RETRAN natural circulation analyses during the Three Mile Island Unit 2 accident

This paper discusses the RETRAN natural circulation analyses which were performed on an emergency basis during the Three Mile Island Unit 2 (TMI-2) Accident in support of the decision to make the transition from forced flow to natural circulation heat removal. The conditions which existed in the containment following the core damage which occurred on March 28, 1979 precluded the long-term use of forced convective core cooling to dissipate fission product decay heat. Natural circulation which uses only the buoyant force of heated water to circulate coolant through the core, was proposed as the most reliable long-term heat removal method. Before the transition could be made, however, it was necessary to determine the capability of the system to successfully achieve stable natural circulation in its damaged state and to evaluate the various modes of steam generator operation which were being proposed for use in this cooling mode