Design of typical nuclear fusion tokamak machine
In an article ('Fusion Plans Announced') in the autumn issue of New Scientist we learned that nuclear fusion engineers are starting the conceptual design for a power station which they "hope will run on the Sun's same energy- nuclear fusion."
This preliminary "conceptual design phase" is specifically for the DEMOnstration power plant (DEMO), "a project backed by a European consortium - EuroFusion - to take take fusion power from the concept stage to a commercial reality." The goal is ambitious for sure and ultimately "plans for the 300 to 500 megawatt reactor to be generating low carbon energy by 2054."
It is important to point out here that there has been no shortage of existing experimental fusion designs and machines (including at Princeton Univ. in the U.S.) which have been used to try to confined and control tokamaks, in the shape of a doughnut (as shown in the top image). None of these devices up to now have been able to achieve the primary goal of "net gain", i.e. getting more energy out of a fusion reaction than goes into it. But there's been progress, for example a "global energy record set last year."
To be more precise: "On 21 December 2021, the U.K.-based JET heated a gas of hydrogen isotopes to 150 million degrees Celsius and held it steady for 5 seconds while nuclei fused together, releasing 59 megajoules (MJ) of energy."
Five seconds duration is impressive for sure but still not enough for a commercial project. But the piece goes on to note that "more may occur when an €18 billion research tokamak in France known as ITER is scheduled to be switched on."
ITER (International Thermonuclear Experimental Reactor) is the "colossus of all tokamaks" but not before 2027 at the earliest. When finished it will be 30 m high and weigh in at 23,000 tons. Its staff will "number in the thousands" and it will hold 840 liters of plasma. The containing magnets alone will require some 100,000 km of niobium tin wire. The stupendous cost - in the tens of billions - is being paid by a global consortium that includes the U.S., Russia, the EU, China, Japan, South Korea and India. It is hoped it will achieve full power by 2035.
Meanwhile, problems remain in attaining the goals, whether for ITER or DEMO. The success of the latter, for example, requires collecting the heat from the fusion reaction and converting it to electricity, all while working 24 hours a day. The basic fusion reaction we are looking at is depicted below:
And written: D + T → He + n.-> 17.6 Mev
Where: T = 3 H = 3.016 u
denotes tritium or hydrogen 3.
The key issue now is in generating enough tritium and deuterium to fuel the fusion reactions in ITER as well as DEMO. Deuterium (heavy water) isn't a huge problem as it can be obtained from sea water. The problem is that supplies of tritium are limited because while it can be found in the Earth's crust it decays quickly. To give a perspective on the limitations, current research projects for fusion have - up to now- only been able to amass and use an amount of tritium in grams. But a feasible fusion- based power station will need amounts in kilograms, or a thousand times what's used now in research efforts. This is why more research is needed to get more 3 H including 'breeding it from lithium ( 3 Li ) or facilitating design changes such that neutrons escaping from the fusion plasma interact with lithium in the tokamak's walls to create more tritium.
Another bugbear mentioned in the article: the DEMO project must proceed in parallel to ITER. The former, in other words, can't wait for the completion of the latter. Otherwise, according to Ambrogio Fasoli - the Chair of the EuroFusion General Assembly- quoted in the piece:
"There will be a big gap of decades and then nobody will have an interest in fusion."
But he does concede that DEMO must learn from ITER. Still, whatever final design DEMO has by 2027, when the plant is finished, it's unlikely to be the first fusion power station. The reason? Several private fusion startups have claimed they will have one operating by the early 2030s. That remains to be seen, including whether the UK's STEP plant will be operational by the 2040s. (Alas, I will not be around to see any of this or comment - but maybe current readers will).
The bottom line is that this energy source cannot be allowed to be stillborn. Too much is at stake. Especially given the planet's population keeps growing (expected to hit the 8 billion mark next month) and the voracious demand for energy is growing with it.
DOE Explains...Deuterium-Tritium Fusion Reactor Fuel | Department of Energy
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