IMHO to generalize, there needs to be a match between the frequency of light produced in a LENR system and the materials that produces that light. For example, nickel/hydrogen-1 produces infrared light and does not absorb it.
Deuterium produces XUV and does not absorb it. The use of water in a deuterium system is bad because pure water absorbs XUV. The interesting case is with Co-deposition in a Pd/D system, When Palladium chloride is added to the water, that mix does not absorb XUV. That is why Co-Deposition works every time, In Mills case, Copper and water produce visible light and does not absorb it.
