3.12. The operator has to be responsible for developing a disposal facility that is practicable and safe and for demonstrating its safety, consistent with the requirements of the regulatory body. This task has to be undertaken in consideration of: the characteristics and quantities of the radioactive waste to be disposed of; the site or sites available; the mining, excavation, construction and engineering techniques available; and the legal and regulatory infrastructure and regulatory requirements. The operator also has to be responsible for developing a safety case, on the basis of which decisions on the development, operation and closure of the disposal facility have to be made (see Requirements 17?19).