From our work with baseline ceramics containing Pu, or Ce substituted for Pu, doped with sets of inactive impurity ions (with supposedly the same valency) and sintered in different atmospheres, the conclusion is that all ions of similar size and valency are indeed crystal-chemically equivalent unless there are volatility problems. However, the real question appears to be what are the appropriate valency states of the multivalent impurity ions under given sintering conditions. For example, when sintered in highly reducing atmospheres (in this case 3.7 % hydrogen in argon) Mo, W, Zn, Fe, Cu, Co and Ni are reduced to metal. The partitioning across the different phases present is apparently not even. The elements from the nominal 2+, 3+, 4+, 5+ and 6+ families will preferentially move to certain phases or result in the formation of new phases if sufficient amounts are present. If the phases of the baseline ceramic (pyrochlore-zirconolite, brannerite and rutile) are saturated with these ions, new phases will form to take up the excess impurity ions. Additional such phases detected in this work included ulvospinel, perovskite, magnetoplumbite, loveringite-like phases, metallic alloys and powellite/scheelite. The Pu and Ce-doped samples give similar results to each other. While samples sintered in air are similar in terms of phases present (with some variations, which are discussed in the text) there are differences in the compositions of the phases. In summary, the (probably) divalent ions Mn, Fe, Co, Ni, and Mg behave similarly, but certainly Cu, and possibly Zn, show some volatility losses. Al, Ga, Cr, and trivalent Fe, and Mn, all behave similarly to each other, with some minor variations. Hf, Zr and Sn also behave similarly to each other--however, the Sn is converted to the metallic state in reducing atmospheres. Nb and Ta are equivalent. Mo and W behaved equivalently other, but displayed significantly different partitioning ratios into the pyrochlore and scheelite/powellite phases; both reduced to metal in hydrogenous atmospheres. We contend V is pentavalent to at least some extent even in Ar atmospheres and acts as a flux. Of the glass formers Al is not equivalent to B as the Al tends to enter the crystalline phases and promotes the formation of zirconolite, whereas B is a much stronger glass former. Na is not equivalent to K. Addition of Na promotes the formation of a Na-Ce perovskite, when the ceramics are sintered in Ar, and Na enters the pyrochlore, zirconolite and glass. K was only found in the glass. Both K and Na are believed to be partially volatile under the sintering conditions tested.