Nuclear fusion -- Il-fużjoni nukleari

Some time ago I had talked about nuclear fission1, now it’s the turn of fusion. This is a technology that has the potential of providing for all mankind’s need for energy, and then some.

The science of nuclear fusion is well known, as it’s the same science that powers the sun, where two groups of two nuclei of hydrogen, an elementary matter, fuse together in a chain reaction and become a single nucleus of another element helium, with a lower nuclear mass, and this difference is released as energy according to the Einstein’s famous mathematical equation E=mc2,, a huge amount of energy which we all feel from 150 million kilometres away in the form of light, heat, wind, waves and the other observable processes on this earth, including life itself.

This fusion is a natural process that occurs under conditions of high temperature (14 million degrees) and under high gravitational forces, at the centre of the sun. Mankind has been trying to replicate this process artificially since the thirties, and as you might imagine, replicating the centre of the sun is anything but trivial!

In fact, artificial fusion has already occurred and so it has been proven that the process can be replicated on earth. Apart from the difficulties of working with extremely high temperature and pressure, other difficulties are that in fact a higher energy is produced than used to create the necessary environment for the process, and also maintaining this process for 24 hours a day, beyond the seconds that experiments have lasted so far.

To date, the better known experiments did not utilise hydrogen, but its isotopes: deuterium, which is abundant in sea water, and tritium, of which only traces exist naturally and is radioactive with a half life of twelve years (by way of comparison, the radioactivity of uranium, depending upon which isotope is being considered, is measured in thousands, millions and billions of years!)2 For tritium to be used in commercial quantities, it needs to be made in a conventional nuclear reactor (that is, a fission reactor) or at the fusion plant itself, where neutrons produced as a process by-product are used to convert lithium into tritium. Lithium is an abundant element in the earth’s crust and is also found in sea water.

Deuterium and tritium fuel is heated and becomes a lasma, where electrons are separated from the proton nucleus. The plasma is lifted and has to be kept from touching the reactor’s walls in some way. One of the methods is a magnetic field, and therefore the magnet’s design is the central feature of each fusion project.

The first design was the so-called tokamak, where the magnet has a toroid form (think doughnut), by the physicists Igor Tamm and the famous Andrei Sakharov. The biggest working tokamak in the world today is the JET (Joint European Torus) in England which has been in operation since 1978. Tokamak projects are still being built, including ITER (International Thermonuclear Experimental Reactor) in France which should be ready this decade, and CFETR (Chinese Fusion Engineering Test Reactor) which should be completed in 2030.3

A variation of the tokamak which is spherical instead of toroid is being built in England (STEP - Spherical Tokamak for Energy Production) which has just generated its first plasma in October 2020.4

A different design is the stellarator, where the magnet initially had the form of a figure of 8, but newer designs have an oval shape. The biggest project of this type is the Wendelstein 7-X in Germany.5 Australia also has a research facility with this design at the Australian National University, called Heliac-1.6

Plasma can also be contained using its own inertia. In this system, a number of powerful lasers are focussed on small pellets (millimetres in diameter) of deuterium and tritium fuel, where the outer layers explode outwards, generating a compression wave inwards to caused fusion at the centre. Projects of this type are NIF (National Ignition Facility) in the US and others in France and China.

A very interesting development this year came from Australia, where a group at the University of New South Wales announced a system, HB11, which works with inertia, where the fuel used is not made of deuterium and tritium but of hydrogen (H) and Boron (B-11). This still produces helium but does not produce neutrons that is difficult to shield from and represent a waste of energy.7 In this way, radioactivity is eliminated from the project.

These and others are enormous and long duration projects, where the industry joke is that every time you ask an insider when is it expected we’d have a functioning electricity power station based on nuclear fusion, the answer is always in thirty years time, any time the question is asked!

We live in hope that this development occurs in our lifetime, as a source of practically limitless energy represents a substantial jump in the capabilities of mankind and can lead to massive developments in many areas.

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Ftit ilu kont tkellimt fuq il-fissjoni nukleari1, issa jmiss il-fużjoni. Din hija teknoloġija għandha l-potenzjal li tipprovdi l-enerġija kollha li l-bniedem għandu bżonn, u bil-wisq iktar.

