Construction of ‘historical’ RAW repositories

As mentioned above, facilities for RAW storage (of the Radon type) are intended for the long-term storage of RAW containing short-lived radio­nuclides with a half-life of less than 30 years, including 137Cs and 90Sr. They only contain LLW and ILW. The RAW suppliers are the nuclear facilities of the nuclear industry (unconnected to the fuel cycle), organizations that operate nuclear reactors for research, and medical, training and scientific research centres that carry out radioisotope production.

The selection of suitable sites for RAW repositories was conducted firstly on the basis that any transfer of radionuclides into underground flowing water or its environs must be avoided. RAW repositories must therefore be placed in a clay massif, with low filtration and high sorption properties for radionuclides. The distance to the nearest water-bearing horizon must exceed 10 m. An area that met these requirements was identified 25 km from the town of Sergiev Posad in the Moscow region. From a geological point of view, the area offers sturdy layers of clay deposits of glacial origin (the Moscow and Dneprovsk moraines) that limit filtration and provide high sorption. The nearest water-bearing horizon within the limits of this area is located where the deposits of the Moscow and Dneprovsk glacial moraines meet at depth intervals of 38-42 m [5]. Groundwater in the area is not subject to regional propagation and remains local to the site, appearing only during autumn and winter in the areas adjacent to the man-made construc­tions. The filtration factors of the glacial clay deposits vary between 0.001 and 0.003 m/day, depending on the presence of sandy interlayers and the disturbance of the integrity of the base soil; these soils also have a high sorption capacity. Given that more than 90% of RAW contains 137Cs with a half-life of less than 30 years, 90Sr (29 years) and 60Co (5 years), the com­position of the soil makes the selected area an ideal location for RAW repositories, meaning that the radiation safety of the population outside the limits of the facility’s protection zone was guaranteed.

The construction of near-surface repositories for LLW and ILW began in the mid-1960s. A number of advances in repository design have since taken place, which have improved hermetic conditions and allowed the creation of reliable monitoring systems. Some key developments are:

• sunken monolithic repositories with a capacity of 400 itf [ a standard 1960s project designed by the USSR State Special Design Institute of Minsredmash (SSDI), a historical repository;

• sunken composite repositories, a historical type of repository designed by MosNPO ‘Radon’;

• sunken composite repositories with a ground-based tier, a 1980s devel­opment by MosNPO Radon;

• sunken monolithic repositories with a capacity of 5,000-10,000 m3 (SSDI);

• sunken monolithic repositories with a hangar superstructure, developed in the 1990s (SSDI);

• large diameter boreholes;

• drill-type repositories for SIS of the SSDI;

• repositories for SIS containing 226Ra, developed by MosNPO Radon.

Near-surface type historical repositories take the form of trench grooves 4-5 m deep, with the bottom of the trench covered with a hydro-insulating layer. The walls are made of reinforced concrete blocks or monolithic rein­forced concrete 0.4 m thick. The top of the repository is covered with reinforced concrete slabs and a layer of asphalt. Internally, the repository is made up of several sections. RAW in the repository was bulked in 1 m thick layers, which were then plugged with cement solution, prepared for use with LRAW with low salinity. In the mid-1980s an additional level, 3.5-4 m high, was built above some of the repositories, creating two-storey constructions with a capacity of about 20,000 m3.

Up until the 1990s these repositories were considered disposal facilities and were intended for the final disposal of LLW and ILW, with the surrounding rocks carrying out a basic barrier role to ensure geo-ecological safety. From the end of the 1990s, following IAEA recommendations, these near-surface type constructions were given a new status as ‘RAW repositories with a limited period of storage’. The new designation was based on the idea that adequate environmental protection from the hazards of RAW is dependent on man-made barriers, i. e. durable matrixes, RAW packing, backfill between packages, and the structural elements of the repository.

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