Analysis of power variations due to a loss of moderator in Candu-6

A postulated small failure of the horizontal non-pressurized calandria vessel of Candu-6 reactor results in a moving surface of heavy water at the top of the cylinder. This is modeled as a moving boundary condition applied to the three dimensional space-time kinetics equations in diffusion theory. Several rates of moderator loss are examined, with the automatic reactor control system of the Candu-6 reactor. The transients are followed for a total time of 900 seconds. It is concluded that the maximum relative bundle power attains a value of 1.18, and happens in the bottom part of the reactor. For a 40 liter/second moderator loss rate, this maximum occurs at 500 seconds during the transient. (authors)