Abstract: In a water moderated reactor, which has a plurality of vertically arranged fuel assemblies enclosed in a moderator tank provided with a cover and positioned by an upper core grid, a sprinkling device is arranged above the core grid and below the cover. The sprinkling device is composed of a plurality of substantially horizontal main sprinkling tubes each provided with a plurality of nozzles. A common distributing pipe supplies sprinkling water to the main sprinkling tubes. There are a auxiliary tubes above the main sprinkling tubes and connected to them hydraulically and mechanically by a plurality of transverse metal tubes. The cover has a detachable lower part in the form of a ring to which the sprinkling device is connected.