BWR type reactor

In a BWR type reactor having primary coolant circuits in which primary coolants are circulated, a peroxide decomposition promoting means is disposed to a path of the primary coolant circulating circuit. The decomposition promoting means comprises a means for increasing the surface area to which the primary coolants in the circulating path are brought into contact. The means for increasing the surface area comprises one of materials selected from SUS 304, SUS 316, SUS 316NG, and it has a net-like or porous structure. The hydrogen peroxide decomposing means is disposed in the primary coolant circulating path at a position from an exit to an inlet of the reactor core in a pressure vessel. With such a constitution, hydrogen peroxide in the primary coolants can be decreased with no worry of accelerating leaching of structural components. Accordingly, corrosive circumstance for the primary coolants can be moderated, thereby enabling to remarkably improve reactor integrity and safety. (T.M.)