ASN Report 2022

1. The 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 or positron (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, up to several 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). In this case we talk of “radiation-induced cancer”. Subsequently, several types of cancers were observed in occupational situations, including certain types of leukaemia, bronchopulmonary cancers (owing to radon inhalation) and jawbone sarcomas. Outside the professional area, the monitoring for more than sixty years of a cohort(1) of about 85,000 people irradiated during the nuclear bombings of Hiroshima and Nagasaki (Japan) has provided data on the morbidity and mortality due to cancer following exposure to ionising radiation, and enabled the doseeffects 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 health consequences of the Fukushima Daiichi Nuclear Power Plant (NPP) in Japan for the neighbouring populations have also formed the subject of work and analyses, some of which are still in progress, in order to learn the epidemiological lessons. The risk of radiation-induced cancer is not linked to the exceeding of a threshold. It is materialised by an increase in the probability of developing cancer according to radiation dose received, and also depends on age and sex. In this case we talk of effects that can be probabilistic, stochastic (whose appearance further to exposure depends on chance) or random. The probability of developing cancer increases with the dose. However, the impact of low doses on the development of a cancer is a subject of scientific debate (see point 1.2). 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. Over and beyond the effects of ionising radiation, some installations can be the source of non‑radiological risks and detrimental effects such as discharges of chemical substances into the environment or noise emission. The various principles with which the nuclear activities must comply, particularly those of nuclear safety and radiation protection, are set out in chapter 2. 100 ASN Report on the state of nuclear safety and radiation protection in France in 2022 • 01 • Nuclear activities: ionising radiation and health and environmental risks