ISP-33 Pre- and Posttest Calculations in the FZR Rossendorf

Calculations relating to the OECD/NEA/CSNI International Standard Problem No. 33 were carried out with the GRS code ATHLET.This problem was a natural circulation experiment with primary coolant inventory reduced stepwise. The experiment was conducted in the PACTEL facility in Lappeenranta (Finland), which is a 1/305 volumetrically scaled, full height three loop simulator of the Russian VVER-440 type reactor. The main events of the experiment could be shown and explained by the ATHLET calculations:

• After the second draining the mass flow in the loops stagnates. Simultaneously, the primary pressure increases and the pressurizer is partly refilled.
• In the periods after the third drain step the mass flow through the three loops is nonequally distributed, which could be reproduced by the ATHLET calculations at least qualitatively.