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277: Nuclear fusion power station -Tokamak reactors

Problem:

The world’s 440 nuclear fission plants generate only 10% of the world’s electrity while presenting the lethal menace of dealing with waste by transporting it to deep earth burial sites.

Solution:

Nuclear fusion is a reaction in which two lighter nuclei, typically isotopes of hydrogen, combine together under conditions of extreme pressure and temperature to form a heavier nucleus, releasing energy in the process. Fusion has been powering the sun and stars since their formation.


Unlike fission, fusion will have a low burden of radioactive waste. The energy released during fusion in the sun makes all life on earth possible. The simplest way to replicate the primordial source of power on earth is via the fusion of deuterium and tritium.

Deuterium is found aplenty in ocean water, enough to last for billions of years. Naturally occurring tritium is extremely rare, but it can be produced inside a reactor by neutron activation of lithium, found in brines, minerals and clays. Moreover, to run a 1,000 MW power plant with a fusion reactor, it is estimated that about 150kg of deuterium and three tonnes of lithium would be required per year, while the current fission reactors consume 25 to 30 tonnes of enriched uranium.

Fusion’s by-product is helium, which is an inert, non-toxic, non-radioactive gas used to inflate balloons. In addition, a fusion power plant would not require transporting hazardous radioactive materials.

The 35-nation International Thermonuclear Experimental Reactor (ITER) including states from theEuropean Union, the USA, India, Japan, South Korea and Russia began construction at Cadarache in France. It is the world’s largest fusion reactor, taking up equivalent to 60 football pitches.

Launched in 2006, ITER was beset with technical delays, labyrinthine decision-making and costs that have soared from an initial estimate of five billion euros to around 20 billion euros.

In the chaos of the United Kingdom’s leaving the European Union, or Brexit, there is now at least one certainty: As the UK’s quest to produce clean energy from nuclear fusion by 2040, The Culham Centre for Fusion Energy Oxfordshire, UK but supported by the European Union will keep operating until the end of 2020, thanks to a €100 million infusion of EU funds.

The deal, agreed in April 2019, will enable the Joint European Torus (JET) to embark on a daring fusion campaign with a rare, tricky fuel that will help pave the way for its successor: the giant ITER fusion reactor under construction in France.

The agreement comes as a relief to fusion researchers, who had feared JET would be shut down after Brexit. Now, they can go ahead with plans to gradually switch to a fuel mix of deuterium and tritium, both hydrogen isotopes. The latter is rare and hard to handle, but the change will provide the most ITER-like dress rehearsal before the main event in 2025. The same “D-T” reactions will ultimately power ITER and the commercial reactors that follow it.

Nuclear fusion is usually done in hollow, donut-shaped reactors called tokamaks, which are filled with rings of plasma as hot as the Sun. Soviet scientists coined the term as a shortening of the Russian for “toroidal magnetic confinement.”

The name is perfectly descriptive. A tokamak is a torus—the math term for a donut. But this takes tremendous effort to maintain the intense pressures and temperatures required for an “artificial star” here on Earth. Eruptions called edge-localized modes (ELMs) have been damaging the walls of reactors, making them less secure and requiring the replacement of parts far too regularly.

The problem was that the plasma used is inherently unstable, and large eruptions can damage the reactors containing it. Recently, physicists from the Princeton Plasma Physics Laboratory (PPPL) have found that creating a series of small ELMs could prevent larger, more damaging ones from occurring.

These smaller eruptions could be triggered by injecting granules of beryllium, measuring about 1.5 mm thick into the boiling plasma at regular intervals. Following computer simulations, the team ran physical experiments in the DIII-D, a tokamak reactor housed in the National Fusion Facility in San Diego prior to testing the technique out on other tokamaks, such as the Joint European Torus (JET).

The next breakthrough came when scientists developed a new superconducting material, essentially a steel tape coated with yttrium-barium-copper oxide (YBCO) enabling smaller and more powerful magnets. This in turn lowers the energy required to get the fusion reacton off the ground. With 18 nobium-in superconducting magnets (aka torroidal-field coils) installed, 150 million degrees celius was finally in sight

November 2019 saw the completion of the seven-storey Tokamak Building, after six million work hours, performed by approximately 850 workers since 2010. Some 105,000 tonnes of concrete, reinforced by approximately 20,000 tonnes of steel rebar, had gone into the building’s construction.

Transport of component parts was been a major undertaking. The PF6 (the second-smallest of the six coils that circle the vacuum vessel) weighing 396 tonnes and measuring 40 ft. (12 m.) long, 36 ft. (11 m.) wide and a little more than 13 ft. (4 m.) high, was made in China under an agreement signed between the Institute of Plasma Physics of the Chinese Academy of Sciences (ASIPP) and the procuring party, the European Domestic Agency.

Transported by ship, having arrived at Fosses-sur-Mer, the port of Marseilles, for this “highly exceptional load” (HEL) to reach the ITER site, approximately 2,220 cubic yards (1,700 cubic m.) of roadside rock and trees had to be removed. This is just one of approximately 100 large components for the magnet feeder system, adding up to 1,600 tonnes of equipment in all and measuring from 100 to 160 ft. (30 to 50 m.) in length.

Among other components to be delivered was the 18 m., or 60 ft. (18 m.), tall 1000-tonne “Central Solenoid,” the superconducting electromagnet that stands along the central axis of the tokamak, sometimes referred to as “the beating heart of ITER,” under manufacture by General Atomics in Poway, California, near San Diego.

This 1,000-metric-ton solenoid will have 5.5 gigajoules of stored energy to enable 100-million-degree-Celsius plasmas within carefully defined magnetic fields. In some locations, there will be only 10 mm of space—the width of a thick pencil—between the massive central solenoid and a 45 foot (13 m.) tall “D”-shaped toroidal field magnet.

Despite the delay caused by the COVID-19 lockdown, the project began its five-year assembly phase in July 2020, launched by the French president, Emmanuel Macron alongside senior figures from ITER members, the EU, UK, China, India, Japan, Korea, Russia and the US. In February 2021, after enduring a battery of rigorous tests, the first of seven 45,000 amp superconducting magnet modules was given the green light. Built at General Dynamics of San Diego, it is now en route for ITER’s central solenoid.
Trials were due to begin in 2021 and if successful, regular power supply will be in 2025. (iter.org)

Meanwhile, by November 2019, following delivery of the coil system, the Southwestern Institute of Physics (SWIP) under the China National Nuclear Corporation (CNNC) completed the construction of HL-2M, the Experimental Advanced Superconducting Tokamak (EAST) at a research centre in Chengdu, the capital city of southwest China’s Sichuan province.
人造太阳 (Rénzào tàiyáng = artificial sun), expected to generate plasmas hotter than 200 million°C should also be operational in 2020. (cnnc.com.cn)

On November 24th 2020, The Korea Superconducting Tokamak Advanced Research (KSTAR), a superconducting fusion device also known as the Korean artificial sun, set the new world record as it succeeded in maintaining the high temperature plasma for 20 seconds with an ion temperature over 100 million degrees Celsius (retention time: about 1.5 seconds) the same temperature as the core of the Sun—its hottest part. In a continuing research program with the Seoul National University (SNU) and Columbia University of the United States, KSTAR aims to continuously operate high-temperature plasma over the 100-million-degree for 300 seconds by 2025.

Discover Solution 278: Orange juice bar – circular economy

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