4.121. To assess the overall containment performance and in particular the measures for radionuclide management, the amount and isotopic composition of the radionuclides postulated to be released from the containment (the source term) should be assessed for the various accidents to be considered. For design basis accidents, this should be done by means of a conservative analysis of the expected behaviour of the core and of the safety systems. Consideration should be given to the most pessimistic initial conditions for the relevant parameters (e. g. for the inventory of radionuclides in systems and for leak rates) within the framework of the allowable limits specified in the technical specifications for the plant.

4.122. The anticipated evolution of the physicochemical forms of the radionu­clides in the containment should be assessed, with account taken of the latest knowledge (e. g. it is known that certain paints enhance the production of organic iodine).

4.123. Once iodine is trapped in water pools inside the containment, it may revolatilize in the medium to long term if appropriate pH conditions are not maintained. It is therefore necessary to assess all conditions that could change the pH of the water pools during an accident and, if necessary, provide the necessary means to keep the water pools alkaline.