LBLOCA in the pressurizer surge line with 207 mm

RELAP5/MOD2.5 calculations were performed for the case of a sudden rupture of one of two parts of the surge line with 207 mm, 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 2.1 s. Coolant flashing leads to a decrease in the mass flow rate through the rupture and slows down the primary pressure drop. Strong hydroaccumulator injection causes steam condensation and a further rapid pressure reduction. At about 480 s the low-pressure injection pump starts delivering 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.)