Reactor containment vessel and boiling water reactor power plant

A boiling water reactor plant comprising:

• an outer wall of a reactor containment vessel;
• a reactor pressure vessel;
• a dry well containing the reactor pressure vessel that contains a core, an outer wall part of the dry well partly constituting the outer wall of the reactor containment vessel;
• a wet well containing a pressure suppression pool communicated with the dry well by way of a vent pipe, an outer wall part of the wet well partly constituting the outer wall of the reactor containment vessel;
• a primary containment vessel including the dry well and the wet well;
• an upper secondary containment vessel arranged above the primary containment vessel and partly constituting the outer wall of the reactor containment vessel;
• and
• a gas-phase vent pipe communicating a gas-phase of the wet well and the upper secondary containment vessel so as to equalize a pressure in the gas-phase of the wet well and a pressure in the upper secondary containment vessel by releasing a non-condensable gas in the gas-phase of the wet well to the upper secondary containment vessel and limit a pressure in the primary containment vessel below a design pressure of the primary containment vessel even if a severe accident occurs,
• wherein the primary containment vessel and the upper secondary containment vessel are integrally forming the reactor containment vessel as a single structure so as to provide an enhanced strength.