A comparison of excretion and retention between the current ICRP lung model and a proposed new model

The current International Commission on Radiation Protection (ICRP) lung model (Health Phys. 12: 173; 1986) was developed from information available in the early 1960s. Since that time considerable new information on lung morphology, deposition, and retention has become available and, where appropriate, has been incorporated into a new model being discussed by a Task Group of the ICRP. This new model is conceptually much simpler in that it contains only three compartments, as opposed to 11 in the current model. The intent of this simpler model is to make it easier to model experimental retention and excretion data, either from in vitro studies, animal or human experiments, or human experience. However, this conceptually simpler model is somewhat more difficult to use than the current model as the new model parameters vary with time after exposure. That is, parameters are time-varying functions rather than constants, as they are in the current model, and retention is not given by the familiar Bateman equations. Default time-varying parameters for the new model have been developed that give results comparable to the current model for Classes D, W, and Y compounds. In addition, parameters have been developed for U ore dust, based on in vitro and in vivo studies, and for UO2 from human experience in U fuel fabrication facilities. The development of these parameters will be described, and the results with the new model compared with those obtained with the current model.