Rudnik urana Žirovski vrh
Uran je kemični element, ki ima v periodnem sistemu simbol U in atomsko število 92. Je težek, srebrno-bel, strupen, kovinski, naravno radioaktiven element, ki pripada skupini aktinidov. V naravi se pojavlja kot uran-238, uran-235 (uporablja se kot gorivo v jedrskih reaktorjih in jedrskem orožju) in zelo majhna količina kot uran-234. Uran navadno najdemo v zelo majhnih količinah v kameninah, prsti, vodi, rastlinah in živalih.
Slika 1: Uran v periodnem sistemu
Uran razpada zelo počasi. Razpolovni čas urana-238 je 4.47 milijarde let, U-235 pa 704 milijonov let. U-235 je edini material v naravi, ki se cepi (fisija). U-238 postane cepilen, če sprejme hitre nevtrone, ki ga transmutirajo v plutonij-239. Če sprejme torij nevtron transmutira uran-233, ki je tudi cepilen. Oba dva izotopa sta pomembna energetska vira v jedrski tehniki, ker je uran-235 sorazmerno malo.
Uran je leta 1789 odkril Martin Heinrich Klaproth, ki ga je poimenoval po planetu Uranu. Eugène-Melchior Péligot je bil prvi ki je ločil (izoliral) material, njegove radioaktivne lastnosti je odkril Henri Becquerel leta 1896.
Uran ima trdoto po Mohsu 6, ki zadostuje za praske stekla. Uran ima zelo visoko gostoto 19.1 g/cm3.
Uran-235 je bil prvi izotop, za katerega so ugotovili, da se lahko cepi. Če se uran-235 bombardira s počasnimi nevtroni, bodo večino časa njegovi atomi razpadli v dvoje manjših jeder in pri tem sproščali v jedru vezano energijo in dodatne nevtrone. Če se ti dodatni nevtroni absorbirajo v drugih jedrih U-235, pride do jedrske verižne reakcije, ki ima za posledico izbruh toplote ali (v posebnih okoliščinah) eksplozijo. V jedrskem reaktorju se ta verižna reakcija upočasni in drži pod nadzorom s pomočjo strupa za elektrone, ki absorbira nekaj prostih nevtronov. Takšni za nevtrone vpojni materiali so pogosto del reaktorskih kontrolnih palic.
Za atomsko bombo iz U-235 je potrebno 7 kg urana 235. Prva v vojni vržena atomska bomba, Little Boy, je bila zasnovana na cepitvi urana, testna jedrska bomba (The gadget) in pa bomba, ki je uničila Nagasaki (Fat Man) sta uporabljali plutonij.
Slika 2: Nevtron povzroči razpad jedra U-235
Slika 3: Uran
Masiv Žirovskega vrha se kot pomol razteza v dinarski smeri od Lavrovca oz. Smrečja na jugovzhodu do Kladja oz. Fužin na severozahodu. Območje je geološko zelo raznovrstno, saj tu najdemo paleozojske in mezozojske kamnine.
Najstarejše kamnine na tem območju so iz karbona (pred 360 – 280 milijoni let) in iz perma (sledil karbonu in se končal pred 250 milijoni let). Obe obdobji spadata v mlajši paleozoik. Ti skladi (pogosto poimenovani permokarbonski skladi) so sestavljeni iz temno sivega glinastega skrilavca, sljudnatega kremenovega alevrolita in peščenjaka ter drobnozrnatega konglomerata. Na geološki karti so označeni z oznako C, P. Najstarejše kamnine so črni glineni skrilavci, ki se pod pritiskom lomijo v plošče ali tanke liste (to so prebivalci Poljanske in Selške doline izkoristili in z njimi prekrivali strehe). Med temi skrilavci lahko najdemo tudi vložke kremenovega peščenjaka in konglomerata. Nad skrilavci so sive, zelene in rdeče kamnine grödenske stopnje (perm). Starost kamnin ni paleontološko dokazana, saj niso našli določljivih ostankov peloda (v skrilavih glinavcih) ali konodontov (v lapornih kamninah). Težave so tudi pri ugotavljanju debeline omenjenih skladov, saj nikjer ni razkrita njihova prvotna podlaga, vsekakor pa ta znaša najmanj 1000 metrov. V obdobje perma (konec paleozoika) se zanesljivo uvrščajo grödenski rdeč in siv peščenjak, konglomerat in alevrolit ter zgornjepermski apnenec in dolomit (na geološki karti kot P22 in P3).
