Dosimetry of metal tritide particles as evaluated by the ICRP 66 model and a biokinetic model from laboratory rats.

Internal radiation from inhalation of metal tritide aerosols may present a significant radiation protection problem for nuclear facility workers. Dose was evaluated for three metal tritides: hafnium, titanium, and zirconium. The study included in vitro and in vivo exposures. The inhalation doses for the three materials were calculated by using the ICRP 66 lung model. The doses also were evaluated by a biokinetic model, which was developed according to the results of animal studies. Results showed that the hafnium tritide particles were the most dense but they had a lower dissolution rate and a higher retention rate. Among these three tritides, hafnium was classified as a Type S material according to the ICRP 66 publication, whereas titanium and zirconium ranked between Type M and F materials. The dissolution rate of hafnium tritide appeared to agree well with the in vitro and in vivo studies. The dissolution rates of the other two materials in the in vitro studies were a little higher than those of the in vivo studies. The doses calculated by the ICRP 66 model for all materials were approximately two orders smaller than the doses obtained by the animal studies. This bias was caused by the different intake methods of the ICRP 66 model (inhalation) and in the animal study (instillation). The doses were on the same order while correcting for deposition fractions. The effective doses for hafnium, titanium, and zirconium tritides were 5.43 x 10(-10), 9.05 x 10(-11), and 6.5 x 10(-10) Sv Bq(-1), respectively, according to the animal studies.