ASN Report 2020

1. State of knowledge of the hazards and risks associated with ionising radiation 1. Cohort: group of individuals considered together and participating in a statistical study of the circumstances of occurrence of diseases. Ionising radiation is defined as being capable of producing ions – directly or indirectly – when it passes through matter. It includes X-rays, alpha, beta and gamma rays, and neutron radiation, all of which are characterized by different energies and penetration powers. 1.1  Biological and health effects Whether it consists of charged particles, for example an electron (beta radiation) or a helium nucleus (alpha radiation), or of photons (X-rays or gamma rays), ionising radiation interacts with the molecules making up the cells of living matter and alters them chemically. Of the resulting damage, the most significant concerns the DNA of the cells and this damage is not fundamentally different from that caused by certain toxic chemical substances, whether exogenous (external to the organism) or endogenous (resulting from cellular metabolism). When not repaired by the cells themselves, this damage can lead either to cell death or to the appearance of harmful biological effects if tissues are no longer able to carry out their functions. These effects, called “deterministic effects”, have been known for a long time, as the first effects were observed with the discovery of X rays by W. Roentgen (in the early 1900’s). They depend on the nature of the exposed tissue and are certain to appear as soon as the quantity of radiation absorbed exceeds a certain dose level. These effects include, for example, erythema, radiodermatitis, radionecrosis and cataract formation. The higher the radiation dose received by the tissue, the more serious the effects. Cells can also repair the damage thus caused, although imperfectly or incorrectly. Of the damage that persists, that to DNA is of a particular nature because residual anomalies in the chromosomes can be transmitted by successive cellular divisions to new cells. A single genetic mutation is far from being sufficient to cause the transformation into a cancerous cell, but this damage due to ionising radiation may be a first step towards cancerisation which appears after a variable lapse of time (5 to 20 years after exposure). The suspicion of a causal link between exposure to ionising radiation and the appearance of a cancer dates back to 1902 (observation of skin cancer in a case of radiodermatitis). Subsequently, several types of cancers were observed in occupa­ tional situations, including certain types of leukemia, broncho- pulmonary cancers (owing to radon inhalation) and jawbone sarcomas. Outside the professional area, the monitoring for more than 60 years of a cohort (1) of about 85,000 people irradiated at Hiroshima and Nagasaki (Japan) has allowed the morbidity and mortality due to cancer following exposure to ionising radiation to be regularly assessed and the dose-effects relationships – which form the basis of current regulations – to be described. 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 (Ukraine) 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 (Japan) 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. Such cases are referred to as probabilistic, stochastic (produced by chance) or random effects. Ionising radiation may be of natural origin or be produced by nuclear activities of human origin. The exposure of the population to naturally occurring ionising radiation results from the presence of radionuclides of terrestrial origin in the environment, radon emanations from the ground and exposure to cosmic radiation. Nuclear activities are defined in the Public Health Code as “ activities involving a risk of exposure of persons to ionising radiation related to the use either of an artificial source, whether substances or devices, or of a natural source, whether natural radioactive substances or materials containing natural radionuclides (...) ”. These nuclear activities include those carried out in Basic Nuclear Installations (BNIs) and during the transport of radioactive substances, as well as in the medical, veterinary, industrial and research fields. The various principles with which the nuclear activities must comply, particularly those of nuclear safety and radiation protection, are set out in Chapter 2. In addition to the effects of ionising radiation, BNIs are similar to all industrial installations in that they are the source of non-radiological risks and detrimental effects such as the discharge of chemical substances into the environment or noise emission. Nuclear activities: ionising radiation and health and environmental risks 01 102 ASN Report on the state of nuclear safety and radiation protection in France in 2020