733 Technical project description

ing to a preliminary estimate, this will take some 50–60 years. (Platom 2013b)

The monitoring activities include:

• monitoring of the ground water conditions and annual

reporting of the results to the authorities,

• monitoring of the leaktightness of the base slab (if used) by checking the leakage water drain located at the lowest point of the slab,

• ambient radiation monitoring, and

• checking the condition of the repository, particularly the surface layers, for any damage.

After the end of the active monitoring period, the monitor- ing of the area can be continued to ensure the preservation of the information concerning the repository, the guard fences, and outdoor identification signs (passive monitor- ing). (Platom 2013b)

3.12.4.2 Operating waste repository

For the final disposal of low and intermediate level waste, Fennovoima will construct an operating waste repository (VLJ repository) in the bedrock of the plant area, at the depth of approximately 100 meters. According to the current plans, the VLJ repository would be taken into operation no earlier than 10 years after the first startup of the plant.

The low and intermediate waste repository may be of either the rock silo or the tunnel type. Of these, the latter solution is more probable. In the case of a tunnel-type repository, the waste would be transported in via a vehicle access tunnel (Figure 3-13). Bedrock will function as the pri- mary release barrier. If necessary, the waste canister and the cement used as binding agent in the solidification process will also function as release barriers. Additionally, various

concrete structures may be used, particularly in the interme- diate level waste repository.

3.13 Spent nuclear fuel

Approximately 20–30 tons of uranium will be removed as spent fuel from the reactor of the nuclear power plant each year. An approximate total of 1,200–1,800 tons of spent nuclear fuel will be generated over the course of the 60 years of operation of the nuclear power plant.

Ninety-five percent of the spent nuclear fuel is ura- nium isotope U-238 and one percent of uranium isotope U-235. Spent nuclear fuel contains new elements generated through the uranium decay process and neutron capture. Most of the new elements are fission products. The rest are elements heavier than uranium, or transuranic elements. Fission products and transuranic elements are radioactive. The higher the burnup of the fuel (the amount of energy produced by the nuclear fuel per unit of mass), the higher the concentration of radionuclides (radiation-emitting atomic nuclei) and the higher the temperature it produces.

According to the Nuclear Energy Act, the producer of nuclear waste shall be responsible for the management of the spent nuclear fuel it has produced until the sealing of the repository, and shall make financial provision for the costs arising from the management of nuclear waste. In order to cover the costs, the producer of nuclear electric- ity shall make an annual payment to the National Nuclear Waste Management Fund, administered by the Ministry of Employment and the Economy. The payments shall be made such that fund contains sufficient funds for the organ- ization of waste management.

Figure 3-13. An example of a low and intermediate level waste repository of the tunnel type.

Nuclear power plant

Driving tunnel Silos Caves Buildings of final disposal facility

74 3 Technical project description

3.13.1 Interim storage at the plant area

Following removal from the reactor, the spent fuel rod bundles will be transferred to the reactor hall water pools, where they are allowed to cool down for 3–10 years.

The activity and, simultaneously, heat production of the fuel will decrease rapidly during the first year after removal from the reactor. From the reactor hall, the spent fuel will be taken in transport containers to interim storage, where it will remain for a minimum of 40 years prior to final dis- posal. During interim storage, the activity and heat genera- tion of the spent fuel will further decrease significantly.

Water pools (Figure 3-14) or dry storage (Figure 3-15) will be used for storing the spent nuclear fuel. The water pools are typically located in buildings made of steel-reinforced concrete or equivalent structures. Water functions as a radia- tion shield and cools the spent fuel.

In dry storage, the spent fuel is packed in special con- tainers designed for the purpose. The heat released by the spent fuel is conducted into the atmosphere via the con- tainer material. Dry storage methods have been developed

in several countries. They are mainly based on the use of metallic (steel or cast iron) containers, concrete containers, or concrete modules. When concrete containers are used, the spent fuel is additionally packed inside a gas-tight thin metallic jacket. The containers can also be used to transport spent fuel. The container functions as a radiation shield and prevents the spreading of radioactivity contained both in gas and in particles. As the thermal conductivity of air is inferior to that of water, the temperature of the fuel decreases at a slower rate in dry storage than in pool stor- age. The containers are stored in dedicated storage build- ings. The storage facilities are cooled as required to reduce the temperature.

The spent fuel interim storage facility will be con- structed in the power plant area similarly to the currently existing power plants in Loviisa and Olkiluoto, where interim storage takes place in water pools. The interim storage concept will be presented in the power plant con- struction license application, and the facility will be con- structed within approximately ten years of the commis- sioning of the plant.

Figure 3-14. A water-pool-type spent fuel interim storage facility located at the Oskarshamn nuclear power plant in Sweden (CLAB).

Figure 3-15. A spent fuel dry storage facility

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