Fluoride volatility
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2008-05-30T05:08:49Z
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'''Fluoride volatility''' is a method for the extraction of elements which form [[Volatility (chemistry)|volatile]] [[fluoride]]s. It is being studied for [[nuclear reprocessing|reprocessing]] of [[nuclear fuel]], either of the conventional fuel rods used in today's [[LWR]]s, or as an integral part of a [[molten salt reactor]] system.
==Reprocessing methods==
[[Uranium oxide]]s react with fluorine to form gaseous [[uranium hexafluoride]], most of the [[plutonium]] reacts to form gaseous plutonium hexafluoride, a majority of [[fission product]]s (especially electropositive elements: [[lanthanide]]s, [[strontium]], [[barium]], [[yttrium]], [[caesium]]) form solid fluorides dropping to the fluorinator bottom, and only a few of the fission product elements (the [[transition metal]]s [[niobium]], [[ruthenium]], [[technetium]], [[molybdenum]], and the [[halogen]] [[iodine]]) form gaseous fluorides that accompany the uranium and plutonium hexafluorides, together with [[inert gas]]es. [[Distillation]] is then used to remove the other volatile metal fluorides and [[iodine]] fluorides from the uranium hexafluoride.<ref> {{cite web
| url= http://www.nea.fr/html/pt/docs/iem/mol98/session2/SIIpaper9.pdf
| title= An Experience on Dry Nuclear Fuel Reprocessing in the Czech Republic
| last= Uhlir | first= Jan
|date= |year= |month= |format= |work= |publisher= [[OECD]] Nuclear Energy Agency
| accessdate= 2008-05-21 }}</ref><ref>
{{cite web
| url= http://www.nea.fr/html/pt/docs/iem/madrid00/Proceedings/Paper13.pdf
| title= R&D of Pyrochemical Partitioning in the Czech Republic
| last= Uhlir | first= Jan
|date= |year= |month= |format= |work= |publisher= OECD Nuclear Energy Agency
| accessdate= 2008-05-21 }}</ref>
The nonvolatile residue of alkaline [[fission product]]s and [[minor actinides]] is most suitable for further processing with 'dry' [[electrochemistry|electrochemical]] processing ([[pyroprocessing|pyrochemical]]) [[Nuclear reprocessing#Non aqueous methods|non-aqueous methods]]. The [[lanthanide]] fluorides would be difficult to dissolve in the [[nitric acid]] used for aqueous reprocessing methods, such as [[PUREX]], [[Nuclear_reprocessing#DIAMEX|DIAMEX]] and [[Nuclear_reprocessing#SANEX|SANEX]], which use [[solvent extraction]]. Fluoride volatility is only one of several [[pyro]]chemical processes designed to reprocess used nuclear fuel.
The [http://www.nri.cz/eng/index.html Řež nuclear research institute] at [[Řež]] in the [[Czech Republic]] tested screw dosers that fed ground uranium oxide (simulating used fuel pellets) into a fluorinator where the particles were burned in fluorine gas to form [[uranium hexafluoride]].<ref> {{cite web
| url= http://www.fjfi.cvut.cz/Stara_verze/k417/web_ads/papers/P-g6.pdf
| title= Development of Uranium Oxide Powder Dosing for Fluoride Volatility Separation Process
| last= Markvart | first= Milos
|date= |year= |month= |format= |work= |publisher=
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-05-21 }}</ref>
==Volatility, valence, and chemical series==
[[Image:fission yield volatile.png|thumb|450px|Blue elements have volatile fluorides or are already volatile; green elements do not but have volatile chlorides; red elements have neither, but the elements themselves are volatile at very high temperatures. Yields at 10<sup>0,1,2,3</sup> years after [[fission]], not considering later [[neutron capture]], fraction of 100% not 200%. [[Beta decay]] [[Kr-85]]→[[Rubidium|Rb]], [[Sr-90]]→[[Zirconium|Zr]], [[Ru-106]]→[[Palladium|Pd]], [[Sb-125]]→[[Tellurium|Te]], [[Cs-137]]→[[Barium|Ba]], [[Ce-144]]→[[Neodymium|Nd]], [[Sm-151]]→[[Europium|Eu]], [[Eu-155]]→[[Gadolinium|Gd]] visible.]]
