Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The Pebble Bed Modular Reactor (PBMR) is a Generation IV graphite-moderated helium
cooled nuclear reactor which is being developed in South Africa. The PBMR design is
based on the German Arbeitsgemeinschaft Versuchreaktor (AVR). The AVR was
decommissioned in December 1988 due to operational and safety problems. The PBMR
project has put a lot of emphasis on safety and therefore all safety issues relating to the
AVR have to be addressed before this technology can be implemented. After the
decommissioning of the AVR plant, technicians found radioactive isotopes of cesium
55Cs137, 55Cs134, silver 44Ag110 and strontium 38Sr90 as well as graphite dust in the primary
coolant loop of the reactor. These isotopes as well as the graphite dust have to be
removed from the helium coolant stream because it can be potentially harmful to
equipment, personnel and the general public. The main objective of this thesis is
therefore to investigate a separation method for removing the graphite dust (and with it
the radioactive isotopes) from the helium coolant stream and also test this method
under different operating conditions and geometrical configurations to determine its
dust separation efficacy. The device chosen to investigate is the Ranque-Hilsch vortex
tube.
The Ranque-Hilsch vortex tube (RHVT) is a simple device having no moving parts that
produces a hot and cold air stream simultaneously at its two ends from a compressed air
source. The vortex generated by the vortex generator located at the inlet of the RHVT
causes strongly rotating flows similar in speed to that of a gas centrifuge. The gas
centrifuge is used for isotope separation. The RHVT, in theory, can therefore be
implemented to separate the graphite/silver isotopes from the helium coolant with the
added benefit of either cooling or heating the coolant and was thus selected as the
separation technique to be tested experimentally.
The dust separation efficiency of the RHVT was tested experimentally using different
grades of graphite dust, different fluids, various inlet volumetric flow rates and volume
fractions and different RHVT geometries. The experimental results showed that the
RHVT has a dust separation efficiency of more than 85 %. A regression analysis was also done with the experimental data to obtain a correlation between the different operating
conditions (such as volumetric flow rate) and the dust separation efficiency that can be
used to predict the dust efficiency under different operating and geometric conditions
(such as the PBMR environment).
An analytical model is also presented to describe the ‘temperature separation’
phenomenon in the RHVT, using basic thermo-physical principals to gain a better
understanding of how the RHVT works. A CFD analysis was also attempted to
supplement the analytical analysis but the solution did not converge and therefore only
the preliminary results of the analysis are discussed. / AFRIKAANSE OPSOMMING: Die “Pebble Bed Modular Reactor” (PBMR) is `n vierde generasie grafiet gemodereede
en helium verkoelde reaktor wat in Suid-Afrika ontwikkel word. Die PBMR ontwerp is
gebaseer op the Duitse Arbeitsgemeinschaft Versuchreaktor (AVR) wat buite werking
gestel is in Desember 1988 as gevolg van operasionele en veiligheidsprobleme. Die
PBMR projek lê baie klem op veiligheid en daarom moet alle veiligheidskwessies van die
AVR eers aangespreek word voor die tegnologie geimplementeer kan word. Nadat die
AVR buite werking gestel is, het AVR tegnisie radioaktiewe isotope van cesium 55Cs137,
55Cs134, silwer 44Ag110 en strontium 38Sr90 asook grafiet stof in die primêre stroomkring
van die reaktor gevind. Hierdie isotope sowel as die grafiet stof moet uit die helium
verkoelingsmiddel in die primere stroomkring van die reaktor verwyder word aangesien
dit dalk skadelik kan wees vir toerusting, personeel en die publiek. Die hoofdoelwit van
hierdie tesis is dus om `n skeidingstekniek te ondersoek wat die stof (en dus ook die
radioaktiewe isotope) uit die helium verkoelingsmiddel kan verwyder. Hierdie tegniek
moet dan getoets word onder verskillende operasionele en geometriese toestande om
die skeidingsbenuttingsgraad te bepaal. Die toestel wat gekies is om ondersoek te word
is die “Ranque-Hilsch Vortex Tube”.
Die “Ranque-Hisch Vortex Tube” (RHVT) is a eenvoudige uitvindsel wat geen bewegende
parte bevat nie en wat warm en koue lug gelyktydig produseer vanaf `n saamgepersde
lugbron. ‘n Baie sterk roteerende vloei word gegenereer in die RHVT wat dieselfde
snelhede bereik as die lug in `n gas-sentrifugeerder. Die gas- sentrifugeerder word
gebruik as `n isotoopskeidingsapparaat. In teorie kan die RHVT dus ook gebruik word om
partikels te skei as gevolg van die sterk roteerende vloei, met die voordeel dat dit ook
die lug kan verhit en verkoel. As gevolg van hierde redes is die RHVT gekies as die
skeidingstegniek om te ondersoek en dus experimenteel te toets.
Die benuttingsgraad van die RHVT se vermoë om die grafiet stof van die lug te skei was
gevolglik eksperimenteel getoets deur gebruik te maak van verskillende gehaltes grafiet
stof, verskillende vloeistowwe (lug of helium), verskillende inlaat volumevloeitempos en
volume fraksies en RHVT geometrieë. Die experimentele resultate het getoon dat die RHVT `n benuttingsgraad van meer as 85 % het. `n Regressie analise was ook gedoen
met die eksperimentele data om `n korrelasie tussen die verskillende opersionele
toestande (soos volumevloeitempo) en die stof skeiding benuttingsgraad te kry. Hierdie
korrelasie kan dan gebruik word om die stofskeidingsbenuttingsgraad onder ander
operasionele en geometriese omstandighede, soos die PBMR omgewing, te voorspel.
`n Analitiese model word ook voorgestel om die “temperatuur-skeidings” meganisme in
die RHVT te verduidelik, met die hulp van basiese termo-fisiese beginsels, om beter te
verstaan hoe dit werk. Daar was ook gepoog om `n CFD analise te doen wat die
analitiese model kon aanvul, maar die numeriese oplossing het nie gekonvergeer nie en
dus word net die voorlopige resultate van dié analise bespreek.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/4201 |
| Date | 03 1900 |
| Creators | Burger, Anja |
| Contributors | Dobson, R. T., Thiart, G. D., University of Stellenbosch. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 84 p. : ill. |
| Rights | University of Stellenbosch |
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