SIMPLIFIED MODEL The radiation dose model for the lungs was developed by the ICRP Task Group on Lung Dynamics (Morrow et al., 1966) and modified in a subsequent report (ICRP 19, 1972). This model is also used to estimate the rate of transfer of inhaled and ingested plutonium to blood and from blood to bone. Figure 3 shows the detailed structure of the lung model including all the compartments and transport pathways. The pulmonary region is used for calculations of radiation dose to the lungs. Bone is not shown in Figure 3 but involves a simple transfer from blood similar to the other transfers indicated in Figure 3. The mechanism and parameters for the transfer from blood to bone and the retention by bone are based on an earlier model presented by the ICRP Committee II (ICRP 2, 1959) and subsequently modified in ICRP 19 (1972). On the basis of Figure 3, the equations for the transport and accumulation of *39%pu in the lung model are: Torr ~ *b¥upp + Aa¥opa + *e%pe + Ag%pg + Ae (1) Tp = AaYnpa + AYepe + MeYrpe * Mima * £5¥ ora (2) dyyp,/dt = fan - O, + AD) yp a (3) dYypp/dt = £D,A, - Og + AD yp, (4) Yyp > Ynpa * Ynpp (5) dying, /dt ~ FD An ~ Cry + AY ape (6) d¥qgq/4t = £40Ay - Og + ADIapg ) Yopeg ~ “e%pe * *g¥pg) TB eg (8) Yu ~ Yope * Yrpa * Yorpeg (9) dy, /dt = fDoan - On + ho Vpe 518 (10)