[[Valence (chemistry)#Valences of the elements|Valence]]s for the majority of elements are based on the highest known fluoride.
Roughly, fluoride volatility can be used to remove elements with a valence of 5 or greater: [[Uranium]], [[Neptunium]], [[Plutonium]], [[Metalloids]] ([[Tellurium]], [[Antimony]]), [[Nonmetals]] ([[Selenium]]), [[Halogens]] ([[Iodine]], [[Bromine]]), and the middle [[transition metal]]s ([[Niobium]], [[Molybdenum]], [[Technetium]], [[Ruthenium]], and possibly [[Rhodium]]). This fraction includes the actinides most easily reusable as nuclear fuel in a [[thermal reactor]], and the two [[long-lived fission product]]s best suited to disposal by transmutation, [[Tc-99]] and [[Iodine-129|I-129]], as well as [[Se-79]].
[[Noble gases]] ([[Xenon]], [[Krypton]]) are volatile even without fluoridation, and will not condense except at much lower temperatures.
Left behind are [[Alkali metals]] ([[Caesium]], [[Rubidium]]), [[Alkaline earth metals]] ([[Strontium]], [[Barium]]), [[Lanthanides]], the remaining [[Actinides]] ([[Americium]], [[Curium]]), remaining [[transition metal]]s ([[Yttrium]], [[Zirconium]], [[Palladium]], [[Silver]], [[Cadmium]]) and [[Poor metals]] ([[Tin]], [[Indium]]). This fraction contains the fission products that are radiation hazards on a scale of decades ([[Cs-137]], [[Sr-90]], [[Sm-151]]), the four remaining [[long-lived fission product]]s [[Cs-135]], [[Zr-93]], [[Pd-107]], [[Sn-126]] of which only the last emits strong radiation, most of the [[neutron poison]]s, and the higher actinides ([[Americium]], [[Curium]], [[Californium]]) that are radiation hazards on a scale of hundreds or thousands of years and are difficult to work with because of gamma radiation but are fissionable in a [[fast reactor]].
==Fluorides by boiling and melting points==
{{element color legend}}
{| class="wikitable sortable"
! [[:Category:Fluorides|Fluoride]]<br> !! [[Atomic number|Z]]<br> !! [[Boiling point|Boiling]]<br>°C !! [[Melting point|Melting]]<br>°C !! Key [[halflife]]<br> !! Yield<br>
|- style="background:{{Element color/Nonmetals}}"
| [[Selenium hexafluoride|SeF<sub>6</sub>]] || 34 || -46.6 || -50.8 || <sup>79</sup>Se:65ky || .04%
|- style="background:{{Element color/Metalloids}}"
| [[Tellurium hexafluoride|TeF<sub>6</sub>]] || 52 || -39 || -38 || <sup>127m</sup>Te:109d
|- style="background:{{Element color/Halogens}}"
| [[Iodine heptafluoride|IF<sub>7</sub>]] || 53 || 4.8 (1 atm) || 6.5 ([[tripoint]]) || <sup>129</sup>I:15.7my || 0.54%
|- style="background:{{Element color/Transition metals}}"
| [[Molybdenum hexafluoride|MoF<sub>6</sub>]] || 42 || 34 || 17.4 || <sup>99</sup>Mo:2.75d
|- style="background:{{Element color/Actinides}}"
| [[Plutonium hexafluoride|PuF<sub>6</sub>]] || 94 || 52 ([[Sublimation (chemistry)|subl]]) || 62 || [[Pu-239|<sup>239</sup>Pu]]:24ky
