An experimental investigation of a passive cooling unit for nuclear plant containment

A set of condensation experiments in the presence of noncondensables (e.g. air, helium) was conducted to evaluate the heat removal capacity of a passi ve cooling unit in a post-accident containment. Condensation heat transfer coefficients on a vertically mounted smooth tube have been obtained for tot al pressure ranging from 2.48 x 10(5) Pa(abs) to 4.55 x 10(5) Pa(abs) and a ir mass fraction ranging from 0.30 to 0.65. An empirical correlation for he at transfer coefficient (h), has been developed in terms of a parameter gro up made up of steam mole fraction (Xs), total pressure (P-t), temperature d ifference between bulk gas and wall surface (dT). This correlation covers a ll data points within 20%. All data points are also in good agreement with the prediction of the diffusion layer model (DLM) with suction and are appr oximately 2.2 times the Uchida heat transfer correlation. Experiments with an axial shroud around the test tube to model the restriction on radial flo w experienced within a tube bundle demonstrated a reduction of the heat tra nsfer coefficient by a factor of about 0.6. The effect of helium (simulatin g hydrogen) on the heat transfer coefficient was investigated for helium mo le fraction in noncondensable gases (X-He/X-nc) at 15, 30 and 60%. It was f ound that the condensation heat transfer coefficients are generally lower w hen introducing helium into noncondensable gas. The difference is within 20 % of air-only cases when X-He/X-ac is less than 30% and total pressure is l ess than 4.55 x 105 Pa(abs). A gas stratification phenomenon was clearly ob served for helium mole fraction in excess of 60%. (C) 2000 Elsevier Science S.A. All rights reserved.