Bubble Worth Variation in Molten Cores from a Hypothetical Core Disruptive Acident

A simple and accurate calculation method is presented for the variation of bubble worth in a molten core. The method depends on previous analysis of the author on reactivity increase due to compaction of unmoderated fissile systems. The average density of the fuel material after it has expanded into the bubble region is the controlling parameter of the proposed method. Comparison with detailed bubble worth calculations due to Nicholson and Goldsmith shows excellent agreement. Given a “quality” base worth case, the bubble worth variation for the perturbed system (of fuel, either moving into or out of the bubble volume) can be accurately calculated in terms of the base worth value. The proposed method can be used to evaluate the physical reasonableness of complex calculations using transport theory or Monte Carlo for estimates of bubble worth.