4.67. For some decisions on the optimization of protection and safety, a qualitative approach based on expert judgement and on utilization of the best available and proven technology may be sufficient. The more complex an issue is and the more interconnections it has with other aspects of the disposal facility, the greater the need to demonstrate optimization. In order to demonstrate that safety can be considered optimized, the following important arguments should be shown to be valid:@@@@- Due attention has been paid to the long term safety implications of various design options at each stage in the development, construction and operation of the disposal facility.@@@@- There is reasonable assurance that the doses and/or risks resulting from the expected evolution of the disposal system will not exceed the constraints, over time frames for which the uncertainties are not so large as to prevent meaningful interpretation of the results.@@@@- The likelihood of events that might disturb the performance of the disposal facility so as to give rise to higher doses or risks has been reduced as far as is reasonably possible by siting or design.