Editing Fusion power (section)

== Accident scenarios and the environment ==
=== Accident potential ===
Accident potential and effect on the environment are critical to social acceptance of nuclear fusion, also known as a [[Corporate social responsibility|social license]].<ref>{{Cite journal |last=Hoedl |first=Seth A. |date=2022 |title=Achieving a social license for fusion energy |url=http://dx.doi.org/10.1063/5.0091054 |journal=Physics of Plasmas |volume=29 |issue=9 |pages=092506 |doi=10.1063/5.0091054 |bibcode=2022PhPl...29i2506H |s2cid=252454077 |issn=1070-664X}}</ref> Fusion reactors are not subject to [[Nuclear meltdown|catastrophic meltdown]].<ref name="McCrackenStott2012"/> It requires precise and controlled temperature, pressure and magnetic field parameters to produce net energy, and any damage or loss of required control would rapidly quench the reaction.<ref name=afraid>{{cite web |url=http://www.iter.org/newsline/107/1489 |title=Who is afraid of ITER? |first=Krista |last=Dulon |website=iter.org |date=2012 |access-date=August 18, 2012 |archive-url=https://web.archive.org/web/20121130221734/http://www.iter.org/newsline/107/1489 |archive-date=November 30, 2012 |url-status=dead }}</ref> Fusion reactors operate with seconds or even microseconds worth of fuel at any moment. Without active refueling, the reactions immediately quench.<ref name="McCrackenStott2012">{{cite book|last1=McCracken|first1=Garry |last2=Stott|first2=Peter |title=Fusion: The Energy of the Universe|url={{google books|plainurl=y|id=e6jEZfO2gO4C|page=198}}|access-date=August 18, 2012|date=2012|publisher=Academic Press|isbn=978-0123846563|pages=198–199}}</ref>

The same constraints prevent runaway reactions. Although the plasma is expected to have a volume of {{Convert|1000|m3|ft3|abbr=on}} or more, the plasma typically contains only a few grams of fuel.<ref name="McCrackenStott2012" /> By comparison, a fission reactor is typically loaded with enough fuel for months or years, and no additional fuel is necessary to continue the reaction. This large fuel supply is what offers the possibility of a meltdown.<ref name="n">{{cite book|last=Angelo|first=Joseph A. |title=Nuclear Technology|url={{google books|plainurl=y|id=ITfaP-xY3LsC|page=474}}|access-date=August 18, 2012|date=2004|publisher=Greenwood Publishing Group|isbn=978-1573563369|page=474}}</ref>

In magnetic containment, strong fields develop in coils that are mechanically held in place by the reactor structure. Failure of this structure could release this tension and allow the magnet to "explode" outward. The severity of this event would be similar to other industrial accidents or an [[MRI]] machine quench/explosion, and could be effectively contained within a [[containment building]] similar to those used in fission reactors.

In laser-driven inertial containment the larger size of the reaction chamber reduces the stress on materials. Although failure of the reaction chamber is possible, stopping fuel delivery prevents catastrophic failure.<ref name="economic prospects">{{Cite book |title=Safety, environmental impact, and economic prospects of nuclear fusion|date=1990|publisher=Plenum Press|editor=Brunelli, B. |editor2=Knoepfel, Heinz |isbn=978-1461306191|location=New York|oclc=555791436}}</ref>

=== Magnet quench ===
A [[magnet quench]] is an abnormal termination of magnet operation that occurs when part of the superconducting coil exits the superconducting state (becomes normal). This can occur because the field inside the magnet is too large, the rate of change of field is too large (causing [[eddy current]]s and resultant [[Joule heating|heating]] in the copper support matrix), or a combination of the two.

More rarely a magnet defect can cause a quench. When this happens, that particular spot is subject to rapid [[Joule heating]] from the current, which raises the [[temperature]] of the surrounding regions. This pushes those regions into the normal state as well, which leads to more heating in a chain reaction. The entire magnet rapidly becomes normal over several seconds, depending on the size of the superconducting coil. This is accompanied by a loud bang as the energy in the magnetic field is converted to heat, and the [[cryogenics|cryogenic]] fluid boils away. The abrupt decrease of current can result in [[kilovolt]] inductive voltage spikes and arcing. Permanent damage to the magnet is rare, but components can be damaged by localized heating, high voltages, or large mechanical forces.

In practice, magnets usually have safety devices to stop or limit the current when a quench is detected. If a large magnet undergoes a quench, the inert vapor formed by the evaporating cryogenic fluid can present a significant [[asphyxiation]] hazard to operators by displacing breathable air.

