On the thermal hydraulics of Magnox reactor pressure vessel insulation

The thermal conductivity of multiple plate insulation used in ‘Magnox’ reactor pressure vessels has been investigated experimentally. In the reactor application the fluid within the insulation pack is carbon dioxide at 20 bar, however, in this experimental investigation the insulation was tested in air at lower pressures. The conductivity of the insulation was measured using a test facility based on the guarded hot plate method for a range of temperatures, pressures, and inclinations. Measurements were made both with the fluid within the insulation pack nominally stationary and with an imposed flow through it, simulating leakage through the insulation pack. The values of thermal conductivity obtained were similar to those for conventional high temperature insulation. The conductivity increased with increases in average temperature, pressure, and inclination, in all cases due to enhanced convection within the insulation. The introduction of forced flows into the insulation pack increased the effective conductivity still further.