Solution of the Fifth Dynamic AER Benchmark Using the Coupled Code DYN3D/ATHLET

The fifth dynamic benchmark is the first benchmark for coupled thermohydraulic system/three-dimensional hexagonal neutron kinetic core models. In this benchmark the interaction between the components of a VVER-440 NPP with the reactor core has been investigated.

The initiating event is a symmetrical break of the main steam header at the end of the first fuel cycle and hot shutdown conditions with one control rod group stucking. This break causes an overcooling of the primary circuit. During this overcooling the scram reactivity is compensated and the scrammed reactor becomes recritical. The calculation was continued until the highly-borated water from the high pressure injection system terminated the power excursion.

Several aspects of this very complex and complicated benchmark problem are analyzed in detail. Sensitivity studies with different hydraulic parameters are made. The influence on the course of the transient and on the solution is discussed.