Design of the Filtered Containment Venting System in Ascó and Vandellós II Nuclear Power Plants
The project consists of the development of a new Filtered Containment Venting System (FCVS) for Ascó I and II and Vandellós II NPPs. The need of the mentioned system comes as a reinforcement of the safety required by the Nuclear Safety Council (Consejo de Seguridad Nuclear, CSN) due to the post-Fukushima stress tests (in which IDOM did also participate). Therefore it would be possible to face different severe accident scenarios beyond the design bases protecting the containment against loss of integrity in the event of internal over-pressurization and, thus, minimizing any unavoidable activity releases into the environment.
IDOM is contracted for the support of the Design Modification Package (DMP) development, Seismic Engineering and Flexibility, and Detail Engineering for all equipment installation and piping systems.
The AREVA FCVS Standard comprises two Venturi Vessels with Venturi Nozzles and scrubbing liquid (i.e., wet section) and two Filter Vessels with Metal Fiber Filter Elements (i.e., dry section). The Vessels are arranged horizontally and are connected to each other while the Filter Vessels are placed above the Venturi Vessels. The FCVS is activated passively when the containment vent pressure is reached by opening the Containment Isolation Valves or by bursting a Rupture Disk. The process can retain the 99,99% of the radioactive particles and the decontaminated flow is released 20 meters over the altitude of the building.
The software used during the development of the project is AUTOPIPE V9.5, SAP2000 Advanced v.14 and SUPERARPA. Activities complied with a wide range of regulations scoping seismic spectrum and validation of pipes and supports, among others. Several thermo-hydraulic analyses were conducted and the severe accident code MAAP5 ® was used to evaluate the thermal hydraulics internal containment conditions and the performance of the venting system.