Nuclear power plant

In a power plant including a containment building which houses a nuclear reactor core containing an enriched uranium fuel in a primary cooling vessel means that partially contains a closed primary cooling circuit for cooling said core, and means for generating in said primary cooling circuit a single pass flow, upwardly through said core, of an organic liquid as primary coolant and moderator with said organic liquid being supplied to the primary cooling circuit initially as feed coolant having a first chemical composition and physical characteristics, and means for maintaining in the primary cooling circuit an operating primary coolant and moderator having a second chemical composition and physical characteristics, an improved passively operating emergency cooling system that is operable to respond automatically to a postulated fault condition comprising a breach of said primary cooling circuit, said emergency cooling system comprising:

• means for flooding said core with emergency coolant on a breach of said primary cooling circuit and heat rejection means for cooling said emergency coolant,
• said flooding means including an accumulator means having a liquid capacity several times greater than the inventory of said primary cooling circuit, organic emergency coolant maintained in said accumulator means at a pressure head above the saturated vapour pressure, at normal operating temperature, of the primary organic coolant and moderator, said organic emergency coolant in said accumulator means being mutually compatible with the said operating primary organic coolant and moderator but having a different chemical composition and physical characteristics including a higher boiling point at atmospheric pressure from either the feed coolant or the operating primary organic coolant and moderator, and pressure responsive means for delivery of said organic emergency coolant from said accumulator means to said core under said pressure head in said accumulator means in response to such a postulated fault condition which include loss of pressure in said primary cooling circuit;
• and said heat rejection means being operable to cool said organic emergency coolant in said core on such a breach of the primary cooling circuit in a manner to maintain cooling of said core without boiling of said organic emergency coolant, and comprising means for establishing, on occurrence of such a postulated fault condition, a first natural convection circuit within said primary cooling vessel means, to maintain a natural convention flow of the said organic emergency coolant through said core sustained by heat rejection to a first heat exchanger and a second natural convection circuit, for establishing a natural convention flow of an intermediate organic coolant through said first heat exchanger sustained by heat rejection to a second heat exchanger, said second heat exchanger being a high-level heat exchanger cooled by atmospheric air externally of the containment building.