Emergency cooling device for a pressurized water nuclear reactor

A pressurized water nuclear reactor comprising a core, a pressure vessel containing said core, a primary circuit in which the pressurized water circulates and arrives in said vessel through parts of said primary circuit called cold legs, a safety enclosure enclosing said pressure vessel and said primary circuit and an emergency cooling system for injecting a cooling liquid into said primary circuit in the event of leakage in said primary circuit, comprising at least one double injection circuit equipped with pump means arranged outside said safety enclosure and at least one set of accumulators containing a predetermined amount of cooling liquid under pressure arranged inside said safety enclosure and communicating with the cold branches of said primary circuit through which the pressurized water arrives in the reactor tank, through a valve whose opening causes the injection of cooling liquid into said primary circuit, said device comprising, by-passing each of said cold branches, with the interposition of a valve and independently of one another,

• (a) a first accumulator of cooling liquid at a first pressure P1 less than the normal pressure of said primary circuit;
• and
• (b) a second accumulator of cooling liquid at a second pressure P2 less than pressure P1;
• (c) the injection of cooling liquid through said first and second accumulators in said primary circuit being caused by the automatic opening of valves corresponding to each of said accumulators when the pressure in said primary circuit falls below P1 and below P2, respectively;
• (d) said pump means in each of said double injection circuits comprising two pumps arranged in series in a pipe communicating upstream with a refrigeration liquid reserve and downstream with said primary circuit, the pump arranged downstream having a rated operating pressure substantially higher than the rated operating pressure of the pump arranged upstream whose delivery is in communication with the suction of the pump arranged downstream, a portion of the circuit by-passed with respect to the pump situated downstream, provided with a closing valve, also enabling the placing of the upstream pump in direct communication with said primary circuit.