ROSA-IV LSTF 5% cold leg break analysis using the RELAP5/Mod2 code

This paper presents the results of the OECD International Standard Problem calculation no. 26 (ISP-26), performed with the RELAP5/Mod2 code (frozen version 36.06 for the CRAY-X/MP) at the Paul Scherrer Institute (PSI) and analyses their comparison with the 5% cold leg break test (run SB-CL-18) conducted on the Large Scale Test Facility (LSTF) of the ROSA-IV program. The principal objective of the present calculation is the analysis of the simulation capability of the code in regards to the main phenomena occurring during a typical Small Break Loss of Coolant Accident (SB-LOCA), such as: natural circulation heat removal; liquid holdup in the up- and downflow sides of the steam generator U-tubes in combination with a reflux condenser mode heat removal, core upper plenum pressure build-up causing manometric liquid level unbalance between core and downcomer; loop seal clearing concurrent with core liquid depression leading to core heat-up; core level recovery after loop seal clearing; vessel inventory boil-off leading to second core uncovering; core reflooding due to accumulator injection intervention. 7 refs., 15 figs., 2 tabs