Last update on September 2014
The PRIODAC (repeated stable iodine prophylaxis in accidental situations) project, launched in March 2014 for five years and coordinated by IRSN, aims to identify procedures for administering stable iodine to people exposed to repeated or prolonged accidental radioactive releases, such as those observed at Fukushima. The aim is to identify the most suitable administration conditions and evaluate potential side effects for different categories of the population (babies, children, adults, pregnant women, etc.). PRIODAC is a project selected and supported financially as part of the Investment for the Future Program by the French National Research Agency (ANR) in a 2012-call for projects concerning nuclear safety and radiation protection research for "Tomorrow's Nuclear Energy".
Background and objectives
Reactor core accidents at nuclear power plants can lead to large amounts of radioactivity being released into the environment in the form of particles and gas, particularly caesium-134, caesium 137, iodine-131 and other short-lived isotopes of iodine. These particles and gas contaminate land affected by deposits and can be inhaled by populations exposed to the plume. One of the main risks of exposure to the different iodine isotopes is cancer of the thyroid, particularly in babies and young children. This exposure/effect relationship has been particularly evident since 1991 in the areas most severely contaminated by fallout from the Chernobyl disaster, in Belarus, Russia and Ukraine.
To prevent exposure to radioactive iodine, there are three types of measure available for protecting the population: evacuation, sheltering, and administration of stable iodine tablets. The aim of the latter is to saturate the thyroid gland with non-radioactive iodine to prevent the intake of radioactive iodine from the plume. In France, the "Iodine CONOPS (concept of operations)" recommends a single administration of potassium iodide tablets, possibly repeated once if it is impossible to evacuate the population. To be effective, these have to be given between two hours before exposure and not later than six hours after. However, the current marketing authorisation (MA) for the iodine tablets does not take into consideration populations exposed to repeated and/or prolonged releases of radioactive iodine. Two questions arise: firstly, the conditions for repeated administrations of stable iodine (side effects, frequency of administration, etc.); and secondly, from a regulatory point of view, whether the MA for potassium iodide tablets, which currently only covers a single administration, repeated once if necessary, can be updated.
Research areas and methods
The PRIODAC project aims to identify procedures for the repeated administration of stable iodine in the case of chronic releases of radioactivity, to update the current MA for 65 mg potassium iodide tablets, to evaluate the side effects of repeated potassium iodide administration on the main physiological systems (e.g. the cardiovascular and central nervous systems) and to learn more about the molecular mechanisms governing the iodine metabolism. The ultimate aim is to be able to provide health authorities with new concepts of preventing exposure to radioactive iodine and to update the current "Iodine CONOPS".
The first research area aims to determine procedures for the repeated administration of stable iodine and identify the potential side effects of this. This area is split into several tasks:
- identifying the best conditions for repeated administration of potassium iodide to all population age groups (amount to be given at each administration, delay between each administration, maximum duration of treatment);
- evaluating the side effects of repeated administration, both on the thyroid and on the cardiovascular, central nervous and immune systems and renal function;
- carrying out mutagenicity tests (the ability to cause genetic mutations) and GLP (Good Laboratory Practice) studies of toxicology, an essential step in the process of requiring updates to the marketing authorisation for 65 mg potassium iodide tablets.
The second research area aims to learn more about the regulation of iodine metabolism. This is also split into a number of tasks:
a study of iodine transfer through the placenta;
a study of iodine elimination in urine and faeces;
characterisation of the molecular mechanisms leading to the retention of hormone precursors (compounds involved in hormone production) and to the inhibition of iodine accumulation through the Wolff-Chaikoff effect (reduction in thyroid activity as a result of a very large influx of iodine);
in vivo study of iodine transporter inhibitors.
Initial results are expected in five years. The conclusion of the project should lead to a proposal for an update to the current marketing authorisation for potassium iodide tablets and a proposal for a new "Iodine CONOPS" in the event of a nuclear accident.