Recent Revisions to MAAP4 for U.S. EPR Severe Accident Applications

摘要

A revision of the MAAP4 code (i.e., version 4.0.7) has been developed to address the severe accident evaluation needs of the U.S. EPR. The U.S. EPR design employs an ex-vessel severe accident strategy involving specific containment regions devoted to debris stabilization and long term cooling. The modifications performed to the MAAP4 code address both the phenomenological aspects and the spatial modeling flexibility consistent with MAAP4's Generalized Containment Model framework. In addition, enhancements have been included in MAAP4 to improve the modeling of other severe accident mitigation features and to improve code usage and level of detail available to the user. The implementation of several new models and enhancements into the MAAP4 code provides the necessary integral analysis capability of U.S. EPR severe accidents from the initiating event, through reactor vessel failure, to long-term containment and ex-vessel melt stabilization. This paper presents a detailed description of the code enhancements supporting the U.S. EPR design certification.