CONTACT CONDUCTANCE BETWEEN CLADDING PRESSURE TUBE AND PRESSURE TUBE CALANDRIA TUBE OF ADVANCED THERMAL REACTOR (ATR)

In some postulated accidents with coincident loss of emergency coolant injection of the Advanced Thermal Reactor (ATR), the rate of heat tra nsfer to the heavy water moderator that acts as heat sink for the deca y heat depends on the contact conductance between cladding and pressur e tube, and the same between pressure and calandria tubes. Experiments were performed to assess these contact conductances for clean plates and plates with simulated crud of Fe2O3 powder that is the main ingred ient of the crud, and the applicable correlations were also studied. T est specimens were cut from actual pressure tube made of Zr-2.5%Nb and calandria tube made of Zircaloy-2 and flattened to sizes. The artific ial waviness of various kinds of height and wave length of 10 mm was m achined on the surface of the pressure tube specimen. The ranges of co ntact pressure, roughness, specimen temperature and gas pressure were from 0.5 to 7 MPa, 4.8 to 100 mum, 400 to 840 K and 0.001 Torr to atmo spheric respectively. The experimental results without crud compare fa vorably with Tachibana's correlation. The experimental contact conduct ances with crud are found to be lowered. Since Tachibana's correlation was not applicable to the present situation, the empirical correlatio n was proposed. The correlation fitted well with the experimental valu es.