Conjugate natural convection flow in a thick walled semi-circular cavity containing molten core material has been analysed numerically. The lower plenum debris bed represents decay heating, heat conduction, and heat convection within the debris. The internal heat generation resulting from the radioactive decay of fission products ensures that most of the pool remains molten and also causes natural convection in the pool. Bottom circular wall of the cavity is taken to be thick with finite conductive properties, while top wall is considered to be isothermal. In carrying out the analysis, various constituents of the core material are assumed to be mixed homogenously. Thus a homogeneous fluid, for which Pr number is 0.45, has been considered while Ra number range from 3.2 x 10(7) to 3.2 x 10(12) has been investigated. Present results for non-conjugate semi-circular cavity compare very well with previously published experimental studies. (C) 2001 Elsevier Science Ltd. All rights reserved.