713 Technical project description

waste appears to remain so little that the construction of a separate surface repository may not be feasible.

Waste for which handling, storage, and disposal of as radioactive waste is not expedient (taking into account the radiation safety principles) can be cleared on the basis of activity limits set by the authorities. The basic radiation safety requirement observed in the clearance procedure is that the annual dose from cleared materials from one nuclear power plant to the general population or the per- sonnel working at the waste processing site does not exceed 10 µSv. Cleared waste will no longer be considered operat- ing waste, and it can be disposed of or re-used like ordinary waste. The Hanhikivi power plant’s solid waste treatment facilities will have a separate area for the processing of waste to be cleared and the related activity measurements.

In the operating waste processing phase, the most important radionuclide in terms of the health effects of radioactive radiation is the cobalt isotope Co-60, which, as a powerful gamma emitter, causes most of the radiation expo- sure of the personnel involved in the processing of waste. However, as Co-60 is a relatively short-lived radionuclide, it is not relevant in terms of final disposal of operating waste. Relevant in terms of final disposal are the longer-lived radi- onuclides Sr-90 and Cs-137, which decay to an insignificant level in about 500 years. When considering the even longer term, extremely long-lived radionuclides, such as Tc-99, I-129, Cs-135, and plutonium isotopes, can be deemed the most relevant. However, their concentration in the operat- ing waste will be very low.

3.12.2 Volume, origin, and quality of operating

waste

Most of the operating waste will be dry waste, mainly con- sisting of contaminated waste generated in conjunction with maintenance and repair work, such as protective cloth- ing, plastic, paper, insulation material, small metal objects, ventilation filters, electric cables, and cleaning utensils. This waste is usually low level waste.

In addition to the waste listed above, operating waste will include metal waste, wet waste, hazardous waste, and power plant decommissioning waste (Section 3.14).

Metal waste will include decommissioned tools, equip- ment, and machine parts, the surfaces of which have been contaminated with radioactive substances. This waste is mainly low level waste. Metal waste will also include com- ponents and equipment removed from inside the reactor pressure vessel that have been activated by neutron radia- tion. This waste is intermediate level waste.

Wet waste will mainly consist of radioactive concentrates and masses accumulated as a result of the plant’s water treatment operations, such as spent ion exchange resins, filter support media, evaporation residue, corrosion sludge, active carbon sludge, and sludge accumulated as a result of cleaning activities.

Bringing unnecessary materials to the controlled area will be avoided in order to minimize the amount of waste generated there. The generation of waste can also be pre- vented by careful planning and implementation of mainte-

nance operations, by choosing the right work methods, by efficient sorting of waste, and by favoring re-usable materi- als as far as possible.

Table 3-5 shows an estimate of the volumes of low and intermediate level waste generated at a plant with a power of about 1,200 MW (Platom 2013a). The estimated volume of waste requiring final disposal generated over the entire ser- vice life of the plant is approximately 5,000 m3_.

3.12.3 Processing of operating waste

According to the regulatory guides on nuclear safety (YVL Guide D.4) issued by the Nuclear Safety Authority (STUK), nuclear power plants must have sufficient facilities for processing and storing low and medium level waste. Sys- tems must be designed for the facilities that allow the safe handling and transfer of waste, as well as measuring the amount and type of radioactive substances that it contains.

Whenever possible, the solid radioactive waste will be sorted at the site where the waste is generated. Sorted waste will be removed from the plant premises without delay. For storage or final disposal, maintenance waste will be packed in vessels (typically, 200-liter drums) which facilitate the transfer of the waste, prevent the spreading of radioactive contamination, and reduce the risk of fire. Before waste is packed in the storage or disposal vessels, its volume will be decreased using various methods (for example, compression or mechanical or thermal cutting). Compression typically

  Waste volume

[m³/v] [m³/60 v] Dry waste

Compressible    

Very low level - -

Low level 12.1 726

Intermediate level 4 240

Non-compressible    

Very low level - -

Low level 22.5 1,350

Intermediate level 3.6 216

Totals for dry waste 42.2 2532

Wet waste

Ion exchange masses

Very low level - -

Low level 16.8 1,008

Intermediate level 18.3 1,098

Other miscellaneous

masses - -

Totals for wet waste 35.1 2,106

Grand total 77.3 4638

Table 3-5. An estimate of the volumes of low and intermediate level waste generated at the power plant annually and over the service life of 60 years (after treatment and packing).

