magistrsko delo
Anže Pungerčič (Author), Luka Snoj (Mentor), Dušan Ćalić (Co-mentor)

Abstract

V magistrskem delu je predstavljena analiza zgorevanja jedrskega goriva v raziskovalnem reaktorju TRIGA Mark II, ki pod okriljem Instituta Jožef Stefan obratuje že od leta 1966 in igra pomembno vlogo pri razvoju jedrske tehnologije v Sloveniji. V tem času je bilo uporabljenih 300 različnih gorivnih elementov, razvrščenih v 220 polnitvenih shem reaktorske sredice. Z zgorevanjem goriva se zaradi jedrskih reakcij spreminja izotopska sestava goriva. V kolikor želimo določiti končno izotopsko sestavo goriva, moramo natančno poznati obratovalno zgodovino reaktorja. V ta namen smo skonstruirali model obratovalne zgodovine, ki vsebuje spremembe moči reaktorja, polnitvene sheme in meritve presežne reaktivnosti. Razvili smo metodologijo, ki avtomatizirano upošteva celotno zgodovino reaktorja TRIGA in omogoča izračune zgorelosti posameznih gorivnih elementov. Celotno obratovalno zgodovino smo izračunali z deterministično in stohastično metodo. Prva rešuje transportno enačbo nevtronov, medtem ko pri drugi simuliramo vsak nevtron posebej in z vzorčenjem velikega števila simulacij pridobimo informacije o populaciji nevtronov. Med seboj smo primerjali končne zgorelosti posameznih gorivnih elementov, izračunane z obema programoma in pri večini opazili dobro ujemanje. Pri nekaterih smo pa opazili razlike višje od 20 %. Ugotovili smo, da so bili to tisti elementi, ki so bili po rekonstrukciji reaktorja leta 1991 vstavljeni skupaj z že zgorelimi gorivnimi elementi. V ta namen smo naredili občutljivostno analizo vpliva starih gorivnih elementov in ugotovili, da je maksimalni vpliv na zgorelost sedanjih gorivnih elementov 5 %. Ostalo odstopanje pa je posledica pomanjkljivosti difuzijske aproksimacije. Izračunane spremembe reaktivnosti sredice zaradi zgorevanja goriva, smo primerjali z meritvami presežne reaktivnosti za celotno zgodovino, kjer se je končna napoved reaktivnosti razlikovala od meritev le za 200 pcm, kar je manj kot 10 %. Zanimalo nas je kateri izotopi vplivajo na spremembo reaktivnosti. V ta namen smo z Monte Carlo metodo naredili občutljivostno analizo vpliva posameznih izotopov, kjer smo ugotovili, da ima največji negativni vpliv Xe-135 in velik pozitivni vpliv Pu-239. Vrednosti 20 pomembnih izotopov smo primerjali z rezultati, pridobljenimi z determinističnimi izračuni v preteklosti, in opazili dobro ujemanje obeh metod. Za konec smo z Monte Carlo metodo določili še prostorsko porazdelitev izotopov znotraj gorivnega elementa in spremembo nevtronskega spektra zaradi zgorevanja goriva, kjer smo ugotovili znižanje fluksa termičnih nevtronov za 10 % pri zgorelem gorivu.

Keywords

jedrska fizika;fisijski jedrski reaktorji;reaktor TRIGA;jedrsko gorivo;zgorevanje goriva;

Data

Language: Slovenian
Year of publishing:
Typology: 2.09 - Master's Thesis
Organization: UL FMF - Faculty of Mathematics and Physics
Publisher: [A. Pungerčič]
UDC: 621.039.572
COBISS: 3251812 Link will open in a new window
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Downloads: 318
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Other data

Secondary language: English
Secondary title: Burnup analysis of TRIGA reactor fuel elements
Secondary abstract: This master thesis focuses on the determination of nuclear fuel burnup for the TRIGA Mark II research reactor at the Jožef Stefan Institute. The reactor has been operating since 1966 and has been playing an important role in developing nuclear technology and safety culture in Slovenia. During this period 300 different fuel elements were used, arranged in 220 core configurations. In order to determine the current isotopic composition of each fuel element we initiated activities to thoroughly document and analyse complete operation history. From the data regarding changes in reactor power, core configurations and measuremets of excess reactivity, we constructed a complete operational model, which could be used as an experimental benchmark for testing and validation of neutron transport and burnup codes. Complete operational history of the reactor was simulated with the deterministic method, which solves diffusion approximation of the neutron transport equation. Operational history after the reconstruction in 1991 was calculated with stochastic Monte Carlo, which simulates high number of individual neutrons and by sampling calculates the needed information about our system. Clear correspondence is observed from the comparison of final fuel element burnup, calculated with both codes. The discrepancies were 5 %, except for around 20 fuel elements where the discrepancies were above 20 %. The reason for this is that the mentioned fuel elements were mixed together with the old already burned ones after the reconstruction of the reactor in 1991. For the further analysis of the discrepancies we performed a sensibility study of the effects of old fuel elements, and found that they contribute up to 5 %. The rest is because of the diffusion approximation in deterministic calculations. The calculated changes in core reactivity due to burnup, clearly matches the ones measured during reactor operation and the discrepancy between measured and calculated core reactivity for final core configuration in 2017 is only 200 pcm or below 10 %. Furthermore the effect of individual isotopes on core reactivity was studied with the Monte Carlo method, where the largest negative contribution is due to Xe-135 build-up and the only visible positive contribution due to Pu-239. The results for 20 important isotopes were compared with deterministic calculations performed in the past, where clear correspondence between both methods is observed. In the end Monte Carlo method was used to determined isotope distribution inside each type of fuel element, together with changes in neutron spectrum due to burnup, where the thermal peak of burned fuel is lower for around 10 %.
Secondary keywords: nuclear physics;nuclear fission reactors;TRIGA reactor;nuclear fuel;fuel burnup;
Type (COBISS): Master's thesis/paper
Study programme: 0
Embargo end date (OpenAIRE): 1970-01-01
Thesis comment: Univ. v Ljubljani, Fak. za matematiko in fiziko, Oddelek za fiziko
Pages: XIII, 125 str.
ID: 10958879