Reconstruction of discharges and environmental doses from a former tritium facility at BNFL Capenhurst

Abstract

The Capenhurst site was established in the early 1950s to enrich uranium, initially for defence purposes. A tritium facility was also operated from 1965 to 1987. When operations ceased the tritium plant was kept under care and maintenance until 1993, since when decommissioning and dismantling of the plant have been undertaken. This is now in its final stages. The operation of this plant has been subject to security classification. Its existence has now been declassified, allowing BNFL to publish information on radioactive discharges. The existence of the plant was made known to the Capenhurst District Liaison Committee in May 1997. An extensive review of original documents has been undertaken, from first commissioning of the plant in 1963, and full operation in 1965, to current discharges arising from decommissioning. While the documents still contain classified information, a full summary is presented here of those records relating to discharges from this facility. Doses to members of the public have been reconstructed. Peak estimated annual doses from routine atmospheric discharges were around 25 - 30 to infants in 1973 - 76 and again in 1985. These coincide with higher releases of tritium as tritiated water. More generally, early doses were around 10 - 15 to all age classes, declining to 1 or 2 over recent years. A number of short-term releases also occurred, primarily in the mid to late 1960s. Specific dose estimates for these events are made. Including routine releases, the maximum annual dose, which occurred in 1966, may have been up to to an infant or to an adult. The next highest annual dose, combining short-term and routine releases, was to an infant or to an adult. The dose limit throughout most of this period was . Recently, a limit of 1000 has applied. For comparison, the average annual dose to the UK population from natural radioactivity is about 2200 . Maximum collective doses from atmospheric releases occurred in the period 1965 - 76, with a projected UK exposure of around 3 to 4 manSv for each year of operation. The total projected collective dose from all aerial releases, 1963 - 96, is 40 manSv to the UK and 51 manSv to the world. Because of the relatively short half-life of tritium, most of this dose is delivered in the first 50 years or so. For comparison, the collective dose to the UK population from natural sources of radioactivity is 130 000 manSv per year, and to the world is 13 000 000 manSv. Liquid discharges of tritium resulted in much lower doses. At the limit of detection applicable throughout the 1960s and 1970s a dose of could apply to children playing in a local watercourse. At the lower limits of detection applicable from 1979, the estimated dose reduces by a factor of 10 to 100. The UK collective dose exposure from liquid discharges, 1963 - 96, is about . The corresponding world dose is 0.035 manSv. These are considered to be negligible.