LES ACTIVITÉS NUCLÉAIRES : RAYONNEMENTS IONISANTS ET RISQUES POUR LA SANTÉ ET L’ENVIRONNEMENT 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 (CSP) 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 radioactive substance transport, as well as in the medical, veterinary, industrial and research fields. The dangers and risks associated with ionising radiation, whether of natural origin or produced by nuclear activities, are closely monitored and controlled. Nuclear safety is defined in the Environment Code as “the set of technical provisions and organisational measures relating to the design, construction, operation, shutdown and decommissioning of basic nuclear installations as well as radioactive substance transport, taken to prevent accidents or to limit their effects”. Radiation protection is for its part defined as “protection against ionising radiation, that is the set of rules, procedures and means of prevention and surveillance for preventing or mitigating the direct or indirect harmful effects of ionising radiation on individuals, including in situations of environmental contamination”. Nuclear safety and radiation protection obey principles and approaches that have been put in place progressively and continually enhanced by a process of Operating Experience Feedback (OEF). The basic guiding principles are advocated internationally by the International Atomic Energy Agency (IAEA). In France, they are included in the Constitution or enacted in law, as well as now figuring in European Directives. 1 – The state of knowledge of the hazards and risks associated with ionising radiation 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 characterised 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 can interact with the molecules making up the cells of living matter and alter 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, radiation necrosis 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 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 the development of cancer 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”. 108 ASNR Report on the state of nuclear safety and radiation protection in France in 2025
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