As an explosion of radiolitically generated hydrogen is listed as a type of severe accident in the new regulation for nuclear fuel cycle facilities, it is important to evaluate the realistic source term of this type of accident. The airborne release fraction (ARF) is a key parameter in evaluating the source term of a hydrogen explosion. Therefore, a pressurization experiment and a hydrogen explosion experiment that induced a hydrogen explosion have been performed. As a result, the ARFs obtained from the pressurization experiment and hydrogen explosion experiment were approximately 1 × 10−5 and 1 × 10−6, respectively. There was no marked difference in the pressure dependency and liquid droplet particle size between the pressurization and hydrogen explosion experiments.