5.3. Geological disposal is suitable for waste, such as ILW and high level waste (HLW), that require a greater degree of containment and isolation from the accessible environment in order to ensure long term safety. For example, radioactive waste containing long lived radionuclides or waste with levels of activity content high enough to generate significant quantities of heat from radioactive decay, such as spent nuclear fuel (when it is considered waste) or HLW from reprocessing, are generally disposed of within deep geological disposal facilities with engineered barriers such that migration of contaminants into the surrounding geosphere will not begin to occur until a period of thousands of years has elapsed. The safety strategy employed is the containment of the radioactive material for a sufficient period to ensure that any release to the biosphere occurs in a slow and controlled manner. In this case, monitoring is focused on providing confidence in the containment system. Monitoring after closure of the facility, if required and stipulated by the regulatory body, may focus on detection of the presence of radionuclides in the environment. As early releases to the environment are highly unlikely, this kind of monitoring is implemented generally for reassurance of the public rather than for ensuring the performance of the disposal system. Examples of safety related features, events and processes for deep geological disposal facilities that, in practice, could be detected by monitoring are the generation of corrosion gases, water inflow and human intrusion.