Thermal insulation material

Thermal insulation material is described for use in a liquid metal environment. Welded stainless steel sheets are sometimes used, defining a number of individual closed gas filled pockets. Whilst this provides a very effective thermal insulation it has been suggested that the integrity of the extensive seam welding may be difficult to prove. In the arrangement described the wall surface of the reactor is clad with thermal insulation material comprising a number of spaced superposed metal membranes arranged substantially parallel to one another and to the wall surface. The membranes define discrete compartments, and a row of closed metal tubes is located within each compartment. In use the membranes discrete layers of substantially static liquid, which reduces heat transfer by convection, whilst the tubes form a series of pockets that may be charged with an inert gas under pressure, or may be evacuated, thereby reducing heat transfer by conduction. The membranes are preferably vertically corrugated, each corrugated accommodating a single tube. This reduces thickness and gives increased rigidity. The tubes may be end closed by welded plugs, and they provide high integrity pockets capable of withstanding the pressure of the liquid metal coolant and strains imposed by thermal cycling of the coolant. (U.K.)