Thermal properties of reinforced concrete for containment pressurisation studies: state of the art and proposals for best estimate and conservative values

In case of loss of coolant accident or severe accident in a nuclear pressurised water reactor, the containment pressure must remain below the design pressure to prevent radioactive releases. The evolution of containment pressure can be estimated by computer codes such ASTEC or MAAP. However, especially for severe accident, the pressurisation kinetics during the first 24 hours is very sensitive to the thermal properties of the containment concrete, which stores most of the decay heat. A wide range of thermal properties (thermal conductivity, specific heat and density) of concrete and reinforced concrete can be found in the literature, depending on the concrete temperature, composition and relative humidity. This paper presents a review of available thermal properties for concrete and reinforced concrete and makes some proposals for best estimate and conservative properties to calculate the evolution of the containment pressure during the first 24 hours after the accident initiator.