Liquid-metal coolants may contain voids due to externally introduced gases or due to vaporization of the coolant itself. Previous sections have already dealt with some aspects of core voiding and its analysis. Section 1.3 outlined modeling of sodium boiling due to an imbalance of heat production and heat removal in a core channel. Section 1.4 discussed the reactivity feedbacks obtainable from voiding and outlined design choices which were available to reduce these void feedback coefficients. Finally Section 2.3 dealt with integrated reactivity effects and reactivity addition rates from possible bubbles passing through a reactor core. This section discusses the sources of possible external gases in a practical system and investigates what effects bubbles in the core might have, in addition to reactivity feedbacks.