A large section of the superconducting magnets in [[CERN]]'s [[Large Hadron Collider]] unexpectedly quenched during start-up operations in 2008, destroying multiple magnets.<ref>{{Cite book|url=https://edms.cern.ch/ui/file/973073/1/Report_on_080919_incident_at_LHC__2_.pdf|title=Interim Summary Report on the Analysis of the 19 September 2008 Incident at the LHC|publisher=CERN|year=2008}}</ref> In order to prevent a recurrence, the LHC's superconducting magnets are equipped with fast-ramping heaters that are activated when a quench event is detected. The dipole bending magnets are connected in series. Each power circuit includes 154 individual magnets, and should a quench event occur, the entire combined stored energy of these magnets must be dumped at once. This energy is transferred into massive blocks of metal that heat up to several hundred degrees Celsius—because of resistive heating—in seconds. A magnet quench is a "fairly routine event" during the operation of a particle accelerator.<ref>{{cite web|last=Peterson|first=Tom|title=Explain it in 60 seconds: Magnet Quench|url=http://www.symmetrymagazine.org/article/november-2008/explain-it-in-60-seconds-magnet-quench|website=Symmetry Magazine|date=November 2008 |publisher=[[Fermilab]]/[[SLAC]]|access-date=February 15, 2013}}</ref>

=== Atmospheric tritium release ===
The natural product of the fusion reaction is a small amount of [[helium]], which is harmless to life. Hazardous tritium is difficult to retain completely.

Although tritium is volatile and biologically active, the health risk posed by a release is much lower than that of most radioactive contaminants, because of tritium's short half-life (12.32 years) and very low decay energy (~14.95&nbsp;keV), and because it does not [[bioaccumulation|bioaccumulate]] (it cycles out of the body as water, with a [[biological half-life]] of 7 to 14 days).<ref name="nuclearsafety-petrangeli">{{cite book|first=Gianni |last=Petrangeli|title=Nuclear Safety|url={{google books |plainurl=y |id=5X2Hxad9BoQC|page=430}} |date=2006|publisher=Butterworth-Heinemann|isbn=978-0750667234|page=430}}</ref> ITER incorporates total containment facilities for tritium.<ref name="ITER" />

Calculations suggest that about {{convert|1|kg}} of tritium and other radioactive gases in a typical power station would be present. The amount is small enough that it would dilute to legally acceptable limits by the time they reached the station's [[perimeter fence]].<ref name="WorldEnergyCouncil" />

The likelihood of small industrial accidents, including the local release of radioactivity and injury to staff, are estimated to be minor compared to fission. They would include accidental releases of lithium or tritium or mishandling of radioactive reactor components.<ref name="economic prospects" />

=== Radioactive waste ===
{{See also|Radioactive waste}}

Fusion reactors create far less radioactive material than fission reactors. Further, the material it creates is less damaging biologically, and the radioactivity dissipates within a time period that is well within existing engineering capabilities for safe long-term waste storage.<ref name="demonstration">{{Cite journal |last1=Gonzalez de Vicente |first1=Sehila M. |last2=Smith |first2=Nicholas A. |last3=El-Guebaly |first3=Laila |last4=Ciattaglia |first4=Sergio |last5=Di Pace |first5=Luigi |last6=Gilbert |first6=Mark |last7=Mandoki |first7=Robert |last8=Rosanvallon |first8=Sandrine |last9=Someya |first9=Youji |last10=Tobita |first10=Kenji |last11=Torcy |first11=David |date=August 1, 2022 |title=Overview on the management of radioactive waste from fusion facilities: ITER, demonstration machines and power plants |journal=Nuclear Fusion |volume=62 |issue=8 |pages=085001 |doi=10.1088/1741-4326/ac62f7 |bibcode=2022NucFu..62h5001G |s2cid=247920590 |issn=0029-5515|doi-access=free }}</ref> In specific terms, except in the case of [[aneutronic fusion]],<ref>{{Cite book|last1=Harms|first1=A. A.|url=https://books.google.com/books?id=DD0sZgutqowC&pg=PA8|title=Principles of Fusion Energy: An Introduction to Fusion Energy for Students of Science and Engineering|last2=Schoepf|first2=Klaus F.|last3=Kingdon|first3=David Ross|date=2000|publisher=World Scientific|isbn=978-9812380333|language=en}}</ref><ref>{{Cite journal|last1=Carayannis|first1=Elias G.|last2=Draper|first2=John|last3=Iftimie|first3=Ion A.|date=2020|title=Nuclear Fusion Diffusion: Theory, Policy, Practice, and Politics Perspectives |url=https://ieeexplore.ieee.org/document/9078039|journal=IEEE Transactions on Engineering Management|volume=69 |issue=4 |pages=1237–1251|doi=10.1109/TEM.2020.2982101|s2cid=219001461|issn=1558-0040}}</ref> the neutron flux turns the structural materials radioactive. The amount of radioactive material at shut-down may be comparable to that of a fission reactor, with important differences. The half-lives of fusion and neutron activation [[radioisotopes]] tend to be less than those from fission, so that the hazard decreases more rapidly. Whereas fission reactors produce waste that remains radioactive for thousands of years, the radioactive material in a fusion reactor (other than tritium) would be the reactor core itself and most of this would be radioactive for about 50 years, with other low-level waste being radioactive for another 100 years or so thereafter.<ref>{{cite journal |first1=Anil |last1=Markandya |first2=Paul |last2=Wilkinson |s2cid=25504602 |url=http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(07)61253-7/fulltext |journal=The Lancet |volume=370 |issue=9591 |year=2007 |title=Electricity generation and health |pages=979–990 |doi=10.1016/S0140-6736(07)61253-7 |pmid=17876910 |access-date=February 21, 2018}}</ref> The fusion waste's short half-life eliminates the challenge of long-term storage. By 500 years, the material would have the same [[radiotoxicity]] as [[coal ash]].<ref name="WorldEnergyCouncil">{{cite web |last1=Hamacher |first1=T. |last2=Bradshaw |first2=A. M. |date=October 2001 |title=Fusion as a Future Power Source: Recent Achievements and Prospects |url=http://www.worldenergy.org/wec-geis/publications/default/tech_papers/18th_Congress/downloads/ds/ds6/ds6_5.pdf |archive-url=https://web.archive.org/web/20040506065141/http://www.worldenergy.org/wec-geis/publications/default/tech_papers/18th_Congress/downloads/ds/ds6/ds6_5.pdf |archive-date=May 6, 2004 |publisher=World Energy Council}}</ref>
Nonetheless, classification as intermediate level waste rather than low-level waste may complicate safety discussions.<ref>{{Cite journal|last1=Nicholas|first1=T. E. G.|last2=Davis|first2=T. P.|last3=Federici|first3=F.|last4=Leland|first4=J.|last5=Patel|first5=B. S.|last6=Vincent|first6=C.|last7=Ward|first7=S. H.|date=February 1, 2021|title=Re-examining the role of nuclear fusion in a renewables-based energy mix|url=https://www.sciencedirect.com/science/article/pii/S0301421520307540|journal=Energy Policy|language=en|volume=149|pages=112043|doi=10.1016/j.enpol.2020.112043|issn=0301-4215|arxiv=2101.05727|bibcode=2021EnPol.14912043N |s2cid=230570595}}</ref><ref name="demonstration" />