|- style="background:{{Element color/Transition metals}}"
| [[Technetium(VI) fluoride|TcF<sub>6</sub>]] || 43 || 55.3 || 37.4 || [[Tc-99|<sup>99</sup>Tc]]:213ky || 6.1%
|- style="background:{{Element color/Actinides}}"
| [[Uranium hexafluoride|UF<sub>6</sub>]] || 92 || 56.5 (subl) || 64.8 || [[U-233|<sup>233</sup>U]]:160ky
<!--
|- style="background:{{Element color/Transition metals}}"
| [[Ruthenium hexafluoride|RuF<sub>6</sub>]] || 44 || || 54 || <sup>106</sup>Ru:374d
|- style="background:{{Element color/Transition metals}}"
| [[Rhodium hexafluoride|RhF<sub>6</sub>]] || 45 || || 70 || <sup>103</sup>Rh:stable
-->
|- style="background:{{Element color/Transition metals}}"
| [[Rhenium heptafluoride|ReF<sub>7</sub>]] || 75 || 73.72 || 48.3 || Not FP
|- style="background:{{Element color/Halogens}}"
| [[Bromine pentafluoride|BrF<sub>5</sub>]] || 35 || 40.25 || −61.30 || <sup>81</sup>Br:stable
|- style="background:{{Element color/Halogens}}"
| [[Iodine pentafluoride|IF<sub>5</sub>]] || 53 || 97.85 || 9.43 || <sup>129</sup>I:15.7my || 0.54%
|- style="background:{{Element color/Metalloids}}"
| [[Antimony pentafluoride|SbF<sub>5</sub>]] || 51 || 141 || 8.3 || <sup>125</sup>Sb:2.76y
|- style="background:{{Element color/Transition metals}}"
| [[Ruthenium tetrafluoride oxide|RuOF<sub>4</sub>]] || 44 || 184 || 115 || <sup>106</sup>Ru:374d
|- style="background:{{Element color/Transition metals}}"
| [[Ruthenium pentafluoride|RuF<sub>5</sub>]] || 44 || 227 || 86.5 || <sup>106</sup>Ru:374d
|- style="background:{{Element color/Transition metals}}"
| [[Niobium pentafluoride|NbF<sub>5</sub>]] || 41 || 234 || 79 || <sup>95</sup>Nb:35d || low
<!--
|- style="background:{{Element color/Transition metals}}"
| PdF<sub>4<sub> || 46 || || ||<sup>107</sup>Pd:6.5my
-->
|- style="background:{{Element color/Poor metals}}"
| [[Tin tetrafluoride|SnF<sub>4</sub>]] || 50 || 705 ||750 (subl) || <sup>121m1</sup>Sn:44y<br><sup>126Sn</sup>230ky || 0.013%<br>?
|- style="background:{{Element color/Transition metals}}"
| [[Zirconium tetrafluoride|ZrF<sub>4</sub>]] || 40 || 905 || 932 (tripoint) || <sup>93</sup>Zr:1.5my || 6.35%
|- style="background:{{Element color/Transition metals}}"
| [[Silver monofluoride|AgF]] || 47 || 1159 || 435 || <sup>109</sup>Ag:stable
|- style="background:{{Element color/Alkali metals}}"
| [[Caesium fluoride|CsF]] || 55 || 1251 || 682 || [[Caesium-137|<sup>137</sup>Cs]]:30.2y<br><sup>135</sup>Cs:2.3my || 6.19%<br>6.54%
|- style="background:{{Element color/Alkali metals}}"
| [[Rubidium fluoride|RbF]] || 37 || 1410 || 795 || <sup>87</sup>Rb:49by
|- style="background:{{Element color/Actinides}}"
| [[Uranium tetrafluoride|UF<sub>4</sub>]] || 92 || 1417 || 1036 || [[U-233|<sup>233</sup>U]]:160ky
|- style="background:{{Element color/Alkali metals}}"
| [[FLiNaK]] || || 1570 || 454 || stable
