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Turbulent hydrogen combustion modelling in experimental containment facility
Holler, Tadej (Author), Kljenak, Ivo (Mentor) More about this mentor... This link opens in a new window

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Abstract
Hydrogen may be produced in a light water reactor nuclear power plant containment during a postulated severe accident. Ensuing hydrogen combustion, which is essentially inevitable, could inflict irreparable damage to the containment itself, resulting in a failure of the final protection barrier for the fission products release to the environment. Since the actual containment volumes surpass the volumes of even the largest available experimental facilities capable of conducting hydrogen combustion experiments for a few orders of magnitude, the computer-aided modelling presents itself as a formidable and accessible tool in this regard. Thus, use and development of reliable computational fluid dynamics modelling approaches for large-scale geometries is imperative for providing relatively cost-effective hydrogen combustion risk assessment. The present dissertation focuses on further theoretical investigation of hydrogen combustion, specifically hydrogen deflagration in large enclosures. This investigation is carried out through the development and validation of hydrogen combustion models and addresses some of the challenges on the way for the computer-aided modelling to become readily available for use in the real-scale containment dimensions. Specifically, it tackles the difficulties of available combustion models in producing the reliable predictions of the large-scale hydrogen deflagration experiments. The validation of combustion models was performed against the results obtained in two large-scale experimental facilities, i.e. THAI and HYKA-A2 experimental vessels. Firstly, a new combustion model was introduced, i.e. the extended eddy break-up (EEBU) model, which was developed from the existing less elaborate eddy break-up (EBU) model, with the additional treatment of the flame phenomenology also in the quasi-laminar combustion regime. This model retains beneficial characteristics of the EBU model, i.e. superior computational efficiency, while at the same time providing improved predictions for hydrogen deflagrations in the considered large-scale experiments. Furthermore, a novel approach was recommended undertaking a focused treatment of the laminar flame speed with the weighted laminar flame speed concept. This approach effectively balances the turbulent reaction rate with the buoyancy effects of the surrounding flow. It was applied to already existing extended turbulent flame speed closure (ETFC) model as well as to the newly introduced EEBU model. When properly executed, it proved to be extremely effective in improving the predictions of both models regarding the flame behavior in the considered large-scale hydrogen deflagration experiments.

Language:English
Keywords:nuclear safety, hydrogen combustion, turbulent flame speed, laminar flame speed, eddy break-up
Work type:Doctoral dissertation (mb31)
Organization:FMF - Faculty of Mathematics and Physics
Year:2019
COBISS.SI-ID:3310948 This link opens in a new window
Views:511
Downloads:180
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Secondary language

Language:Slovenian
Title:Modeliranje turbulentnega zgorevanja vodika v eksperimentalni napravi zadrževalnega hrama
Abstract:
V primeru težke nesreče v lahkovodni jedrski elektrarni lahko pride do nastajanja vodika. Nadaljnje zgorevanje vodika, ki je v bistvu neizogibno, lahko povzroči nepopravljivo škodo na samem zadrževalnem sistemu, kar bi pomenilo odpoved končne zaščitne ograde za izpustitev radioaktivnih fisijskih produktov v okolje. Ker dejanske geometrije zadrževanja več sto krat presegajo geometrije celo največjih razpoložljivih eksperimentalnih objektov, v katerih se lahko izvaja poskuse zgorevanja vodika, se v tem pogledu računalniško podprto modeliranje ponuja kot izjemno uporabno in dostopno orodje. Zato je uporaba in razvoj zanesljivih modelov za modeliranje dinamike tekočin za obsežne geometrije nujna za zagotavljanje relativno stroškovno učinkovite ocene zgorevanja vodika. Disertacija se osredotoča na nadaljnje teoretične raziskave zgorevanja vodika, zlasti deflagracije vodika v velikih zaprtih prostorih jedrskih elektrarn. Ta raziskava se izvaja z razvojem in validacijo modelov zgorevanja vodika in naslavlja nekatere izzive na poti do računalniško podprtega modeliranja, ki bi bilo na voljo za uporabo v realnih dimenzijah zadrževalnih hramov. Konkretno se spopada s težavami razpoložljivih modelov zgorevanja pri kreiranju zanesljivih napovedi obsežnih eksperimentov deflagracije vodika. Validacija modelov izgorevanja je bila izvedena v primerjavi z rezultati pridobljenimi v dveh obsežnih eksperimentalnih objektih, tj. eksperimentalnih posodah THAI in HYKA-A2. Najprej je formuliran in predstavljen nov, t.i. razširjen model razpada vrtincev (ang. »extended eddy break-up model« - EEBU), ki smo ga razvili z nadgradnjo obstoječega modela razpada vrtincev (ang. »eddy break-up model« - EBU), z dodatno obravnavo fenomenologije plamena tudi v kvazi-laminarnem režimu zgorevanja. Novo formirani EEBU model ohranja koristne značilnosti modela EBU, tj. boljšo računsko učinkovitost, hkrati pa zagotavlja boljše napovedi deflagracije vodika v obravnavanih eksperimentih. Poleg tega je bil predstavljen tudi nov pristop, ki je usmerjen v obravnavo hitrosti laminarnega plamena s konceptom utežene hitrosti laminarnega širjenja plamena. Uveden pristop učinkovito uravnava turbulentno hitrost reakcije z vzgonskimi učinki okoliškega pretoka. Uporabljen je bil za že obstoječi razširjen model zgorevanja temelječ na turbulentni hitrosti plamena (ang. »extended turbulent flame speed closure model« - ETFC), kot tudi za novo predstavljen model EEBU. Ko je ta pristop ustrezno izveden, se izkaže za izjemno učinkovitega pri izboljšanju napovedi omenjenih modelov v zvezi z obnašanjem plamena v obravnavanih obsežnih eksperimentih deflagracije vodika.

Keywords:jedrska varnost, zgorevanje vodika, turbulentna hitrost plamena, laminarna hitrost plamena, razpad vrtincev

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