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reduces the volume of the waste to half, sometimes even one-tenth, of the original volume. The spreading of con- tamination will be prevented by equipping the processing equipment with suction or filtering for exhaust air, or by using a processing method that does not generate dust.

Wet and liquid radioactive waste, ion exchange resins, sludge materials, and concentrates will be processed by dry- ing. Wet waste will be solidified in cement order to facilitate safe handling and final disposal. Dried and solidified wet waste will be typically packed in 200-liter drums for storage and final disposal.

For further treatment and final disposal of the waste, it will be characterized, i.e. its properties will be determined. This means that the physical, chemical, and radiological properties of the waste or waste packages will be established through different measurements. Details of each lot of waste will be collected in a bookkeeping and monitoring system. Because of this, the characterization details of a certain lot of waste will accompany it all the way to final disposal.

Packed and characterized waste will be stored under supervision in a storage building located in the immediate vicinity of the solid waste treatment facilities in the plant area. According to the plan, enough storage capacity for 10 years will be built for very low, low, and intermediate level waste.

3.12.4 Final disposal of operating waste

Table 3-5 shows an estimate of the annual volume of operat- ing waste (after treatment) requiring final disposal.

For final disposal, very low level waste to be placed in the surface repository can be baled or packed into flexible intermediate bulk containers or drums. In the case that a surface repository will not be built, very low level waste will be compressed and packed into 200-liter drums in the same way as other low and intermediate level waste. For final disposal, the intermediate level waste packed into drums will be further placed into concrete crates. The con- crete crates will function as radiation shields and technical release barriers.

The principle of final disposal is to isolate the radioactive substances contained in the waste from living nature so that the safety of the environment is not endangered at any stage.

The final disposal methods of very low, low, and interme- diate level waste can be roughly divided into two categories on the basis of the disposal location:

• Disposal in a repository located on, or immediately below, the ground surface (Section 3.12.4.1)

• Disposal in a repository located below the ground sur- face, excavated at the minimum depth of several dozens of meters, inside the geological layers (Section 3.12.4.2).

3.12.4.1 Surface repository

In Finland, only very low level waste, with an average activity concentration not exceeding 100 kBq/kg, may be disposed of in ground repositories, or surface reposito- ries. Fennovoima is considering the construction of a surface repository for very low level waste. As mentioned

above, the disposal of very low level waste in a sur- Figure 3-12. The principle of a surface repository.

Drainage layer Sealing cover Absorption material Waste packages Base slab Surface layer

face repository would have substantially decreased the required volume of the repository to be constructed in the bedrock, particularly in the case of a boiling water plant. Should Fennovoima decide to build a surface repository, it is estimated to reach operational status approximately two years after the of the first startup of the power plant. Should Fennovoima decide not to build a surface repository, very low level waste will be disposed of in underground repositories in the same way as other, higher level operating waste.

A surface repository is an overground structure (Fig- ure 3-12) in which the waste is loaded on a concrete slab. Any leakage water is recovered from the slab surface. Alternatively, the surface repository can be constructed on a well-insulated base which admits the flow of leakage water, while the release barrier retains any contaminants. In either case, the surface repository will be completely or nearly completely insulated by means of waterproof surface layers (clay or geotextile layers). This will keep the waste dry, making the water permeability of the ground significant only in postulated failure situations, such as the failure of the isolating surface layer of the waste and the concrete slab. The small amounts of leakage water, if any, will be admitted out of the repository. The packing of waste and the filling of the space left between the waste packages with a water-permeable filling will ensure that as little leakage water as possible is filtered through the waste. Releases are thus prevented by the concrete slab or a release barrier installed beneath the base.

The repository will be ready for operation when the base layer is ready and the construction of transportation accessways and systems (e.g. the ground water measuring system) is completed. The first deposit campaign may be carried out when enough waste requiring final disposal has been packed for a campaign. Furthermore, sufficient amounts of filling and covering materials shall be stored, in an appropriate manner, in the vicinity of the repository. Following the final sealing of the repository, it will be actively monitored until the radioactivity of the disposed waste has been reduced to an insignificant level. Accord-

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