An experimental apparatus was used to simulate the annular crevice formed by a heated tube and drilled tube support plate (TSP) in a pressurized water reactor recirculating steam generator. The aim of the experiment was to explore the conditions required for the formation and maintenance of a dry region. Water at 0.69 MPa or atmospheric pressure was circulated through the crevice. Visual observations and tube wall temperature measurements were obtained and compared to synthesize a description of the crevice boiling processes. It was determiend that a stable dry patch exists about a line of contact between tube and TSP above a wall superheat of 2–3°C. However, separating the tube and TSP by about 0.025 mm allows the dry patch to be rewet.