Geo&Bio (Dec 2020)
Sources of tritium in natural-technogenic systems
Abstract
The radioactive decay of tritium is caused by the β-decay of one of the two neutrons in the nucleus of the hydrogen isotope atom (triton) into a proton, electron, and electron antineutrino with the formation of a monatomic gas and a half-life of 12.33 years due to a change in the quark structure of the neutron. The average energy of a β-particle is 5.7 keV. Tritium is formed by natural and man-made paths. Natural tritium occurs as a result of the collision of high-energy particles of the solar wind (neutrons, protons, deuterons) with air molecules in Earth’s atmosphere. The total amount of cosmogenic tritium in the hydrosphere and atmosphere is about 2.7 kg. The formation of technogenic tritium began as a result of atmospheric testing of nuclear and thermonuclear weapons and continued with the production of electricity at nuclear power plants. “Bomb” tritium is evenly dispersed in the biosphere as a result of planetary air and gulf stream. The current “bomb” tritium residue in the biosphere is about 23.3 kg, of which 65 % are dissolved in the oceans and 35 % are distributed between the land and the atmosphere. The generation of tritium at nuclear power plants corresponds to the dynamics of the power of nuclear reactors and depends on their types and lifetime. In nuclear reactors, tritium is formed as a result of triple fission of fuel nuclei, capture of neutrons by B and Li nuclei, and as a result of the (n, γ)-reaction on deuterium nuclei in the reactor coolant. According to the estimates of the United Nations Scientific Committee on the Effects of Atomic Radiation, as of August 2019, in the nuclear reactors of nuclear power plants in the world (taking into account their service life) the production of tritium, normalized to power generation capacity, was 2,85 • 1018 bq (7.5 kg). Plants for the reprocessing of spent nuclear fuel are also an important source of tritium entering the environment. Of these, 25 % of tritium in gas-aerosol forms enters the atmosphere and up to 75 % in liquid form (NTO) is discharged into the surface and ground waters. In general, the release of tritium into the environment from nuclear power plants (nuclear power plants and plants for reprocessing spent fuel) can be 1.26 • 1018 Bq • year-1 (3.5 kg • year-1). This is more than 20 times higher than its annual formation from natural sources (0.15 kg • year-1) and may cause the annual doubling of the total tritium reserve in the biosphere.
Keywords
