Rupture of accumulator line connected to the upper plenum

RELAP5/MOD2.5 calculations were performed for the case of a sudden rupture of the accumulator surge line to the upper plenum, unit 3 of the Bohunice power plant being the reference plant. The initial conditions used are listed, the main characteristics of steady-state calculation are given as are the system boundary conditions and the timing of main events. Due to the large rupture area, rapid system depressurization occurs and the pressurizer is empty very soon, resulting in a reactor scram at 0.975 s. Coolant flashing leads to a decrease in the mass flow rate through the rupture and slows down the primary pressure drop. At 18.95 s the high-pressure injection pump starts to deliver water to the primary circuit, the coolant and cladding temperature decreases. The pressure and temperature of the secondary circuit falls down as the circuit cools down via the primary circuit. Results of the calculation are presented in numerous graphs in three appendices. (A.K.)