The safety of the disposal of nuclear waste in Finland
The safety of the final disposal of nuclear waste
According to the general principles of nuclear waste management, the final disposal may not, now or in the future, cause radiation damage that is hazardous to human health or otherwise damaging to the environment or to property. The responsibility for proving the safety of the final disposal lies with the licensee.
According to the safety requirements, the processing of nuclear waste may not lead to practically any emissions in normal use. The starting point for the requirements applicable to long-term safety is for the dosage of a person who receives a maximum dosage not to exceed 0.1 milliSieverts a year (mSv/a). This equals approximately two per cent of the annual average radiation exposure to which people in Finland are naturally exposed.
The safety of final disposal is based on several release barriers
The use-time safety of a final disposal facility is based on the meticulous design of the facility’s premises, functions, radiation protection, radiation measurements and practical radiation protection arrangements.
The long-term safety of the final disposal of nuclear waste is based on long-term isolation and protective structures. In accordance with the multibarrier principle, release barriers that complement one another delay and slow down the release and migration of radioactive substances. The operation of release barriers must be planned in such a way that the defectiveness of a single barrier or a predictable geological shift does not compromise long-term safety.
The long-term safety of a final disposal facility and the reliability of safety assessments are ensured by analysing technical and scientific materials, observations, experiments, tests and other evidence. When conducting a safety assessment, improbable events are also reviewed in addition to probable developments at the final disposal facility. The potential radiation effects of both the probable and improbable chains of events are analysed over a very long time period. In addition to the potential radiation effects of the final disposal on humans, the effects on animal and plant species will also be analysed.
The rock surrounding the final disposal facility for nuclear waste is meant to isolate the waste from the living environment/habitat while protecting the final disposal from natural phenomena and human activities. The location of final disposal must contain boulders that are sufficiently large, stable and tight to provide favourable conditions for the final disposal of nuclear waste. Favourable conditions mean, among other things, that there will be no major rock displacements in the final disposal premises when stress in the bedrock is released, that groundwater flow is minor and that the concentrations of the groundwater’s chemical properties that have an effect on, for example, salinity and corrosion, are favourable for the operation of the release barriers. The aim is to implement the construction of facilities in the bedrock such that the disturbance caused to the surrounding bedrock and groundwater conditions is kept to the minimum.
The purpose of the rock is to slow down the transfer of radioactive substances to the surface biosphere and thereby to humans, plants or animals. The transfer of radioactive substances is slowed down by the scant flow of groundwater as well as the adherence of radioactive substances to the surfaces of the cracks in the rock.
Technical release barriers
Technical release barriers include, e.g. the waste matrix to which the radioactive substances are bound, the waste package and the buffer material protecting it as well as the materials used for filling and sealing the disposal facility. The purpose of the technical release barriers is to isolate the radioactive substances from the surrounding bedrock and restrict their release into the groundwater.
The durability requirements concerning technical release barriers depend on the activity of the waste subject to final disposal. The protection provided by the surrounding rock and the concrete sealing of the disposal premises suffice for low-level waste. Intermediate-level waste is isolated from the surrounding rock with the help of concrete structures that retain their durability for longer. The plan is to place fuel that remains dangerous for a very long period of time in cast iron/copper canisters that are isolated from the surrounding rock with a concrete clay material that restricts the flow of groundwater.
The safety requirements imposed by STUK require that, in the context of the final disposal of spent nuclear fuel, the technical release barriers isolate the radioactive substances and prevent them from being released to the bedrock for at least 10,000 years, after which the radioactivity of the spent fuel has decreased considerably. The corresponding requirement applicable to short-lived low and intermediate-level waste is 500 years.
The safety of the final disposal facility is subject to STUK’s regulation (STUK Y/4/2018). STUK’s YVL instructions include more detailed instructions pertaining to nuclear waste management.