Factors affecting the inhalation dose from tritiated dust and flakes

Abstract

Tritiated dust and flakes were produced in JET during D–T campaigns. Measurements showed some atypical radiological effects; a very large T concentration and off-gas rate. A higher dose per unit intake was foreseen and it is a consequence of the particulate nature of the material and of the expected longer biological retention. Particle size plays an important role in the deposition pattern in the human respiratory tract. Larger particles are mostly deposited in the anterior nasal passage and remaining airways of the head and neck and removed in less than 1 day. Smaller particles are mostly retained in the bronchial and bronchiolar regions and alveoli and cleared in longer periods (up to 1 year). The only clearing mechanism of tritium in the latter case is its absorption into lung fluid, an important phenomenon which can be reproduced by in vitro tests to determine doses and dose conversion factors. Based on a review of initial in vitro tests performed on JET dust and from a literature study related to in vitro dissolution experiments, some recommendations for next in vitro experiments on JET dust were formulated.