The author of the Washington Post article got back to me and stated that "It is my understanding that Pakistan's existing stocks of HEU limits their ability to produce high-yield bombs and they need the plutonium to both shrink the size of their warheads to make them more accurate/travel longer, and deliver higher payloads." Now this makes sense, but its also 180 degrees around from what was said in the WaPo article. Using Plutonium in place of Uranium would allow you to reduce the weight of the warhead while maintaining the yield. This would allow for an increase in missile range over a similar yield Uranium warhead. And one must remember the Pakistani's started with all Uranium weapons. So the plutonium is used to shrink their bombs, to increase the range of their missiles, while not dropping the yield.
I think we just learned what the development sequence will be for the Iranians: They will start with a heavy uranium bomb that limits their range, or they have to drop the amount of Uranium to make a bomb light enough to go the distance. As they improve they will add Plutonium to increase the yield while not reducing range. Then they will further incorporate Plutonium to maintain yield while reducing weight and increasing range. The limit will then be reached regarding the max yield of their bombs based on the maximum amount of Plutonium they can use. Re-incorporating Uranium will allow for higher yields, but at the cost of missile range unless a new missile is deployed. And I haven't even mentioned how the Hydrogen bomb comes into this. And I will leave that for a later date.
I think we just learned what the development sequence will be for the Iranians: They will start with a heavy uranium bomb that limits their range, or they have to drop the amount of Uranium to make a bomb light enough to go the distance. As they improve they will add Plutonium to increase the yield while not reducing range. Then they will further incorporate Plutonium to maintain yield while reducing weight and increasing range. The limit will then be reached regarding the max yield of their bombs based on the maximum amount of Plutonium they can use. Re-incorporating Uranium will allow for higher yields, but at the cost of missile range unless a new missile is deployed. And I haven't even mentioned how the Hydrogen bomb comes into this. And I will leave that for a later date.