Ix-xjenza tal-fużjoni nukleari hija magħrufa sew, għax hija l-istess xjenza li tħaddem ix-xemx, fejn żewġ gruppi ta’ żewġ nuklei tal-materja elementari l-idroġenu jagħmlu fużjoni b’katina ta’ reazzjonijiet, u jsiru nukleu wieħed ta’ element ieħor l-elju, b’massa nukleari inqas, u dan in-nuqqas jiġi kkonvertit f’enerġija skont l-ekwazzjoni matematika famuża ta’ Einstein E=mc2, enerġija kbira mmens li l-effett tagħha inħossuha minn 150 miljun kilometru ‘l bogħod fid-dawl, is-sħana, ir-riħ, il-mewġ u l-proċessi l-oħra osservabbli fuq din id-dinja, inkluża l-ħajja nnifisha.

Din il-fużjoni hija proċess naturali li jseħħ taħt kundizzjonijiet ta’ temperatura għolja (14-il miljun gradi) u forza ta’ gravità kbira, fiċ-ċentru tax-xemx. Il-bniedem ilu mit-tletinijiet jipprova jirreplika dan il-proċess b’mod artifiċjali, u kif tistgħu tobsru, mhux daqs tazza ilma biex tirreplika l-ġewwieni tax-xemx!

Fil-fatt, il-fużjoni b’mod artifiċjali diġà seħħ u għalhekk ġie ppruvat li jista’ jiġi rreplikat fuq din id-dinja. Apparti d-diffikultajiet li taħdem b’temperaturi u pressjonijiet tant għoljin, d-diffikultajiet oħra kbar huma li fil-fatt tieħu enerġija iktar milli tkun użajt biex tikkreja l-ambjent neċessarju għall-proċess, u wkoll li tmantni l-proċess għal 24 siegħa kuljum, iktar mis-sekondi li l-esperimenti s’issa damu.

S’issa, l-esperimenti l-iktar magħrufa ma sarux bl-idroġenu, imma minn isotopi tiegħu: id-dewterju, li huwa abbundanti fl-ilma baħar; u t-tritju, li traċċi żgħar biss jinstabu b’mod naturali u huwa radjuattiv b’nofs ħajja ta’ tnax-il sena (bħala tqabbil, ir-radjutattività tal-uranju, li tiddependi fuq liema isotopi tiegħu qiegħdin nikkunsidraw, titkejjel bl-eluf, miljunu u biljuni ta’ snin!)2 Biex it-tritju jkun jintuża f’livelli kummerċjali, jrid jiġi magħmul f’reattur konvenzjonali nukleari (jiġifieri tal-fissjoni) jew f’impjant ta’ fużjoni nnifsu, fejn newtroni prodotti bħala parti mill-proċess jintużaw biex jikkonvertu l-litju fi tritju. Il-litju huwa element li huwa abbundanti fil-qoxra tad-dinja u jinstab ukoll fil-baħar.

Il-fuwil ta’ dewterju u tritji jissaħħan u jsir plasma, fejn l-elettroni jinfirdu min-nukleu ta’ protoni. Il-plasma jiġi merfugħ u miżmum milli jmiss mal-ħitan tar-reattur b’xi mod. Wieħed mill-modi huwa permezz ta’ erja manjetika, u għalhekk id-disinn tal-kalamita huwa l-fus ta’ kull proġett ta’ fużjoni.

L-ewwel disinn kien wieħed imsejjaħ tokamak, fejn il-kalamita tkun f’forma ta’ torojd (immaġina downut), mill-fiżiċisti Igor Tamm u l-famuż Andrei Sakharov. L-ikbar tokamak fid-dinja jaħdem illum huwa JET (Joint European Torus) fl-Ingilterra li ilu jaħdem mill-1978. Proġetti b’tokamak għadhom jinbnew, inklużi ITER (International Thermonuclear Experimental Reactor) fi Franza li għandu jitlesta f’dan id-dekadu, u CFETR (Chinese Fusion Engineering Test Reactor) li għandu jitlesta fl-2030.3

