Technetium-99(99Tc) is an isotope oftechnetiumwhich decays with ahalf-lifeof 211,000 years to stableruthenium-99,emittingbeta particles,but no gamma rays. It is the most significantlong-lived fission productof uranium fission, producing the largest fraction of the total long-lived radiation emissions ofnuclear waste.Technetium-99 has afission product yieldof 6.0507% forthermal neutronfission ofuranium-235.
 | |
| General | |
|---|---|
| Symbol | 99Tc |
| Names | technetium-99, 99Tc, Tc-99 |
| Protons(Z) | 43 |
| Neutrons(N) | 56 |
| Nuclide data | |
| Natural abundance | trace |
| Half-life(t1/2) | 211100±1200 years |
| Spin | 9/2+ |
| Excess energy | −87327.9±0.9keV |
| Binding energy | 8613.610±0.009keV |
| Decay products | 99Ru |
| Decay modes | |
| Decay mode | Decay energy(MeV) |
| Beta decay | 0.2975 |
| Isotopes of technetium Complete table of nuclides | |
The metastabletechnetium-99m(99mTc) is a short-lived (half-life about 6 hours)nuclear isomerused innuclear medicine,produced from molybdenum-99. It decays byisomeric transitionto technetium-99, a desirable characteristic, since the very long half-life and type of decay of technetium-99 imposes little further radiation burden on the body.
Radiation
editThe weak beta emission is stopped by the walls of laboratory glassware. Soft X-rays are emitted when the beta particles are stopped, but as long as the body is kept more than 30 cm away these should pose no problem. The primary hazard when working with technetium is inhalation of dust; suchradioactive contaminationin the lungs can pose a significant cancer risk.[citation needed]
Role in nuclear waste
edit| Thermal | Fast | 14 MeV | |
|---|---|---|---|
| 232Th | notfissile | 2.919 ±.076 | 1.953 ± 0.098 |
| 233U | 5.03 ± 0.14 | 4.85 ± 0.17 | 3.87 ± 0.22 |
| 235U | 6.132 ± 0.092 | 5.80 ± 0.13 | 5.02 ± 0.13 |
| 238U | notfissile | 6.181 ± 0.099 | 5.737 ± 0.040 |
| 239Pu | 6.185 ± 0.056 | 5.82 ± 0.13 | ? |
| 241Pu | 5.61 ± 0.25 | 4.1 ± 2.3 | ? |
Due to its high fission yield, relatively long half-life, and mobility in the environment, technetium-99 is one of the more significant components of nuclear waste. Measured in becquerels per amount of spent fuel, it is the dominant producer of radiation in the period from about 104to 106years after the creation of the nuclear waste.[2]The next shortest-lived fission product issamarium-151with a half-life of 90 years, though a number ofactinidesproduced byneutron capturehave half-lives in the intermediate range.
Releases
edit| Nuclide | t1⁄2 | Yield | Q[a 1] | βγ |
|---|---|---|---|---|
| (Ma) | (%)[a 2] | (keV) | ||
| 99Tc | 0.211 | 6.1385 | 294 | β |
| 126Sn | 0.230 | 0.1084 | 4050[a 3] | βγ |
| 79Se | 0.327 | 0.0447 | 151 | β |
| 135Cs | 1.33 | 6.9110[a 4] | 269 | β |
| 93Zr | 1.53 | 5.4575 | 91 | βγ |
| 107Pd | 6.5 | 1.2499 | 33 | β |
| 129I | 16.14 | 0.8410 | 194 | βγ |
An estimated 160TBq(about 250 kg) of technetium-99 was released into the environment up to 1994 by atmospheric nuclear tests.[2]The amount of technetium-99 from civilian nuclear power released into the environment up to 1986 is estimated to be on the order of 1000 TBq (about 1600 kg), primarily by outdated methods ofnuclear fuel reprocessing;most of this was discharged into the sea. In recent years, reprocessing methods have improved to reduce emissions, but as of 2005[update]the primary release of technetium-99 into the environment is by theSellafieldplant, which released an estimated 550 TBq (about 900 kg) from 1995–1999 into theIrish Sea.From 2000 onwards the amount has been limited by regulation to 90 TBq (about 140 kg) per year.[3]
In the environment
editThe long half-life of technetium-99 and its ability to form ananionicspecies make it (along with129I) a major concern when considering long-term disposal ofhigh-level radioactive waste.[citation needed]Many of the processes designed to remove fission products from medium-active process streams in reprocessing plants are designed to removecationicspecies likecaesium(e.g.,137Cs,134Cs) andstrontium(e.g.,90Sr). Hence the pertechnetate escapes through these treatment processes. Current disposal options favor burial in geologically stable rock. The primary danger with such a course is that the waste is likely to come into contact with water, which could leachradioactive contaminationinto the environment. The naturalcation-exchange capacityof soils tends to immobilizeplutonium,uranium,andcaesiumcations. However, the anion-exchange capacity is usually much smaller, so minerals are less likely toadsorbthepertechnetateandiodideanions, leaving them mobile in the soil. For this reason, the environmental chemistry of technetium is an active area of research.