|- style="background:{{Element color/Alkali metals}}"
| [[Lithium fluoride|LiF]] || 3 || 1676 || 848 || stable
|- style="background:{{Element color/Actinides}}"
| [[Thorium(IV) fluoride|ThF<sub>4</sub>]] || 90 || 1680 || 1110
|- style="background:{{Element color/Lanthanides}}"
| [[Cadmium fluoride|CdF<sub>2</sub>]] || 48 || 1748 || 1110 || <sup>113m</sup>Cd:14.1y
|- style="background:{{Element color/Transition metals}}"
| [[Yttrium trifluoride|YF<sub>3</sub>]] || 39 || 2230 || 1150 || <sup>91</sup>Y:58.51d
|- style="background:{{Element color/Transition metals}}"
| [[Indium halides|InF<sub>3</sub>]] || 49 ||>1200 || 1170 ||<sup>115</sup>In:441ty
|- style="background:{{Element color/Alkaline earth metals}}"
| [[Barium fluoride|BaF<sub>2</sub>]] || 56 || 2260 || 1368 || <sup>140</sup>Ba:12.75d
|- style="background:{{Element color/Lanthanides}}"
| [[Neodymium trifluoride|NdF<sub>3</sub>]] || 60 || 2300 || 1374 || <sup>147</sup>Nd:11d
|- style="background:{{Element color/Lanthanides}}"
| [[Cerium trifluoride|CeF<sub>3</sub>]] || 58 || 2327 || 1430 || <sup>144</sup>Ce:285d
|- style="background:{{Element color/Lanthanides}}"
| [[Samarium trifluoride|SmF<sub>3</sub>]] || 62 || 2427 || 1306 || [[Samarium-151|<sup>151</sup>Sm]]:90y<br><sup>146</sup>Sm:10<sup>8</sup>y || 0.419%<br>?
|- style="background:{{Element color/Alkaline earth metals}}"
| [[Strontium fluoride|SrF<sub>2</sub>]] || 38 || 2460 || 1477 || [[Strontium-90|<sup>90</sup>Sr]]: 29.1y || 5.8%
|}
Missing: [http://www.freepatentsonline.com/5076839.html Pd] 46, La 57, Pr 59, Pm 61, Eu 63 and up
Missing top fluorides: TcF<sub>7</sub> AgF<sub>4</sub> XeF<sub>6</sub> LaF<sub>3</sub> CeF<sub>4</sub> PrF<sub>4</sub> PmF<sub>3</sub> EuF<sub>3</sub> GdF<sub>3</sub> TbF<sub>4</sub>
Inert: Kr 36, Xe 54
{{element color legend}}
== Notes ==
{{reflist}}
==See also==
*[[FLiNaK]]
*[[Molten salt reactor]]
== External links ==
*[http://www.nea.fr/html/pt/docs/iem/lasvegas04/07_Session_II/S2_03.pdf STUDY OF ELECTROCHEMICAL PROCESSES FOR SEPARATION OF THE ACTINIDES AND LANTHANIDES IN MOLTEN FLUORIDE MEDIA] ([[PDF]])
*[http://www.fjfi.cvut.cz/con_adtt99/papers/P-g5.pdf Separation and purification of UF6 from volatile fluorides by rectification] (PDF)
*[http://www.energyfromthorium.com/pdf/ORNL-4577.pdf Low-pressure distillation of a portion of the fuel carrier salt from the Molten Salt Reactor Experiment] (PDF)
*[http://www.studentpipeline.org/afci/theses/milliron.pdf USE OF THE FLUORIDE VOLATILITY PROCESS TO EXTRACT TECHNETIUM FROM TRANSMUTED SPENT NUCLEAR FUEL] (PDF)
*[https://e-reports-ext.llnl.gov/pdf/238572.pdf A Peer Review of the Strategy for Characterizing Transuranics and Technetium Contamination in Depleted Uranium Hexafluoride Tails Cylinders] (PDF)
[[Category:Nuclear reprocessing]]
[[Category:Nuclear chemistry]]
[[Category:Fluorides]]