Thermal-hydraulics in uncovered core of light water reactor in severe core damage accident. (I) Development of models.

Abstract

A computer code SEFDAN is developed for one-dimensional thermal-hydraulics in a partially uncovered core of a light water reactor during a severe core damage accident. The developed models include: 1. Froth level (or dry-out level) calculation 2. Transition and mixing between convection flow regimes in convective heat transfer 3. Radiant heat transfer between solid walls and flowing gas 4. Heat generation by zirconium-water reaction 5. Crucibilization effect of zirconium-oxide layer 6. Steam starvation effect on zirconium-water reaction. This code does not calculate motion of fuel rod material but predicts the beginning of relocation. The major affecting models, froth level calculation model, heat transfer model and crucibilization model, are verified through analyses of experiments. This code can be used for thermal hydraulic analysis of a severe accident and fuel damage experiment until significant material relocation occurs.