Slika 4: Geološka karta
Grödenske sklade na območju Žirovskega vrha delimo na spodnji del oz. sivo serijo in zgornji del oz. rdečo serijo. Uran najdemo v sivi seriji. Po raziskavah je bilo ugotovljeno, da so se s sive plasti usedale ob morskem obrežju, rdeče pa na kopnem – verjetno v puščavah. Na grödenske plasti so bili naloženi zgornjepermski apnenec, lapor in dolomit. Te plasti – debele več 1000 metrov – so gorotvorne sile v terciarju nagubale in so plasti bogate z uranovo rudo prišle na površje. Proti koncu perma in naprej v mezozoik se je nadaljevala sedimentacija. Na tem območju je največ kamnin iz obdobja triasa (mezozoik). Jurskih in krednih sedimentov ni veliko. Raziskave so pokazale, da so uranovo rudi najverjetneje naplavile podzemne vode, ki so omogočile strjevanje peska in drobnega proda v današnji peščenjak in konglomerat. Voda je vsebovala tudi majhno količino uranovih ionov. Peščenjak pa je bil ugodno kemično okolje za obarjanje uranove spojine.
SLika 5: Geološka karta Žirovskega vrha
Slika 6: Prečni profil rudišča
Najbogatejše rudišče urana pri nas so odkrili beograjski geologi. Poleg Žirovskega vrha na Škofjeloškem najdemo uran še v Bodoveljski grapi, Beznici pod Malim Lubnikom, na severnem pobočju Lubnika, na Polhovcu, v Sopotnici, na Sv. Tomažu in pri Sv. Valentinu. Leta 1976 je bil ustanovljen rudnik urana Žirovski vrh. Deloval je do leta 1990. Predelovali so rudi, ki je imela vsaj 0,03 % urana. V tem času so pridobili 633.000 ton rude in proizvedli 452 ton uranovega koncentrata. Rudnik je v zapiranju.
Naloge za vpis:
1. V muzeju na prostem so trije rudniški vagoni. Uporabite srednjo prostornino (zapisana na vagonu) in izračunajte kolikšna bi bila najmanjša količina urana, ki bi ga pridobili iz teh treh vagonov uranove rude.
2. Koliko jalovine in revne rude so nakopali v rudniku (upošteva se podatek na informacijski tabli)?
3. Sprehodite se naokrog in opazujte kamnine. Ali bi lahko našli kamnino, ki vsebuje uranovo rudo? Odgovor utemeljite.
4. Ozrite se po bregu navzgor. Ali so kamninski skladi vzporedni s pobočjem ali so nanj pravokotni?
Uranium mine Žirovski vrh
Uranium is a chemical element with symbol U and atomic number 92. It is a heavy, silvery-white, poisonous, natural radioactive metal in the actinide series of the periodic table. In nature we are the most common isotopes uranium-238 and uranium-235 (used for fuel in nuclear reactors and nuclear weapon). Uranium-234 is very rare. Uran is present in very small amounts in rocks, soil, water, vegetation and animals. Its hardness by Mohs is 6, what is enough to damage the glass. Uranium has high density - 19.1 g/cm3.
Figure 1: Uranium in poeriodic system
The half-life of uranium-238 is about 4.47 billion years and that of uranium-235 is 704 million years. Uranium-235 is the only naturally occurring fissile isotope, which makes it widely used in nuclear power plants and nuclear weapons. However, because of the tiny amounts found in nature, uranium needs to undergo enrichment so that enough uranium-235 is present. Uranium-238 is fissionable by fast neutrons, and is fertile, meaning it can be transmuted to fissile plutonium-239 in a nuclear reactor. Another fissile isotope, uranium-233, can be produced from natural thorium and is also important in nuclear technology. Uranium-238 has a small probability for spontaneous fission or even induced fission with fast neutrons; uranium-235 and to a lesser degree uranium-233 have a much higher fission cross-section for slow neutrons. In sufficient concentration, these isotopes maintain a sustained nuclear chain reaction. This generates the heat in nuclear power reactors, and produces the fissile material for nuclear weapons.
The 1789 discovery of uranium in the mineral pitchblende is credited to Martin Heinrich Klaproth, who named the new element after the planet Uranus. Eugène-Melchior Péligot was the first person to isolate the metal and its radioactive properties were discovered in 1896 by Henri Becquerel.
Figure 2: A neutron-induced nuclear fission event involving U-23
Figure 3: Uranium
Massif of Žirovski vrh extends as pier in the dinaric direction from Lavrovec -Smrečje in the southeast to Kladje - Fužine in the northwest. The area is geologically very diverse. Here we can find Palaeozoic and Mesozoic rocks.
