Modeling of flow blockage due to swell and rupture for analysis of LBLOCA using a multiple fuel rods scheme under high burnup condition

Abstract

The present study discusses a model of Large Break Loss-Of-Coolant Accident (LBLOCA) calculation using the multiple fuel rods modeling scheme which was developed to consider the fuel rods with different burnup in preparation for the recently proposed revision of Emergency Core Cooling System (ECCS) rule in the United States of America and in Korea. The thermal conductivity of the fuel pellet, the initial oxide layer thickness of the cladding, the size of gap and the rod internal pressure, and the effective thermal conductivity of the cladding considering the oxide layer are reflected by an input as functions of the burnup. Further, through the analysis on the division of hydraulic channels in which the multiple fuel rods are located, the influences of division of the hydraulic channel and the crossflow between channels on cladding thermal response are evaluated. Also a modeling scheme to calculate the flow blockage due to swell and rupture of cladding for the current system thermal-hydraulic code such as MARS-KS code is discussed. To consider the uncertainty of the swell and rupture model of the code and the uncertainty in the present flow blockage modeling scheme, a multiplication factor is introduced and used to evaluate the influence of the flow blockage on ECCS performance.