This thesis work is about the dynamical behavior of advanced nuclear systems, in particular lead-cooled fast reactors (LFRs). As they are currently under study and development, it is extremely important to provide accurate, though flexible and straightforward, computational tools to investigate their efficiency and safety under normal and off-normal conditions. This is done with reference to a demonstrator unit currently under design phase in Sweden, SUNRISE-LFR. Its primary circuit (reactor core, hot let, cold leg and cold pool) is modeled with a zero-dimensional plant simulator named BELLA, while a new model for the steam generator is built adopting the well-established moving boundary approach. The integrated code is adopted in MATLAB/Simulink to perform safety analysis under four reference accidental scenarios: unprotected transient overpower (UTOP), unprotected loss of flow (ULOF), unprotected loss of heat sink (ULOHS) and station blackout (a combination of ULOF and ULOHS). The results obtained are physically reasonable and explainable in terms of causal relations between input and output variables. Moreover, they allow to critically discuss the design of SUNRISE-LFR with reference to the targeted safety margins to fuel melting and cladding creep rupture. In addition, they may constitute the basis and provide the means to further improve the codes, in particular working on the secondary side and on control strategies for such innovative nuclear systems.
Questo lavoro di tesi riguarda il comportamento dinamico di sistemi nucleari avanzati, in particolare reattori veloci refrigerati a piombo fuso. Durante il loro studio e sviluppo, è estremamente importante elaborare strumenti computazionali accurati, ma al tempo stesso semplici e flessibili, per indagare la loro efficienza e la loro sicurezza in condizioni di funzionamento normali ed anomale. Questo viene fatto rispetto ad un'unità dimostrativa attualmente in fase di progettazione in Svezia, di nome SUNRISE-LFR. Il circuito primario (nocciolo del reattore, gamba calda, gamba fredda e piscina fredda) viene modellato con un simulatore di impianto zero-dimensionale di nome BELLA, mentre per il generatore di vapore viene costruito un nuovo modello basato sul già dimostrato approccio alle frontiere mobili. Il codice integrato è scritto in MATLAB/Simulink per eseguire analisi di sicurezza rispetto a quattro scenari incidentali di riferimento: unprotected transient overpower (UTOP), unprotected loss of flow (ULOF), unprotected loss of heat sink (ULOHS) e station blackout (una combinazione di ULOF e ULOHS). I risultati ottenuti sono fisicamente ragionevoli e spiegabili in termini delle relazioni causali tra le variabili di ingresso e di uscita. Inoltre, permettono di discutere criticamente le scelte di progettazione di SUNRISE-LFR rispetto ai margini di sicurezza prefissati. Per di più, possono costituire la base e fornire i mezzi per ulteriori miglioramenti del codice, lavorando in particolare sul circuito secondario e su strategie di controllo dell'impianto complessivo.
Transient analysis of SUNRISE-LFR with an updated version of BELLA plant simulator
Persico, Alessandro
2020/2021
Abstract
This thesis work is about the dynamical behavior of advanced nuclear systems, in particular lead-cooled fast reactors (LFRs). As they are currently under study and development, it is extremely important to provide accurate, though flexible and straightforward, computational tools to investigate their efficiency and safety under normal and off-normal conditions. This is done with reference to a demonstrator unit currently under design phase in Sweden, SUNRISE-LFR. Its primary circuit (reactor core, hot let, cold leg and cold pool) is modeled with a zero-dimensional plant simulator named BELLA, while a new model for the steam generator is built adopting the well-established moving boundary approach. The integrated code is adopted in MATLAB/Simulink to perform safety analysis under four reference accidental scenarios: unprotected transient overpower (UTOP), unprotected loss of flow (ULOF), unprotected loss of heat sink (ULOHS) and station blackout (a combination of ULOF and ULOHS). The results obtained are physically reasonable and explainable in terms of causal relations between input and output variables. Moreover, they allow to critically discuss the design of SUNRISE-LFR with reference to the targeted safety margins to fuel melting and cladding creep rupture. In addition, they may constitute the basis and provide the means to further improve the codes, in particular working on the secondary side and on control strategies for such innovative nuclear systems.| File | Dimensione | Formato | |
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2022_04_Persico_01.pdf
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Descrizione: Thesis Classical Form
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18.92 MB
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2022_04_Persico_02.pdf
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Descrizione: Executive Summary
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657.1 kB
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https://hdl.handle.net/10589/188392