Calculation of the response of the WWER-440/213 reactor core to an accident associated with main steam header break by means of the ATHLET system code in combination with with the three-dimensional reactor dynamics code DYN3D

A survey is given of the behavior of the reactor core during an accident associated with main steam header break. This problem is a benchmark exercise for the verification of thermohydraulic system codes connected with three-dimensional hexagonal reactor dynamics codes. The accident is initiated by a symmetrical break of the main steam header at the end of the 1st fuelling cyclein the hot shutdown condition with the control rod groups fully inserted except for group 4. The calculations were performed by using the externally coupled codes ATHLET Mod. 1.1 Cycle C and DYN3DH1.1/M3. The two codes are described at their external coupling is outlined. The standard WWER-440/213 input deck of the ATHLET code was used. The tresults of steady-state calculations as well as burnup calculations are given. The analysis of the transient process is aimed at the time behavior of safety related parameters in selected components of the primary and secondary circuits as well as at the global parameters of the reactor core and behavior in selected fuel assemblies