Nuclear reactor plant

A pressurized water nuclear reactor comprises a reactor vessel arranged in a pool made in the form of a pressure vessel, the pool being filled with a strongly neutronabsorbing liquid, for example borated water. The reactor vessel, in addition to being connected to a primary system, is provided with a lower shutdown opening, arranged below the reactor core, for pool liquid and with an upper shutdown opening, arranged above the core, for pool liquid. The reactor vessel, the two emergency shutdown openings and the liquid-filled space of the pool are included in an emergency shutdown circuit, in which the difference in density between the liquid in the pool and the relatively warmer cooling water in the reactor vessel constitutes a pressure difference which by itself, or alternatively with the aid of some other pressure generation means, balances the pressure drop of the reactor cooling water across the core in such a way that no significant flow circulates in the emergency shutdown circuit during normal reactor operation