5.16. Both conservative and realistic calculations might be necessary in radiological impact assessment for the period after closure, and both approaches can be used to increase confidence in the safety of the disposal facility. For example, conservative models can be used, especially in early phases of assessment, to assess quickly the performance of part of or the entire disposal system. Simple conservative models may also be used to increase confidence in results obtained with more complex models. Conservative models are also necessary to deal with uncertainties that are not amenable to quantification. Conservative estimates may be used in the assessment for some parameters, while realistic values based on detailed characterization and/or more realistic models may be used for others.