Separation of technetium-99
editSeveral methods have been proposed for technetium-99 separation including: crystallization,[4][5]liquid-liquid extraction,[6][7][8]molecular recognition methods,[9]volatilization, and others.
In 2012 the crystalline compound Notre Dame Thorium Borate-1 (NDTB-1) was presented by researchers at the University of Notre Dame. It can be tailored to safely absorb radioactive ions from nuclear waste streams. Once captured, the radioactive ions can then be exchanged for higher-charged species of a similar size, recycling the material for re-use. Lab results using the NDTB-1 crystals removed approximately 96 percent of technetium-99.[10][11]
Transmutation of technetium to stable ruthenium-100
editAn alternative disposal method,transmutation,has been demonstrated atCERNfor technetium-99. This transmutation process bombards the technetium (99
Tcas ametaltarget) withneutrons,forming the short-lived100
Tc(half-life 16 seconds) which decays bybeta decayto stableruthenium(100
Ru). Given the relatively high market value of Ruthenium[12]and the particularly undesirable properties of Technetium, this type of nuclear transmutation appears particularly promising.
See also
editReferences
edit- ^"Cumulative Fission Yields".IAEA.Retrieved18 December2020.
- ^abK. Yoshihara, "Technetium in the Environment" in "Topics in Current Chemistry: Technetium and Rhenium", vol. 176, K. Yoshihara and T. Omori (eds.), Springer-Verlag, Berlin Heidelberg, 1996.
- ^Tagami, Keiko (2003)."Technetium-99 Behavior in the Terrestrial Environment".Journal of Nuclear and Radiochemical Sciences.4(1): A1–A8.doi:10.14494/jnrs2000.4.A1.ISSN1345-4749.
- ^Xie, Rongzhen; Shen, Nannan; Chen, Xi gian; Li, Jie; Wang, Ya xing; Zhang, Chao; Xiao, Chengliang; Chai, Zhifang; Wang, Shuao (2021-05-03). "99 TcO 4 – Separation through Selective Crystallization Assisted by Polydentate Benzene-Aminoguanidinium Ligands".Inorganic Chemistry.60(9): 6463–6471.doi:10.1021/acs.inorgchem.1c00187.ISSN0020-1669.
- ^Volkov, Mikhail A.; Novikov, Anton P.; Grigoriev, Mikhail S.; Kuznetsov, Vitaly V.; Sitanskaia, Anastasiia V.; Belova, Elena V.; Afanasiev, Andrey V.; Nevolin, Iurii M.; German, Konstantin E. (January 2023)."New Preparative Approach to Purer Technetium-99 Samples—Tetramethylammonium Pertechnetate: Deep Understanding and Application of Crystal Structure, Solubility, and Its Conversion to Technetium Zero Valent Matrix".International Journal of Molecular Sciences.24(3): 2015.doi:10.3390/ijms24032015.ISSN1422-0067.PMC9916763.
- ^Bulbulian, S. (1984-11-01)."Methyl ethyl ketone extraction of Tc species".Journal of Radioanalytical and Nuclear Chemistry.87(6): 389–395.doi:10.1007/BF02166797.ISSN1588-2780.
- ^Moir, D. L.; Joseph, D. L. (June 1997)."Determination of99Tc in fuel leachates using extraction chromatography".Journal of Radioanalytical and Nuclear Chemistry.220(2): 195–199.doi:10.1007/bf02034855.ISSN0236-5731.
- ^Kołacińska, Kamila; Samczyński, Zbigniew; Dudek, Jakub; Bojanowska-Czajka, Anna; Trojanowicz, Marek (July 2018)."A comparison study on the use of Dowex 1 and TEVA-resin in determination of 99Tc in environmental and nuclear coolant samples in a SIA system with ICP-MS detection".Talanta.184:527–536.doi:10.1016/j.talanta.2018.03.034.
- ^Paučová, Veronika; Remenec, Boris; Dulanská, Silvia; Mátel, Ľubomír; Prekstová, Martina (2012-08-01)."Determination of 99Tc in soil samples using molecular recognition technology product AnaLig® Tc-02 gel".Journal of Radioanalytical and Nuclear Chemistry.293(2): 675–677.doi:10.1007/s10967-012-1710-5.ISSN1588-2780.
- ^William G. Gilroy (Mar 20, 2012)."New Method for Cleaning Up Nuclear Waste".Science Daily.
- ^Wang, Shuao; Yu, Ping; Purse, Bryant A.; Orta, Matthew J.; Diwu, Juan; Casey, William H.; Phillips, Brian L.; Alekseev, Evgeny V.; Depmeier, Wulf; Hobbs, David T.; Albrecht-Schmitt, Thomas E. (2012). "Selectivity, Kinetics, and Efficiency of Reversible Anion Exchange with TcO4− in a Supertetrahedral Cationic Framework".Advanced Functional Materials.22(11): 2241–2250.doi:10.1002/adfm.201103081.S2CID96158262.
- ^"Daily Metal Price: Ruthenium Price Chart (USD / Kilogram) for the Last 2 years".