[en] The design limits for the permissible discharge of radioactive gaseous effluents from nuclear stations in normal operation may be subject to variation from time to time. In the light of this there is a need for continuing re-assessment of the assumptions and data used in calculating the possible magnitude of gaseous effluents from water reactors to be built in the future. The interpretation placed on the available information reflects back on the integrity likely to be demanded from the fuel elements. Important aspects include the release of volatile fission products from failed fuel, the distribution of the fission products between water, steam, surfaces, and the off-gases, the possibilities for filtration and deposition outside the reactor, and the form of the species eventually released to atmosphere. This paper discusses some of these topics, making use of experience gained within the UKAEA's prototype Steam Generating Heavy Water Reactor (SGHWR) and comparing and contrasting this with information gained elsewhere where this is helpful. Some areas where information is lacking are noted and possible advantageous effects which could merit investigation are speculatively identified