Year: 2011
Type: dissertation
Abstract: earbon-14 ( 14 C) in large concentrations can be a hazard to living things due to its long radioactive ha lf-Ufe , and the ease with whic h it can enter the biosphere.During the o peration of high temperature gas-cooled reactors (such as the Pebble Bed Modular Reactor) 14 C is created in the graphite components.The Waste Minimiz ation Project o f PBMR (Pty) Ltd. is investigating methods o f 14 e removal fi•om graphite to a llow simplified disposa l or reuse of this high quality nuc lear grade material.The work summarized in this thesis represents pre liminary steps taken to assess the feasibility o f micro bia l remediatio n o f irradiated graphite.Scoping e xperime nts were designed and perfo rmed to establish baseline co nditio ns for future experiments us ing irradiated graphite.Experiment objectives were to ( I) test the compatibil it y o f candidate bacteria with a graphite system, (2) identify the bacterial growth medium optimum for the syste m, and (3) create a bioreactor environme nt in whic h bacteria consume a source o f surrogate graphite 14 C. T o achieve the first two objectives.a selection of live single bacterial spec ies a nd a mixed bacteria culture were introduced separate ly to media conta ining glucose and/or graphite as the carbon source.Da ily monito ring of bacterial growth in the bioreactors was accomplished via measurement of vis ible light absorbency and/o r pH o f the liquid medium.The measured va lues indicated that to r all species growth was least in the syste ms w ith g raphite and no g lucose.However. it was unc lear if graphite had the expected negative e ffect on growth when g lucose was present.On average, the most significant bacteria l growth occuiTed in the systems containing the mixed culture, as o pposed to the single species.This pre liminary screening resulted in the c ho ice of the mixed bacte ria culture and St yriakova growth rn~;;Jium (with at Jca ~t pa rtia l g lucose) for use in subsequ ent experiments.To address the third objective, bioreactor media were suppleme nted with o ne or two carbon containing salts (sodium acetate, ae 2 H 3 0 2 , and sodium bicarbonate, NaHC0 3 ) chosen to re present the possible c hemical bonding type o f 14 e in iiTadiated graphite.To increase the probability ofbac teria l consump t ion ofthis alternate carbon iii Or.Pete r W illiams, for the ir interest, he lp and expert g uidance in the course of <I supervis ing this researc h project.Without the financ ia l support of the Pebble Bed Modula r Reactor (PBM R) Pty Ltd, I wo uld no t have had this opportunity to comple te this research and my studies, fo r this, I thank the m.The staff o f Un iversity of Preto ria • s Che mica l Eng ineering departme nt.especia lly Ryno Prctorius.for his help in desig ning a nd setting up the experimenta l set-up.A spec ia l tha nk you goes to Lebogan g Phihlela , vvho kept me on the straig ht and narrow and he lped with many including administrati ve tasks.My sincere g ratitude to my mother.Elizabeth Ba pela fo r making it possible for me to achieve this degree.and without forgetting my wife.J udy, and son Nco, fo r allowing me to be a part-time husband and father, during this thesis w rite-up.To my co lleagues and everyone who has made a n input towards the completio n of this work.A phenomena l Tha nk You to All of You vi
Author: I I Mashifane
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2566107033