RELAP5/MOD3.1 analysis of main steam header rupture in VVER-440/213 NPP

The paper focuses on two topics. At first, modelling of the PGV-4 steam generator to be used by the RELAP5 code is described. The result of steady-state calculations under standard conditions are compared with results of measurement. The problem of longitudinal subdivision of steam generator tubes is analyzed and evaluated. Further, a best-estimate analysis is presented of a main steam header rupture accident in a nuclear power plant equipped with a WWER-440/213 reactor. The low initiation reliability of the alarm signal 'Main Steam Header Rupture' would lead to considerable loss of secondary coolant, full depressurization of the secondary system (except the feedwater system), extremely fast cooldown of both the secondary and the primary circuits, opening of the pressurizer by-pass valve with later liquid outflow, possible secondary criticality due to failure of the high-pressure injection system, etc. 17 figs., 3 tabs., 7 refs