Huh? Plutonium is not ammunition. It is a material necessary to make the nukes.
The nuclear missiles themselves are "ammo" for nuclear missile batteries. (And it takes several game months to produce ONE missile, if that is what you mean--the estimated production will say something like 0.15. Actual production may be a bit above or below due to hiring and salaries--my nuke missile corps produce 0.2 nuke missiles per month, each. And this decimal is "added" to the stockpile each month; a nuke will appear in stock when the total production over the last few game months adds up to 1.)
If it seems like your nuclear missile corp is not using plutonium to make teh nook, check its contracts--it may already have a monthly contract to supply what it needs every month, and nothing more. In this case, its plutonium in stock will remain constant, or fairly so.
Are you SURE it is such a good idea for you to be building nooks?