Understanding Neutron Radiography Reading V-Kodak Part 2 of 3

As used here, replenishment means the addition of a stronger-than-original
solution, to revive or restore the developer to its approximate original strength.
Thus, the replenisher performs the double function of maintaining both the
liquid level in the developing tank and the activity of the solution. Merely
adding original-strength developer would not produce the desired
regenerating effect; development time would have to be progressively
increased to achieve a constant degree of development.
The quantity of replenisher required to maintain the properties of the
developer will depend on the average density of the radiographs processed. It
is obvious that if 90 percent of the silver in the emulsion is developed, giving
a dense image over the entire film, more developing agent will be consumed.
Therefore, the developer will be exhausted to a greater degree than if the film
were developed to a low density. The quantity of replenisher required,
therefore, depends on the type of subject radiographed. In the processing of
industrial radiographs that have a relatively large proportion of dense
background, some of the original developer must be discarded each time
replenisher is added.
Charlie Chong/ Fion Zhang
Radiography in Modern Industry. Rochester, NY: Eastman Kodak Co. 1980