On the thermal analysis of pressure tube/calandria tube contact in CANDU reactors

Under abnormal conditions contact between a pressure tube and the surrounding calandria tube in the core of a CANDU reactor may take place. The resulting temperature field may adversely affect the hydrogen diffusion characteristics in the pressure tube material. This paper is concerned with the thermal aspects of contacting pressure and calandria tubes. A critical review of existing thermal interfacial conductance correlations and their applicability to this problem was carried out. Experiments were also carried out to obtain detailed temperature distribution in the walls of typical pressure and calandria tubes in contact under simulated operating conditions. The thermal fields in both tubes were obtained as functions of the contact pressure and system temperatures. The results showed that the heat flow within the contact area is essentially one-dimensional. The data was used to calculate the interfacial thermal conductance as a function of contact pressure. The results were compared with available interfacial conductance correlations and an assessment of their applicability was accordingly made.