THERMAL-HYDRAULIC CHARACTERISTICS OF A NEXT-GENERATION REACTOR RELYING ON STEAM-GENERATOR SECONDARY-SIDE COOLING FOR PRIMARY DEPRESSURIZATION AND LONG-TERM PASSIVE CORE COOLING

System experiments were conducted at the ROSA-V Large Scale Test Facil ity (LSTF) for investigation of new safety systems to mitigate consequ ences of postulated accidents in pressurized water rectors (PWRs). Tes ted systems included a steam generator (SG) secondary-side automatic d epressurization system (SADS) and gravity-driven injection system (GDI S), which are candidates of safety systems for some next-generation PW R designs. The experimental results showed several thermal-hydraulic b ehaviors typical of these safety systems, including the primary depres surization due to natural circulation cooling, a nonuniform flow behav ior among SG U-tubes, an accumulation of the non-condensable gas origi nally contained in the injected water, liquid holdup in U-tubes due to the countercurrent flow limiting, and long-term passive core cooling with the GDIS injection. From the assessment of the RELAP5/MOD3 code u sing the present data, it was found that the inability of the code to predict the U-tube nonuniform flow behavior resulted in overprediction of the primary depressurization rate at a pressure less than 1 MPa, a nd exaggerated oscillation of the natural circulation flow rate in the primary loop. (C) 1998 Elsevier Science S.A. All rights reserved.