Computations of heterogeneous dilution transients using CFX and HEMERA V1

Heterogeneous boron dilution can occur in a PWR in case of a leakage of a primary pump exchanger. Unborated cold water can accumulate in the U-leg during shutdown states and form a plug. When the primary pump restarts, this plug is transported toward the core and may lead to the core re-criticality. To evaluate the consequences of this transient, a sequential calculation involving the CFD code CFX (for the vessel) and the fully coupled 3D computational chain HEMERA V1 (for the core) is used. This paper is divided into three parts. The first one describes the codes used for the transport of the unborated water (CFX) and for the core response (HEMERA). The second part focuses on the modeling of the heterogeneous boron dilution transient and the third one presents the results. In order to demonstrate the capability of this calculating scheme, two responses of the core have been calculated. The first one keeps the core sub-critical during whole dilution transient and the second one assumes a prompt critical jump in order to demonstrate the capability of the calculation scheme. (author)