Tritium - intake and clearance. Verification of ICRP Model based on Cernavoda NPP individual monitoring data

Operating experience to date of CANDU reactors has indicated that the major contributor to the internal dose is the tritium oxide. Special consideration of routine individual monitoring for internal exposure of workers to tritium oxide is necessary. Data on many humans have indicated that a single exponential essentially describes the retention of tritiated water over the first months or more following the intake. A typical value of the effective half time for tritium is 10 days. Lower tritium effective half-lives, 5.43 and 6.55 days, respectively, were observed in case of internal contamination if diuresis was accelerated. The dose factor for tritiated water incorporation was calculated as a function of the ICRP model parameters. The principal objectives of individual monitoring for intakes of radionuclides are: - to obtain an assessment of the committed effective dose; - to contribute to the control of operation and the design of the plant; - in the case of accidental exposure, to provide valuable information for the initiation and support of any appropriate health surveillance and treatment. Exposure to an atmosphere contaminated by tritiated water results in intake of that substance both by inhalation and by absorption through the intact skin, in a ratio assumed to be 2 to 1. Vapours of tritiated water are considered to be of SR-2 absorption class, that means the tritiated water is instantaneously absorbed into body fluids and uniformly distributed among all the soft tissues. Tritium (H-3) is a pure beta emitter, with an average energy of beta radiation of 0.0186 MeV. Its presence in the body can be detected by measuring the urine samples using the liquid scintillation counting and it presents no detection problems. (authors)