EDF MAAP5.04 LOCA Transient Simulation Improvements

During a loss-of-coolant-accident (LOCA) transient in a pressurized water reactor (PWR), water from the primary circuit is lost at the break. PWR designs are equipped with safety systems (SS) such as safety injection or accumulators to inject water into the primary circuit and prevent the core from being degraded. Depending on the size, position, and orientation of the break, a part of the safety system injection (SSI) into the primary circuit will be lost at the break. This parameter has a significant influence on the time the core uncovers in case the SS are lost. MAAP5.04 enables users to define the part of SSI that is lost at the break. Apart from a double-ended–break LOCA transient, users struggle to define precisely the part of SSI lost at the break, but this choice can have an important impact on the transient key event times. Thanks to its detailed equations and nodalization, the reference Code for Analysis of Thermal Hydraulics during an Accident of Reactor and safety Evaluation (CATHARE) enables one to evaluate the part of SSI lost at the break. Numerous CATHARE calculations have been performed taking into account different break sizes, positions, and orientations to determine the part of SSI lost at the break in each case. A metamodel has been created from the constituted database and implemented in EDF MAAP5.04. This paper also presents the impact of these improvements on LOCA transients where SS are lost.