Nuclear plant

The present invention relates to a nuclear reactor plant comprising a casing enclosing a primary space, a reactor vessel arranged in the primary space, a reactor core provided in the reactor vessel, and an upper space provided above the primary space, the reactor core being separated from the upper space by means of an openable cover arrangement A nuclear power plant comprising a casing which encloses a primary space, a reactor vessel arranged in the primary space, and a reactor core provided in the reactor vessel. The plant further comprises an upper space provided above the casing. The reactor core is separated from the upper space by means of an openable cover arrangement. The casing is designed in such a manner that the primary space is completely closed against the environment to at least the level corresponding to the most highly located part of the reactor core. The upper space is arranged to house a volume of a liquid sufficiently large to permit the filling of the primary space with the liquid to a level located above the most highly located part of the reactor core.