Historical research guide · 0946 · 2002
Role of Fusion Energy in a Sustainable Global Energy Strategy
Wayne Meier · Farokh Najmabadi · John Schmidt · John Sheffield
In one minute
Four people who ran the American fusion programme — Wayne Meier of Lawrence Livermore, Farokh Najmabadi of UC San Diego, John Schmidt of Princeton and John Sheffield of Oak Ridge — wrote this for the World Energy Congress as the field’s own case for itself. Their argument is not that fusion is exciting but that it is one of only a few truly long-term energy options, and that the fuel question is already answered: deuterium is one part in 6,500 of all hydrogen, and the lithium that makes tritium is in the crust and in seawater. They walk both routes to a power plant — magnetic bottles holding a plasma steadily, and laser-imploded pellets fusing in bursts — set out what a finished station looks like in each, and then do what roadmaps usually skip. They price the electricity, date the plants, and count the waste. The conclusion is a schedule: a demonstration plant in the decade before 2050, deployment from 2050, and fusion as a real share of North American electricity by 2100.
Connection
Chapter 12 argues that every device on this site needs a small source of very large energy first, and this is the establishment’s own ledger of what that costs and when it arrives — written by the four laboratories that would have to build it. Chapter 9 gets the plasma underneath: how hot, how dense, how long it holds, and what the authors say still has to be measured before a magnetically confined burn can be called a power source.
From the source
The fuel supply is settled arithmetic rather than a hope. The least difficult reaction on Earth is deuterium with tritium, which at an optimum ion temperature near 100 million degrees Celsius — ten kilo-electronvolts — releases about 17 MeV as a 3.2 MeV helium nucleus and a 14.06 MeV neutron; deuterium is essentially unlimited at one part in 6,500 of all hydrogen, and the tritium is bred by catching those neutrons in a lithium-bearing blanket around the chamber, so the net transaction converts deuterium and lithium into two helium ions.Section 1.3, Fusion reactions
Eighty per cent of the power from deuterium-tritium fusion leaves as neutrons, which is why that cycle causes the highest radiation damage and the lowest heat flux on the chamber wall. The alternatives are named with their prices: deuterium-deuterium and deuterium-helium-3 have substantially lower reaction rates and need about 30 kilo-electronvolts, and although the deuterium-helium-3 reaction generates no neutrons of its own, roughly 1 to 5 per cent of the power still appears as neutrons from inevitable deuterium-deuterium reactions — and helium-3 is not abundant on Earth, though the authors note a resource of order a billion kilograms on the lunar surface.Section 1.3, Fusion reactions, deuterium-helium-3 paragraph
On the plasma itself the authors report that multi-hundred-million-degree temperatures have been obtained at densities close to the power plant range, that plasma pressures have reached power plant levels — which matters because fusion power is roughly proportional to the square of the pressure — and that twenty years of work has brought deuterium-tritium plasmas to near energy break-even, an energy gain Q near one, against the Q above ten a power source requires. Their own verdict on what is missing is exact: a high-Q experiment is needed to confirm predictions for power plant conditions.Section 1.5, Paths to fusion, and Figure III; Section 3.1, Progress in magnetic fusion physics and technology
An attractive plant is a materials problem before it is a plasma problem, and the ARIES-AT tokamak design is offered as the answer: silicon-carbide fibre-reinforced composite as the structure, lithium-lead as both breeder and coolant, a coolant outlet temperature as high as 1,100 degrees Celsius and about 60 per cent thermal conversion efficiency on a Brayton gas cycle, giving an estimated cost of electricity of 47.5 mills per kilowatt-hour at one gigawatt electric, falling to 34 mills for a four-gigawatt plant sized for hydrogen production.Section 2.2, Magnetic fusion energy power plants, and Figure IV; Section 4, Table I
The safety case is quantitative. Only a few grams of fuel sit in the chamber at any moment, and any abnormal behaviour of the plasma cools it and terminates the reaction, so there is no possibility of an uncontrolled large-scale energy release and the reaction products themselves are not radioactive. With low-activation materials the time-integrated biological hazard potential can be lower than an equivalent fission reactor by factors approaching 100,000; after 100 years the radioactivity remaining can be millions of times less than fission, low enough that components qualify as low-level waste or better and some can be recycled on site.Section 1.4, Environmental and safety aspects, and Figure I; Section 2.2, closing paragraphs
For the inertial route the requirements are stated as numbers a programme can be judged against: target gains of 50 to 150 for economically attractive inertial fusion energy, against the gain of 10 to 20 the National Ignition Facility was designed to reach; a factory making of order a hundred million targets a year, each under a gram and costing less than about 50 cents; injection about five times a second, some four billion driver pulses over a thirty-year plant life; and a recirculating power fraction held below about 25 per cent. The deployment scenario that follows puts a demonstration plant in the decade before 2050, growth at 1 to 2 per cent of demand a year against the 7 per cent France reached with fission, and about 6 terawatt-years of fusion production this century leaving roughly 0.4 million cubic metres of compacted activated waste, against about a million cubic metres of licensed low-level capacity in the United States.Section 2.3, Inertial fusion energy power plants; Section 4, Fusion Power Deployment, and Figure VI
The way in
https://doi.org/10.1260/095830502320939606How to cite it
Wayne Meier, Farokh Najmabadi, John Schmidt, John Sheffield (2002) Role of Fusion Energy in a Sustainable Global Energy Strategy doi:10.1260/095830502320939606