption in the question of a short life is unjustified.
Q: This is called cheap electricity but the cost to build, per megawatt, is at least 20 times the cost of Whitelees Windfarm
A: It’s worth noting that Whitelees occupies more than 50 times the area proposed for STEP, but its maximum electricity generation is only 3 or 4 times the minimum of STEP. However, we shouldn’t view this in a negative competition: they are both critical to the development of carbon-free electrical power for the people. We need to have a range of options for power – including a capacity that can be switched on regardless of the prevailing weather.
Q: How does this plan fit in with the Scottish Government’s policy against new nuclear?
A: The SG energy policy is against nuclear fission, but has currently no stance on fusion; it is anticipated that this policy will be refreshed to account for this new type of power generation.
Q: What is nuclear fusion? How is it different from fission?
A: Fusion and fission are two different processes which occur at the atomic scale.
In fusion, the atoms in light elements, like hydrogen, are joined together, releasing energy in the process. Fusion reactions occur naturally in our sun, and power every star in the galaxy.
In fission, the atoms in heavier elements like uranium are broken apart. Energy is also released during this process. Fission is the process which is used in conventional nuclear power plants.
The only by-product of fusion reactions is helium, a harmless gas which has no significant impact on the environment.
Unlike fission which splits heavy atoms and creates toxic waste, fusion creates helium from hydrogen inside a specially shaped reaction chamber that uses powerful magnetic fields to control the reaction.
STEP proposes to harness the potential of fusion reactions to deliver clean, reliable, carbon-free power to homes, businesses, and infrastructure
Q: How safe is the technology and process?
A:Unlike conventional nuclear fission reactors, fusion machines, often known as ‘tokamaks’, produce no potentially harmful waste during their reactions – instead, their only product aside from power is helium, a harmless inert gas.
The kinds of uncontrollable runaway reactions, sometimes called meltdowns, that have sometimes occurred in fission reactors are simply not possible in a fusion reactor.
That is because the process of fusion cannot occur naturally on Earth, as it does in the sun and stars. In order for the fusion reaction to be sustained, the special conditions created in the interior of the tokamak must be perfectly maintained at all times: if interrupted the reaction will stop instantly.
STEP will use deuterium and tritium as fuels for the fusion process. Both deuterium and tritium are isotopes of hydrogen, and both will be consumed completely during the process of fusion.
Deuterium is a common isotope, abundant in seawater. Tritium is much rarer, making up only trace elements of the Earth’s atmosphere.
While tritium is radioactive, it is commonly used in medicine as a tracer for diagnostic procedures. It has a half-life of just 12 years, vastly shorter than that of the heavy radioactive elements used in fission reactors, which can be tens of thousands of years.
Inside the STEP reactor, the fusion of deuterium and tritium will produce energetic neutrons and helium. The neutrons will be captured in a liquid metal blanket around the machine, which will also generate more tritium fuel.
The neutrons heat the blanket, and that heat is used to drive a conventional steam turbine to generate electricity.
These neutrons pose no environmental threat, since they are entirely contained within the tokamak building.
Q: Can you clarify this what levels of radioactive waste are produced?
A: There is no radioactive waste produced. The only waste product from the fusion reaction itself is helium.
However, the vessel, called a tokamak, used in the process will become irradiated during the process. The level of radioactivity is similar to that arising from radioisotope production for medicine. Affected material can be stored on-site and the aim is to recycle as much as possible back into use at the facility.
The Regulatory Horizons Council Report on Fusion Energy Regulation notes that no high-level waste (such as spent fuel rods in fission power stations) will be generated by fusion, and that the waste hazard posed by fusion will be ‘orders of magnitude lower than fission’. Fusion reactors ‘are considered inherently safe’.
Q: Why do we need fusion when we have wind, solar, tidal energy etc; and hydrogen is being developed?
A: Fusion is one part of the energy mix that is needed to ensure we can develop sustainable low carbon energy provision – it shouldn’t be thought of as an either / or option. We need a variety of sources and a secure energy generation method that is not weather dependent, to serve the baseline requirement. Since coal and gas are not viable, and nuclear fission, which currently provides at least 20% of our power in Scotland alone, is retiring, we need to fill the gap.
Solar, wind and tidal generation are all valuable sources of renewable power for national energy grids. However, their ability to generate electricity can fluctuate with the availability of the natural resources which power them.
STEP will provide a constant baseline flow of electricity to the grid, helping to ensure that power needs are met as the UK and nations around the world transition to low-carbon generation processes.
Q: How does STEP compare to other fusion projects around the world?
A: There are a number of exciting fusion energy projects currently underway around the world, including ITER in France and JET and MAST in the UK, each of which have already made major contributions to our understanding of generating power through fusion.
STEP is aiming to build on those achievements by building a prototype plant which can demonstrate the ability to generate net electricity from fusion and deliver it to the National Grid. STEP will be a fully integrated power plant, not just a fusion machine, and its plan to connect to national infrastructure is part of what sets it apart from other fusion reactor projects.
Other useful sources of information are:
International Atomic Energy Authority (IAEA) Frequently Asked Questions
Culham Centre for Fusion Energy (CCFE) Frequently Asked Questions
Eurofusion Frequently Asked Questions