 Consequently, the concept of the collective dose was introduced to facilitate cost–benefit analysis and to restrict the uncontrolled build-up of exposure to long-lived radio nuclides in the environment.With the global expansion of nuclear reactors and reprocessing it was feared global doses could again reach the levels seen from atmospheric testing of nuclear weapons.So, by 1977, the establishment of dose limits was secondary to the establishment of cost–benefit analysis and use of collective dose.