4.88. At the earliest stages of the programme to develop a disposal facility, there may be many open questions and uncertainties, and the safety case should include clear plans for dealing with these at future stages (e.g. by site characterization or by optimization of system design) and should set out an approach by which these plans will be achieved. At later stages of the programme, and certainly by the time the safety case is to be presented as part of a licence application, uncertainties and open questions on safety should have been addressed in a manner appropriate for the decision at hand. The manner in which this has been done should be reflected in the safety case. Some uncertainties will inevitably remain (a geological barrier, for example, can never be fully characterized without, in the process, perturbing its favourable characteristics to some extent), but the safety case should indicate the reasons why these uncertainties do not undermine the arguments for the safety of the facility.