Varjazzjoni waħda tat-tokamak li huwa tond minflok torojd qed jinbena fl-Ingilterra (STEP - Spherical Tokamak for Energy Production) li għadu kif iġġenera l-ewwel plasma f’Ottubru 2020.4

Disinn daqsxejn differenti huwa stellarator, fejn il-kalamita fil-bidu kellha forma tan-numru 8 imma disinji ġodda kellhom is-sura ovali. L-ikbar proġett ta’ dan it-tip huwa l-Wendelstein 7-X fil-Ġermanja5. L-Awstralja għandha faċilità ta’ riċerka b’dan id-disinn fl-Australian National University jismu Heliac-1.6

Il-plasma jista’ wkoll jiġi miżmum bl-inerzja tiegħu innifsu. B’din is-sistema, numru ta’ lejżers qawwija jiġu ffukati fuq pelits żgħar (b’dijametru ta’ millimetri) bil-fjuwil ta’ dewterju u tritju, fejn il-faxxi ta’ barra jisplodu ‘l barra u jiġġeneraw mewġa ta’ kompressjoni ‘l ġewwa sabiex iseħħ il-fużjoni fiċ-ċentru. Proġetti ta’ dan it-tip huma NIF (National Ignition Facility) fl-Amerika, u oħrajn fi Franza u ċ-Ċina.

Żvilupp interessanti ħafna f’dan il-qasam ġie din is-sena mill-Awstralja, fejn grupp mill-Università ta’ New South Wales ħabbar sistema , imsejħa HB11, li taħdem bl-inerzja, fejn il-fuwil ma jkunx ta’ dewterju u tritju iżda tal-idroġenu (H) u l-boron (B-11). Dan xorta jipproduċi l-elju iżda ma jipproduċix newtroni li hu diffiċli li tagħmel tarka kontrihom u jirrappreżentaw ħela ta’ enerġija.7 Għalhekk jiġi eliminat ir-radjuazzjoni mill-proġett.

Dawn u oħrajn bħalhom huma proġetti enormi u fit-tul, li ċ-ċajta fl-industrija hi li kull darba li tistaqsi ‘l min hu midħla tagħhom meta jistennew li se jkollna impjant tal-elettriku ġej mill-fużjoni, ir-risposta dejjem tkun tletin sena oħra, tistaqsihom meta tistaqsihom!

Nisperaw li f’ħajjitna din il-ħaġa sseħħ, għax sors ta’ enerġija prattikament bla limitu tirrappreżenta qabża sostanzjali fil-kapaċitajiet tal-bniedem u tista’ twassal għal żviluppi kbar f’ħafna oqsma.

1L-Enerġija Nukleari, The Voice of the Maltese, Nru. 166, p10

2https://web.evs.anl.gov/uranium/faq/uproperties/faq5.cfm, retrieved 16/12/2020

3https://www.world-nuclear.org/information-library/current-and-future-generation/nuclear-fusion-power.aspx, retrieved 16/12/2020

4https://www.bbc.com/future/article/20201214-the-uks-quest-for-affordable-fusion-by-2040, retrieved 16/12/2020

5https://www.businessinsider.com.au/germany-is-turning-on-its-monster-stellarator-2015-10, retrieved 16/12/2020

6https://science.anu.edu.au/research/field-sites-facilities/australian-plasma-fusion-research-facility, retrieved 6/12/2020

7https://www.labroots.com/trending/chemistry-and-physics/16964/quicker-path-fusion-power-australian-scientists-claimed-astonishing-breakthrough, retrieved 6/12/2020

1L-Enerġija Nukleari, The Voice of the Maltese, Nru. 166, p10

2https://web.evs.anl.gov/uranium/faq/uproperties/faq5.cfm, retrieved 16/12/2020

3https://www.world-nuclear.org/information-library/current-and-future-generation/nuclear-fusion-power.aspx, retrieved 16/12/2020

4https://www.bbc.com/future/article/20201214-the-uks-quest-for-affordable-fusion-by-2040, retrieved 16/12/2020

5https://www.businessinsider.com.au/germany-is-turning-on-its-monster-stellarator-2015-10, retrieved 16/12/2020