Patent Number: 046559981
Section: summary

BACKGROUND OF THE INVENTION This invention relates to nuclear reactors, and in particular to liquid metal cooled nuclear reactors. Such reactors are generally of the fast breeder type. A liquid metal cooled nuclear reactor is usually housed in a steel vessel which is itself enclosed within a concrete containment vault, and in order to prevent damage to the concrete due to heat radiated from the vessel containing the reactor core it is usual to interpose thermal insulation between vessel and vault. It is an object of the present invention to provide a construction of thermal insulation capable of protecting the concrete of the vault from heat radiation from the reactor vessel, even under fault conditions. FEATURES AND ASPECTS OF THE INVENTION According to the invention, in a liquid metal cooled nuclear reactor comprising a nuclear fuel assembly in a coolant-containing primary vessel housed within a concrete containment vault and having thermal insulation interposed between the vessel and the vault, the thermal insulation consists of a plurality of adjoining units each hung from metal structure secured to and projecting from the concrete of the vault, each unit including a pack of thermal insulating material and also including a contained void co-extensive with the said pack, such void being situated between the pack and the concrete and being connected to the void of at least one adjoining unit so as to form a continuous duct or ducts for a fluid coolant. Adjoining units of the thermal insulation are advantageously interleaved or overlapped in order to present a barrier to radiation passing between the units and to minimise leakage of fluid coolant from said duct or ducts. The said metal structure is preferably formed so that the said units are themselves spaced from the concrete of the vault in order to provide a volume in which the environmental atmosphere remains generally static, thereby to assist in thermal insulation. The said metal structure preferably consists of stanchions secured to spaced pads embedded in the concrete of the vault, there being pegs projecting from the stanchions at convenient intervals and from which the said units are hung with a keyhole or other suitable engagement. Conveniently there are two pegs for each unit arranged symmetrically. Each unit is preferably of sheet metal construction and defining the void, with the pack of heat insulation material mounted on that void boundary which is remote from the concrete, and the edges of both metal sheets defining the void and the thermal insulation being arranged so that there is interleaving or over-lapping between adjoining units after assembly.