Safety assessment of iodine and hydrogen released during a severe accident in a pressurised water reactor

Abstract

In the case of a severe accident in a nuclear power plant, iodine is considered one of the most important fission products, from the health effect point of view, and hydrogen represents a great risk to the containment integrity. Using the containment spray system, to reduce the amount of iodine released to the environment, may increase the probability of hydrogen combustion by condensing steam. In this work, we have developed and assessed an integrated model that relates the iodine removal model to the temperature and pressure variations as a result of spray operation or hydrogen combustion, after a severe reactor accident. This model was used to study the effect of steam content on the final temperature and pressure in the case of hydrogen combustion, and on the percentage of iodine available for release at the instant of combustion. It was concluded that hydrogen combustion in a low steam content environment will expose the containment to peaks of temperature and pressure higher than the design values, which may threaten the containment integrity. It was also concluded that the spray system operation would drive the containment atmosphere to be combustible before the iodine concentration reaches acceptable values.