Spent fuel disposed of in Finland
The import and export of spent nuclear fuel were prohibited when the Nuclear Energy Act was amended in 1994. The amendment entered into force in 1996. The only derogation from these provisions concerns the spent fuel of the research reactor FiR 1, which can be returned to the United States. Until 1996, the spent fuel of the Loviisa nuclear power plant was sent back to Russia.
Every year, approximately 65 tonnes of spent nuclear fuel are generated in Finland. By the end of 2015, a total of 13 500 bundles, which correspond approximately 2,040 tonnes of uranium, had accumulated in Finland as a result of nuclear energy use. Based on Finnish Nuclear Energy Act, spent nuclear fuel generated in Finland shall be permanently disposed of in Finland. Accordingly, spent nuclear fuel generated abroad shall not be permanently disposed of in Finland.
In a reactor, uranium fuel is used as bundles of fuel rods. The uranium itself is in the rods in the form of ceramic pellets. Each bundle is about three to four meters long and contains 120–180 kilogrammes of uranium, and there are a few hundred bundles in each reactor. The fuel is handled as bundles, and each bundle is replaced with a new one every three to five years. At that point, the proportion of the fissile uranium isotope U-235 has decreased to the level found in natural uranium.
Spent nuclear fuel is still mainly uranium (96%), even though the uranium also produces different fission products (e.g. iodine, cesium and technetium) in the reactor, as well as some other substances, such as plutonium.
Fuel bundles cooled down before final disposal
Certain heavy nuclei, such as -235 ja Pu-239, are utilized in nuclear power plants for controlled fission chain reaction for production of electricity. The chain reaction occurs in the reactor core. When the nuclear fuel is taken out of the reactor, the heat generated by the fission reactions cannot be utilized any more in electricity production and thus the fission reactions will be prevented by taking care of the proper handling and storage circumstances of the fuel bundles.
The fuel removed from the reactor, the spent nuclear fuel, includes significant amounts of radioactive substances. The radioactive substances decay and thus emit electromagnetic radiation and produce decay heat.
In Finland, fuel bundles are transferred from the reactor to water-filled pools in the reactor building to cool down for a few years. After a year in a pool, the radioactivity of fuel bundles has decreased to a hundredth of the level at the moment of removal from the reactor. In principle, the fuel could also be cooled down using gas or air.
After the cooling stage, fuel bundles are transferred in transport casks to intermediate storage at the plant site, to wait for final disposal in the bedrock. Typical cooling time in intermediate storage is some tens of years.
In some countries, spent fuel is reprocessed. During reprocessing, the usable uranium and plutonium are separated from the spent nuclear fuel for further use. Reprocessing does not eliminate the need for final disposal, as the process always leaves a certain amount of high‑level waste that has to be permanently disposed of eventually.
There is not a reprocessing facility for spent nuclear fuel in Finland and construction of such a facility is not cost-effective. It is also forbidden to export the spent fuel for reprocessing according to Finnish Nuclear Energy Act.
Further information: linda.kumpula(at)tem.fi