Nuclear reactor, allows liquid to flow by gravity into reactor basin from liquid basins when cover arrangement for reactor core is open

At least one pipe extends from the liquid basin(s) (32, 33) to the reactor basin (31) in order for liquid to flow into the latter when the cover arrangement (41, 42) for the reactor core is open. A nuclear installation comprises a reactor enclosure (1) containing a primary region (2), inside which is a reactor tank (9) containing a reactor core (10). The reactor tank extends through a wall (25) separating the primary region from an upper region (26) above the reactor enclosure. An openable cover arrangement separates the reactor core from the upper region. At least one liquid basin capable of receiving a volume of liquid is located in the upper region. A reactor basin located above the cover arrangement is also located in the upper region. At least one pipe extends from the liquid basin(s) to the reactor basin in order for liquid to flow into the latter when the cover arrangement is open and the reactor core is exposed to the upper region. An Independent claim is also included for a method for operating this installation.