The oldest rocks in this area are from Carbon (from 360 to 280 million years ago) and Perm (followed Carbon and ended 250 million years ago). Both periods are from late Paleozoic. These layers (often called Perm-Carbon layers) consist of dark gray slate, mica quartz-alevrolite and fine-grained sandstone and conglomerate. On the geological map are marked C, P. The oldest rocks are black clay shale, which under pressure breaks to boards or thin sheets (residents of Poljane and Selca Valley took advantage of them and used them for overlapping roofs). Among these slates can be found some quartz sandstone and conglomerate. Above the slate are gray, green and red rocks of Gröden period (Perm). Age of rock is paleontological not proved, because they did not find identifiable remains of pollen (in slates) or Conodonts (in marl rocks). There are also problems in determining the thickness of these layers, because their original basis is nowhere disclosed, but certainly they are thick at least 1000 meters. In the Permian period (late Paleozoic) are reliably classified layers of gröden red and gray sandstone, conglomerate and alevrolite and late Perm limestone and dolomite (on a geological map as P22 and P3).
Figure 4: Geological map
Gröden layers in the area Žirovski vrh are divided into the lower part (gray series) and upper part (red series). Uranium is found in the gray series. According to research, it was found that the gray layer sedimented on the seashore and red on the land - probably in the desert. Above gröden layers sedimented late Permorogen limestone, marl and dolomite. These layers - thick over 1,000 meters – were transformed with orogenesis in the Tertiary. Layer rich in uranium ore came to the surface. Towards the end of the Permian and Mesozoic sedimentationc ontinued. In this area, the maximum of the rocks is from the Triassic period (Mesozoic). There is no many Jurassic and Cretaceous sediments. Studies have shown that uranium ore probably swept along by groundwater, which led to the hardening of sand and small pebbles in today's sandstone and conglomerate. Water contained a small amount of uranium ions. Sandstone was favorable chemical environment for expeling uranium from the solution.
Figure 5: Geological map of Žirovski vrh
Figure 6: Cross section of Žirovski vrh ore deposit
The richest uranium ore deposits in Slovenia were discovered by Belgrade geologists. In addition to Žirovski vrh we can find in the area of Škofja Loka uranium also in Bodoveljska ravine, Beznica under Mali Lubnikom, on the northern slope of Lubnik, on Polhovcu, in Sopotnica, Sv. Tomaž and Sv. Valentin. In 1976 the uranium mine was established. It worked until 1990. They used ore that contained at least 0,03 % uranium. During this time, gained 633 thousand tons of ore and produced 452 tons of uranium concentrate. The mine is under closing.
Logging tasks:
1. In the outdoor museum are three mine cars. Take average volume (written on one of them) and calculate how much would be the smallest amount of uranium that would be gained from the three wagons of uranium ore.
2. How much waste material and pure ore was dug out (according to the data on the information board)?/strong>
3. Walk around and observe the rocks. Could you find rock containing uranium ore? Explain your answer.
4. Look uphill. Are rock layers parallel to the slope or perpendicular to it?
Viri: / Sources:
- https://commons.wikimedia.org/wiki/File:Uranium.svg
- https://sl.wikipedia.org/wiki/Uran
- https://en.wikipedia.org/wiki/Uranium
- Pustavrh, M., 2016: Prostorska in funkcijska preobrazba območja Rudnika urana Žirovski vrh. Ljubljana, Zaključna seminarska naloga, Filozofska fakulteta, 43 str., citirano/quoted 30. 4. 2017 - http://geo.ff.uni-lj.si/pisnadela/pdfs/zaksem_201610_miha_pustavrh.pdf
- Florjančič, P. A., Uranovo rudišče Žirovski vrh. V: Jeršek, M. (ur.). Mineralna bogastva Slovenije. Ljubljana, Prirodoslovni muzej Slovenije, str. 101-105, citirano/quoted 30. 4. 2017 – http://www.dlib.si/details/URN:NBN:SI:DOC-N1VANFAR
- Omaljev, V.: Eksploatacijsko raziskovanje v uranovem rudišču Žirovski vrh, citirano/quoted (30. 4. 2017) - http://www.geologija-revija.si/dokument.aspx?id=185
- Budkovič, T.: Sedimentološka kontorla uranove rude na Žirovskem vrhu, citirano/quoted (30. 4. 2017) - www.dlib.si/stream/URN:NBN:SI:DOC-E01USHVL/8f9e51c9-b4bd-44fb.../PDF
- https://sciencenotes.org/92-uranium-tile-2/