Makoto Akinaga

Three Types of a Passive Safety Containment for a Near Future BWR With Active and Passive Safety Systems

The paper presents three types of a passive safety containment for a near future BWR. They are tentatively named Mark S+ , Mark D and Mark X containments in the paper. They all have a leak tight secondary containment vessel (SCV) in order to meet the reactor site criteria without relying on an active standby gas treatment system at a DBA LOCA. One of their common features is very low peak pressure at severe accidents without venting the containment atmosphere to the environment. The containment pressure can be limited within the design pressure. Even if a large amount of hydrogen is generated at a severe accident, it can be released into the SCV. Hydrogen detonation or deflagration is completely prevented without using igniters. Another feature is the capability to submerge the PCV and the RPV above the core level without relying on accident management. The core debris is completely submerged not only ex-vessel but also in-vessel. The third feature is robustness against external events such as a large commercial airplane crash. All the containments have built-in passive safety systems (BIPSS) including a passive containment cooling system (PCCS) and a passive cooling core catcher that has radial cooling channels. The Mark S+ and Mark D containments are applicable to a large power BWR up to 1830 MWe. The SCV is made of steel-concrete composite. The PCV can be vented into the inerted part of the SCV at a severe accident. The Mark X containment has the steel secondary containment vessel (SSCV) and can be cooled by natural convection of outside air. It can accommodate a medium power BWR up to about 1000 MWe and has a permanent grace period without replenishing the PCCS pool. In all cases the plants have active and passive safety systems constituting in-depth hybrid safety (IDHS). The IDHS provides in-depth protection against severe accidents and also enables N+2 design. All the three containments coupled with the IDHS can potentially provide an evacuation free plant at a severe accident caused by severe natural disasters such as a giant earthquake, a tsunami, a mega hurricane, and so on.Copyright