The Integral Inherently Safe Light Water Reactor (I2S-LWR) is a concept reactor that combines large power output with integral technology and passive safety. The goal of the this study is to apply this rationale to the I2S-LWR Spent Fuel Pool (SFP), in light of the events occurred to the Fukushima Daiichi unit 4 due to the earthquake and subsequent tsunami on March 11th, 2011. The objective of the research focuses on developing a Passive Cooling System (PCS) for the I2S-LWR SFP, that could in principle withstand a Station Black-Out (SBO). The specifications of the I2S-LWR SFP are introduced. The pool dimensions were adapted to the Fuel Assemblies (FAs) racks. Those latter ones were designed on the basis of the AP1000 racks and adjusted to the I2S-LWR FAs. The SFP PCS was designed with an intermediate loop that removes the decay heat of spent FAs from pool water through an external Intermediate Heat Exchanger (IHX) and it rejects the power to a dry cooling tower through an Air Heat Exchanger (AHX). Then, a correlation was used to calculate the thickness of the tubes of both HXs. Since the results obtained led to excessively thin tubes, it was decided to analyze the influence of such thickness on the overall study through a simple sensitivity analysis: two different values of thickness were taken into account, separately studied and then compared. Meanwhile, a simple model of the I2S-LWR SFP PCS was developed using the RELAP5-3D/4.0.3 code. After a brief study of few correlations, the one of the ANS (2005) was chosen to model the decay heat generated by the FAs during the 11 years of residence in the SFP. The SBO event was also defined, along with the maximum heat load that the SFP PCS must deal with. Subsequently, the preliminary optimization process was conducted. The study focuses mainly on three quantities of the HXs: tubes inner diameter, pitch length and number of tubes for each HX. Both thickness cases were analyzed, considering also the economic consequences on the system costs. Finally, a Fukushima-like transient simulation was conducted and the feasibility of a PCS for a SFP was proven.
L’Integral Inherently Safe Light Water Reactor (I2S-LWR) è un reattore innovativo per unire un’elevata potenza a una configurazione integrale e una sicurezza passiva. Scopo dello studio è applicare tale logica alla piscina di combustibile esaurito (Spent Fuel Pool, SFP) dell’I2S-LWR, alla luce di quanto accaduto l’11 marzo 2011 all’unità 4 della centrale di Fukushima Daiichi, a causa del terremoto e conseguente tsunami. Obiettivo della ricerca è sviluppare un sistema di raffreddamento passivo (Passive Cooling System, PCS) in grado di resistere ad un black-out elettrico totale (Station Black-Out, SBO). Segue una descrizione dettagliata della SFP. La piscina è stata dimensionata sulla base delle misure delle rastrelliere (racks) del combustibile, ispirate a quelle del reattore AP1000 e adattate alle dimensioni del combustibile dell’I2S-LWR. Il PCS è composto da un circuito intermedio che asporta la potenza di decadimento tramite uno scambiatore di calore intermedio (Intermediate Heat Exchanger, IHX) esterno alla piscina e poi cede il calore all’ambiente esterno grazie ad uno scambiatore ad aria (Air Heat Exchanger, AHX), sito in una torre di raffreddamento a secco. Lo spessore dei tubi degli scambiatori, inizialmente calcolato molto basso, è stato poi utilizzato per un’analisi semplice di sensitività, grazie al confronto con un secondo valore di spessore Si è utilizzato il codice RELAP5-3D/4.0.3 per sviluppare un semplice modello del PCS e della SFP. La correlazione ANS (2005) è stata scelta tra altre per modellizzare il calore di decadimento generato dal combustibile esausto durante 11 anni di deposito all’interno della SFP. Si sono definiti l’evento SBO e anche la massima potenza che il PCS deve smaltire. Poi l’ottimizzazione preliminare del sistema si è concentrata su tre grandezze degli scambiatori: il diametro interno, il passo e il numero di tubi per ciascuno scambiatore. Si sono considerati entrambi gli spessori studiati, tenendo anche conto delle conseguenze economiche sul costo totale del sistema. Infine si è simulato un transitorio per riprodurre l’evento di Fukushima e si è quindi dimostrata la fattibilità di un sistema passivo di raffreddamento della SFP.
Preliminary study of the I2S-LWR spent fuel pool passive cooling system
BANZATTI, ALESSANDRO MARIA GIUSEPPE
2013/2014
Abstract
The Integral Inherently Safe Light Water Reactor (I2S-LWR) is a concept reactor that combines large power output with integral technology and passive safety. The goal of the this study is to apply this rationale to the I2S-LWR Spent Fuel Pool (SFP), in light of the events occurred to the Fukushima Daiichi unit 4 due to the earthquake and subsequent tsunami on March 11th, 2011. The objective of the research focuses on developing a Passive Cooling System (PCS) for the I2S-LWR SFP, that could in principle withstand a Station Black-Out (SBO). The specifications of the I2S-LWR SFP are introduced. The pool dimensions were adapted to the Fuel Assemblies (FAs) racks. Those latter ones were designed on the basis of the AP1000 racks and adjusted to the I2S-LWR FAs. The SFP PCS was designed with an intermediate loop that removes the decay heat of spent FAs from pool water through an external Intermediate Heat Exchanger (IHX) and it rejects the power to a dry cooling tower through an Air Heat Exchanger (AHX). Then, a correlation was used to calculate the thickness of the tubes of both HXs. Since the results obtained led to excessively thin tubes, it was decided to analyze the influence of such thickness on the overall study through a simple sensitivity analysis: two different values of thickness were taken into account, separately studied and then compared. Meanwhile, a simple model of the I2S-LWR SFP PCS was developed using the RELAP5-3D/4.0.3 code. After a brief study of few correlations, the one of the ANS (2005) was chosen to model the decay heat generated by the FAs during the 11 years of residence in the SFP. The SBO event was also defined, along with the maximum heat load that the SFP PCS must deal with. Subsequently, the preliminary optimization process was conducted. The study focuses mainly on three quantities of the HXs: tubes inner diameter, pitch length and number of tubes for each HX. Both thickness cases were analyzed, considering also the economic consequences on the system costs. Finally, a Fukushima-like transient simulation was conducted and the feasibility of a PCS for a SFP was proven.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/106586