View source for Selenium-79

{{Short description|Long-lived radioisotope of selenium}}
{{Infobox isotope
 | alternate_names =
 | symbol = Se
 | mass_number= 79
 | mass =
 | num_neutrons =45
 | num_protons = 34
 | abundance = [[trace radioisotope|trace]]
 | halflife = {{val|327,000|28,000|u=years}}
 | image =
 | decay_product = bromine-79
 | decay_symbol = Br
 | decay_mass = 79
 | decay_mode1 = [[Beta decay]]
 | decay_energy1 = 0.1506
 | decay_mode2 =
 | decay_energy2 =
 | decay_mode3 =
 | decay_energy3 =
 | decay_mode4 =
 | decay_energy4 =
 | parent =
 | parent_symbol =
 | parent_mass =
 | parent_decay =
 | parent2 =
 | parent2_symbol =
 | parent2_mass =
 | parent2_decay =
 | spin = 7/2+
 | excess_energy = {{val|−75917.46|0.22}}
 | binding_energy = {{val|8695.592|0.003}}
}}

'''Selenium-79''' is a [[radioisotope]] of [[selenium]] present in [[spent nuclear fuel]] and the [[nuclear waste|wastes]] resulting from [[nuclear reprocessing|reprocessing]] this fuel. It is one of only seven [[long-lived fission product]]s. Its [[fission product yield|fission yield]] is low (about 0.04%), as it is near the lower end of the mass range for [[fission products]]. Its [[half-life]] has been variously reported as 650,000 years, 65,000 years, 1.13 million years, 480,000 years, 295,000 years, 377,000 years and most recently with best current precision, 327,000 years.<ref>{{cite web|url=http://www.ptb.de/en/org/6/nachrichten6/2010/60710_en.htm|title=Home|date=22 June 2017|website=Ptb.de|accessdate=2017-07-14}}</ref><ref>Jörg, G., Bühnemann, R., Hollas, S., Kivel, N., Kossert, K., Van Winckel, S., Lierse v. Gostomski, Ch. ''Applied Radiation and Isotopes'' '''68''' (2010), 2339–2351</ref>

<sup>79</sup>Se decays to <sup>79</sup>Br by emitting a [[beta particle]] with no attendant [[gamma radiation]] (i.e., 100%&nbsp;''β'' decay). This complicates its detection and [[liquid scintillation counting]] (LSC) is required for measuring it in environmental samples. The low [[specific activity]] ({{nowrap|5.1 × 10<sup>8</sup> Bq/g}}) and relatively low energy (151&nbsp;keV) of its beta particles have been said to limit the radioactive hazards of this isotope.<ref>{{cite web|url=http://www.ead.anl.gov/pub/doc/selenium.pdf|title=ANL factsheet|website=Ead.anl.gov|accessdate=2017-07-14|url-status=dead|archiveurl=https://web.archive.org/web/20040615114154/http://www.ead.anl.gov/pub/doc/selenium.pdf|archivedate=2004-06-15}}</ref>

Performance assessment calculations for the Belgian [[deep geological repository]] estimated <sup>79</sup>Se may be the major contributor to activity release in terms of [[becquerel]]s (decays per second), "attributable partly to the uncertainties about its migration behaviour in the Boom Clay and partly to its [[conversion factor]] in the [[biosphere]]." (p.&nbsp;169).<ref name="safir">{{cite web|url=http://www.nirond.be/engels/PDF/Safir2_apercutech_eng.pdf|format=PDF|author=Marivoet |display-authors=etal |date=2001|title=Safir-2 report|website=Nirond.be|accessdate=2017-07-14}}</ref> However, "calculations for the Belgian safety assessments use a half-life of 65 000 years" (p.&nbsp;177), much less than the currently estimated half-life, and "the migration parameters ... have been estimated very cautiously for <sup>79</sup>Se." (p.&nbsp;179)

[[Neutron absorption]] [[Absorption cross section|cross section]]s for <sup>79</sup>Se have been estimated at 50 [[Barn (unit)|barns]] for [[thermal neutrons]] and 60.9 barns for [[resonance integral]].<ref>{{cite web |url=http://www-nds.iaea.org/j33/data/comments/za034079.html |title=Archived copy |accessdate=2008-05-11 |url-status=dead |archiveurl=https://web.archive.org/web/20110605112920/http://www-nds.iaea.org/j33/data/comments/za034079.html |archivedate=2011-06-05 }}</ref>

Selenium-80 and [[selenium-82]] have higher [[fission product yield|fission yields]], about 20 times the yield of <sup>79</sup>Se in the case of [[uranium-235]], 6 times in the case of [[plutonium-239]] or [[uranium-233]], and 14 times in the case of [[plutonium-241]].<ref>{{cite web|url=http://www-nds.iaea.org/sgnucdat/c1.htm|title=Nuclear Data for Safeguards|website=Nds.iaea.org|accessdate=2017-07-14}}</ref>

==Mobility of selenium in the environment==
Due to [[redox|redox-disequilibrium]], selenium could be very reluctant to [[abiotic]] chemical reduction and would be released from the waste (spent fuel or vitrified waste) as [[selenate]] ({{Chem|Se|O|4|2–}}), a soluble Se(VI) species, not [[sorption|sorbed]] onto [[clay minerals]]. Without [[solubility|solubility limit]] and [[retardation factor|retardation]] for aqueous selenium, the dose of <sup>79</sup>Se is comparable to that of <sup>129</sup>I. Moreover, selenium is an essential [[micronutrient]] as it is present in the catalytic centers in the [[glutathione peroxidase]], an [[enzyme]] needed by many organisms for the protection of their  [[cell membrane]] against [[oxidative stress]] damages; therefore, radioactive <sup>79</sup>Se can be easily [[bioconcentration|bioconcentrated]] in the [[food web]]. In the presence of [[nitrate]] ({{Chem|N|O|3|–}}) released in deep geological clay formations by [[bitumen|bituminized]] waste issued from the spent fuel dissolution step during their reprocessing, even reduced forms of selenium could be easily [[oxidation|oxidised]] and mobilised.<ref>
{{Cite journal
| doi = 10.2134/jeq1999.00472425002800040019x
| last = Wright
| first = Winfield G.
| title = Oxidation and mobilization of selenium by nitrate in irrigation drainage
| journal = J. Environ. Qual.
| volume = 28
| issue = 4
| pages = 1182–1187
| accessdate = 2008-05-11
| date = 1999-07-01
| url = http://jeq.scijournals.org/cgi/content/abstract/joenq;28/4/1182
| url-access = subscription
}}
</ref>

{{Long-lived fission products}}

==References==
{{reflist}}

==See also==
*[[Isotopes of selenium]]
*[https://web.archive.org/web/20040615114154/http://www.ead.anl.gov/pub/doc/selenium.pdf ANL factsheet]
*[http://www.rsc.org/publishing/journals/JA/article.asp?doi=b209253k Journal of Analytical Atomic Spectrometry]

[[Category:Fission products]]
[[Category:Isotopes of selenium]]
[[Category:Radioactive waste]]