OECD international standard problem ISP-50 on the ATLAS DVI line break test

An international standard problem (ISP) exercise, ISP-50 was progressed with the Advanced Thermal-Hydraulic Test Loop for Accident Simulation (ATLAS) integral effect test results on 50% break of the cross section of a Direct Vessel Injection (DVI) nozzle of the APR1400. This exercise consisted of two serial phases: blind and open calculation. In the open calculation, a total of 16 calculations was collected from 11 organizations and seven leading safety analysis codes were used, including APROS, ATHLET, KORSAR, MARS-KS, RELAP5/MOD3, CATHARE, and TRACE. Local 3-D phenomena such as a down-comer mixing, a radial peak cladding temperature (PCT) distribution, and an asymmetric inventory distribution were highlighted in this exercise. Overall progress of the ISP-50 is outlined in this paper. (author)