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NF: Management of solid radioactive waste

Publish date: February 6, 2003

The refuelling/defuelling of reactors and repair of nuclear installations, as well as the decommissioning of nuclear powered submarines resulted in the generation of 14,000 m3 of solid radioactive waste from the Northern Fleet.

This waste includes various parts of equipment, packages, filters, garbage, sediments generated during the processing of liquid radioactive waste, contaminated soil etc. The defuelled reactor compartments are also categorised as solid radioactive waste, but due to their large size, they must be handled in very specific ways during processing, transportation and storage.

There are no storage sites for solid radioactive waste and reactor compartments in north-western Russia that would meet current safety requirements. All of the existing sites are filled to capacity and are exposed to harsh weather, with no system in place to collect rainwater. The reactor compartments are temporarily stored afloat at the piers in shipyards and in Sayda Bay at the Kola Peninsula.

The radioactivity in the reactor compartment arose from the neutron irradiation of iron and metal components during the operation of the reactor(s). There are also some radioactive corrosion and wear products that have been circulated by the reactor coolant, having become radioactive from exposure to neutrons in the reactor core, and then deposited onto internal piping systems. The reactor design and its operational lifetime vary somewhat between the different classes and individual submarines, and consequently, the radioactivity within the reactor compartments will also vary.

It is not known how much of the piping systems were dried up before the reactor compartments were towed away from the naval yards. It is also possible that some of the reactor compartments contain many more fission products as a result of different forms of leakage and cracking in the cladding of the fuel elements inside the reactor core. To provide a safe storage for the reactor compartment, it is essential to get a clear picture of the radioactivity inside the reactors before the compartments are prepared for long term storage. Solid radioactive waste is divided in three groups depending on the radioactivity level. The main factor for evaluating activity is the type of radiation that dominates — alfa or beta — and the intensity of the gamma rays on the surface of solid radioactive waste.

The hull and the equipment inside the nuclear reactor, placed inside the biological shield are considered to be high level radioactive waste. Radioactive contamination is generally defined by:

  • cobalt-60 (half-life of about 5.3 years), radioactivity higher than 4.8*1012 Bq/kg;
  • serium-144 (half-life of about 264 days), radioactivity higher than 1.0*1014 Bq/kg;
  • caesium-137 (half-life of about 30 years), radioactivity higher than 3.22*1012 Bq/kg.

    High level radioactive waste constitutes around 10% of the total weight of radioactive waste generated during the decommissioning of a nuclear submarine.

    The second group consists of medium level radioactive waste. Most of this takes the form of the equipment placed outside the biological shield, including the circulation pumps of the primary circuit, the heat-exchange pipes, metal carcasses and so forth. This equipment has low-level exposure radiation and a high degree of surface contamination by radionuclides.

    The third group is the low level radioactive waste largely in the form of contaminated systems and equipment. Examples of this would include tanks and other parts of biological protection, pipes and equipment of the third circuit and some other parts. The biological protection equipment makes up for around 50% of the nuclear installation weight.

    The total activity of the waste accumulated in the Northern Fleet is around 5,000 Ci. The annual accumulation of waste is around 1,000 tons. Taking into consideration the increased rate at which nuclear submarines are being decommissioned, these numbers could double.

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