The choice of materials is less constrained than in conventional fission, where many materials are required for their specific [[neutron cross-section]]s. Fusion reactors can be designed using "low activation", materials that do not easily become radioactive. [[Vanadium]], for example, becomes much less radioactive than [[stainless steel]].<ref>{{Cite journal |last1=Cheng |first1=E. T. |last2=Muroga |first2=Takeo |date=2001 |title=Reuse of Vanadium Alloys in Power Reactors |url=http://dx.doi.org/10.13182/fst01-a11963369 |journal=Fusion Technology |volume=39 |issue=2P2 |pages=981–985 |bibcode=2001FuTec..39..981C |doi=10.13182/fst01-a11963369 |issn=0748-1896 |s2cid=124455585}}</ref> [[Carbon fiber]] materials are also low-activation, are strong and light, and are promising for laser-inertial reactors where a magnetic field is not required.<ref>{{Cite journal|last1=Streckert|first1=H. H.|last2=Schultz|first2=K. R.|last3=Sager|first3=G. T.|last4=Kantncr|first4=R. D.|date=December 1, 1996|title=Conceptual Design of Low Activation Target Chamber and Components for the National Ignition Facility|url=https://doi.org/10.13182/FST96-A11962981|journal=Fusion Technology|volume=30|issue=3P2A|pages=448–451|doi=10.13182/FST96-A11962981|bibcode=1996FuTec..30..448S |issn=0748-1896|citeseerx=10.1.1.582.8236}}</ref>

=== Fuel reserves ===
Fusion power commonly proposes the use of deuterium as fuel and many current designs also use [[lithium]]. Assuming a fusion energy output equal to the 1995 global power output of about 100 [[exa-|E]]J/yr (= 1 × 10<sup>20</sup> J/yr) and that this does not increase in the future, which is unlikely, then known current lithium reserves would last 3000 years. Lithium from sea water would last 60&nbsp;million years, however, and a more complicated fusion process using only deuterium would have fuel for 150&nbsp;billion years.<ref>{{cite web |title=Energy for Future Centuries |url=http://www.agci.org/dB/PDFs/03S2_MMauel_SafeFusion%3F.pdf |url-status=dead |archive-url=https://web.archive.org/web/20110727135814/http://www.agci.org/dB/PDFs/03S2_MMauel_SafeFusion?.pdf |archive-date=July 27, 2011 |access-date=June 22, 2013}}</ref> To put this in context, 150&nbsp;billion years is close to 30 times the remaining lifespan of the Sun,<ref name="sunlife">{{cite web |last=Christian |first=Eric |display-authors=etal |title=Cosmicopia |url=http://helios.gsfc.nasa.gov/qa_sun.html#sunlife |url-status=dead |archive-url=https://web.archive.org/web/20111106095009/http://helios.gsfc.nasa.gov/qa_sun.html#sunlife |archive-date=November 6, 2011 |access-date=March 20, 2009 |publisher=NASA}}</ref> and more than 10 times the estimated age of the universe