“Tritium: Defence in Depth” working group Mr Roland Masse, Chairman Sources of tritium releases The natural balance of tritiumwas profoundly altered by atmospheric atomic weapons testing between 1945 and 1963, releasing approximately 240 EBq (650 kg) of tritium into the environment. These emissions increased the concentration in rainwater to several hundred Bq.L1 in the Northern hemisphere. It has now fallen back to approximately 1 Bq.L-1. The oceans form the receiving destination for all tritium releases. In 1998, surface-level concentration in seawater at the equator was 0.1 Bq.L-1. Average concentration is of the order of 10 Bq.L-1 in the Channel, and is locally several hundred Bq.L-1, which is generally related to discharges from nuclear facilities. In some rivers, the value can get as high as several hundred Bq.L-1 locally. The world’s nuclear reactors discharge 12,000 TBq (0.035 kg) of tritium on an annual basis, chiefly in liquid form as tritiated water and 6,000 TBq (0.018 kg) as tritium gas. Fuel reprocessing plants, chiefly the La Hague plant, discharge 12,000 TBq (0.035 kg) of tritium in liquid form and 70 TBq (0.0002 kg) as tritium gas. In France, tritium releases from military facilities have significantly fallen in the last 20 years. The overall trend is also decreasing, but this is a result of the gradual disappearance of the tritium inventory formed due to atmospheric testing (of which approximately 10.5 EBq (30 kg) remained in 2010). Developments in civilian industrial technologies and the implementation of optimisation principles have led to significant reductions in discharges of most radioactive elements into the environment over the last few decades. This does not however apply to tritium, the noble gases and carbon 14. Industrial sources of tritium releases have, for instance, doubled over the last twenty years at the La Hague reprocessing centre (because the electricity generated by the reprocessed fuel doubled over the same period) and also due to: a growing fleet of operating NPPs, changes both in fuels used and reactivity controls in PWR plants, the potential commissioning of fusion reactors in the future, which suggests that the trend will be lasting, even though the use of fusion energy will initially give tritium a high added-value, which will have the effect of reducing losses. The issue of reducing tritium’s impact The OSPAR Convention recommends that the aim should be to bring radionuclide concentrations towards their natural levels, taking into account their impact and the possible reduction techniques (Sintra accords). It is therefore legitimate to seek to reduce the impact of tritium, even if it is already low. This goal should be set within an overall radiation protection framework, because planned solutions to reduce the impact of tritium should not hinder the overall policy of reducing collective doses or lead to an inequitable increase in dose for workers. The need to refer to an assessment of the overall radiological impact of practices highlights the relatively low radiotoxic potential of tritium (although this is disputed) and the differentiated potential of tritium gas, tritiated water and organic compounds (OBT: organically bound tritium) with respect to other sources of human exposure. Using the dose conversion factors specified in current legislation, tritium exposure causes an annual dose of less than 0.1 μSv for the reference groups at La Hague (contribution less than 1% of the impact over and above natural background radiation) and 0.4μSv for the reference groups in villages close to Valduc. These conversion factors could be increased (see the conclusions of the “Radiological Impact” working group), but whatever the final values, the expected result does not seem likely to alter the order of magnitude of the impact or the optimisation of practices. The initial source of tritium production in France is the operation of PWR nuclear power plants. Tritium production in the fuel remains sequestered and only makes a marginal contribution to human exposure. The main source of tritiated discharges is due to neutron activation within the reactor coolant system. Tritium production could be reduced by increasing the isotopic concentration of boron 10 and lithium 7, but the benefit would only be slight. The boron in the reactor coolant system of PWR plants cannot be replaced. The
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