14 



large distances (r > D), However, in the case of a line source in the absence 

 of current, a steady state of concentration is not possible ; the diffusive flux 

 is not sufficiently great at large distances, and the concentration continually 

 builds up in the presence of a sustained source. The concept of no mean current 

 at all is quite unrealistic, and as we have seen from the analysis of part I, a 



steady state of C. is possible in the presence of a sustained source and a 



-1 /2 

 current U v^ich leads to a relation of the type C . proportional to x ' . 



Using relation (19) we can investigate the question: What order of magnitude 

 of M. is required for all packages in the disposal area in order to develop a 

 gross Q. for the area which is equal to the average rate of addition of activity 

 of a given isotope to the area, assuming that the dispersal is governed by 

 leaching (rather than by destruction or erosion of the packages) ? In other words, 

 what is the equilibrium level of activity in all packages in the disposal area con- 

 sidering a continued supply of packages per year ? 



If we consider Q. as the average rate of addition of activity for isotope i 



to the disposal area , then for all packages in the disposal area 



2 

 2 Mi = -^ Qi (24) 



Estimating k^ as 10" cm /sec as before and taking a as 36 cm gives 



5Mi — 14 Q. (25) 



where Q. is expressed in terms of curies per year and SM. in curies. 

 Thus if our estimate of k. is reasonable , it will take 14 years accumulation 

 of packages in the area to maintain a steady dispersal equal to the rate of supply, 

 assuming that leaching governs the dispersal rate . This discloses an important 



