The management of the large quantities of very low level radioactive material that arise during the decommissioning of the increasing numbers of nuclear power stations reaching the end of their commercially useful lives, has become a major subject of discussion. This has very significant economic implications for the nuclear decommissioner. Much larger quantities — 2–3 orders of magnitude larger — of material, radiologically similar to the candidate material for recycling from the nuclear industry, arise in non-nuclear industries like coal, fertiliser, oil and gas, mining, etc. In such industries, naturally occurring radioactivity is artificially concentrated in products, by-products or waste to form TENORM (Technologically Enhanced Naturally Occurring Radioactive Material). It is only in the last decade that the international community has become aware of the prevalence of TENORM, specially the activity levels and quantities arising in so many non-nuclear industries. The first reaction of international organisations seems to have been to propose different standards for the nuclear and non-nuclear industries, with very stringent release criteria for radioactive material from the regulated nuclear industry and up to thirty to a hundred times more liberal criteria for the release/exemption of TENORM from the as yet unregulated non-nuclear industries. The radiological effects of these TENORM releases have recently been dramatically highlighted by the Marina II study, which showed that over 90% of the total exposures of the European population from discharges into the North European marine waters are from radioactive discharges from non-nuclear industries. The results of an international project to validate, by actual measurement, dose calculation codes RESRAD-RECYCLE (USA) and CERISE (France) for recycling, have indicated an overestimation of doses by the codes by an order of magnitude. For the nuclear decommissioner and other producers of large volumes of slightly radioactively contaminated material, clearance levels determined on the basis of such a degree of conservatism in calculations can lead to huge volumes of material unnecessarily being condemned to burial as radioactive waste. Earlier estimates of the quantitative risk levels of exposure to ionising radiation have almost exclusively been based on doses taken by exposed populations of Hiroshima and Nagasaki (ICRP 60). The populations studied have been exposed to over 200 mSv at a dose rate of 6 Sv/s. The effects of such high dose/dose-rate exposure are being used as the basis for risk judgment at doses/dose-rates lower by a factor 1012–1015. The validity of such an extrapolation in risk judgement is an area of prime interest for discussion. In this connection, an interesting development, for both the nuclear and non-nuclear industries, is the increased scientific scrutiny that the populations of naturally high background dose level areas of the world are being subject to. Preliminary biological studies have indicated that the inhabitants of such areas, exposed to many times the permitted occupational doses for nuclear workers, have not shown any differences in cancer mortality, life expectancy, chromosome aberrations or immune function, in comparison with those living in normal background areas. The paper discusses these and other strategic issues regarding the management of redundant low radiation material from both the nuclear and non-nuclear industries, underlining the need for consistency in regulatory treatment.
Outdoor measurements of thoron progeny in a 232Th-rich area with deposition-based alpha track detectors and corrections for wind bias
