ASN Report 2018

Epidemiological investigation is complementary to monitoring. Its purpose is to highlight an association between a risk factor and the occurrence of a disease, between a possible cause and an effect, or at least to enable such a causal relation to be asserted with a very high degree of probability. The intrinsic difficulty in conducting these surveys or in reaching a convincing conclusion when the illness is slow to appear or when the expected number of cases is low, as is the case in particular with low exposure levels of a few tens of millisieverts (mSv), must be borne in mind. Cohorts such as that of Hiroshima and Nagasaki have clearly shown an excess of cancers, with the average exposure being about 200 mSv; studies on nuclear industry workers published in recent years suggest risks of cancer at lower doses (cumulative doses over several years). These results support the justification of radiological protection of populations exposed to low doses of ionising radiation (nuclear industry workers, medical personnel, medical exposure for diagnostic purposes, etc.). When there are no data on the impact of low doses on the occurrence of a cancer, estimates are provided by making linear no-threshold extrapolations of the observed effects described for high doses. These models give estimations of the risks run during exposure to low doses of ionising radiation, which nevertheless remain scientifically controversial. Studies on very large populations are currently underway to develop these models. On the basis of the scientific syntheses of the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), the International Commission on Radiological Protection (ICRP) has published the risk coefficients for death by cancer due to ionising radiation, i.e. 4.1% excess risk per Sievert (Sv) for workers and 5.5% per Sievert for the general public (see ICPR publication 103). The evaluation of the risk of lung cancer due to radon (1) is based on a large number of epidemiological studies conducted 1. Radon is a natural radioactive gas, a progeny product of uranium and thorium, an emitter of alpha particles and has been classified as a known human pulmonary carcinogen by the International Agency for Research on Cancer (IARC) since 1987. directly in the home in France and on an international scale. These studies have revealed a linear relationship, even at low exposure levels (200 Bq/m 3 ) over a period of 20 to 30 years. The World Health Organisation (WHO) has made a synthesis of the studies and recommends maximum annual exposure levels of between 100 and 300 Bq/m 3  for the general public. ICRP publication 115 compared the risks of lung cancer observed through studies on uranium miners with those observed in the overall population and concluded that there was a very good correlation between the risks observed in these two conditions of exposure to radon. The ICRP recommendations consolidate those issued by the WHO which considers that radon constitutes the second-highest risk factor in lung cancer, coming far behind tobacco. Furthermore, for given levels of exposure to radon, the risk of lung cancer is much higher in smokers; three quarters of the deaths by lung cancer that can be attributed to radon reportedly occur in smokers. In metropolitan France, about 12 million people spread over some 7,000 municipalities are potentially exposed to high radon concentrations. According to the French national public health agency (2018), an estimated 4,000 new cases of lung cancer are caused by radon in metropolitan France each year, far behind the number due to tobacco (nearly 69,000). A national plan for managing radon-related risks has been implemented since 2004 on the initiative of ASN and is updated periodically (see point 3.2.2). 1.3  ̶  Scientific uncertainties and vigilance The action taken in the fields of nuclear safety and radiation protection to prevent accidents and limit detrimental effects has led to a reduction in risks but not to zero risk, whether in terms of the doses received by workers or those associated with discharges and releases from BNIs. Many uncertainties persist; they induce ASN to remain attentive to the results of scientific work in progress in radiobiology and radiopathology for example, with possible consequences for radiation protection, particularly with regard to management of risks associated with low doses. The recommendations of the International Commission on Radiological Protection (ICRP) In 2007, the ICRP published new recommendations for the calculation of effective and equivalent doses (publication 103). Since then, the ICRP has been updating the values of the effective dose coefficients for internal and external exposure taking these latest recommendations into account. Its last publication 137 (2017), entitled “ Occupational intakes of radionuclides – Part 3 ”, concerns fourteen radionuclides, including radon. The doses delivered by radon and its progeny depend on many parameters (variability of exposure situations, individuals, etc.). The preceding dose coefficients recommended by the ICRP (publication 65 – 1993) for exposure to radon and its progeny were based on an epidemiological approach. ICRP publication 115 (2010) updated the risk of lung cancer associated with radon exposure on the basis of new epidemiological studies. The ICRP had concluded that the risk of death from lung cancer in adults having been chronically exposed to low concentrations of radon was nearly two times higher than that estimated on the basis of the knowledge available in 1993. The dose coefficients for radon taken from ICRP publication 137 (2017) are based on a dosimetric approach, in the same way as for the other radionuclides. For an equal given level of exposure to radon and its progeny, they lead to a significant increase in the annual effective dose received by workers exposed to radon (nearly two times higher). In view of these developments and pending the updating of the regulations (*) to revise the dose coefficients applicable for radon and its progeny, ASN has asked the Advisory Committee for Radiation Protection in Industrial and Research Applications of Ionising Radiation and for the Environment (GPRADE) to identify to the difficulties that could arise from application of the new ICRP coefficients (publication 137 - 2017). The GPRADE report is expected in 2019. (*) Order of 1 September 2003 defining the methods for calculating effective doses and equivalent doses resulting from human exposure to ionising radiation. 92  ASN report on the state of nuclear safety and radiation protection in France in 2018 01 – NUCLEAR ACTIVITIES: IONISING RADIATION AND HEALTH AND ENVIRONMENTAL RISKS