ASN Report 2017

47 ASN report on the state of nuclear safety and radiation protection in France in 2017 Chapter 01  - Nuclear activities: ionising radiation and health and environmental risks 150th anniversary of the birth of Marie Curie. for more than 60 years of a cohort of about 85,000 people irradiated at Hiroshima and Nagasaki has enabled the regular assessment of the morbidity 1 and mortality due to cancer following exposure to ionising radiation, and the description of the dose-effects relationships – which often form the basis of current regulations. Other epidemiological work has revealed a statistically significant rise in cancers (secondary effects) among patients treated using radiotherapy and attributable to ionising radiation. We can also mention the Chernobyl accident which, as a result of the radioactive iodine released, caused in the areas near the accident an excess in the incidence of thyroid cancers in young people exposed during their childhood. The consequences of the Fukushima Daiichi accident on the health of the neighbouring populations are not yet sufficiently known and analysed to draw epidemiological lessons from them. The risk of radiation-induced cancer appears at different levels of exposure and is not linked to the exceeding of a threshold. It is revealed by an increase in the probability of cancer in a population of a given age and sex. These are then called probabilistic, stochastic or random effects. The internationally established public health objectives related to radiation protection aim to prevent the appearance of deterministic effects and reduce the probabilities of cancers arising from exposure to ionising radiation, which are also known as radiation-induced (or radio-induced) cancers; the results of the studies as a whole seem to indicate that radiation-induced cancers represent the predominant health risk associated with exposure to ionising radiation. 1. Number of persons suffering from a given disease for a given time – usually one year – in a population unit. 1.2 Evaluation of risks linked to ionising radiation The monitoring of cancers in France is based on 14 general registers in metropolitan France (covering 18 départements and the greater Lille urban area) and 3 registers in the overseas French départements . In addition to this, there are 12 specialised registers: 9 département registers covering 16 continental départements , 2 national cancer registers for children under 15 years of age concerning malignant haemopathy and solid tumours, and 1 multicentric mesothelioma register for France as a whole. The aim of the register for a given area is to highlight differences in spatial distribution, to reveal changes over time in terms of increased or reduced incidence in the different cancer locations, or to identify clusters of cases. This method of monitoring aims to be descriptive but is unable to highlight any causal effect between an exposure to ionising radiation and cancers, given that other environmental factors may also be suspected. Furthermore, it should be noted that the département registers do not necessarily cover the areas close to the nuclear installations. Epidemiological investigation is complementary to monitoring. The purpose of epidemiological surveys 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, which is the case with low exposure levels of a few tens of millisieverts (mSv) for example, 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.). Low-dose risks are assessed for risk-management purposes by extrapolating the risks observed at higher doses. This calculation gives an estimate of the risks entailed by exposure to low doses of ionising radiation. For these estimates, the prudent hypothesis of a linear no-threshold relationship between exposure and the number of deaths from cancer has been adopted internationally. This hypothesis implies that there is no dose threshold below which one can assert that there is no effect. The legitimacy of these estimates and of this hypothesis nevertheless remains scientifically controversial, as very large scale studies would be necessary to further support the hypothesis. 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, chapter 3, point 1.1.1).