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 shall not cause radiation damage that is hazardous to human health or otherwise damaging to the environment or to property.
According to the safety requirements, the handling of nuclear waste shall 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 three per cent of the annual average radiation exposure that people in Finland are naturally exposed to.
The safety of final disposal is based on several release barriers
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 evolution does not compromise long-term safety.
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 blocks 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.
Technical release barriers
Technical release barriers are meant to isolate the radioactive substances from the surrounding bedrock and curb 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 with longer durability. Spent nuclear fuel that remains dangerous for a very long period of time is intended to be placed in iron-copper canisters that are isolated from the surrounding rock with a 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.